The thermal comfort conditions in a complex urban area is influenced by the surrounding structures and obstacles which modify the incoming radiation fluxes. A measure of this modification is the sky view factor (SVF), which could be estimated in each point of a selected area if a high resolution digital elevation model (DEM), or other urban morphological data including the manmade infrastructure, are available. The goal of this study is to model the continuous SVF for a complex building environment in the campus of National and Kapodistrian University of Athens, based on a high resolution DEM (0.09 m). For this purpose, we applied the structure-from-motion (SfM) technique, which takes advantage of the interpretation of ultra-high resolution colour images acquired by remotely piloted airborne systems, also known as drones or unmanned aerial vehicles. A quantitative analysis, by applying statistical metrics, yields perfect agreement between modelled and observed SVF values, over the examined area. The proposed methodology could be applied for human-biometeorology research in micro scale complex urban environments.

{ERA-Interim, ECMWF's reanalysis product, includes wave and atmospheric characteristics, with high temporal and spatial scale, providing more information on the marine state. Even though their assimilation process has been validated and verified in numerous studies, their performance in more local scales is still under examination. This research focuses on the evaluation of performance of ERA-Interim reanalysis datasets in the Greek Seas for wind and wave characteristics in comparison to POSEIDON buoy data. The results prove fair to good correlation for wave height (r=0.67-0.94) and wind speed (r=0.71-0.83) and different error statistics per sub-region. The analysis of the upper 10% (90th percentile) shows an underestimate of 10-15% for wind speed and wave height from ERA-Interim in relation to the buoy measurements. The ERA-Interim and the buoy monthly means and standard deviations are also presented and discussed according to seasonal patterns. The results of the study are compared to other researches of wave hindcasting and wind reanalysis data for the Greek Seas and globally. It is shown that ERA-Interim products could be regarded as representative for the Greek Seas, although their application should be made with caution regarding the assessment of extreme conditions (i.e. given in analyses of upper percentiles) and especially at nearshore locations due to complex coastline configuration enhanced by the great number of islands.}

Mountain Ainos is the highest mountain of the Ionian Islands with a maximum elevation of 1628 m. Its National Park is characterized by rich flora including endemic species such as Greek fir. In order to exploit fully its touristic potential, it is necessary to examine the mountain climate. However in situ measurements of climatic parameters in mountain areas pose difficulties as far as to access areas of interest. The current study addresses one specific object: Estimating the air temperature at different altitudes of the southeastern side of Mt. Ainos, having air temperature data at the exact same altitudes of the northwestern side which is more easily accessible. We performed linear regression analysis to estimate the mean, maximum and minimum daily air temperature of the southeastern sites from data measured at the northwestern one. The results are considered satisfactory in air temperature estimation at all examined altitudes. More accurate estimations were provided in the case of the mean air temperature at the altitude of 1580 m. Also, linear models indicated noticeable estimations of the minimum temperatures at 1300 and 1580 m.

The objective of the study is to assess the human thermal comfort at a University Campus in the metropolitan area of Athens. The equipment setup consists of all the necessary sensors for human thermal comfort estimation along with a high resolution GPS, mounted on a cargo bicycle. The experiment was carried out for midday and night on July 29, 2015. Besides, long term 5 min measurements from a meteorological station, established on the roof of a building within the University Campus, were also used to quantify the mean thermal environment. The densely carried out bicycle measurements every 5 s was the input data utilized by the ENVI-met model; a three-dimensional microclimate model designed to simulate the surface-plant-air interactions in urban environment. The in situ measurements along with the model's output results reveal the thermal comfort regime of the selected area and the ability of the model to estimate accurately the micrometeorological conditions.

{This study shed light on the long term air temperature changes in the troposphere over the Mediterranean. For this purpose, we utilized the radiosonde datasets for the barometric levels at 850, 700, 500, 300, 200, 150, and 100 hPa from seventeen meteorological stations within the Mediterranean, for the period 1965-2015. Besides, the gridded reanalysis products of upper air temperature for the respective barometric pressure levels from the European Centre for Medium-Range Weather Forecasts (ECMWF, ERA-Interim) and the National Center for Environmental Prediction-National Center for Atmospheric Research (NCEPNCAR) were used and compared to stations' datasets. We analyzed the trends and variability of upper air temperature on seasonal and annual basis. The impact of atmospheric circulation, by means of specific climatic indices such as Mediterranean Oscillation Index (MOI), North Sea Caspian Pattern Index (NCPI) and North Atlantic Oscillation Index (NAOI), was also examined. The results of our analysis indicate the anthropogenic forcing to climate variability, especially in lower/middle troposphere against upper troposphere over the Mediterranean.}

{In the present study, the dynamical downscaling technique was applied in the Advanced Weather Research and Forecasting numerical model WRF-ARW, to investigate and validate the performance of different physics parameterizations. The WRF model, was forced by ERA-INTERIM reanalysis data, for a short period of one year (January 2002-December 2002), over the area of the MED-CORDEX domain of 20 km horizontal resolution, downscaled to the domain of Greece with grid spacing of 5 km. Simulations with the Yonsei University (YSU) and Mellor-Yamada- Janjic (MYJ) schemes for boundary layer parameterizations were chosen, along with the corresponding surface layer schemes, as well as, cumulus physics schemes of Kain-Fitsch and Grell-Devenyi. The results of the model simulations have been compared with all available station measurements from the European Climate Assessment and Dataset (ECA&D) for the daily precipitation and 2-m air temperature, through the computation of statistical metrics. The study led to a more reliable choice of physics configurations schemes for the WRF model, in order to simulate future climate model experiments to assess the impact of climate change over the domain of interest.}

{The main objective of this work is the assessment of the annual number of hospital admissions for respiratory disease (HARD) due to the exposure to inhalable particulate matter (PM10), within the greater Athens area (GAA), Greece. Towards this aim, the time series of the particulate matter with aerodynamic diameter less than 10 mu m (PM10) recorded in six monitoring stations located in the GAA, for a 13-year period 2001-2013, is used. In this study AirQ2.2.3 software developed by the WHO, was used to evaluate adverse health effects by PM10 in the GAA during the examined period. The results show that, the mean annual HARD cases per 100,000 inhabitants ranged between 20 (suburban location) and 40 (city centre location). Approximately 70 % of the annual HARD cases are due to city centre residents. In all examined locations, a declining trend in the annual number of HARD cases is appeared. Moreover, a strong relation between the annual number of HARD cases and the annual number of days exceeding the European Union daily PM10 threshold value was found.}

{The goal of this study is to quantify the impact of airborne coarse particles between 2.5 and 80 mu m (PM2.5-PM80) on hospital admissions for respiratory diseases, acquired from the two main hospitals in Heraklion, Crete Island. The atmospheric coarse particles were collected in Heraklion city from November 18, 2011 to May 31, 2013, using the Sigma-2 passive sampler technique. Further, the Scanning Electron Microscopy (SEM), was utilized to identify the qualitative structure of PMs. On one hand, we applied Generalized Addictive Models (GAMS) in order to assess the impact of coarse particles on respiratory diseases. The findings of the analysis revealed that the highest estimates were 7.3 % (Cl: 1.00-1.01) and 7.1 % (Cl: 1.00-1.01) increases in weekly respiratory admissions associated with an increase of 10 mu g m(-3) with respect to coarse particles between 10 and 20 mu m, for men and women, respectively. On the other hand, using SEM technique, the PMs were identified by means of their chemical composition. It is worth noting the presence of Rutile (a mineral composed primarily by Titanium Dioxide), which was found in our samples with possible origin from Saharan desert, causing adverse respiratory problems.}

{The COnsortium for Small-scale MOdeling (COSMO) was formed in October 1998, and its general goal is to develop, improve and maintain a non-hydrostatic limited-area atmospheric model, while the Hellenic National Meteorological Service joined the consortium in 1999. The COSMO model has been designed both for operational numerical weather prediction (NWP) as well as various scientific applications on the meso-beta and meso-c scale. Two tornado case studies were selected to investigate the ability of COSMO model to depict the characteristics of severe convective weather, which favored the development of the associated storms. The first tornado occurred, close to Ag. Ilias village, 8 km northwestern from Aitoliko city over western Greece on February 7, 2013, while the second tornado developed close to Palio Katramio village, 8 km southern from Xanthi city over northern Greece on November 25, 2015. Although both tornadoes had a short lifetime, they caused significant impacts. The COSMO. GR atmospheric model was initialized with analysis boundary conditions obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF). The resulting numerical products with spatial resolution of 0.020 degrees (similar to 2 km) over the geographical domain of Greece depicted very well the severe convective conditions close to tornadoes formation.}

{Towards the evaluation of the thermodynamic characteristics of a high impact tornadic event in Skala Lakonia, southern Peloponnese, in September 21, 2015, Weather Research and Forecasting (AR-WRF) mesoscale model was used. For the particular model setup used in this study, different configurations were pre-tested based on different spatial resolution and parameterization schemes. The current study downscales ECMWF reanalysis initial and boundary conditions to 300 m spatial resolution to assess the convective available potential energy (CAPE), the reflectivity perceived by radar (dBZ) and the energy helicity index (EHI). The validation was conducted using in situ and remote sensing observations of the surrounding area. The results illustrate deep convective activity with CAPE values indicating a strong instability in the region of interest. Furthermore, the model seems to capture well the southwesterly-northeasterly front propagation of the convective initiation of the storm, as well as the troughs that affected the south part of Peloponnese, assessing the pre-frontal nature of the particular tornadic event. Finally, the EHI values demonstrate the tornadic activity in the region of Skala Lakonia, as the model appears to simulate accurately the low pressure system along the east coast of the Lakonia Gulf.}

{A hurricane-like cyclone with an `eye', eyewall convection and strong winds affected central Mediterranean basin on 7-8 November 2014. The maximum observed sustained wind speed was 22 m/s (tropical storm strength) at Lampedusa. Significant damages were reported from this island and the coastal regions of eastern Sicily. Thus, it is essential to study medicanes and calibrate the numerical weather prediction models in order to simulate them adequately. Operational ECMWF analyses are used together with the non-hydrostatic Weather Research and Forecasting numerical model with the Advanced Research dynamic solver (WRF-ARW ver 3.7.1). The aims of this study are to simulate the system and investigate the sensitivity of the model on the microphysical scheme, the number of vertical levels and the global input dataset. The main characteristics of the medicane are represented in good agreement with observations and analyses, but, no single setup is able to provide the best reproduction of all its features.}

{The objective of this study is the analysis of heavy precipitation events occurred in Attica region during the period 2007-2013, along with the determination of their characteristics depending on the season and their corresponding impact. These events were selected according to two criteria; the lightning occurrence-information that was acquired from the Hellenic National Meteorological Service Precision Lightning Sensors Network (HNMS-PLN)-and the high rainfall intensity, provided by the Hydrological Observatory of Athens (HOA) rainfall network. On the one hand, the composite means and anomalies of the respective synoptic conditions, which were based on the reanalysis data sets acquired from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR), along with the frontal activity over Greece, have been analyzed. On the other hand, special attention has been given to the configuration of specific instability indices, during the examined rainfall events. The aforementioned study is an effort to shed light to the rainfall events' features, with respect to their seasonal incidence and their relation to phenomena such as floods and hail.}

{Several epidemiological studies have shown an association between particulate air pollution and adverse health effects. The consensus among the scientific community is that suspended particulate matter is one of the most harmful pollutants, particularly the inhalable particulate matter with aerodynamic diameters less than 10 mu m (PM10) causing respiratory health effects and heart diseases. The effects of aerosols on human health are determined by both their size and their chemical composition. Average daily concentrations exceeding the EU daily threshold concentration appear, among other cases, during Sahara dust episodes, a natural phenomenon that degrades the air quality in the urban area of Volos. The city of Volos is a coastal city of medium size in the eastern seaboard of Central Greece. The main objective of this work is the study of the temporal evolution and the assessment of weekend effect in particulate matter concentration levels in the centre of the city of Volos. PM10 data obtained by a fully automated station that was established by the Hellenic Ministry of Environment and Energy, for a 5-year period (2010-2014) are analyzed in order to study the day-of-week variations during the cold and warm period of the year. As these variations are mostly expected to be due to the human working cycle, a strong weekly cycle would be indicative of the dominance of anthropogenic particles.}

It is a great consensus in the scientific community that environmental factors, such as weather conditions and ambient air pollution, have vital impacts on respiratory diseases. Further, these factors imply the potential to have many significant impacts on aeroallergens, and therefore related diseases such as asthma and allergic rhinitis. The impacts are more pronounced in sensitive groups of population, such as children and elderly, living in urbanized areas. Over the last three decades, studies have shown changes in production, dispersion and allergen content of pollen and spores, which may be region- and species-specific. In addition, these changes may have been influenced by air pollutants interacting directly with pollen. It is not easy to evaluate the impact of climate change and air pollution on the prevalence of asthma in general and on the timing of asthma exacerbations. However, the global rise in asthma prevalence and severity suggests that air pollution and climate changes could be contributing. The objective of this review is to summarize the environmental impacts on pulmonary diseases in children based on recent literature over the world. © 2015, Frontiers in Bioscience. All rights reserved.

The goal of this study is to contribute to the climatology of upper air temperature in the Mediterranean region, during the period 1965-2011. For this purpose, both radiosonde recordings and gridded reanalysis datasets of upper air temperature from National Center for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) were used for seven barometric levels at 850. hPa, 700. hPa, 500. hPa, 300. hPa, 200. hPa, 150. hPa and 100. hPa. Trends and variability of upper air temperature were analyzed on annual and seasonal basis. Further, the impact of atmospheric circulation, by means of correlation between upper air temperature at different barometric levels and specific climatic indices such as Mediterranean Oscillation Index (MOI), North Sea Caspian Pattern Index (NCPI) and North Atlantic Oscillation Index (NAOI), was also quantified. Our findings have given evidence that air temperature is increasing at a higher rate in lower/middle troposphere against upper, and this is very likely due to increasing greenhouse gas concentrations. © 2013 Elsevier B.V.

The aim of this study is to analyze and quantify the future projections of heat waves in Greece. For this reason, specific climatic indices were used in the analysis concerning absolute, percentile and duration indices defined by the CCl/CLIVAR/JCOMM Expert Team (ET) on Climate Change Detection and Indices (ETCCDI). The future projections (SRES A1B) of these indices such as summer days, tropical days, maximum daily maximum air temperature, warm days, tropical nights, maximum daily minimum air temperature, warm nights and warm spell duration were carried out using six regional climate models from the ENSEMBLES project, concerning the near future 2031-2050 and the far future 2071-2100 compared to the reference period 1961-1990. The ensemble means along with the inter-model-standard deviations of the examined extreme indices for the future model projections are presented and analyzed. Further, the findings of this analysis are discussed against recent recorded heat waves during 2007, in order to understand if such events are even more extreme or common in the future climate. It is very likely, that the anomalies observed in 2007, especially for extreme indices of minimum air temperature, could be more frequent considered as typical events by the end of the 21th century. © 2014 Elsevier B.V.

Extreme daily precipitation events are involved in significant environmental damages, even in life loss, because of causing adverse impacts, such as flash floods, in urban and sometimes in rural areas. Thus, long-term forecast of such events is of great importance for the preparation of local authorities in order to confront and mitigate the adverse consequences. The objective of this study is to estimate the possibility of forecasting the maximum daily precipitation for the next coming year. For this reason, appropriate prognostic models, such as Artificial Neural Networks (ANNs) were developed and applied. The data used for the analysis concern annual maximum daily precipitation totals, which have been recorded at the National Observatory of Athens (NOA), during the long term period 1891-2009. To evaluate the potential of daily extreme precipitation forecast by the applied ANNs, a different period for validation was considered than the one used for the ANNs training. Thus, the datasets of the period 1891-1980 were used as training datasets, while the datasets of the period 1981-2009 as validation datasets. Appropriate statistical indices, such as the coefficient of determination (R2), the index of agreement (IA), the Root Mean Square Error (RMSE) and the Mean Bias Error (MBE), were applied to test the reliability of the models. The findings of the analysis showed that, a quite satisfactory relationship (R2=0.482, IA=0.817, RMSE=16.4mm and MBE=+5.2mm) appears between the forecasted and the respective observed maximum daily precipitation totals one year ahead. The developed ANN seems to overestimate the maximum daily precipitation totals appeared in 1988 while underestimate the maximum in 1999, which could be attributed to the relatively low frequency of occurrence of these extreme events within GAA having impact on the optimum training of ANN. © 2013 Elsevier B.V.

