- Email: [email protected]
Atmospheric Processes in the Mediterranean
Atmospheric Research 152 (2015) 1–3
Contents lists available at ScienceDirect
Atmospheric Research journal homepage: www.elsevier.com/locate/atmos
Preface
Atmospheric Processes in the Mediterranean
Keywords: Atmospheric processes Mediterranean
This Special Issue of Atmospheric Research entitled “Atmospheric Processes in the Mediterranean” hosts selected papers that were presented at the 11th Conference of Meteorology, Climatology and Atmospheric Physics, held in Athens, Greece, from 30 May to 1 June 2012. The title reflects the wide range of papers presented on various atmospheric processes taking place in the Mediterranean. • In the study of Jacovides et al., an effort for estimating daily solar global broadband along with solar spectral global UV and PAR radiant fluxes is conducted by using Artificial Neural Networks (ANN). The analysis is based on hourly radiometric data collected at the semi-urban Athalassa site, in Cyprus for a 3-year period (2004–2006). In this study, only one hidden layer is sufficient for estimating daily global spectral radiant fluxes through both solar and atmospheric parameters. Sunshine duration plays an important role in obtaining acceptable model predictions, whereas other parameters used may produce conflicting influences on the ANN models' performance. Comparisons between proposed ANN models and conventional regression models revealed that the results of both methods are statistically significant. Nevertheless, on closer examination of several error measures, it is clear that the ANN models perform better. • The impact of topography on the distribution and the amount of precipitation in Epirus, NW Greece are investigated by Sindosi et al. A precipitation event with typical wintertime characteristics (high precipitation amounts on 3 November, 2009) is simulated, by applying the numerical model MM5 on a high resolution grid (2 × 2 km). The topography in the model is modified either by reducing the height of the mountains (type RT) or by elevating the terrain height (type ET). The results show that in the RT type, the precipitation field appears more homogeneous, with weaker maxima on the windward sides and above the mountain ridges. In the ET type, rain increases in the windward coastal
http://dx.doi.org/10.1016/j.atmosres.2014.07.027 0169-8095/© 2014 Elsevier B.V. All rights reserved.
zone of Epirus, while it is reduced in the inland areas where the air is less humid. Thus, the bogus modification of topography does not only affect the areas close to the mountains (windward or leeward sides), but it also affects the flow near the surface. • Katavoutas et al. investigated the urban thermal environment of the large coastal metropolitan city of Athens, utilizing the thermo-physiological index PET. The analysis was based on three hour measurements derived from three-year datasets (2006–2009), at 12 monitoring sites located in the urban complex of Athens, on its boundaries and beyond them. The frequency and spatial distribution of PET as well as the urban/ rural differences of PET have also been analyzed. The analysis reveals that among the stations considered, those located inside the urban complex and the industrialized area present urban thermal characteristics, regardless of the fact that they are installed either in a park and on a hill or in an open field. Further, the spatial distribution of PET, at 0200 LST, shows a difference of about 3 to 4 °C, on the main axis of the city (SSW–NNE) in the summer period, while the difference exceeds 2.5 °C in the winter period. The PET differences between urban and rural sites hold a positive sign, except those at 0500 LST and at 0800 LST. Finally, the trend analysis reveals a statistically significant increasing heat stress for certain stations and months. • The vertical structure and the spectral characteristics of the marine Low Level Jets (LLJs) which are associated with frontal events were analyzed by Helmis et al. The data used are based on remote sensing (sodar) and in-situ instrumentation measurements, during the summer 2003, which were collected within the framework of the Coupled Boundary Layers AirSea Transfer Experiment in Low Winds (CBLAST-Low), at Nantucket Island, MA, U.S.A. The results showed that the lowest 100 to 200 m are characterized by strongly stable atmospheric conditions that are changed to slightly stable or almost neutral at higher levels. The frequent development of LLJs was also observed and was associated with frontal events, depending on the meteorological conditions. Further, in order to understand the influence of the different physical processes, the Hilbert–Huang Transform (HHT) algorithm
2
•
•
•
•
Preface
was applied to the time series of the wind data from the sodar, at different levels. The analysis of the wind speed data showed high amplitude variations corresponding to contributions from inertial but also from diurnal and meso-scale motions. Meteorological (T and RH values) and air pollution data (PM10, NO2 and O3 concentrations) observed in Athens, Thessaloniki and Volos were analyzed by Papanastasiou et al., in order to assess the synergy of air quality and the thermal comfort conditions, when extremely hot weather prevailed in Greece during the period 2001–2010. The analysis was based on the suggestion made by the IPCC to define an extreme weather event. Accordingly, a heat wave day is defined when the daily maximum hourly temperature value exceeds its 90th percentile. Mean pollution levels during the heat wave days and the non-heat wave days were calculated in order to examine the impact of the extreme hot weather on air quality. The analysis revealed a synergetic effect between air pollution and discomfort conditions in the three