Publications by Year: 2014

Matsangouras, I.T., Pytharoulis, I. & Nastos, P.T. Numerical modeling and analysis of the effect of complex Greek topography on tornadogenesis. Natural Hazards and Earth System Sciences 14, 1905 - 1919 (2014). WebsiteAbstract
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).
Nastos, P.T., Paliatsos, A.G., Koukouletsos, K.V., Larissi, I.K. & Moustris, K.P. Artificial neural networks modeling for forecasting the maximum daily total precipitation at Athens, Greece. Atmospheric Research 144, 141 - 150 (2014). WebsiteAbstract
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.
Nastos, P.T., Matsangouras, I.T. & Chronis, T.G. Spatio-temporal analysis of lightning activity over Greece - Preliminary results derived from the recent state precision lightning network. Atmospheric Research 144, 207 - 217 (2014). WebsiteAbstract
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.
Matsangouras, I.T., Nastos, P.T., Bluestein, H.B. & Sioutas, M.V. A climatology of tornadic activity over Greece based on historical records. International Journal of Climatology 34, 2538 - 2555 (2014). WebsiteAbstract
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.
Kaskaoutis, D.G., Rashki, A., Houssos, E.E., Goto, D. & Nastos, P.T. Extremely high aerosol loading over Arabian Sea during June 2008: The specific role of the atmospheric dynamics and Sistan dust storms. Atmospheric Environment 94, 374 - 384 (2014). WebsiteAbstract
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.
Bleta, A., Nastos, P.T. & Matzarakis, A. Assessment of bioclimatic conditions on Crete Island, Greece. Regional Environmental Change 14, 1967 - 1981 (2014). WebsiteAbstract
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.
Matzarakis, A., Endler, C. & Nastos, P.T. Quantification of climate-tourism potential for Athens, Greece - Recent and future climate simulations. Global Nest Journal 16, 43 - 51 (2014). WebsiteAbstract
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.
Moustris, K.P., et al. Prognosis of maximum daily surface ozone concentration within the greater Athens urban area, Greece. Global Nest Journal 16, 873 - 882 (2014). WebsiteAbstract
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.
Nastos, P.T. & Matsangouras, I.T. Analysis of synoptic conditions for tornadic days over western Greece. Natural Hazards and Earth System Sciences 14, 2409 - 2421 (2014). WebsiteAbstract
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.
Matsangouras, I.T., Nastos, P.T. & Pytharoulis, I. Numerical simulation of tornadoes' meteorological conditions over Greece: A case study of tornadic activity over NW Peloponnese on March 25, 2009. EGU General Assembly Conference Abstracts 16, 8776 (2014).
Kamperakis, N.C., Nastos, P.T. & Matsangouras, I.T. Using data mining methods in forecasting waterspouts over south Aegean Sea, Greece. (2014).
Nastos, P.T., et al. Present and future bioclimatic conditions of importance to tourism over the Mediterranean. EGU General Assembly Conference Abstracts 16, 8334 (2014).
Matsangouras, I.T., Pytharoulis, I. & Nastos, P.T. Numerical modeling and analysis of the effect of Greek complex topography on tornado genesis. Natural Hazards and Earth System Sciences Discussions 2, 1433–1464 (2014).
Matsangouras, I.T. & Nastos, P.T. Predictability and extended-range prognosis in natural hazard risk mitigation process: A case study over west Greece. EGU General Assembly Conference Abstracts 16, 10616 (2014).
Kotsopoulos, S., et al. Water resources management of coastal agricultural environments–resilience of climate change impacts. Proc. of International Water Association (IWA) (2014).
Matzarakis, A., Endler, C., Nastos, P.T. & others, Quantification of Climate-Tourism Potential for Athens, Greece–Recent and Future Climate Simulations. Global NEST Journal 16, 43–51 (2014).
Kaskaoutis, D.G., et al. Synoptic weather conditions and aerosol episodes over Indo-Gangetic Plains, India. Climate Dynamics 43, 2313–2331 (2014).
Nastos, P.T., Matsangouras, I.T. & Chronis, T.G. Spatio-temporal analysis of lightning activity over Greece—Preliminary results derived from the recent state precision lightning network. Atmospheric Research 144, 207–217 (2014).
Moustris, K.P., et al. Energy consumption based on heating/cooling degree days within the urban environment of Athens, Greece. Theoretical and Applied Climatology 122, 517-529 (2014). Website
Matsangouras, I.T., Nastos, P.T. & Zacharopoulos, K. Spatial and temporal analysis of lightning impacts over Greece. COMECAP2014–ebook of contributions, edited by: Kanakidou, M., Mihalopoulos, N., and Nastos, P., Proceedings 12th International Conference of Meteorology, Climatology and Physics of the Atmosphere, Greece, Crete University Press (2014).
Matzarakis, A., Endler, C. & Nastos, P.T. Quantification of climate for tourism and recreation under climate change conditions-The example of Athens. Global Nest Journal 16, 43-51 (2014).
Matsangouras, I.T., Nastos, P.T., Pytharoulis, I. & Migglieta, M.M. Atmospheric conditions analysis of waterspout events based on thermodynamic environment and sea surface temperature distribution over south Aegean Sea. (COMECAP2014–ebook of contributions, edited by: Kanakidou, M., Mihalopoulos, N., and Nastos, P., Proceedings 12th International Conference of Meteorology, Climatology and Physics of the Atmosphere, Greece, Crete University Press : 2014).
Papachristopoulou, K., Matsangouras, I.T. & Nastos, P.T. Waterspout cloud top detection using MSG SEVIRI Infrared brightness temperature over south Aegean Sea. COMECAP2014–ebook of contributions, edited by: Kanakidou, M., Mihalopoulos, N., and Nastos, P., Proceedings 12th International Conference of Meteorology, Climatology and Physics of the Atmosphere, Greece, Crete University Press 3, 26–30 (2014).
Nastos, P.T., Kapsomenakis, I., Giannakopoulos, C., Matzarakis, A. & Zerefos, C.S. Present and future projections of human-bioclimatic conditions over Peloponnese, based on regional climate model simulations. COMECAP2014–ebook of contributions, edited by: Kanakidou, M., Mihalopoulos, N., and Nastos, P., Proceedings 12th International Conference of Meteorology, Climatology and Physics of the Atmosphere, Greece, Crete University Press (2014).
Nastos, P.T. & Matsangouras, I.T. Seasonal analysis of composite mean and anomaly of synoptic conditions during waterspout days over north Cretan Sea, Greece. COMECAP2014–ebook of contributions, edited by: Kanakidou, M., Mihalopoulos, N., and Nastos, P., Proceedings 12th International Conference of Meteorology, Climatology and Physics of the Atmosphere, Greece, Crete University Press (2014).