The objective of this study was to assess and analyze the human bioclimatic conditions of Crete Island, by applying two human thermal indices: physiological equivalent temperature (PET), derived from the Munich Energy-balance Model for Individuals human energy balance model, and Universal Thermal Climate Index (UTCI), based on the Fiala multi-node model of human thermoregulation. Human bioclimatic studies provide a framework for considering the effects of climatic conditions on human beings and highlighting the social/economic factors that mitigate or amplify the consequences of environmental changes. In order to estimate the thermal effect of the environment on the human body, it has been considered that the total effects of all thermal components, not only of individual parameters, should be taken into account. The climatic data (air temperature, relative humidity, cloudiness, wind speed) used in this study were acquired from the archives of the Hellenic National Meteorological Service, regarding ten meteorological stations in Crete Island. These data, covering the 30-year period 1975–2004, were used for the calculation of PET and UTCI in order to assess thermo-physiological stress levels. The findings of this analysis, such as bioclimatic diagrams, temporal and spatial distributions of PET and UTCI as well as trends and variability, will help stake holders to understand and interpret the island’s current bioclimate, in order to make any necessary adaptations and become more resilient to the foreseen climate change. © 2013, Springer-Verlag Berlin Heidelberg.

In this study, the climatology of tornadoes, waterspouts and funnel clouds over Greece is presented for the period 1709-2012. The climatology consists of two datasets. An historical dataset (1709-1999) is based on newspaper archives, historical archives, published tornado literature, administrative records and reports of Hellenic National Meteorological Service (HNMS). A recent dataset (2000-2012) is based on newspaper articles, eyewitness reports to the media, HNMS's reports and an open-ended online tornado report database which has been developed and maintained by the Laboratory of Climatology & Atmospheric Environment of the University of Athens. Altogether, 612 Greek tornadic events compose the climatology: 171 tornadoes, 374 waterspouts and 67 funnel clouds. Tornadic events during the past 13years (2000-2012) have occurred all over the Greek territory and there is frequent tornadic occurrence over north Crete and Corfu Island. Tornadoes are more frequent to occur over NW Peloponnesus followed by south parts of Corfu Island. However, waterspouts are more frequent over north Crete followed by Corfu Island. Tornadic monthly variability depicts a maximum during October, followed by September and November. October is the month with the highest tornado frequency, followed by November and July. The highest waterspout frequency month is September followed by October and December. Tornadoes most commonly develop during the warm time of the day, as more than 75% of all cases occur during 08:00-15:00hours UTC with a maximum at 12:00hours UTC. Waterspout frequency of occurrence has two maxima during the day, the first early in the morning (07:00-09:00hours UTC) and the second after the noon time period (14:00-15:00hours UTC). The dominant (27.7% of total cases) intensity of tornadoes in Greece is T4 based on the T-scale during the 300-year period (1709-2012); there have been at least 114 injured and 29 deaths. © 2013 Royal Meteorological Society.

This study focuses on analyzing the extreme aerosol loading and the mechanisms, source areas and meteorological conditions that favored the abnormal dust exposure towards Arabian Sea during June 2008. The analysis reveals that the spatial-averaged aerosol optical depth (AOD) over Arabian Sea in June 2008 is 0.5 (78.2%) higher than the 2000-2013 mean June value and is mostly attributed to the enhanced dust activity and several (18) dust storms originated from the Sistan region (Iran-Afghanistan borders). Landsat images show that the marshy lakes in Sistan basin got dried during the second half of June 2008 and the alluvial silt and saline material got easily eroded by the intense Levar winds, which were stronger (>15-20ms-1) than the climatological mean for the month of June. These conditions led to enhanced dust exposure from Sistan that strongly affected the northern and central parts of the Arabian Sea, as forward air-mass trajectories show. The NCEP/NCAR reanalysis reveals an abnormal intensification and spatial expansion of the Indian low pressure system towards northern Arabian Sea in June 2008. This suggests strengthening of the convection over the arid southwest Asia and exposure of significant amount of dust, which can reach further south over Arabian Sea favored by the enhanced cyclonic circulation. MODIS imagery highlighted several dust storms originated from Sistan and affecting Arabian Sea during June 2008, while the SPRINTARS model simulations of increased AOD and dust concentration over Sistan and downwind areas are in agreement with ground-based and satellite observations. © 2014 Elsevier Ltd.

Tornadoes have been reported in Greece over recent decades in specific sub-geographical areas and have been associated with strong synoptic forcing. While it has been established that meteorological conditions over Greece are affected at various scales by the significant variability of topography, the Ionian Sea to the west and the Aegean Sea to the east, there is still uncertainty regarding topography's importance on tornadic generation and development. The aim of this study is to investigate the role of topography in significant tornadogenesis events that were triggered under strong synoptic scale forcing over Greece. Three tornado events that occurred over the last years in Thebes (Boeotia, 17 November 2007), Vrastema (Chalkidiki, 12 February 2010) and Vlychos (Lefkada, 20 September 2011) were selected for numerical experiments. These events were associated with synoptic scale forcing, while their intensities were T4-T5 (on the TORRO scale), causing significant damage. The simulations were performed using the non-hydrostatic weather research and forecasting model (WRF), initialized by European Centre for Medium-Range Weather Forecasts (ECMWF) gridded analyses, with telescoping nested grids that allow for the representation of atmospheric circulations ranging from the synoptic scale down to the mesoscale. In the experiments, the topography of the inner grid was modified by: (a) 0% (actual topography) and (b)-100% (without topography), making an effort to determine whether the occurrence of tornadoes-mainly identified by various severe weather instability indices-could be indicated by modifying topography. The principal instability variables employed consisted of the bulk Richardson number (BRN) shear, the energy helicity index (EHI), the storm-relative environmental helicity (SRH), and the maximum convective available potential energy (MCAPE, for parcels with maximum (θe). Additionally, a model verification was conducted for every sensitivity experiment accompanied by analysis of the absolute vorticity budget. Numerical simulations revealed that the complex topography constituted an important factor during the 17 November 2007 and 12 February 2010 events, based on EHI, SRH, BRN, and MCAPE analyses. Conversely, topography around the 20 September 2011 event was characterized as the least significant factor based on EHI, SRH, BRN, and MCAPE analyses. © 2014 Author(s).

In recent decades, there has been an increasing interest in the prognosis of maximum surface ozone concentrations due to the adverse effects on human health, animal population, agricultural productivity and forestry. The present study deals with the development and application of Artificial Neural Network (ANN) models in predicting the maximum daily surface ozone concentration in several locations within the greater Athens area (GAA), 24-hours in advance. Meteorological and air pollution data during the period 2001 to 2005 were provided by the network of the Hellenic Ministry of the Environment, Energy and Climate Change. Hourly values of barometric pressure and total solar irradiance for the same period have been recorded by the National Observatory of Athens. A training data set for the ANN prognostic model was generated by employing the superposed epoch analysis.The evaluation of the performance of the developed model, using appropriate statistical indices, clearly indicates that the risk of surface ozone values exceeding the European Union (EU) threshold for human health protection can be successfully predicted. This suggests that the proposed ANN model can be used to issue warnings for the general public and especially certain sensitive groups of the population. © 2014 Global NEST Printed in Greece. All rights reserved.

The aim of this paper is to present in a useful and understandable way how climatic change could be interpreted for tourism and recreation. Future climate change conditions are analyzed using the Climate Version of the Local Model (CLM) based on the COSMO model, which is currently used-among other weather services-by the DWD (Deutscher Wetterdienst) for operational weather forecast. The climate simulations concern the future periods 2021-2050 and 2071-2100 against the reference period 1961-1990, under A1B scenario. Based on regional climate simulations, the analysis for tourism can be performed using the Climate-Tourism-Information-Scheme (CTIS). The CTIS contains detailed climate information, which can be used by tourists to anticipate thermal comfort, aesthetical and physical conditions for planning their vacations. Furthermore, the Physiologically Equivalent Temperature (PET), which is one of the most popular physiological thermal indices derived from the human energy balance, is used in the analysis in order to describe the effect of climate. The future simulations concerning PET and CTIS for the area for Athens have been exemplary used, in order to consider them for tourism industry and local authorities for tourism planning. © 2014 Global NEST Printed in Greece. All rights reserved.

Lightning is a natural phenomenon in the atmosphere, being a major cause of storm related deaths, main trigger of forest fires and affects many electrochemical systems of the body. Significant scientific interest has come up in the last decades, as numerous lightning detection networks have been established in operational basis, providing lightning data to assess and mitigate lightning impact to the local society by spatio-temporal analysis.In this study, a preliminary analysis of spatial and temporal variabilities of recorded lightnings over Greece during the period from January 2008 to December 2009 is presented. The data for retrieving the location and time-of-occurrence (TOA) of lightning were acquired from the Hellenic National Meteorological Service (HNMS). An operational precision lightning network (PLN) has been established since 2007 by HNMS, consisting of eight time-of-arrival (TOA) sensors, spatially distributed across Greek territory.The spatial variability of lightnings revealed their incidence within specific geographical sub-regions while the temporal variability concerns the seasonal and monthly distributions. All the analyses were carried out with respect to cloud to cloud (CC), cloud to ground (CG) and ground to cloud (GC) lightnings, within the examined time period. During the autumn season, lightning activity was the highest, followed by summer and spring. Higher frequencies of stokes appear over Ionian Sea and Aegean Sea than over land during winter period against continental mountainous regions during summer period. © 2013 Elsevier B.V.

Tornadoes have been reported in Greece during the last few decades and recent studies have given evidence that western Greece is an area vulnerable to tornadoes, waterspouts and funnel clouds In this study, the composite means and anomalies of synoptic conditions for tornadic events (tornadoes, waterspouts and funnel clouds) over western Greece are analyzed and discussed. The daily composite means of synoptic conditions were based on the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data sets, for the period 12 August 1953 to 31 December 2012. The daily composite anomalies were calculated with respect to 30 years of climatological study (1981-2010) of the synoptic conditions. The analysis was carried out in terms of seasonal and monthly variability of composite means and anomalies of synoptic conditions for specific isobaric levels of 500, 700, 850, 925 hPa and the sea level pressure (SLP). In addition, an analysis and discussion about the dynamic lifted index from NCEP-NCAR reanalysis data sets is presented. The daily composite mean analysis of 500 hPa revealed a trough line across the northern Adriatic Sea and central Italy, associated with a SW upper-air stream over western Greece. The maximum composite anomalies were depicted at the isobaric level of 500 hPa during autumn, spring and summer, against winter when the anomaly appeared at 925 hPa isobaric level. In addition, 48% of tornado events during the autumn season occurred in pre-frontal weather conditions (cold fronts) and 27% developed after the passage of the cold front. Furthermore, the main difference in synoptic patterns between tornado and waterspout days along western Greece during the autumn season is the maximum daily composite anomaly over the Gulf of Taranto. © Author(s) 2014. CC Attribution 3.0 License.

The occurrence of non-fatal acute coronary syndromes (ACS) is examined in relation with the local bioclimatic conditions in the Ierapetra area, in the southernmost part of Crete Island, Greece, during the period 2004-2007. Daily ACS counts and corresponding meteorological parameters, such as maximum and minimum air temperature, relative humidity, wind speed and cloudiness, were analyzed. Besides, the daily values of the human thermal index, physiologically equivalent temperature (PET) was evaluated. Pearson's 2 test and generalized linear models (GLM) with Poisson distribution were applied. The ACS syndromes present a multiple variation within the year, with the primary maximum in August and the secondary in May, while relative high ACS frequencies exist in early winter time. The impact of the weather variability on the ACS incidence is not statistically significant (C.L. 95%). © 2013 Copyright Taylor and Francis Group, LLC.

The forecast of extreme weather events become imperative due to the emerging climate change and possible adverse effects in humans. The objective of this study is to construct predictive models in order to forecast rain intensity (mm/day) in Athens, Greece, using Artificial Neural Networks (ANN) models. The ANNs outcomes concern the projected mean, maximum and minimum monthly rain intensity for the next four consecutive months in Athens. The meteorological data used to estimate the rain intensity, were the monthly rain totals (mm) and the respective rain days, which were acquired from the National Observatory of Athens, for a 111-year period (1899-2009). The results of the developed and applied ANN models showed a fairly reliable forecast of the rain intensity for the next four months. For the evaluation of the results and the ability of the developed prognostic models, appropriate statistical indices were taken into consideration. In general, the predicted rain intensity compared with the corresponding observed one seemed to be in a very good agreement at a statistical significance level of p. <. 0.01. © 2011 Elsevier B.V.

The objective of this paper is to study the spatial and temporal variability of the Aridity Index (AI) in Greece, per decade, during the 50-year period (1951-2000). Besides, the projected changes in ensemble mean AI between the period 1961-1990 (reference period) and the periods 2021-2050 (near future) and 2071-2100 (far future) along with the inter-model standard deviations were presented, based on the simulation results, derived from a number of Regional Climatic Models (RCMs), within the ENSEMBLE European Project. The projection of the future climate was done under SRES A1B.The climatic data used, concern monthly precipitation totals and air temperature from 28 meteorological stations (22 stations from the Hellenic National Meteorological Service and 6 stations from neighboring countries, taken from the Monthly Climatic Data for the World). The estimation of the AI was carried out based on the potential evapotranspiration (PET) defined by Thornthwaite (1948). The data processing was done by the application of the statistical package R-project and the Geographical Information Systems (GIS).The results of the analysis showed that, within the examined period (1951-2000), a progressive shift from the "humid" class, which characterized the wider area of Greece, towards the "sub-humid" and "semi-arid" classes appeared in the eastern Crete Island, the Cyclades complex, the Evia and Attica, that is mainly the eastern Greece. The most significant change appears during the period 1991-2000. The future projections at the end of twentieth century, using ensemble mean simulations from 8 RCMs, show that drier conditions are expected to establish in regions of Greece (Attica, eastern continental Greece, Cyclades, Dodecanese, eastern Crete Island and northern Aegean). The inter-model standard deviation over these regions ranges from 0.02 to 0.05 against high values (0.09-0.15) illustrated in western mountainous continental Greece, during 2021-2050. Higher values of inter-model standard deviation appear in the 2071-2100 ranging from 0.02 to 0.10 reaching even 0.50 over mountainous regions of the country. © 2011 Elsevier B.V.