cities that was more pronounced during heat wave days. When air quality deteriorates, discomfort conditions became worse and vice versa. The intensity of discomfort conditions was related to the spatial coverage and the population of the urban agglomeration. Georgiou et al. analyzed the variability of the thermohaline characteristics of the deep-water masses in the Aegean Sea and the possible impact of the regional atmospheric forcing variability for the period 1960–2012. Due to its small size, the Aegean Sea surface responds rapidly to the meteorological changes and/or the variability of the lateral fluxes and this variability propagates in the thermohaline characteristics of the deep water masses of the basin through deep water formation processes. During the period examined, the deep waters of the Aegean Sea sub-basins present great sensitivity to various forcings exhibited by the large interannual variability of their characteristics. The impact of extreme events in the deep water formation processes in the northcentral Aegean is more intense than in the south. Roussi et al. compared two different methods of pattern recognition, Principal Component Analysis (PCA) and Self Organizing Maps (SOM) on the basis of two teleconnection patterns, namely, the North Atlantic Oscillation (NAO) and the North Sea–Caspian Pattern (NCP) at 500 hPa for winter over the broader Europe area. The ECHAM5/MPI General Circulation Model was evaluated regarding the representation of the two teleconnection patterns for a reference (1971–2000) and a future (2071–2100). Both PCA and SOM methodologies capture the NAO pattern; SOM is capable of capturing even less pronounced patterns, such as the NCP. In the future simulations, the atmospheric circulation during winter seems to be more pronounced. Salamalikis et al. studied the stable isotopic composition of water vapor resulting from a three-year sampling and its relationship with meteorological parameters. A weak but significant relationship between δ18Ο and temperature was found. A periodic model on the isotope values was applied, revealing a significant seasonal dependence, with a peak in the beginning of June. Finally, in order to identify the potential sources affecting the isotopic composition (dexcess) of water vapor, a Concentration Weighted Trajectory model was used. The d-excess in Patras vapor field was
•
•
•
•
found to be affected mainly by air parcels having traveled through the Mediterranean. In Avgoustoglou and Tzeferi, two sub-grid schemes of COSMOS model were used in an evaluation of stratus Clouds: a semiempirical scheme used in the radiation module and a statistical scheme in the turbulence module. The possibility of implementing the statistical scheme in the radiation mode was investigated on the basis of a spring test case with synoptic conditions that favor stratiform clouds in the wider Balkan region, giving rise to a strong coexistence of continental as well as marine clouds. The results are evaluated through direct comparisons with satellite data and measurements from fifty Greek synoptic meteorological stations. It was found that the daily 2 m minimum temperature was better simulated when the statistical scheme was implemented in the radiation module. Also, the implementation of the statistical scheme led to an underestimation of low cloud cover contrasting medium cloud cover. Hatzaki and Wu explored the relationship between the North Atlantic sea surface temperature (SST) and the winter precipitation of south-eastern Europe with the aid of EOF analysis along with possible changes of this relationship in the past. For this purpose, precipitation data of 54 stations were employed for the period 1958–2000, together with the NOAA Extended Reconstruction SST with 2.0° × 2.0° resolution. The first EOF, explaining about 44% of interannual variability, is highly correlated with the tropical North Atlantic SST anomalies with a time lag reaching up to two seasons. Furthermore, it was found that the observed interdecadal changes of the relationship between southeastern Europe winter precipitation and tropical North Atlantic SST can be attributed to possible variations of the Atlantic storm path. Philandras et al. performed a climatology of the upper air temperature in the Mediterranean region, during the period 1965–2011 employing radiosonde recordings and gridded NCEP-NCAR reanalysis datasets at seven isobaric levels. Trends and variability of upper air temperature were analyzed on annual and seasonal basis. Further, the correlation between upper air temperature and teleconnection indices, was estimated. It was found that air temperature is increasing at a higher rate in the lower and middle compared to the upper troposphere, and this is very likely due to increasing greenhouse gas concentrations. Pyrina et al. estimated the cloud effects on the shortwave (SW), longwave (LW) and net all-wave radiation budgets in the Mediterranean basin using a detailed radiative transfer model. The model radiation fluxes were validated against satellite data and ground-based station measurements. The cloud radiative effects were obtained for low, middle, highlevel clouds, and for total cloud cover. It was found that the effect on solar radiation is to produce radiative cooling at the top of atmosphere and at the surface that more than balances the warming effects on terrestrial radiation. Furthermore, high clouds play an important role in net surface cooling through the combination of SW reflection to space and a much reduced LW warming effect at the surface. The geographical patterns of the effects are mainly characterized by a strong south to north increasing gradient. The seasonal variation of net radiative effects is dominated by solar radiation with maxima in spring and minima in winter.
