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.

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.

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.

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 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).

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.

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.

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).