The objective of this study is to compare and analyze satellite precipitation extremes of Tropical Rainfall Measuring Mission level 3 output (TRMM 3B42) over Mediterranean region against the respective high resolution gridded precipitation datasets (0.25. ×. 0.25) based on the E-OBS project, for the period 2000-2011.The Tropical Rainfall Measuring Mission (TRMM) is a joint U.S.-Japan satellite mission to monitor tropical and subtropical precipitation and to estimate its associated latent heating. The E-OBS data set (a European daily high-resolution gridded dataset of surface temperature and precipitation) was developed as part of the European Union Framework 6 ENSEMBLES project, with the aim being to use it for validation of Regional Climate Models (RCMs) and for climate change studies.The indices used in the analysis can be divided in three categories: percentile, absolute and duration indices. The percentile indices concern: very wet days (the number of days with daily precipitation amount above the 95th percentile from the examined period) and extremely wet days (the number of days with daily precipitation amount above the 99th percentile from the examined period). The absolute threshold indices concern: number of heavy precipitation days (number of days with daily precipitation amount above 10. mm), number of very heavy precipitation days (number of days with daily precipitation amount above 20. mm) and simple daily intensity index (daily precipitation amount on wet days in a period per number of wet days in the period). The duration indices concern consecutive dry days (the largest number of consecutive days with daily precipitation amount below 1. mm) and consecutive wet days (the largest number of consecutive days with daily precipitation amount above 1. mm).The spatial distribution of the differences between the two datasets along with the spatial distribution of the correlation coefficients are presented and analyzed. Results show considerable regional differences of precipitation indices over the Mediterranean Region. © 2013 Elsevier B.V.

The surface ozone is a pollutant of major concern due to its impact on receptors, at currently occurring ambient levels in many regions of the world. The aim of this work is to present the results derived from an analysis of hourly surface ozone concentrations, measured at the urban station of Volos, a coastal medium-sized city at the eastern seaboard of Central Greece, during the 8-year period 2001-2008. The regional climate that is characterized by hot and dry summers with intense sunshine plays an important role in the observed exceedances of the air quality ozone limits. The analysis showed that, ozone diurnal patterns depict daytime photochemical ozone built up, during the sunlight hours of the day. It is remarkable that the maximum daily 8-h averages often exceeded the standard value that is assigned by the EU Directive for human health protection, during almost the warm period of the year, mainly at noon and afternoon hours. © 2013 Global NEST Printed in Greece. All rights reserved.

The study of atmospheric concentration levels at a local scale is one of the most important topics in environmental sciences. Multivariate analysis, fuzzy logic, and neural networks have been introduced in forecasting procedures in order to elaborate operational techniques for level characterization of specific atmospheric pollutants at different spatial and temporal scales. Particularly, approaches based on artificial neural networks (ANNs) have been proposed and successfully applied for forecasting concentration levels of PM10, NO2, SO2, CO, and O3. The present study explores the development and application of ANN models for forecasting, 24 h ahead, not only the daily concentration levels of PM10 but also the number of hours exceeding the PM10 concentration threshold during the day in five different regions within the greater Athens area (GAA). The ANN modeling was based on measurements and estimates of the mean daily PM10 concentration, the maximum hourly NO2 concentration, air temperature, relative humidity, wind speed, and the mode daily value of wind direction from five different monitoring stations for the period 2001-2005. The evaluation of the model performance showed the risk of daily PM10 concentration levels exceeding certain thresholds as well as the duration of the exceedances can be successfully predicted. Despite the limitations of the model, the results indicate that ANNs, when adequately trained, have considerable potential to be used for 1 day ahead PM10 concentration forecasting and the duration within the GAA. © Springer Science+Business Media Dordrecht 2013.

The objective of this work is the assessment of human thermal bioclimatic conditions in the Athens University Campus (AUC), including the Faculties and their respective Departments of the largest state institution of higher learning in Greece, and among the largest universities in Europe. The analysis of bioclimate was carried out, using the physiologically equivalent temperature (PET), which is based on the energy balance model of the human body. The meteorological data required for the calculation of PET concern hourly values of air temperature, relative humidity, wind speed and total solar radiation, for the time period 1999-2007. The recorded data sets were obtained from the meteorological station of the Laboratory of Climatology and Atmospheric Environment of the University of Athens. The results revealed the hours of the day in which thermal comfort or stress prevails, as well as the trends and variability of PET, for the studied period. Finally, the intense heat waves occurred during summer 2007 along with extreme cold conditions during December 2003-February 2004 were analyzed in terms of PET classes and compared to the respective average bioclimatic conditions of the study period. © 2013 Panagiotis T. Nastos and Andreas Matzarakis.

The objective of this study is to present and analyse the indoor and outdoor temporal variability of the particulate matters of different sizes (namely: PM10, with diameter less than 10 μm; PM7, with diameter less than 7 μm; PM2.5, with diameter less than 2.5 μm and PM1, with diameter less than 1 μm) found in Athens, Greece. Four detectors were used for indoor and outdoor recordings. More specifically, the indoor recordings were performed in seminar rooms, full of students attending lectures, at the University of Athens and the Technological Education Institute of Piraeus. Findings of this research show that on one hand, the indoor particulate matter concentrations remained at lower levels than the thresholds set by the European Council Directives, but on the other hand, the outdoor particulate matter concentrations exceeded the thresholds many times. © The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Kriging interpolation technique is adapted to create the mapping of surface ozone seasonality and trends across Europe during 1997-2006, based on European Monitoring and Evaluation Programme ground measurements. The climatology, the annual and seasonal trends and the altitude above sea level (asl) dependence were studied as well as the relation with the North Atlantic Oscillation (NAO). The mean seasonal cycle amplitude and seasonal maximum display an increasing gradient from northwest to southeast, with high levels in Austria and eastern Mediterranean. Significantly close to 0 positive trends appear in UK, Slovakia, southern Scandinavia and Austria in winter and autumn. In Northern Hemisphere winter (December-February), about 40 % of near-surface ozone variability in the western edge of Europe may be attributed to circulation changes and ozone precursors' transport related to NAO. © 2013 Springer Science+Business Media Dordrecht.

The results of a comparison between monthly mean ozone column variations calculated from the chemical transport model Oslo CTM2 and those derived from solar backscatter ultraviolet (SBUV) satellite observations are presented for the period 1998-2009. Monthly mean total ozone derived from improved model simulations were used to compute monthly zonal means over 10 latitude zones over the northern and southern hemispheres. Ozone column variations from Oslo CTM2 are highly correlated with SBUV retrievals at all latitude zones. Equatorial zonal winds at 30 hPa were used as index to study the impact of quasi-biennial oscillation (QBO) on ozone. Correlations between modeled ozone and the QBO were found to be the order of +0.8 in the tropics. The impact of QBO was most pronounced at equatorial latitudes with amplitudes of +4 to -4 %. Seasonal variations in surface ozone and tropospheric ozone column calculated by the model are also presented. © 2013 Springer Science+Business Media Dordrecht.

Natural hazards pose an increasing threat to society and, for this reason, it is necessary to develop models and methodologies for better understanding and forecasting extreme weather events. A new structure of the Greek Regional Administration (Kallikratis) was established in 2011, based on geographical criteria, in order to create an operational and capable administration. An Atmospheric Hazards Early Warning System (AHEWS) could be characterised as an ultimate tool for the local authorities (first and second tier level) in order to organise and implement efficient plans to mitigate the risk. New operation centres (related to regional and municipality administration level) are suggested to be staffed and equipped with the proposed Early Warning System (EWS). The AHEWS will link to extensive Geographical Information Systems (GIS) datasets and methodologies for safety plans by government agencies and services in order to mitigate the impacts caused by atmospheric extreme events. AHEWS involves high-resolution Numerical Weather Prediction (NWP) products, ground observation network, lightning detection network and satellite information in terms of early convective, initiation and Now-Casting. Storms, lightings, gale winds, snow, hail, tornadoes, low temperatures, heatwaves and several others extreme events are weather phenomena that AHEWS deals with in order to prevent and mitigate impacts on humans and constructions. An automated dissemination procedure is described here for individual and administrative users, followed by safety and action plans, respectively. © 2013 Taylor & Francis.

The present study, deals with the 24-hour prognosis of the outdoor biometeorological conditions in an urban monitoring site within the Greater Athens area, Greece. For this purpose, artificial neural networks (ANNs) modelling techniques are applied in order to predict the maximum and the minimum value of the physiologically equivalent temperature (PET) one day ahead as well as the persistence of the hours with extreme human biometeorological conditions. The findings of the analysis showed that extreme heat stress appears to be 10.0% of the examined hours within the warm period of the year, against extreme cold stress for 22.8% of the hours during the cold period of the year. Finally, human thermal comfort sensation accounts for 81.8% of the hours during the year. Concerning the PET prognosis, ANNs have a remarkable forecasting ability to predict the extreme daily PET values one day ahead, as well as the persistence of extreme conditions during the day, at a significant statistical level of P < 0.01. © 2013 K. P. Moustris et al.

This paper investigates whether there is any association between the daily mortality for the wider region of Athens, Greece and the thermal conditions, for the 10-year period 1992-2001. The daily mortality datasets were acquired from the Hellenic Statistical Service and the daily meteorological datasets, concerning daily maximum and minimum air temperature, from the Hellinikon/Athens meteorological station, established at the headquarters of the Greek Meteorological Service. Besides, the daily values of the thermal indices Physiologically Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI) were evaluated in order to interpret the grade of physiological stress. The first step was the application of Pearson's χ 2 test to the compiled contingency tables, resulting in that the probability of independence is zero (p = 0. 000); namely, mortality is in close relation to the air temperature and PET/UTCI. Furthermore, the findings extracted by the generalized linear models showed that, statistically significant relationships (p < 0. 01) between air temperature, PET, UTCI and mortality exist on the same day. More concretely, on one hand during the cold period (October-March), a 10°C decrease in daily maximum air temperature, minimum air temperature, temperature range, PET and UTCI is related with an increase 13%, 15%, 2%, 7% and 6% of the probability having a death, respectively. On the other hand, during the warm period (April-September), a 10°C increase in daily maximum air temperature, minimum air temperature, temperature range, PET and UTCI is related with an increase 3%, 1%, 10%, 3% and 5% of the probability having a death, respectively. Taking into consideration the time lag effect of the examined parameters on mortality, it was found that significant effects of 3-day lag during the cold period appears against 1-day lag during the warm period. In spite of the general aspect that cold conditions seem to be favourable factors for daily mortality, the air temperature and PET/UTCI exceedances over specific thresholds depending on the distribution reveal that, very hot conditions are risk factors for the daily mortality. © 2011 Springer-Verlag.

Artificial Neural Network (ANN) models were developed and applied in order to predict the total weekly number of Childhood Asthma Admission (CAA) at the greater Athens area (GAA) in Greece. Hourly meteorological data from the National Observatory of Athens and ambient air pollution data from seven different areas within the GAA for the period 2001-2004 were used. Asthma admissions for the same period were obtained from hospital registries of the three main Children's Hospitals of Athens. Three different ANN models were developed and trained in order to forecast the CAA for the subgroups of 0-4, 5-14-year olds, and for the whole study population. The results of this work have shown that ANNs could give an adequate forecast of the total weekly number of CAA in relation to the bioclimatic and air pollution conditions. The forecasted numbers are in very good agreement with the observed real total weekly numbers of CAA. © 2012 Taylor & Francis.

This study analyses the Saharan dust (SD) events over Athens during 2000-2005 using daily Moderate Resolution Imaging Spectroradiometer (MODIS) and Total Ozone Mapping Spectrometer (TOMS) satellite data. The dust events were identified using the MODIS daily observations over Greece and the dates with detectable dust plumes were collected. The aerosol optical depth (AOD 550) and fine-mode (FM) values from Terra-MODIS and Aerosol Index (AI) values from TOMS were obtained over Athens for the dusty days focusing on analysing the seasonality, intensity, transport pathways and mechanisms of dust. Seventy-nine dusty days were identified corresponding to SD events with duration from 1 to 4 consecutive days; the majority of SD events occur in April-May and July, with less during winter. The dust frequency presents large seasonal and intra-annual variation, with a maximum of 20 dust events in 2002 and a minimum of 7 in 2003. The use of TOMS-AI seems to be adequate for the characterization of dust over Athens despite the fact that 35% of the dusty days do not correspond to high AI values. The dust events are more intense during spring, mostly associated with dust transport from near surface to mid troposphere (vertical transport mechanism), while dust events detected only within the boundary layer have the lowest AOD values. On the other hand, the dust events in summer are of larger duration due to stable weather conditions and absence of precipitation and transportation at elevated heights. © 2012 Taylor and Francis Group, LLC.

The goal of this work is the analysis of particulate matter with aerodynamic diameter less than 10 μm (PM10) recorded in the urban area of Volos, a medium-sized Greek coastal city on the eastern seaboard of Central Greece. For this purpose, concentration measurements of PM10, for a seven-year period (2001-2007) are analyzed. Air pollution data were obtained by a monitoring station, fully automated, that was established by the Hellenic Ministry of the Environment, Energy and Climatic Change, in order to measure air pollution levels in Volos. The extracted findings showed that the mean diurnal variation of the examined air pollutant concentrations within the cold and the warm period of the year show a double peak structure with respect to morning and evening hours. Additionally, the intra annual variation of PM10 concentrations shows a double peak pattern. The dominant peak is observed in February and the secondary peak in May/June. Besides, the role of wind seems to be significant as the PM10 exceedances are strongly associated with predominant wind directions. © by PSP 2012.

An attempt is made to forecast the daily maximum surface ozone concentration for the next 24 hours, within the greater Athens area (GAA). For this purpose, we applied Multiple Linear Regression (MLR) models against a forecasting model based on Artificial Neural Network (ANN) approach. The availability of basic meteorological parameters is of great importance in order to forecast the ozone's concentration levels. Modelling was based on recorded meteorological and air pollution data from thirteen monitoring sites within the GAA (network of the Hellenic Ministry of the Environment, Energy and Climate Change) over five years from 2001 to 2005. The evaluation of the performance of the constructed models, using appropriate statistical indices, shows clearly that in every aspect, the prognostic model by far is the ANN model. This suggests that the ANN model can be used to issue warnings for the general population and mainly sensitive groups. © 2012 K. P. Moustris et al.

The aim of this work is to study the bioclimatic conditions as well as the air quality for three different regions of the greater Athens area (GAA), during the warm period of the year for the time period 2001-2005. Furthermore, the thermal discomfort and the air pollution persistence within 24 hours were studied. Finally, both the variability and the trend of the bioclimatic and air quality conditions during the examined period were studied. In order to determine the human thermal comfort-discomfort levels, a widely used biometeorological index, the Cooling Power Index, and microclimatic data (air temperature and wind speed) were used. On the other hand, data concerning the air pollutant concentrations surface ozone (O 3) and particulate matter with aerodynamic diameter less than 10μm (PM 10) measured over this area were used for the determination of the air quality levels. The performed analysis indicates throughout the examined area degradation of the air quality and intensive thermal discomfort episodes. More specifically, during the warm period of the year a relatively high frequency of days, in the city center of Athens showing thermal discomfort and air quality degradation, simultaneously, is observed. On the contrary, on the suburban GAA's monitoring sites a reduction of the frequency of days with thermal discomfort is observed while the number of days with air pollution exacerbations is relatively high. In any case, during the examined period the environmental conditions due to bioclimatic and air quality parameters seem to be rather degraded. © by PSP.

This study analyses the weather conditions, the main pathways and transport mechanisms favouring the presence of specific aerosol types over Athens, Greece. On the basis of the aerosol optical depth at 550 nm (AOD 550) and fine mode (FM) values from a Terra-MODIS dataset in the period 2000-2005, three main aerosol types are identified (urban/industrial, UI; clean maritime, CM; and desert dust, DD), each one corresponding to different optical characteristics and source regions. The UI aerosols are associated with polluted air masses from Europe, the CM aerosols with clean Atlantic air masses and the DD aerosols with air masses from North African arid regions carrying significant amount of dust in certain cases. The comparison of the three aerosol types with the air masses from their favourable sector constitutes a first 'quick-validation' of the identification scheme. Thus, the incidence of transport from Europe explain 81% of the variability in the observed UI type, while the 73% of the Atlantic air masses correspond to the CM type; the 50% of the African air masses can be considered as DD aerosols over Athens. The mean synoptic meteorological patterns, favouring the presence of each aerosol type, are also investigated. Further analysing the air-mass trajectories at three altitudes, the transport mechanisms of the aerosol types are identified. The results clearly show that the UI aerosols are mainly transported within the boundary layer, while the CM conditions are associated with Atlantic air masses at higher altitudes. Moreover, the DD aerosols are transported either in the upper atmosphere or in the whole atmospheric column. This is among the first studies conducted over Athens aiming at investigating the weather conditions, pathways and transport mechanisms that favour the presence of aerosols of different characteristics. © 2011 Royal Meteorological Society.