Preface
• Nastos and Kapsomenakis analyzed and quantified the future projections of heat waves in Greece. 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 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. • Rizou et al. studied the impact of the Indian summer monsoon on the large scale variability of the atmospheric circulation over the Mediterranean, on an inter-annual time scale. Composite and correlation analysis results are presented, outlining different circulation patterns in the upper and lower troposphere for strong and weak monsoon years. ERA-40 reanalyses at various isobaric levels together with the standardized All India Rainfall Index for boreal summer (June–July–August–September) of a 44-year period were employed. During strong monsoon years, many atmospheric circulation systems appear strengthened over Eurasia, resembling a well-organized Rossby wave train over the area. In the upper troposphere, a meridional shift of the jet streams over the examined area was also identified during extreme monsoon years. Also, during strong
3
monsoon years, enhanced northerlies (Etesians) appear to dominate over Eastern Mediterranean along with intensified subsidence. As the Managing Guest Editors of this Special Issue of Atmospheric Research, we would like to thank all the authors for their contributions to this volume and their adherence to the strict reviewing procedures. We also wish to express our sincere appreciation to the international panel of expert reviewers for making available their knowledge and proficiency in the effort to attain the highest scientific value of this volume. We wish to express our special thanks to the staff of Elsevier B.V. for their technical support. Last but not least, we wish to thank Prof. José Luis Sánchez, Editor-in-Chief for Atmospheric Research, for his supervision and guidance during all the stages of the production of this volume.
Silas Michaelides Department of Meteorology, Nicosia, Cyprus Corresponding author. E-mail address: [email protected]. Panagiotis Nastos Helena Flocas University of Athens, Athens, Greece E-mail addresses: [email protected] (P. Nastos), efl[email protected] (H. Flocas).
Contents lists available at ScienceDirect
Atmospheric Research journal homepage: www.elsevier.com/locate/atmos
Preface
Atmospheric Processes in the Mediterranean
Keywords: Atmospheric processes Mediterranean
This Special Issue of Atmospheric Research entitled “Atmospheric Processes in the Mediterranean” hosts selected papers that were presented at the 11th Conference of Meteorology, Climatology and Atmospheric Physics, held in Athens, Greece, from 30 May to 1 June 2012. The title reflects the wide range of papers presented on various atmospheric processes taking place in the Mediterranean. • In the study of Jacovides et al., an effort for estimating daily solar global broadband along with solar spectral global UV and PAR radiant fluxes is conducted by using Artificial Neural Networks (ANN). The analysis is based on hourly radiometric data collected at the semi-urban Athalassa site, in Cyprus for a 3-year period (2004–2006). In this study, only one hidden layer is sufficient for estimating daily global spectral radiant fluxes through both solar and atmospheric parameters. Sunshine duration plays an important role in obtaining acceptable model predictions, whereas other parameters used may produce conflicting influences on the ANN models' performance. Comparisons between proposed ANN models and conventional regression models revealed that the results of both methods are statistically significant. Nevertheless, on closer examination of several error measures, it is clear that the ANN models perform better. • The impact of topography on the distribution and the amount of precipitation in Epirus, NW Greece are investigated by Sindosi et al. A precipitation event with typical wintertime characteristics (high precipitation amounts on 3 November, 2009) is simulated, by applying the numerical model MM5 on a high resolution grid (2 × 2 km). The topography in the model is modified either by reducing the height of the mountains (type RT) or by elevating the terrain height (type ET). The results show that in the RT type, the precipitation field appears more homogeneous, with weaker maxima on the windward sides and above the mountain ridges. In the ET type, rain increases in the windward coastal
http://dx.doi.org/10.1016/j.atmosres.2014.07.027 0169-8095/© 2014 Elsevier B.V. All rights reserved.