In this work, artificial neural networks (ANNs) were developed and applied in order to forecast the discomfort levels due to the combination of high temperature and air humidity, during the hot season of the year, in eight different regions within the Greater Athens area (GAA), Greece. For the selection of the best type and architecture of ANNs-forecasting models, the multiple criteria analysis (MCA) technique was applied. Three different types of ANNs were developed and tested with the MCA method. Concretely, the multilayer perceptron, the generalized feed forward networks (GFFN), and the time-lag recurrent networks were developed and tested. Results showed that the best ANNs type performance was achieved by using the GFFN model for the prediction of discomfort levels due to high temperature and air humidity within GAA. For the evaluation of the constructed ANNs, appropriate statistical indices were used. The analysis proved that the forecasting ability of the developed ANNs models is very satisfactory at a significant statistical level of p < 0. 01. © 2012 Springer-Verlag.

The Mediterranean Basin and southern Europe are often affected by Saharan dust outbreaks, which influence the aerosol load and properties, air quality standards, visibility and human health. The present work examines, mainly of the meteorological point of view, three intense dust outbreaks occurred over Greece with duration of one or two days, on 4 and 6 February and 5-6 March 2009. The synoptic analysis on the dusty days showed the presence of low-pressure systems in the west coasts of Europe and the north Tyrrhenian Sea, respectively, associated with a trough reaching the north African coast. The result of these conditions was the strong surface and mid troposphere winds that carried significant amounts of dust over Greece. During the dusty days extensive cloud cover associated with the dust plume occurred over Greece. The air-mass trajectories showed a clear Saharan origin in all atmospheric levels, while the satellite (MODIS Terra/Aqua) observations as well as the model (DREAM) predictions verified the intense dust outbreaks over eastern Mediterranean and Greece. The ground based particulate matter concentrations in Athens were excessively increased on the dusty days (PM 150-560 g/m3), while significant dry and wet deposition occurred as forecasted by DREAM model. © 2012 P. T. Nastos.

Background/Aims: The transmission rate of air-borne infectious diseases may vary secondary to climate conditions. The study assessed time trends in the seasonality of hospitalized varicella cases in a temperate region in relation to climatic parameters prior to the implementation of universal varicella immunization. Methods: A retrospective descriptive study was conducted among all pediatric and adolescent varicella patients (n = 2366) hospitalized at the "Aghia Sophia" Children's Hospital during 1982-2003 in Athens, Greece. Date of infection was computed based on hospital admission date. Seasonal and monthly trends in the epidemiology of varicella infection were assessed with time series analysis (ARIMA modeling procedure). The correlation between the frequency of varicella patients and the meteorological parameters was examined by the application of Generalized Linear Models with Gamma distribution. Results: During 1982-2003, the occurrence of hospitalized varicella cases increased during summer (p = 0.025) and decreased during autumn (p = 0.021), and particularly in September (p = 0.003). The frequency of hospitalized varicella cases was inversely associated with air temperature (p<0.001). In contrast, the occurrence of hospitalized varicella cases was positively associated with wind speed (p = 0.009). Conclusions: Pediatric hospitalizations for varicella infection rates have increased during summer and decreased during autumn in the examined temperate region. Time trends in hospitalized varicella cases are associated with climatic variables. © 2012 Critselis et al.

We investigated the short-term effects of particulate matter with aerodynamic diameter <10γg/m3 (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) on pediatric asthma emergency admissions in Athens, Greece over the period 2001-2004. We explored effect modification patterns by season, sex, age and by the presence of desert dust transported mainly from the Sahara area.We used daily time-series data provided by the children's hospitals and the fixed monitoring stations. The associations were investigated using Poisson regression models controlling for seasonality, weather, influenza episodes, day of the week and holiday effects.A 10γg/m3 increase in PM10 was associated with a 2.54% increase (95% confidence interval (CI): 0.06%, 5.08%) in the number of pediatric asthma hospital admissions, while the same increase in SO2 was associated with a 5.98% (95% CI: 0.88%, 11.33%) increase. O3 was associated with a statistically significant increase in asthma admissions among older children in the summer. Our findings provide limited evidence of an association between NO2 exposure and asthma exacerbation. Statistically significant PM10 effects were higher during winter and during desert dust days, while SO2 effects occurred mainly during spring.Our study confirms previously reported PM10 effects on emergency hospital admissions for pediatric asthma and further provides evidence of stronger effects during desert dust days. We additionally report severe effects of SO2, even at today's low concentration levels. © 2011 Elsevier Inc.

Surface air temperature trends in the wider region of Greece during the period 1951-2007, related to atmospheric circulation, are examined in this work. A network of 31 meteorological stations in the Hellenic area and the Asia Minor coasts and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets were used for this purpose. The NCEP/NCAR reanalysis datasets were created by assimilating climate observations from different sources including ships, satellites, ground stations, radiosonde observations and radar. The general purpose of conducting the reanalyses was to produce multiyear global state-of-the-art gridded representations of atmospheric states, generated by a constant model and a constant data assimilation system. The findings of the analysis show that the mean annual surface air temperature in the wider region of Greece exhibits a pronounced cooling trend from the beginning of the 1950s up to the mid-1970s. It then remained at low levels until the beginning of the 1990s, and then increased up to 2000, when a turning-point is clear although the temperature remained at high levels. The well-known atmospheric circulation indices of the wider region of Europe, namely the North Atlantic Oscillation Index (NAOI), the Mediterranean Oscillation Index (MOI) and the North Sea Caspian Pattern Index (NCPI), were used to investigate the relationship between surface air temperature and atmospheric circulation in this region of the Eastern Mediterranean. The surface air temperature is not correlated to the NAOI, while it is statistically significantly (95% confidence level (CL)) correlated to the MOI, but only during wintertime. On the contrary, good correlations, which are statistically significant (95% CL), appear between the NCPI and the surface air temperature during all seasons, but particularly in winter. © 2011 Taylor & Francis.

To describe the tourism potential of an area, not only single meteorological parameters have to be taken into account, but also thermal sensation and people's thermal comfort. The latter can be estimated by the use of human energy balance models and the derived thermal indices, which comprise all relevant meteorological parameters like air temperature, air humidity, wind speed, and short and long wave radiation fluxes. This paper makes an attempt to assess and analyze climatological parameters and the thermal comfort of Crete, its variations and trends for the period of time 1955-2001. In addition, a definition and quantification of the island's tourism potential is carried out. Long term data from several stations are used from the existing climatic and synoptic network of Crete, including daily mean, maximum and minimum temperature, relative humidity, wind speed, and cloud cover over the whole island, in order to derive the daily Physiologically Equivalent Temperature (PET) and precipitation. In addition, possible trends of thermal comfort and precipitation on an annual and seasonal basis are analyzed. Additionally, data of the 10-minutes climatology of the Climate Research Unit of the University of Norwich have been processed in order to create high resolution (1 km) mean monthly maps for climatological parameters such as air temperature, precipitation and Physiologically Equivalent Temperature. © 2011 Global NEST Printed in Greece. All rights reserved.

In recent years, significant changes in precipitation regimes have been observed and these manifest in socio economic and ecological problems especially in regions with increased vulnerability such as the Mediterranean region. For this reason, it is necessary to estimate the future projected precipitation on short and long-term basis by analyzing long time series of observed station data. In this study, an effort was made in order to forecast the monthly maximum, minimum, mean and cumulative precipitation totals within a period of the next four consecutive months, using Artificial Neural Networks (ANNs). The precipitation datasets concern monthly totals recorded at four meteorological stations (Alexandroupolis, Thessaloniki, Athens, and Patras), in Greece. For the evaluation of the results and the ability of the developed prognostic models, appropriate statistical indexes such as the coefficient of determination (R2), the index of agreement (IA) and the root mean square error (RMSE) were used. The findings from this analysis showed that the ANN's methodology provides satisfactory precipitation totals in four consecutive months and these results are better results, than those obtained using classical statistical methods. A fairly good consistency between the observed and the predicted precipitation totals at a statistical significance level of p < 0.01 for the most of the examined cases has been revealed. More specifically, the Index of Agreement (IA) ranges between 0.523 and 0.867 and the coefficient of determination (R2) ranges between 0.141 and 0.603. The most accurate forecasts concern the mean monthly and the cumulative precipitation for the next four consecutive months. © 2011 Springer Science+Business Media B.V.

The paper studies the climatology of the Discomfort Index (DI) and the Common Air Quality Index (CAQI) in a large Mediterranean urban center (Greater Thessaloniki Area), examines the relations between the indices and the climatic conditions in the study area and investigates the linkage between the Urban Heat Island (UHI) effect and the enhanced discomfort and poor air quality in the city center. Discomfort conditions are more enhanced during July and August. Atmospheric conditions when the population suffers discomfort and feels severe stress are found mainly in the summer season hours with total frequency that can be up to about 4% in a month. Throughout the year, air quality conditions are unhealthier in the stations of urban characterization. Very high daily CAQI values are more frequent during the cold period (about 14%) than during the warm period (1-2%) of the year in the urban stations. Daily DI∈≥24°C could be more associated to increased temperature than relative humidity and is strongly related to high and very high CAQI values. During summer, when daily CAQI is ≥76, the feeling of discomfort is the most probable. Consequently, a strong synergy between discomfort and bad air quality exists in summertime. High and very high CAQI values and the discomfort feeling by the majority of the population are related to stagnant atmospheric conditions. During summer season, the poor air quality and the unfavorable comfort conditions for the majority of the population in the city center are associated with the greater frequency of a more intense UHI effect. The above phenomenon is more pronounced during nighttime than daytime. © 2011 Springer Science+Business Media B.V.

The objective of this study is to examine the synergistic environmental impacts (thermal bioclimatic conditions and air quality due to particulate pollution) with cardiovascular and respiratory syndromes, in Heraklion in the northern part of Crete Island, during a Saharan dust episode on March 22-23, 2008. Daily counts of admissions for cardiovascular and respiratory syndromes were obtained from the two main hospitals in Heraklion. The corresponding daily meteorological parameters, such as maximum and minimum air temperature, relative humidity, wind speed and cloud cover, from the meteorological station of Heraklion (Hellenic National Meteorological Service), were processed in order to estimate and analyze the bioclimatic conditions expressed by the Physiologically Equivalent Temperature (PET), which is based on the energy balance models of the human body. Dust concentrations were derived from the SKIRON forecast model of the University of Athens, while Moderate Resolution Imaging Spectroradiometer (MODIS) products such as aerosol optical depth at 550 nm (AOD550), aerosol small mode fraction (SM), Ångström exponent in the 550-865 nm band and mass concentration, were used for the episode. Besides, daily composite anomalies (reference period: 1968-1996) of the air temperature and vector wind from the middle to the lower atmospheric levels (500 hPa - mean sea level) on March 23, 2008, were calculated from the reanalysis datasets of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The analysis of MODIS and SKIRON products showed that high AOD 550 values (>0.9) and high dust concentration (>250 μg/m 3), respectively, appear on March 23, 2008, while the respiratory admissions were five-fold than the mean daily admissions on the same day of the emergence of the Saharan dust episode (key day). According to the analysis, this is due to the existence of coarse-mode particles along the dust pathway, which trigger respiratory syndromes more than cardiovascular, which are associated more with ultra-fine particles. The admissions concerning the cardiovascular syndromes did not appear any significant change. The analysis of the bioclimatic conditions on the key day revealed that moderate thermal stress existed and this may be attributed mainly to the geomorphology of the island, which is responsible for special weather conditions such as Fohn winds. The drier atmospheric conditions, as a result of strong, desiccating winds on the leeward side of the mountains, contribute more to the already high hospital admissions for respiratory symptoms. © Gebrüder Borntraeger, Stuttgart 2011.

The goal of this study is the analysis of heat waves and their impact on humans, using human biometeorological indices, which are based on the energy balance of the human body. The implications for humans are not only described through the intensity of the heat waves, but also through their duration over consecutive days. Both intensity and duration were analyzed for the Greater Athens Area during the period 1955 to 2001. The analysis was carried out using the daily physiologically equivalent temperature and the daily minimum air temperature. Based on these two parameters, the results showed an increase in the average duration of heat waves. Furthermore, the use of the Gaussian filter revealed the intra-annual variation of heat stress conditions and their relevance to humans. The results could be used for the management of the negative consequences of heat waves in cities suffering from environmental pollution and also for climate impact studies. © 2010 Springer-Verlag.

In this study, the trends and variability of annual precipitation totals and annual rain days over land within the Mediterranean region are analyzed. Long term ground-based observations concerning, on one hand, monthly precipitation totals (1900-2010) and rain days (1965-2010) from 40 meteorological stations within the Mediterranean region were obtained from the Hellenic National Meteorological Service and the World Climate Data and Monitoring Programme (WCDMP) of the World Meteorological Organization. On the other hand, high spatial resolution (0.5 × 0.5 ) gridded monthly data CRU TS 3.1 were acquired from the Climatic Research Unit, University of East Anglia, for the period 1901-2009. The two datasets were compared by means of trends and variability, while the influence of the North Atlantic Oscillation (NAO) in the Mediterranean precipitation was examined. In the process, the climatic changes in the precipitation regime between the period 1961-1990 (reference period) and the period 2071-2100 (future climate) were presented using climate model simulations (RACMO2.1/KNMI). The future climate projections were based on SRES A1B. The findings of the analysis showed that statistically significant (95% confidence level) negative trends of the annual precipitation totals exist in the majority of Mediterranean regions during the period 1901-2009, with an exception of northern Africa, southern Italy and western Iberian peninsula, where slight positive trends (not statistically significant at 95% CL) appear. Concerning the annual number of rain days, a pronounced decrease of 20 %, statistically significant (95% confidence level), appears in representative meteorological stations of east Mediterranean, while the trends are insignificant for west and central Mediterranean. Additionally, NAO index was found to be anticorrelated with the precipitation totals and the number of rain days mainly in Spain, southern France, Italy and Greece. These correlations are higher within the rain season (October-March) than the entire year. Based on the results of regional climate model RACMO2.1/KNMI, precipitation is very likely to decrease almost 20% in the period 2071-2100 compared to 1961-1990, under SRES A1B. © Author(s) 2011.

Urban particulate matter (PM 10-PM 2.5 and PM 2.5) from Athens (Greece) atmosphere, primarily investigated by SEM-EDS, was further studied in the FLUO and SUL-X beamlines of ANKA Synchrotron facility (KIT, Germany). The SR μ-XRF study showed both geological (e.g. CaTi, CaK and CaSrKRb) and anthropogenic particles exhibiting heavy metal combinations such as FeCo, FeCoCuV and ZnV. It was also revealed that very hazardous metalloids and heavy metals, namely As and Pb, are concentrated in isolated respirable (PM 2.5) microparticles. It was attempted to investigate the oxidation state of As by means of μ-XANES. The As K-edge XANES spectrum of the sample shows a main peak at about 11.874 keV which matches adequately with the As(V) reference spectrum but part of the As seems to have a lower oxidation state (most probably As(III)). This is the first non-bulk study with regard to the partitioning and solid-state speciation of hazardous chemical elements in urban atmospheric microparticles from greater Athens area, rated as an alpha-world city with a population of ca. 4 million people. © 2011 Elsevier B.V. All rights reserved.

The main objective of the present study is to perform a trend analysis and investigate the possible changes in the frequency and wind intensity of the Etesians during June to September of the years 1979 to 2009. The analysis is based mainly on the use of Reanalysis-1 data from the National Centers for Environmental Prediction/National Center for Atmospheric Research. The results are indicative of negative trends in the frequency and wind speed (WS) of the Etesians. During the 31-year period studied, the total number of Etesian days from June to September decreased by about 4.6 days, while the monthly maximum intensity of the daily WS was reduced by almost 1 m s-1. The above indications are strengthened by similar results derived from the trend analysis of observational wind data in the central Aegean for the years 1955 to 2002. The negative trend in the frequency of the Etesian days could be explained by a decreasing trend in the pressure gradient between the central and southern Europe high-pressure center and the Middle East low-pressure center, which cause the Etesians system. In the study, a possible association between the Southern Oscillation and the Etesian winds is also revealed. The negative trend in the frequency and WS of the Etesian winds could imply a reduced cooling mechanism in the eastern Mediterranean in the summer period due to climate change. © 2011 Springer-Verlag.

In this study, the variability and trends of the mean annual and seasonal maximum and minimum surface air temperature in Greece are examined, using monthly data sets of 26 meteorological stations from the Hellenic National Meteorological Service (HNMS) and gridded data from the National Center for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) Reanalysis project for the period 1955-2001. NCEP-NCAR reanalysis data sets are created by assimilating climate observations from different sources, including ships, satellites, ground stations, radiosonde observations and radar. The general purpose of conducting reanalyses is to produce multi-year global state-of-the-art gridded representations of atmospheric states, generated by a constant model and a constant data-assimilation system. The trends of the mean extreme air temperatures were evaluated, using the Mann-Kendall criterion, and, in the process, factor analysis was applied to both the stations' and the NCEP-NCAR grid points time series. Regarding the mean maximum air temperature, the first main factor, which explains a high percentage of the total variance, presents a statistically significant (CL = 95%) negative trend only during the winter. The first main factor of the mean minimum air temperature manifests a statistically significant (CL = 95%) positive trend during the summer and the year, and a statistically significant (CL = 95%) negative trend in autumn and winter. These findings were compared to the respective ones of the NCEP-NCAR reanalysis data and significant differences in the spatial distribution and temporal variability of the extracted new factors were found. These differences between the two examined data sets could be attributed to topographical factors such orography and land-sea distribution, which could not be represented properly by the reanalysis model. © 2011 Taylor & Francis.

Biomass burning and associated emissions of aerosols into the atmosphere play a vital role in atmospheric composition and climate change. During summer of 2007, Greece faced the worst natural disaster recorded in recent decades in terms of human losses, number of fire outbreaks and extent of the estimated burned area (more than 12% of the total forested areas in Greece). The present study aims at analyzing the impact of these fire events in western Peloponnese on atmospheric aerosol concentrations using satellite data. MODIS-derived Aerosol Optical Depth (AOD), effective radius, Ångström exponent, mass concentration, cloud-condensation nuclei (CCN) and OMI Aerosol Index (AI), single scattering albedo, absorption and extinction optical depths were analyzed. MODIS data showed smoke plumes traversing thousands of kilometers southwards influencing the central Mediterranean as well as the north African coastal regions. These thick smoke plumes dramatically affected AOD and aerosol-mass concentrations over the region and altered the microphysical aerosol properties, such as the effective radius and absorption coefficient. Model calculations suggested that the shortwave radiation at the ground was reduced by ∼50 Wm2, while that at the top of the atmosphere was reduced by ∼20 Wm2 resulting in atmospheric heating of ∼30 Wm2 over the areas affected by the smoke plumes. © 2010 Elsevier Ltd.

In this paper we examined whether the recorded precipitation changes cause erosion in Naxos Island, Greece using precipitation indices derived from daily precipitation totals, during the period 1955-2007, in order to develop an erosion risk model. Although the mean annual precipitation appear to be low (∼360.0 mm), the erosion processes of the area are very intense, because of the intensive character of precipitation, the high slope relief, the differential lithology and the absence of important land cover The results of the analysis showed that the climatic changes in precipitation and the changes in land cover and land use are the main drivers for the erosion. This is why the 2nd (1971-1985) and 3rd (1986-2007) studied sub-periods may be called of high erosion risk, and especially the second one mainly because of the increased frequency of extreme precipitation events. © 2010 Author(s).

The application of harmonic analysis to the annual variability of precipitation is the object of this study, so that the modes, which compose the annual variability, be elicited. For this purpose, monthly precipitation totals from 30 meteorological stations of the Hellenic National Meteorological Service (HNMS), for the period 1950-2000, were used. The initial target is to reduce the number of variables and to detect structure in the relationships between the variables. The most commonly used technique for this purpose is the application of Factor Analysis (FA) resulted in five main factors (sub-regions) with common precipitation characteristics, explaining 77% of the total variance. For each sub-region, a representative station is selected for the analyses, mainly, as the station within the sub-region with the highest factor loading. In the process, the Fourier Analysis is applied to the mean monthly precipitation, so that 2 harmonic components are derived, which explain more than 90% of the total variability of each station, and are due to different synoptic and thermodynamic processes associated with Greece's precipitation regime. Finally the calculation of the time of the maximum precipitation, for each harmonic component, gives the spatial distribution of the appearance of the maximum precipitation in the Greek region.

Ship-borne sunphotometer measurements obtained in the Arabian Sea (AS) in the pre-monsoon season (18 April-10 May 2006) during a cruise campaign (ICARB) have been used to retrieve the Aerosol Optical Depth (AOD; τ) and the Ångström wavelength exponent (α). The continents surrounding the AS produce natural and anthropogenic aerosols that have distinctive influences on α and its spectral distribution. The α values were estimated by means of the least-squares method over the spectral bands 340-1020 nm and 340-870 nm. The spectral distribution of AOD in logarithmic co-ordinates could be fit using a 2nd order polynomial with higher accuracy in the wavelength band 340-1020 nm than in the 340-870 nm band. A polynomial fit analytically parameterizes the observed wavelength dependencies of AOD with least errors in spectral variation of α and yields accurate estimates of the coefficients (α1 and α2). The coarse-mode (positive curvature in the ln λ vs. ln λ) aerosols are mainly depicted in the Northern part of the AS closely associated with the nearby arid areas while fine-mode aerosols are mainly observed over the far and coastal AS regions. In the study period the mean AOD at 500 nm is 0.25±0.11 and the α340-1020 is 0.90±0.19. The α340-870 exhibits similar values (0.92±0.18), while significant differences revealed for the constant terms of the polynomial fit (α1 and α2) proportionally to the wavelength band used for their determination. Observed day-to-day variability in the aerosol load and optical properties are direct consequence of the local winds and air-mass trajectories along with the position of the ship. © Author(s) 2010.

In this study, the mean rain intensity (mm/h) in Athens and Thessaloniki, Greece, is examined during the period 1930-2007. The daily meteorological data were acquired from the meteorological stations of the National Observatory of Athens (Thissio) and the University Campus of Thessaloniki. These stations have recorded the longest and reliable daily rain time series in Greece. The trends of the annual and seasonal mean, as well as the maximum rain intensity, are analyzed. On the one hand, all of the time series in Athens present higher figures of mean rain intensity during the period 1990-2007 compared to the period 1930-1990. On the other hand, regarding the time series in Thessaloniki, the mean rain intensity remains in lower level than the respective one in Athens without significant trend at the Confidence Level (CL) 95%. As far as the annual and seasonal maximum rain intensity is concerned, similar patterns appear. However, the summer maximum rain intensity in Thessaloniki remains at higher levels till 1970's. The atmospheric circulation patterns for the extreme rain intensities show intense negative anomalies centred over Greece and positive anomalies to the north, with centre over Scandinavia.

The goal of this work is the analysis of air quality levels in the area of Volos, a city of average size on the eastern seaboard of Central Greece. For this purpose, concentration measurements of sulfur dioxide, nitrogen oxide, and nitrogen dioxide, for a 4-year period (2001-2004) are analyzed. Air pollution data were obtained by a monitoring station, fully automated, which was established by the Hellenic Ministry of the Environment, Physical Planning, and Public Works, in order to measure air pollution levels in Volos, a medium-sized city, which faces the effects of industrialization. The main conclusions from the statistical analysis of the 4-year measurements of hourly SO2, NO2, and NO concentrations in the city of Volos, showed that the mean seasonal variation of the examined air pollutant concentration presents a minimum during the warm period of the year and a maximum during the cold period. Although the local geomorphology and meteorology encourage particularly the accumulation of air pollutants, the analysis shows that the SO2 and NO2 concentration levels remain lower than corresponding thresholds for human health protection set by the European Union, in this urban measuring site, during the examined period. The application of harmonic analysis revealed the difference between the annual variation of the SO2 and NO x concentrations. Regarding NO x, the variation is mainly due to the first harmonic term (anthropogenic factor), while the SO2 variation is interpreted by the two harmonic terms, which represent the anthropogenic and meteorological factors, respectively. © 2009 Springer Science+Business Media B.V.

Tornado activity is associated with extreme convective weather which can cause extended damage and even in some cases the loss of life. The complex inland terrain of Greece along with the Ionian Sea at the west and the Aegean Sea at the east appear to be a favorable area for fury phenomena such as tornadoes, waterspouts and funnel clouds. In this study, the spatial and temporal variability of tornado activity in Greece for the period 1900g-1999 are presented. The spatial distribution of tornadoes, waterspouts and funnel clouds reveals the vulnerability of specific geographical areas, such as the west Greece and the south Aegean Sea. As far as the intra annual variability is concerned, the maximum of tornado activity dominates within the cold period of the year (Octoberg-March) while according to the daily distribution, tornadoes happen frequently during the warm hours of the day. It is remarkable to mention that in Greece, within the 20th century, the tornado activity caused the loss of 4 lifes, the injury of 40 people and numerous damages on human constructions and cultivations. © 2010 Author(s).

The Aerosol Index (AI) observations derived from the Ozone Monitoring Instrument (OMI) on board the Dutch-Finnish Aura satellite are analyzed over Greece covering the period from September 2004 to August 2008. The AI data cover the whole Greek territory (34°-42°N, 20°-28°E) with a spatial resolution of 0.25° × 0.25° The results show significant spatial and temporal variabilities of the seasonal and monthly-mean AI, with higher values at the southern parts and lower values over northern Greece. On the other hand, the AI values do not show significant differences between the western and eastern parts and, therefore, the longitude-averaged AI values can be utilized to reveal the strong south-to-north gradient. This gradient significantly changes from season to season being more intense in spring and summer, while it is minimized in winter. Another significant remark is the dominance of negative AI values over northern Greece in the summer months, indicating the presence of non-UV-absorbing aerosols, such as sulfate and sea-salt particles. The great geographical extent of the negative AI values in the summer months is indicative of long-range transport of such aerosols. In contrast, the high positive AI values over southern Greece, mainly in spring, clearly reveal the UV-absorbing nature of desert-dust particles affecting the area during Saharan dust events. The annual variation of spatial-averaged AI values shows a predominant spring maximum (0.424 ± 0.329, in April) due to dust particles, which dominate this average and a summer minimum due to the negative AI values observed over northern Greece. In the cold period of the year (November to February) the AI values are higher over northern Greece compared to those in south, while in the rest of the year the opposite is true. © 2010 Elsevier B.V.

Extreme precipitation events have significant environmental consequences because they may cause considerable damages to urban as well as rural areas. The aim of this work is to construct a threshold model which will describe the exceedances over a threshold for the daily precipitation totals over Athens, Greece. The data used are daily precipitation totals recorded at the National Observatory of Athens, for a 115-year period (1891-2005). The generalized Pareto distribution is considered as the proper distribution for the study of the exceedances. The threshold of u=15.8 mm (10% upper limit) is used for the construction of the optimal return level function. © Author(s) 2010.

This study focused on Saharan dust (SD) events over Athens, Greece, based on measurements of the daily aerosol optical depth at 550 nm (AOD550) and the fine-mode fraction (FM) derived from Terra Moderate Resolution Imaging Spectroradiometer (MODIS) observations. Back-trajectories ending at Athens at altitudes of 500, 1000 and 4000 m were calculated by means of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Several criteria were taken into account to identify the SD events. According to these criteria and the altitudes of the air masses, three dust transport mechanisms were identified: (1) vertical transport (VT), including the whole atmospheric column, (2) upper atmosphere transport (UAT), above the atmospheric boundary layer, and (3) boundary layer transport (BLT), only within the lower atmospheric levels. The Aerosol Index (AI) derived from Total Ozone Mapping Spectrometer (TOMS) data was found to be adequate for characterization of the dust load over Athens, while higher values of the AI were found in cases where the dust was transported in the upper atmosphere. The predictions of the Dust Regional Atmospheric Model (DREAM) were consistent with the satellite observations and back trajectories, indicating the suitability of the model for monitoring dust transport over the Mediterranean. The analysis presents three case studies, one for each transport mechanism, where the aerosol field deduced from satellites and models is presented over the Eastern Mediterranean. In conclusion, this study shows that the combination of remote sensing measurements and back-trajectory calculations constitutes a powerful tool for the identification of SD events over Athens, while modelling can monitor the spread of the dust. © 2010 Taylor & Francis.

Background: Particulate matter with diameter less than 10 micrometers (PM10) that originates from anthropogenic activities and natural sources may settle in the bronchi and cause adverse effects possibly via oxidative stress in susceptible individuals, such as asthmatic children. This study aimed to investigate the effect of outdoor PM10concentrations on childhood asthma admissions (CAA) in Athens, Greece. Methods: Daily counts of CAA from the three Children's Hospitals within the greater Athens' area were obtained from the hospital records during a four-year period (2001-2004, n = 3602 children). Mean daily PM10concentrations recorded by the air pollution-monitoring network of the greater Athens area were also collected. The relationship between CAA and PM10concentrations was investigated using the Generalized Linear Models with Poisson distribution and logistic analysis. Results: There was a statistically significant (95% CL) relationship between CAA and mean daily PM10concentrations on the day of exposure (+3.8% for 10 μg/m3 increase in PM10concentrations), while a 1-day lag (+3.4% for 10 μg/m3 increase in PM 10concentrations) and a 4-day lag (+4.3% for 10 g/m3 increase in PM10concentrations) were observed for older asthmatic children (5-14 year-old). High mean daily PM10concentration (the highest 10%; >65.69 μg/m3) doubled the risk of asthma exacerbations even in younger asthmatic children (0-4 year-old). Conclusions: Our results provide evidence of the adverse effect of PM10on the rates of paediatric asthma exacerbations and hospital admissions. A four-day lag effect between PM10peak exposure and asthma admissions was also observed in the older age group. © 2010 Nastos et al; licensee BioMed Central Ltd.

It is well-known that natural and anthropogenic emissions of ambient pollutants affect air quality, and as a consequence the public health. Air pollution indices are commonly used to indicate the level of severity of air pollution to the public. The objective of this study is the assessment of the air quality levels in the urban environment of Athens, Greece using the Air Quality Index (AQI), which presents advantages as an administrative tool for early warning in the context of public health protection. The AQI is a complex index and calculated by compounding appropriately the concentrations of surface ozone (O3), nitrogen dioxide (NO2), sulphur dioxide (SO2), carbon monoxide (CO) and particles with aerodynamic diameter less than 10 μm (PM 10). For this purpose, available hourly data of the above ambient pollutants recorded by the Athens air pollution monitoring network, during the period 2001-2006, were analyzed for the development of the proposed index. The temporal and spatial distribution of the mean annual AQI values within greater Athens area (GAA) is examined, and the results are analyzed in terms of the meteorological conditions. The effect of wind speed and direction on AQI levels is found to be significant, among the other meteorological parameters such as air temperature, relative humidity, sunshine and total solar radiation. The analysis revealed that the higher values of AQI, during the warm period of the year, are strongly associated with sea breeze than with northern wind flow. The knowledge of the sea breeze characteristics over GAA contributes to the comprehension of the local air quality formation levels. Β© by PSP.