zone of Epirus, while it is reduced in the inland areas where the air is less humid. Thus, the bogus modification of topography does not only affect the areas close to the mountains (windward or leeward sides), but it also affects the flow near the surface. • Katavoutas et al. investigated the urban thermal environment of the large coastal metropolitan city of Athens, utilizing the thermo-physiological index PET. The analysis was based on three hour measurements derived from three-year datasets (2006–2009), at 12 monitoring sites located in the urban complex of Athens, on its boundaries and beyond them. The frequency and spatial distribution of PET as well as the urban/ rural differences of PET have also been analyzed. The analysis reveals that among the stations considered, those located inside the urban complex and the industrialized area present urban thermal characteristics, regardless of the fact that they are installed either in a park and on a hill or in an open field. Further, the spatial distribution of PET, at 0200 LST, shows a difference of about 3 to 4 °C, on the main axis of the city (SSW–NNE) in the summer period, while the difference exceeds 2.5 °C in the winter period. The PET differences between urban and rural sites hold a positive sign, except those at 0500 LST and at 0800 LST. Finally, the trend analysis reveals a statistically significant increasing heat stress for certain stations and months. • The vertical structure and the spectral characteristics of the marine Low Level Jets (LLJs) which are associated with frontal events were analyzed by Helmis et al. The data used are based on remote sensing (sodar) and in-situ instrumentation measurements, during the summer 2003, which were collected within the framework of the Coupled Boundary Layers AirSea Transfer Experiment in Low Winds (CBLAST-Low), at Nantucket Island, MA, U.S.A. The results showed that the lowest 100 to 200 m are characterized by strongly stable atmospheric conditions that are changed to slightly stable or almost neutral at higher levels. The frequent development of LLJs was also observed and was associated with frontal events, depending on the meteorological conditions. Further, in order to understand the influence of the different physical processes, the Hilbert–Huang Transform (HHT) algorithm
2
•
•
•
•
Preface
was applied to the time series of the wind data from the sodar, at different levels. The analysis of the wind speed data showed high amplitude variations corresponding to contributions from inertial but also from diurnal and meso-scale motions. Meteorological (T and RH values) and air pollution data (PM10, NO2 and O3 concentrations) observed in Athens, Thessaloniki and Volos were analyzed by Papanastasiou et al., in order to assess the synergy of air quality and the thermal comfort conditions, when extremely hot weather prevailed in Greece during the period 2001–2010. The analysis was based on the suggestion made by the IPCC to define an extreme weather event. Accordingly, a heat wave day is defined when the daily maximum hourly temperature value exceeds its 90th percentile. Mean pollution levels during the heat wave days and the non-heat wave days were calculated in order to examine the impact of the extreme hot weather on air quality. The analysis revealed a synergetic effect between air pollution and discomfort conditions in the three cities that was more pronounced during heat wave days. When air quality deteriorates, discomfort conditions became worse and vice versa. The intensity of discomfort conditions was related to the spatial coverage and the population of the urban agglomeration. Georgiou et al. analyzed the variability of the thermohaline characteristics of the deep-water masses in the Aegean Sea and the possible impact of the regional atmospheric forcing variability for the period 1960–2012. Due to its small size, the Aegean Sea surface responds rapidly to the meteorological changes and/or the variability of the lateral fluxes and this variability propagates in the thermohaline characteristics of the deep water masses of the basin through deep water formation processes. During the period examined, the deep waters of the Aegean Sea sub-basins present great sensitivity to various forcings exhibited by the large interannual variability of their characteristics. The impact of extreme events in the deep water formation processes in the northcentral Aegean is more intense than in the south. Roussi et al. compared two different methods of pattern recognition, Principal Component Analysis (PCA) and Self Organizing Maps (SOM) on the basis of two teleconnection patterns, namely, the North Atlantic Oscillation (NAO) and the North Sea–Caspian Pattern (NCP) at 500 hPa for winter over the broader Europe area. The ECHAM5/MPI General Circulation Model was evaluated regarding the representation of the two teleconnection patterns for a reference (1971–2000) and a future (2071–2100). Both PCA and SOM methodologies capture the NAO pattern; SOM is capable of capturing even less pronounced patterns, such as the NCP. In the future simulations, the atmospheric circulation during winter seems to be more pronounced. Salamalikis et al. studied the stable isotopic composition of water vapor resulting from a three-year sampling and its relationship with meteorological parameters. A weak but significant relationship between δ18Ο and temperature was found. A periodic model on the isotope values was applied, revealing a significant seasonal dependence, with a peak in the beginning of June. Finally, in order to identify the potential sources affecting the isotopic composition (dexcess) of water vapor, a Concentration Weighted Trajectory model was used. The d-excess in Patras vapor field was