In this study, the spatial and temporal variability of the mean annual rain intensity in Greece are examined during a 41-year period (1962-2002). The meteorological datasets concern monthly rain amounts (mm) and the respective monthly durations (h) recorded at thirty two meteorological stations of the Hellenic National Meteorological Service, which are uniformly distributed on Greek territory, in order to calculate the mean monthly rain intensity. All the rain time series used in the analysis were tested by the application of the short-cut Bartlett test of homogeneity. The spatial distribution of the mean annual rain intensity is studied using the Kriging interpolation method, while the temporal variability, concerning the mean annual rain intensity trends along with their significance (Mann-Kendall test), is analysed. The findings of the analysis show that statistically significant negative trends (95% confidence level) appear mainly in the west sub-regions of Greece, while statistically significant positive trends (95% confidence level) appear in the wider area of Athens and the complex of Cyclades Islands. Further analysis concerning the seasonal rain intensity is needed, because there are different seasonal patterns, taking into account that, convective rain in Greece occurs mainly within the summer season. Β© 2010 Author(s).

A discrimination of the different aerosol types over the Arabian Sea (AS) during the Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB-06) is made using values of aerosol optical depth (AOD) at 500 nm (AOD500) and Ångström exponent (α) in the spectral band 340-1020 nm (α340-1020). For this purpose, appropriate thresholds for AOD500 and α340-1020 are applied. It is shown that a single aerosol type in a given location over the AS can exist only under specific conditions while the presence of mixed aerosols is the usual situation. Analysis indicates that the dominant aerosol types change significantly in the different regions (coastal, middle, and far) of AS. Thus the urban/industrial aerosols are mainly observed in coastal AS, the desert dust particles occur in the middle and northern AS, while clear maritime conditions mainly occur in far AS. Spectral AOD and Ångström exponent data were analyzed to obtain information about the adequacy of the simple use of the Ångström exponent and spectral variation of a for characterizing the aerosols. Using the least squares method, α is calculated in the spectral interval 340-1020 nm along with the coefficients a1 and a2 of the second-order polynomial fit to the plotted logarithm of AOD versus the logarithm of wavelength. The results show that the spectral curvature can effectively be used as a tool for their discrimination, since the fine mode aerosols exhibit negative curvature, while the coarse mode particles exhibit positive curvature. The correlation between the coefficients a1 and a2 with the Ångström exponent, and the atmospheric turbidity, is further investigated. Copyright 2009 by the American Geophysical Union.

In this study, the distribution patterns of physical (sand%, loam%, clay%, pH and organic matter%o) and chemical (calcium carbonate (CaCO3), sodium (Na+), magnesium (Mg+2), phosphorus (P), boron (B), iron (Fe), manganese (Mn) and zinc (Zn)) parameters of soil commonly assayed in analytical chemistry laboratories, are reported. Three representative areas (lowland (LL), semi-mountainous (SM), and coastal (C)) and 170 sample sites were selected, 510 soil samples were collected and analyzed for a 3-years period (2002-2004), in the prefecture of Larissa, Thessaly, central Greece. In each studied site, the kind of cultivation is also reported. Soils in LL area of the prefecture of Larissa were found to be rich in organic matter, Mg, B, but poor in Fe, Mn and Zn, when compared to the other two sites. The studied SM area of Larissa's prefecture constituted from clayey soils showed big concentrations of Mg, Zn, high value of clay and low value of sand, when compared to the other two studied areas. The studied C area is characterized by the sandy soils near the coastal areas of the prefecture of Larissa. In each studied area, the parameters are principally separated into two main clusters, each of them divided additionally into sub-clusters with slight differences. Six latent factors explain 78.1%, 74.3%, and 74.6% of the total variance of the LL-site, SM-site, and C-site, respectively, which is an indication for the factor analysis model adequacy.

Relativistic electrons (with energies >150 keV) which originate in the outer radiation belt and detected by the Russian 'Meteor' series of satellites have been correlated with the atmospheric total ozone data compiled by almost 90 stations located around the world within the latitude zone 40°-70°N. In more than 60% of the stations examined we have detected a clear decrease of the ozone 3-5 days after the electron flux excess. A numerical model has been applied to approximate this effect based on relativistic electron initiated nitric oxides creation in the upper mesosphere with subsequent atmospheric transport (both vertical and horizontal) towards the upper stratosphere. A first attempt of local and temporal prediction of ozone depletion because of energetic electrons impact in the middle atmosphere has been illustrated. © 2008 COSPAR.

Precipitating electrons from the radiation belts with energies greater than from 150 keV to 5 MeV have been correlated with ozone data of a large number of stations located within 40-70° N. Energetic electrons have been collected by the low altitude polar Russian satellite METEOR while ozone data have been compiled from almost ninety (90) stations located all over the world within the latitude zone 40-70° N. In more than 60% of the stations examined, we detect a clear decrease of the ozone variation during and after the occurrence of an electron flux excess, which recovers within 3-5 days. The more northern is a station located, the deeper is the ozone decrease. Moreover, clear evidence that the solar cycle affects ozone destruction through energetic electron events is presented. The preliminary results of the present work stimulate a future attempt for a simple ozone destruction mechanism formulation, which could describe atomic nitrogen ionization by energetic electrons, which in the following merge to atomic oxygen and produce nitrogen oxides. Finally, nitrogen oxides destruct ozone creating characteristic decreases on the normal ozone variation. © 2008 COSPAR.

Measurements of positive and negative small atmospheric ion concentrations have been made regularly since 1968 at the National Observatory of Athens (NOA). In this paper the 17-year period 1968-1984 is summarized. The diurnal and annual variations are examined, and Fourier analysis is also used for the study of the diurnal variation. The concentrations of small ions follow a double diurnal course. The maxima occur near 3-5 h and 13-16 h local time (LT = GMT + 2 h). The minima are observed at 6-8 h and 21-23 h. The annual course of small ions presents maximum concentration values around the summer season. The mean of the small ion concentration (SIC) for the 17-year period (1968-1984) is n+ = 188.8 ions/cm3 for positive ions and n- = 151.1 ions/cm3 for negative ions. Their ratio is equal to 1.25. The year-to-year variation of SIC for the examined period shows a negative trend. The results from multiple regression analysis show that wind speed and SIC are positively correlated, while relative humidity, smoke and sulphur dioxide are negatively correlated. © 2008 Elsevier B.V. All rights reserved.

The objective of this study is to find out the spatial and temporal variability of the dry and wet spells in Greece, during the period 1958-2007. The meteorological data with respect to daily precipitation totals were acquired from 27 meteorological stations of the Hellenic National Meteorological Service, which are uniformly distributed over the country. The dry spells concern consecutive dry days (CDD); the largest number of consecutive days with daily precipitation amount less than 1 mm, within a year. The wet spells concern consecutive wet days (CWD); the largest number of consecutive days with daily precipitation amount more than or equal to 1 mm, within a year, as defined by the Expert Team on Climate Change Detection and Indices (ETCCDI), jointly sponsored by the Commission for Climatology (CCl) of the World Meteorological Organization's (WMO) World Climate Data and Monitoring Programme (WCDMP), the Climate Variability and Predictability (CLIVAR) Programme of the World Climate Research Programme (WCRP) and the Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology (JCOMM). As results from the analysis, the spatial distributions of the mean annual CDD and the mean annual CWD along with their trends, within the examined period, are presented. The findings indicate that CDD obtain maxima in the Cyclades Islands and the southeastern Aegean Sea, while minima are found in the northwestern Greece. On the contrary, the longest CWD are observed in western Greece and western part of Crete Island and the shortest in the eastern continental Greece and in the majority of the Aegean Sea. On an annual basis, the temporal variability of CWD shows statistically significant (confidence level of 95%) negative trends, mainly in the western region of Greece, while insignificant positive trends for CDD appear almost all over the country with emphasis in the southeastern region. Finally, in order to interpret the drier and wetter periods within the examined period, the 850 hPa and the 500 hPa geopotential height (m) composites of the anomalies from 1958-1996 climatological normal (clino), are analysed using the National Centers for Environmental Prediction (NCEP) reanalysis data. © 2009 Elsevier B.V. All rights reserved.

The purpose of the present study is to identify the various factors that decision makers must take into account when ranking destinations for placing a spa resort/hotel in the thriving health and wellness industry. The study will suggest a decision support system (DSS) based on key factors as climate, tourism development and attractions. The DSS, using a computer based information system, will evaluate the aforementioned factors and will propose a hierarchical structure for rating destinations, useful for private or public planners in the wellness market. The research categorized the prefectures of Ahaia, Arkadia, Ilia, Korinthia, Messinia in the region of Peloponnese. © University of the Aegean.

A discrimination of the different aerosol types over the Arabian Sea (AS) during the Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB-06) is made using values of aerosol optical depth (AOD) at 500 nm (AOD500) and Ångström exponent (α) in the spectral band 340-1020 nm (α340-1020). For this purpose, appropriate thresholds for AOD500 and α340-1020 are applied. It is shown that a single aerosol type in a given location over the AS can exist only under specific conditions while the presence of mixed aerosols is the usual situation. Analysis indicates that the dominant aerosol types change significantly in the different regions (coastal, middle, and far) of AS. Thus the urban/industrial aerosols are mainly observed in coastal AS, the desert dust particles occur in the middle and northern AS, while clear maritime conditions mainly occur in far AS. Spectral AOD and Ångström exponent data were analyzed to obtain information about the adequacy of the simple use of the Ångström exponent and spectral variation of a for characterizing the aerosols. Using the least squares method, α is calculated in the spectral interval 340-1020 nm along with the coefficients a1 and a2 of the second-order polynomial fit to the plotted logarithm of AOD versus the logarithm of wavelength. The results show that the spectral curvature can effectively be used as a tool for their discrimination, since the fine mode aerosols exhibit negative curvature, while the coarse mode particles exhibit positive curvature. The correlation between the coefficients a1 and a2 with the Ångström exponent, and the atmospheric turbidity, is further investigated. Copyright 2009 by the American Geophysical Union.

Precipitating electrons from the radiation belts with energies greater than from 150 keV to 5 MeV have been correlated with ozone data of a large number of stations located within 40-70° N. Energetic electrons have been collected by the low altitude polar Russian satellite METEOR while ozone data have been compiled from almost ninety (90) stations located all over the world within the latitude zone 40-70° N. In more than 60% of the stations examined, we detect a clear decrease of the ozone variation during and after the occurrence of an electron flux excess, which recovers within 3-5 days. The more northern is a station located, the deeper is the ozone decrease. Moreover, clear evidence that the solar cycle affects ozone destruction through energetic electron events is presented. The preliminary results of the present work stimulate a future attempt for a simple ozone destruction mechanism formulation, which could describe atomic nitrogen ionization by energetic electrons, which in the following merge to atomic oxygen and produce nitrogen oxides. Finally, nitrogen oxides destruct ozone creating characteristic decreases on the normal ozone variation. © 2008 COSPAR.

Measurements of positive and negative small atmospheric ion concentrations have been made regularly since 1968 at the National Observatory of Athens (NOA). In this paper the 17-year period 1968-1984 is summarized. The diurnal and annual variations are examined, and Fourier analysis is also used for the study of the diurnal variation. The concentrations of small ions follow a double diurnal course. The maxima occur near 3-5 h and 13-16 h local time (LT = GMT + 2 h). The minima are observed at 6-8 h and 21-23 h. The annual course of small ions presents maximum concentration values around the summer season. The mean of the small ion concentration (SIC) for the 17-year period (1968-1984) is n+ = 188.8 ions/cm3 for positive ions and n- = 151.1 ions/cm3 for negative ions. Their ratio is equal to 1.25. The year-to-year variation of SIC for the examined period shows a negative trend. The results from multiple regression analysis show that wind speed and SIC are positively correlated, while relative humidity, smoke and sulphur dioxide are negatively correlated. © 2008 Elsevier B.V. All rights reserved.

The objective of this study is to find out the spatial and temporal variability of the dry and wet spells in Greece, during the period 1958-2007. The meteorological data with respect to daily precipitation totals were acquired from 27 meteorological stations of the Hellenic National Meteorological Service, which are uniformly distributed over the country. The dry spells concern consecutive dry days (CDD); the largest number of consecutive days with daily precipitation amount less than 1 mm, within a year. The wet spells concern consecutive wet days (CWD); the largest number of consecutive days with daily precipitation amount more than or equal to 1 mm, within a year, as defined by the Expert Team on Climate Change Detection and Indices (ETCCDI), jointly sponsored by the Commission for Climatology (CCl) of the World Meteorological Organization's (WMO) World Climate Data and Monitoring Programme (WCDMP), the Climate Variability and Predictability (CLIVAR) Programme of the World Climate Research Programme (WCRP) and the Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology (JCOMM). As results from the analysis, the spatial distributions of the mean annual CDD and the mean annual CWD along with their trends, within the examined period, are presented. The findings indicate that CDD obtain maxima in the Cyclades Islands and the southeastern Aegean Sea, while minima are found in the northwestern Greece. On the contrary, the longest CWD are observed in western Greece and western part of Crete Island and the shortest in the eastern continental Greece and in the majority of the Aegean Sea. On an annual basis, the temporal variability of CWD shows statistically significant (confidence level of 95%) negative trends, mainly in the western region of Greece, while insignificant positive trends for CDD appear almost all over the country with emphasis in the southeastern region. Finally, in order to interpret the drier and wetter periods within the examined period, the 850 hPa and the 500 hPa geopotential height (m) composites of the anomalies from 1958-1996 climatological normal (clino), are analysed using the National Centers for Environmental Prediction (NCEP) reanalysis data. © 2009 Elsevier B.V. All rights reserved.

The purpose of the present study is to identify the various factors that decision makers must take into account when ranking destinations for placing a spa resort/hotel in the thriving health and wellness industry. The study will suggest a decision support system (DSS) based on key factors as climate, tourism development and attractions. The DSS, using a computer based information system, will evaluate the aforementioned factors and will propose a hierarchical structure for rating destinations, useful for private or public planners in the wellness market. The research categorized the prefectures of Ahaia, Arkadia, Ilia, Korinthia, Messinia in the region of Peloponnese. © University of the Aegean.

Precipitating electrons from the radiation belts with energies greater than from 150 keV to 5 MeV have been correlated with ozone data of a large number of stations located within 40-70Β° N. Energetic electrons have been collected by the low altitude polar Russian satellite METEOR while ozone data have been compiled from almost ninety (90) stations located all over the world within the latitude zone 40-70Β° N. In more than 60% of the stations examined, we detect a clear decrease of the ozone variation during and after the occurrence of an electron flux excess, which recovers within 3-5 days. The more northern is a station located, the deeper is the ozone decrease. Moreover, clear evidence that the solar cycle affects ozone destruction through energetic electron events is presented. The preliminary results of the present work stimulate a future attempt for a simple ozone destruction mechanism formulation, which could describe atomic nitrogen ionization by energetic electrons, which in the following merge to atomic oxygen and produce nitrogen oxides. Finally, nitrogen oxides destruct ozone creating characteristic decreases on the normal ozone variation. Β© 2008 COSPAR.

Volos, a coastal medium-sized city in the region of Thessaly and extended along the northern part of the Pagassitikos Gulf at the eastern seaboard of Central Greece, is among the cities which suffer from the air pollution in Greece. The case of Volos is an interesting example, where in the last decades the urbanization and the increased industrialization have resulted in the degradation of the air quality in the area. Meteorological factors play an important role in the air pollution development, while the complex topography of Volos exacerbates air pollution episodes. In this study, the relationships between PM10 (particulate matter with diameter less than 10 ΞΌm) and meteorological parameters such as wind speed, relative humidity and air temperature have been analyzed from 2005 to 2007 on the basis of 24-hour continuous measurements. According to the results obtained from the multiple linear regression analysis, there is a strong relation between meteorological parameters and the particulate matter concentrations in Volos city. Moreover, the calculation of the 72-hour air mass back trajectories during (eight) Saharan dust events, took place within the examined period, was carried out by applying the HYSPLIT 4 model of Air Resources Laboratory of NOAA for three different levels: 500, 1500 and 4000 m (a.m.s.1.). It is worthy to remark the high PM 10 values observed, indicating the contribution of such natural events in exacerbating the air quality in the area of Volos. Β© 2009 American Institute of Physics.

In this study, the variability and trends of the mean annual and seasonal surface air temperature in Greek peninsula are examined. The climatic data used, concern mean monthly values of air temperature of 20 meteorological stations of the Hellenic Meteorological Service, for the period 1951-2000. The air temperature time series for each station are analyzed, so that the variability and trends be described. Regarding the annual time series, a cooling trend is observed since the early 1960's till the middle of the decade of 1970, when the trend reverses to heating till nowadays. It is remarkable that the today air temperature levels do not exceed the levels of the middle of the century. During the winter, it is crystal clear that a cooling trend exists from the middle of the decade of 1950 to the end of the decade of 1980, especially in the south region of the country. Afterwards an increasing trend is obvious till nowadays. The pattern in spring appears a slight heating trend in the northern region of Greece and a cooling trend in the south. The summer time series are similar to the annual ones, so the contribution of summer to annual variability is unquestionable. Generally speaking, the air temperature in autumn follows the same distribution in time. In the process, the Factor Analysis is applied on the mean annual and seasonal air temperature and thereafter the regions, within the air temperature covariates, are defined. Finally, the application of spectral analysis to annual and seasonal air temperature is regarded necessary so that the periodicities are derived. © 2008 Global NEST Printed in Greece. All rights reserved.

The changes in daily precipitation totals in Greece, during the 45-year period (1957–2001) are examined. The precipitation datasets concern daily totals recorded at 21 surface meteorological stations of the Hellenic National Meteorological Service, which are uniformly distributed over the Greek region. First and foremost, the application of Factor Analysis resulted in grouping the meteorological stations with similar variation in time. The main sub groups represent the northern, southern, western, eastern and central regions of Greece with common precipitation characteristics. For representative stations of the extracted sub groups we estimated the trends and the time variability for the number of days (%) exceeding 30 mm (equal to the 95% percentile of daily precipitation for eastern and western regions and equal to the 97.5% percentile for the rest of the country) and 50 mm which is the threshold for very extreme and rare events. Furthermore, the scale and shape parameters of the well fitted gamma distribution to the daily precipitation data with respect to the whole examined period and to the 10-year sub periods reveal the changes in the intensity of the precipitation.

In the present study an assessment of the influence of the ambient air pollution on the incidence of the Childhood Asthma Admissions (CAA) is attempted by using cross spectrum analysis. The medical data concern the hospital registries of the three main Children's Hospitals of Athens for the 14-year period, 1987-2000. The air pollution data used in this study were mean monthly concentrations of CO, Black Smoke (BS), NOx, SO2, and O3, averaged over all the available stations, for each air pollutant, in the network of the Greek Ministry of the Environment, Physical Planning and Public Works (GMEPPPW) for the aforementioned 14-year period. The performed analysis revealed that a pronounced seasonal variation of asthma exacerbation among Athenian children does exist, rising during the cold damp period in pre-schoolers and peaking around May in the schoolchildren. We found that asthma admissions are associated with ambient air pollution at different frequencies. Asthma exacerbation among the first age group (0-4 years) is strongly depended on winter air pollution whereas older children (5-14 years) appear to be more vulnerable to the exposure of primary air pollutants mainly during late spring. Our findings strengthen the aspect that weather conditions such as sea breeze, mainly happen at the late spring or early summer in association with air pollution episodes could affect childhood asthma exacerbation. © 2008 Global NEST Printed in Greece. All rights reserved.

The aim of this study was to determine whether there is any association between weather variability and asthma admissions among children in Athens, Greece. Medical data were obtained from hospital registries of the three main Children's Hospitals in Athens during the 1978-2000 period; children were classified into two age groups: 0-4 and 5-14 years. The application of Generalized Linear Models with Poisson distribution revealed a significant relationship among asthma hospitalizations and the investigated parameters, especially for the children aged 0-4 years. Our findings showed that Hospital admissions for childhood asthma in Athens, Greece, is negatively correlated with discomfort index, air temperature and absolute humidity whereas there is a positive correlation with cooling power, relative humidity and wind speed. Copyright © 2008 Informa Healthcare USA, Inc.

The aim of this study was to examine the effects of the daily minimum air temperature and human-biometeorological variables, as well as their day-to-day changes, on sleep disturbances (SD) in the inhabitants of Athens, Greece. The SD dataset used for the analysis included the daily records of the psychiatric emergency unit of the Athens University Medical School for the years 1989 (with mild thermal load) and 1994 (with heavy thermal load). The meteorological variables for the estimation of the thermal indices were recorded by the meteorological station of Hellenikon, which is located at the headquarters of the Hellenic National Weather Service. The mean radiant temperature (T mrt) and the thermal indices predicted mean vote (PMV), physiologically equivalent temperature (PET) and standard effective temperature (SET*) have been analyzed. The first step was to assess the SD frequencies as a function of the meteorological and human-biometeorological variables on the basis of 10-day intervals to determine the influence of the examined variables on SD. The daily SD records were included as Poisson random variables in the applied Generalized Linear Models (GLM). The extracted results suggested that a considerable increase in SD existed in 1994 compared to 1989. This was due to the many consecutive days with heavy thermal load (PET >35°C and Tmin >23°C) in 1994 compared to the lack of such days in 1989. Furthermore, statistically significant (p<0.01) positive relationships were found between minimum air temperature, all thermal indices and SD. © SAGE Publications 2008.

Springtime constitutes the most favorable period for Sahara dust outbreaks and transport over Eastern Mediterranean. This study investigates the aerosol properties during April 2005 using remote-sensing and ground-based measurements. Three dust events with high aerosol optical depth (AOD) values have been observed during the measuring period, with duration of two days, i.e. 11-12, 16-17 and 25-26 April 2005. In this paper we mainly focus on the intense dust event of 16-17 April 2005, when a thick dust layer transported from Libya affected the whole Greek territory. Very high AOD values obtained from Aqua-MODIS sensor were observed over Greece (mean 2.42 ± 1.25) on 17 April, while the respective mean April value was 0.31 ± 0.09. The AOD at 550 nm (AOD 550) values over Crete were even larger, reaching ∼4.0. As a consequence, the PM 10 concentrations over Athens dramatically increased reaching up to 200 μg m -3. On the other hand, the fine-mode fraction values obtained from Terra-MODIS showed a substantial decrease in the whole Greek area on 17 April with values below 0.2 in the Southern regions. The intense dust layer showed a complex behavior concerning its spatial and temporal evolution and allowed us to study the changes in the optical properties of the desert dust particles along their transport routes due to the mixing processes with other aerosol types. The results from different measurements (ground-based and remote-sensing) did not contradict each other and, therefore, are adequate for monitoring of dust load over the Eastern Mediterranean. © 2008 Elsevier Ltd. All rights reserved.

Tropical days (TD) are defined as the days with a maximum air temperature greater than 30.0°C. It is clear that the study of TD includes also the absolute maximum temperatures, which are of great interest for the description of a region's climate. These days are considered as very hot, and they particularly are of great importance not only for bioclimatology and applied sciences, but also for the individuals who are sensitive in the heat-stress. The regime of the TD in Greece is the focus of this study. The aim is to demonstrate their changes from decade to decade, for the time period 1960-2000. For this study, the Annual Number of Tropical Days (ANTD) recorded by each of the 26 meteorological stations of National Meteorological Service, which are uniformly distributed in the Hellenic peninsula, was calculated and analysed. In terms of quantifying the conditions in a human-biometeorological manner, the thermal index Physiological Equivalent Temperature (PET) and the consecutive days for Athens have been included in this study. The trends of the TD for each station were analysed through the Mann-Kendall technique, while the spatial distribution per decade reveals the regions with change (increase or decrease) in the ANTD during the examined period. Two characteristic periods of change for the ANTD appear in the majority of the meteorological stations in Greece. The first period (1955-1976) is determined by a negative trend, which is statistically significant (c.l. 95%), for adequate stations. In the period between 1976 and 2000, the increase in the ANTD and the maximum temperature exceed the corresponding maximum that appeared in the beginning of the 1950s for several of the examined meteorological stations. The human-biometeorological analysis shows that the consecutive days of PET >35°C have had a positive trend in the last two decades of the last century. © Springer-Verlag 2007.

The determination of the chemical composition of rainfall related to the origin of the air masses, in two urban sites in Greece during the year 2006, is investigated in this study. Two model automatic rain samplers were installed, the first in the city of Larissa, Thessaly, central Greece and the second in Heraklio, Attica, a northern suburb of Athens. The concentrations (ppm) of the major cations (H+, Na+, K+, Ca2+, NH4+ and Mg2+) and major anions (NO 3-, NO2-, HCO3 -, and SO42-), as well as total hardness (ppm CaCO3), pH and electric conductivity in 25°C (μS/cm) for 27 rainfall samples -11 samples in Larissa and 16 samples in Heraklio (Athens)- were determined. In Larissa, the figures of pH range from 5.13 to 6.13 while in Heraklio (Athens), the pH within the range 5.62 to 7.88 indicates a shift of the rainfalls towards alkalinity. The electric conductivity in Larissa ranges from 16.30 μS/cm to 110.60 μS/cm and in Heraklio (Athens) from 7.00 μS/cm to 151.00 μS/cm. The analysis showed that Ca2+ and Mg2+ appear the highest concentrations out of the examined cations, while HCO 3- and SO42- present the highest concentrations within the anions. Moreover, in order to find out the origin of the air masses, the air mass back trajectories were calculated using the HYSPLIT 4 model of Air Resources Laboratory of NOAA for two different levels: 1500 and 3000 m (a.m.s.l.). © by PSP 2008.

The associations between various meteorological parameters, concentrations of PM10, SO2, and O3 pollutants and bronchial asthma of residents of the wider region of Athens are examined in this study. For this purpose, 1,288 patients’ admissions (412 males and 876 females) recorded in 13 pneumonological clinics of Sotiria Hospital, which is the major Hospital for respiratory diseases in Athens, were analyzed for the period 1/1/2001–31/12/2002. The meteorological data were available by the National Observatory of Athens and the concentrations of PM10, SO2, and O3 pollutants were obtained by the air pollution network of 10 stations of the Ministry of Environment (Directorate of Air and Noise pollution Control).The evaluation of the possible relationship between the bronchial asthma admissions (BAA) and the meteorological variables was achieved by the application of Generalized Linear Models with Poisson distribution, because the medical dataset presents large divergence from a Gaussian distribution. The results showed that a statistically significant (p < 0.01) negative correlation between all examined air temperature variables, water vapor pressure, evaporation, sunshine, total solar irradiance, and BAA exists. Moreover, the findings of the analysis showed that a statistically significant relationship between the examined pollutants and BAA on the same day does not exist, with the exception of O3, which is correlated negatively (p < 0.01) with BAA. Nevertheless, there is a statistically significant lag effect (7–8 days) between the increase in BAA and the peak in the concentrations of PM10, SO2, and O3 pollutants. During the cold period of the year (October–April), BAA is significantly associated with O3 lag 2 day. The interannual variation of bronchial asthma admissions (BAA) reveals peaks within the transitional seasons of the year (spring and autumn), while the main minimum is apparent during summer period and especially in August.

Objective - Genetic polymorphisms in the gene for endothelial nitric oxide synthase have been considered as potential risk factors for the development of coronary artery disease in some populations. Methods - We studied two polymorphisms of the NOS3 gene, the VNTR in intron 4 (4VNTR) and the Glu298Asp polymorphism in exon 7, in relation to the existence of premature coronary artery disease and the occurrence of myocardial infarction. A total number of 370 individuals of the Greek population was examined by PCR-RFLP method. The patient group consisted of 209 subjects, aged less than 58 years presenting symptomatic coronary artery disease, documented by coronary angiography. Results - The frequencies for bb, ab and aa genotypes of 4VNTR polymorphism were 0.67, 0.29, 0.04, respectively, for the patient group and 0.73, 0.24, 0.03 for the control group. The frequencies for GG (Glu/ Glu), GT (Glu/Asp), TT (Asp/Asp) of the Glu298Asp polymorphism were 0.52, 0.41, 0.07, respectively, in patients compared to 0.47, 0.46, 0.07, in control subjects. Statistical analysis indicated that there are no significant differences in the frequencies of the genotypes between patients and control subjects for both polymorphisms. The combined analysis of the two polymorphisms indicated no synergistic effect of the a and T alleles on coronary artery disease. Conclusions - We have found no evidence for association between the a allele of the 4VNTR polymorphism, or the T allele of Glu298Asp polymorphism and the risk for premature coronary artery disease or occurrence of myocardial infarction. Furthermore, no synergistic contribution of these polymorphisms to the development of premature coronary artery disease has been observed.

A long-term (2000–2005) data set of aerosol optical properties obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) is analyzed focusing on the Greater Athens Area in the Eastern Mediterranean region. The MODIS aerosol optical depth standard product (AOD at 550 nm) and its respective ratio attributed to fine-mode particles (FM) are employed to evaluate the inter-annual and seasonal variability of the aerosol properties over Athens. Based on AOD550 and FM values three specific aerosol types are discriminated corresponding to different aerosol load and optical properties. The aerosol types considered correspond to urban/industrial aerosols, coarse-mode particles and clean maritime conditions. This study focuses on the seasonal and year-to-year fluctuation of the number of occurrences as well as the AOD550 and FM values of each aerosol type. The coarse-mode particles are observed mainly in the summer, while spring is the most favorable season for the occurrence of urban/industrial aerosols. On the other hand, clean maritime conditions occur mainly in the winter. The AOD550 values for the coarse-mode particles are higher in spring, while the urban/industrial and clean maritime aerosols exhibit slightly higher values in the summer. The seasonal distribution of the aerosol properties is related to anthropogenic and dust emissions in the spring/summer period, but is modified by atmospheric dispersion and precipitation in late autumn/winter. The main conclusion of the study is that the coarse-mode particles exhibit much stronger interannual and seasonal variability compared to the urban/industrial aerosols. Finally, three cases corresponding to each aerosol type are analyzed with the aid of synoptic weather maps, air mass trajectories and MODIS data.

The study of particulate matter with diameter less than 1 μm (PM 1) in Athens' atmosphere and their impacts on human health is the goal of this study. PM1 concentrations were recorded by three detectors (light scattering method) at six vital points in high traffic peak roads, during the period 1/10/2006-30/9/2007. The collected PM1 samples concern the same hour of the day, in absence of wind. The spatial distributions of the PM1 concentrations for the warm (April to September) and the cold (October to March) period of the year were achieved by the use of Kriging method. Further to, in order to find out the impacts of PM1 concentrations on health, we analyzed daily admissions for non-fatal arrhythmias to emergency units of the Social Security Institute and a Regional Hospital of Athens. Results demonstrate a significant relationship of PM1 with sinus arrhythmias, which confirms the assumption that PM1 represent one of the main hazards in cardio respiratory syndromes in the most polluted cities of Europe, which confront high traffic problems, due to the enormous number of exhausts emissions.