•
•
•
•
found to be affected mainly by air parcels having traveled through the Mediterranean. In Avgoustoglou and Tzeferi, two sub-grid schemes of COSMOS model were used in an evaluation of stratus Clouds: a semiempirical scheme used in the radiation module and a statistical scheme in the turbulence module. The possibility of implementing the statistical scheme in the radiation mode was investigated on the basis of a spring test case with synoptic conditions that favor stratiform clouds in the wider Balkan region, giving rise to a strong coexistence of continental as well as marine clouds. The results are evaluated through direct comparisons with satellite data and measurements from fifty Greek synoptic meteorological stations. It was found that the daily 2 m minimum temperature was better simulated when the statistical scheme was implemented in the radiation module. Also, the implementation of the statistical scheme led to an underestimation of low cloud cover contrasting medium cloud cover. Hatzaki and Wu explored the relationship between the North Atlantic sea surface temperature (SST) and the winter precipitation of south-eastern Europe with the aid of EOF analysis along with possible changes of this relationship in the past. For this purpose, precipitation data of 54 stations were employed for the period 1958–2000, together with the NOAA Extended Reconstruction SST with 2.0° × 2.0° resolution. The first EOF, explaining about 44% of interannual variability, is highly correlated with the tropical North Atlantic SST anomalies with a time lag reaching up to two seasons. Furthermore, it was found that the observed interdecadal changes of the relationship between southeastern Europe winter precipitation and tropical North Atlantic SST can be attributed to possible variations of the Atlantic storm path. Philandras et al. performed a climatology of the upper air temperature in the Mediterranean region, during the period 1965–2011 employing radiosonde recordings and gridded NCEP-NCAR reanalysis datasets at seven isobaric levels. Trends and variability of upper air temperature were analyzed on annual and seasonal basis. Further, the correlation between upper air temperature and teleconnection indices, was estimated. It was found that air temperature is increasing at a higher rate in the lower and middle compared to the upper troposphere, and this is very likely due to increasing greenhouse gas concentrations. Pyrina et al. estimated the cloud effects on the shortwave (SW), longwave (LW) and net all-wave radiation budgets in the Mediterranean basin using a detailed radiative transfer model. The model radiation fluxes were validated against satellite data and ground-based station measurements. The cloud radiative effects were obtained for low, middle, highlevel clouds, and for total cloud cover. It was found that the effect on solar radiation is to produce radiative cooling at the top of atmosphere and at the surface that more than balances the warming effects on terrestrial radiation. Furthermore, high clouds play an important role in net surface cooling through the combination of SW reflection to space and a much reduced LW warming effect at the surface. The geographical patterns of the effects are mainly characterized by a strong south to north increasing gradient. The seasonal variation of net radiative effects is dominated by solar radiation with maxima in spring and minima in winter.
Preface
• Nastos and Kapsomenakis analyzed and quantified the future projections of heat waves in Greece. 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 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. • Rizou et al. studied the impact of the Indian summer monsoon on the large scale variability of the atmospheric circulation over the Mediterranean, on an inter-annual time scale. Composite and correlation analysis results are presented, outlining different circulation patterns in the upper and lower troposphere for strong and weak monsoon years. ERA-40 reanalyses at various isobaric levels together with the standardized All India Rainfall Index for boreal summer (June–July–August–September) of a 44-year period were employed. During strong monsoon years, many atmospheric circulation systems appear strengthened over Eurasia, resembling a well-organized Rossby wave train over the area. In the upper troposphere, a meridional shift of the jet streams over the examined area was also identified during extreme monsoon years. Also, during strong
3
monsoon years, enhanced northerlies (Etesians) appear to dominate over Eastern Mediterranean along with intensified subsidence. As the Managing Guest Editors of this Special Issue of Atmospheric Research, we would like to thank all the authors for their contributions to this volume and their adherence to the strict reviewing procedures. We also wish to express our sincere appreciation to the international panel of expert reviewers for making available their knowledge and proficiency in the effort to attain the highest scientific value of this volume. We wish to express our special thanks to the staff of Elsevier B.V. for their technical support. Last but not least, we wish to thank Prof. José Luis Sánchez, Editor-in-Chief for Atmospheric Research, for his supervision and guidance during all the stages of the production of this volume.
Silas Michaelides Department of Meteorology, Nicosia, Cyprus Corresponding author. E-mail address: [email protected]. Panagiotis Nastos Helena Flocas University of Athens, Athens, Greece E-mail addresses: [email protected] (P. Nastos), efl[email protected] (H. Flocas).