A long-term (2000-2005) monitoring of aerosol data from the moderate resolution imaging spectroradiometer (MODIS) is analyzed focusing on the Greater Athens Area (GAA) in the Eastern Mediterranean region. The MODIS aerosol optical depth standard product (AOD at 550 nm) and its respective ratio attributed to fine-mode (FM) particles are employed to evaluate the seasonal variability of the aerosol properties over Athens. The climatological trend of both parameters in the period 2000-2005 is nearly absent, while remarkable year-to-year variability can be observed. The seasonal analysis reveals a significant AOD variability over Athens, with minimum values in winter (AOD550 ∼ 0.2), and maximum in summer (AOD550 ∼ 0.45). Regarding the FM fraction, maximum values are present in spring and minimum in summer, thus revealing the dominance of FM and coarse-mode particles, respectively. For the whole data set, a method is implemented to distinguish the main aerosol types (urban/industrial (hereafter UI), clean maritime (hereafter CM type) and desert dust (hereafter DD) over Athens, based on both AOD and FM values. Because of the mixing processes in the atmosphere the majority of the cases (46.6%) belong to a mixed (hereafter MT) aerosol type. The UI aerosols are more frequent in spring (41.2%) and less in winter (9.1%), while the coarse particles, probably DD, more frequent in summer (35.8%) and less in winter (3.5%). In contrast, the clean atmospheric conditions are more frequent in winter (23.9%), when the mixing processes are also well established (63.5%). For each aerosol type, the mean AOD550 and FM values are also computed. Their seasonal variability exhibits a clear summer maximum for UI, CM and MT aerosols, while the DD exhibits maximum in spring. As regards the FM values of the different aerosol types they exhibit a rather constant variation with small fluctuations from season to season. © 2007 Elsevier Ltd. All rights reserved.

The goal of this study is to determine the chemical composition of rain, in the wider region of Athens, Greece for the time period 1st September 2001 to 31st August 2002. Two model automatic rain samplers were installed in the Meteorological Station of Laboratory of Climatology (latitude: 37Β° 58β€² N, longitude: 23Β° 47β€² E) inside the Athens University Campus and in a site at Heraklio Attica, a northern suburb of Athens (latitude: 38Β° 03β€² N, longitude: 23Β° 45β€² E). The concentrations (ΞΌeq l -1) of the major cations (H +, Na +, K +, Ca 2+ and Mg 2+) and anions (Cl -, NO 3 -, HCO 3 - ΞΊΞ±ΞΉ SO 4 2-, as well as pH and conductivity of rain in 39 total samples were determined. The figures of pH range from 6.4 to 8.4 and conductivity from 8 to 207 ΞΌS cm -1. The analysis showed that Ca 2+ ions are abundant within all examined samples, while HCO 3 - and SO 4 2- present the highest concentrations from the anions. In order to find out the origin of the air masses, the air mass back trajectories were calculated. Five sectors of the origin of air masses were revealed: the North, the South, the Local, the West and the East sector. Multivariate methods included Factor Analysis and Discriminant Analysis were applied to the examined ion concentrations and three main factors were extracted, which discriminated the ions according to their origin. The first group of ions is interpreted as the result of the anthropogenic activity, the second group represents the acidity-alkalinity independently of their source and the third one the marine influence. Β© 2007 Springer Science+Business Media B.V.

The paper studies changes in daily precipitation records at the National Observatory, Athens, during the period 1891-2004. This is the longest available time series of precipitation for Greece. The results show that both the shape and scale parameter of a fitted two parameter gamma distribution for the last two decades do show a significant difference of these parameters, when compared to any previous period from the 1890s through the 1970s. Also important changes are observed in daily precipitation totals exceeding various thresholds such as 10, 20, 30 and 50 mm. More specifically, a negative trend in the number of wet days (remarkable after 1968) and a positive trend in extreme daily precipitation are evident. The changes of heavy and extreme precipitation events in this part of SE Europe have significant environmental consequences which cause considerable damage and loss of life.

In the present study the involvement of human activities is assessed in the revalorization of groundwater quality. The groundwater quality was assessed on the basis of physical and chemical analysis (electric conductivity, pH, total dissolved solids (TDS), total hardness, NO3 -, NO2 -, SO4 -2, Fe, Mn, Zn, Cu, B, residual sodium absorption (RSC) and sodium absorption ratio (SAR) for the period 2000-2004. From the analysis of results, it emerges that there are significant differences on the quality of water among the sample areas studied. The degradation of groundwater quality is mainly due to the pollution caused by the rural use of land, as well as its intensive exploitation. The salination and toxicity are potential problems of groundwater quality, especially in some areas, indicating that there is a need to take direct actions for the purpose of the optimum management of water resources in the Region of Thessaly. Β© 2007 Elsevier B.V. All rights reserved.

Two periods of transboundary transport of volcanic aerosols and debris following recent eruptions of Mount Etna, Italy, were examined using ground-based and satellite spectrophotometric measurements together with Light Detection And Ranging (LiDAR) and aerosol filter observations in Athens and Thessaloniki, Greece. Independent columnar SO2 measurements from ground and space identified peaks at Greek sites after the volcanic eruptions. LiDAR measurements of the aerosol extinction at Thessaloniki and Athens performed in July 2001 have shown the height of the volcanic plume to be about 3.5 km asl and the optical thickness of the dust layer to be of the order of 3 Γ—10-3 at 532 nm. Strong ozone depletion observed at the volcano plume level by using ozonesonde ascents may be attributed to the in-plume processes that generate reactive halogens, which in turn destroy ozone. The chemical and elemental composition of aerosol samples, taken at the Earth's surface, was analysed and confirmed the volcanic origin of the dust.

The aim of this study was to investigate the influence of weather conditions on the number of admissions for childhood asthma in Athens, Greece. Daily counts of childhood asthma admissions (2764) of the three main Children's Hospitals in Athens, from hospital registries during a 3-year period (2001-2003), were obtained. The meteorological data reviewed consists of daily values of 20 parameters recorded at the National Observatory of Athens during the study period: maximum temperature (Tmax); minimum temperature (Tmin); mean temperature (Tmean); diurnal temperature range (Trange = Tmax - Tmin); day-to-day change in maximum temperature (Ξ”Tmax); day-to-day change in minimum temperature (Ξ”Tmin); day-to-day change in mean temperature (Ξ”Tmean); day-to-day change in diurnal temperature range (Ξ”Trange); mean relative humidity (RH); day-to-day change in mean relative humidity (Ξ”RH); mean water vapor pressure (e); day-to-day change in mean water vapor pressure (Ξ”e); mean atmospheric pressure at sea level (P); day-to-day change in mean atmospheric pressure (Ξ”P); mean irradiance (I); day-to-day change in mean irradiance (Ξ”I); mean sunshine (S); day-to-day change in mean sunshine (Ξ”S); mean wind speed (v) and day-to-day change in mean wind speed (Ξ”v). The performed statistical methods were: (i) Pearson's Ο‡2 test, using contingency tables and (ii) Factor and Cluster analysis. The application of this 2-part analysis revealed the relationship between the extracted weather types and the frequency of childhood asthma admissions in Athens. The results showed that weather conditions with low temperature, low water vapor pressure and cold anticyclonic presence were significantly correlated with an increase in the number of asthma admissions among children in Athens. The impact of these specific weather conditions on asthma exacerbation should be interpreted either by the asthmogenic effect of humid weather per se or the association with respiratory viral infection, mold's and mites' allergy. Β© by PSP 2006.

A multivariate analysis of 4797 cases of patients who were cured of their psychological symptoms and their notes filed by the psychiatric clinic of the Eginition Hospital in Athens, during the year 1994, has been done. The results of this analysis imply significant contribution of environmental variations, expressed by a discomfort index, in the aggravation of psychological symptoms like depression, sleep disturbances, anxiety, aggressiveness, etc. Moreover, geomagnetic field variations expressed by the international geomagnetic index (DST) manifest significant indications that they contribute to the aggravation of sleep disturbances. A clear seasonal variation, with a maximum around August and a minimum at the end of the year, appears in the environmental index, while a double oscillation with a period of about six months is obvious in the geomagnetic index. The same more or less seasonal variation was mirrored in most of the psychological symptoms we analysed in the present study. Β© 2006 SAGE Publications.

In this study the contribution of meteorological parameters to the total variability of respiratory infections (RI) is analysed. For this purpose, data on the daily numbers of general practitioner (GP) consultations for RI during the year 2002 were used. This dataset has been compiled by the Local Health Service in the surroundings of Athens, Greece (Acharnes city). The meteorological data obtained by the Meteorological Station of the National Observatory of Athens comprise daily values of mean, maximum, and minimum air temperature, air temperature range, relative humidity, absolute humidity, sunshine, surface atmospheric pressure, wind speed, as well as day-to-day changes of these parameters. Furthermore, the following biometeorological parameters and thermal indices were also evaluated: mean radiant temperature (T mrt), predicted mean vote (PMV), physiologically equivalent temperature (PET) and standard effective temperature (SET*) as well as their day-to-day changes. First, the relationship between every meteorological-biometeorological parameter and consultations for RI was examined by applying the Pearson Chi-Square Test (χ 2) to the data of the 25 compiled contingency tables. In the second stage, the application of generalised linear models (GLM) with Poisson distribution to the data revealed how much the weather variability leads to statistically important changes in consultations for RI. The results of this study contribute to the evidence that there is an association between weather conditions and the number of GP consultations for RI. More specifically, the influence of air temperature and absolute humidity on consultations on the same day is weaker than the lag effect (∼2 weeks) related to cold existence and absolute humidity, while a strong wind during the preceding 3days drives a peak in GP consultations. © ISB 2006.

In this work, the characteristics of the long-term precipitation time series in Athens area (1891-2000). Statistical analysis shows that higher values of annual precipitation observed in the 1930s, while the lowest values were observed in the 1890s and 1980s. There is no significant trend in the annual precipitation time series. Moreover, the annual number of days with high precipitation (ANDHP) remains constant, during the investigated period. Spectral analysis by the Blackman-Tukey method that applied to the time series of ANDHP, showed in most cases peaks at frequencies corresponding to the following time periods: about 2.6 and 4.0 years. Β© by PSP.

Objective: We examined the association between climatologic parameters and daily admissions for non-fatal acute coronary syndromes (ACS) to emergency units of hospitals in the greater Athens area, from January 2001 to August 2002. Methods: Daily mean, maximum and minimum temperatures, relative humidity, wind speed, barometric pressure and a thermo-hydrological index (T.H.I.) were measured at the meteorological station of the Laboratory of Climatology of the Geology Department of the University of Athens. In addition, the daily number of admissions for acute myocardial infarction or unstable angina in the five major general hospitals in the greater Athens area was recorded. Generalized additive models (GAM) were applied to regress-time-series of daily numbers of outpatients with acute cardiac events against climatological variations, after controlling for possible confounders and adjustment for over dispersion and serial correlation. Results: Five thousand four hundred fifty-eight Athenians with non-fatal acute cardiac events were admitted to the selected hospitals during the period of the study, 4093 (75%) males and 1365 (25%) females. There was a negative correlation between hospital admissions and mean daily temperature (MDT) with a 1Β°C decrease in mean air temperature yielding a 5% increase in hospital admissions (P<0.05). This association was stronger in females and the elderly (P<0.01). Relative humidity was positively correlated with hospital admissions (P<0.05). Conclusion: Despite the relatively short study period (<2 years), these findings suggest a significant association between cold weather and increased coronary heart disease incidence, especially in the elderly and females. Β© 2003 Elsevier Ireland Ltd. All rights reserved.

The aim of this paper is to discuss the concept of health tourism product as a competitive tourism product with a focus on Ikaria Island, Greece. The diversification of the health tourism product is explored and the study identifies key components for a successful development of a spa resort. The paper also examines the prospects for the thermal/mineral springs of Ikaria Island, taking account of the climatic and bioclimatic regimes of the area. The study concludes that there are prospects for future development if the spa product is diversified. This, in combination with the good climatic conditions of the area, can be a starting point for providing services in order to satisfy potential clients. Β© 2003 anatolia Printed in Turkey. All rights reserved.

The goal of this study is to estimate the relation between air temperature and precipitation in Greece and, thereafter, to define the regions of the covariability of the two parameters. For that purpose, the air temperature and precipitation mean monthly data of 30 meteorological stations, for the period 1950-2000, are analyzed. The first step is the application of Factor Analysis (FA) to each of the two variable groups of the seasonal air temperature and precipitation. The aim is to reduce the number of variables in each group and, more specific, to define the main significant factors for each parameter. The second step is the application of Canonical Correlation Analysis (CCA) to the factor scores of each parameter, derived by the use of PCA, so that the canonical pairs are extracted and the number of the pairs are equal to the minimum number of variables in either set. In the process, the computed canonical scores are correlated to the respective original data, aiming to define regions of positive and negative correlations between the canonical roots of the air temperature and precipitation.

The effects of urbanization on the Athens National Observatory (NOA) long records are investigated, in the present study, examining the mean monthly maximum and minimum air temperature for the period 1925-1996, for NOA and the corresponding time series for Aliartos (ALI), a rural station located 70 km NW of Athens. The existing small urbanization effect in NOA before the second world war period increased after the war and up to about 1990, when the effect became stationary. The urbanization effect in NOA referred mainly to maximum temperature and to the warmer seasons of the year. It is attributed to the extensive building of Athens after the war around NOA site and up to the sea which increases the temperature of the sea breeze. The effect is also attributed to the rapid increase of the population and the number of motor vehicles mainly after 1970. Moreover the decreasing trend of precipitation during the period 1970-1990 may have contributed to the increase of maximum air temperature. The urbanization effect on maximum temperatures of NOA amounts about 2 Β°C in spring, summer and less in fall, while no urbanization effect is clear in winter.

The patterns of monthly precipitation distributions in Greece, during the months of the year, are studied. Using factor analysis T-mode on mean monthly precipitation for a long period, we try to establish characteristic patterns of precipitation distribution. Only two of the eigenvectors (factors) were found statistically significant, namely factor I, explaining 67% of total variance and referring to the months of the period from October to March (cold period) and factor II, explaining 23% of total variance and referring to the months from April to September (warm period). During the cold period precipitation is maximum on Western Greek mainland and along the Western Asia Minor coast and islands while minima are shown in Cyclades islands, Attika, Thessaly, Macedonia and Thrace. On the other hand, during the warm period precipitation shows maxima in Central and North continental areas and the interior of Peloponese while minima appeared again in Cyclades, Dodecanese and Crete. Finally, the various areas of the country are distributed in 4 categories, depending on the combination of plus or minus of the normalized factor scores, for each period.

In this paper, we deal with the ARIMA (Box-Jenkins) model of the gridded mean annual air temperature for the area included by the co-ordinates: 20°- 30°E, 35°- 45°N, (thus the South Balkan area, the most of its percentage covered by Greek peninsula). We analyse the gridded temperature time series which existed from 1851 to 1996. With the theoretical model's construction, we try to forecast the annual temperature till the year 2006, and the results were satisfactory enough. Also, from the analysis we found that the autocorrelation function (ASF) and the partial autocorrelation function (PASF) of the residuals were not significant, and the ARIMA model is quite reliable.

Wet precipitation-only samplers were used to collect wet deposition at two sites in the Athens basin, Greece for the period March 1986 - February 1987. Concentrations of major cations (H +, NH 4 +, Na +, K +, CA 2+) and major anions (Cl -, NO 3 - and SO 4 2-) were determined for the first time in rainwater samples in Greece. Bicarbonate concentrations were calculated. The relative importance of natural and anthropogenic sources were estimated by a chemical balance. The majority of rain collected has a neutral or alkaline character. Acidity was due to the presence of H 2SO 4 and HNO 3. The statistical analysis of the correlation between the concentration of chemical species confirm the influence of natural and anthropogenic sources. In all samples, SO 4 2- concentrations exceed NO 3 - concentrations exceed NO 3 - concentrations despite the dominance of low S oil burning in the region. The wet flux of S was calculated to be 0.34 g m -2 a -1.