This paper evaluates the role of meteorological factors on the configuration of the complex aerosol’s character at a suburban area of Athens, Greece. To this effort, 4-month period measurements of hourly PM2.5 aerosol samples were employed, being collected with the aid of a conventional R&P TEOM (model 1400a) at Aghia Paraskevi. The simultaneous daily PM10 and PM2.5.10 concentrations are also discussed. Then, the entire daily data set was divided in 5 different classes at similar proportion by one decimal point for each one of assessed meteorological parameter, temperature, relative humidity and wind speed. The present study discusses not only the variations of the recorded levels of the three PM fractions and their seasonality but also the inter-fraction relationship for all possible matching of the aerosol’s pairs and the PM ratios in connection with the differentiation of the meteorological parameters’ values. PM10 and PM2.5-10 appeared to have the same character as in all the cases they proved to be strongly correlated. It was found that temperature enhanced the concentrations of the PM fractions and especially those with bigger diameter while relative humidity seemed to favour the formation of fine particles. Wind direction appeared to play a key role on the recorded PM profile. The transportation from the ’polluted’ Athens center proved to be the major mechanism which deters the ’clean atmosphere’ of the suburban area. © by PSP.

In this study, an updated and extended climatology of cyclonic tracks affecting the eastern Mediterranean region is presented, in order to better understand the Mediterranean climate and its changes. This climatology includes intermonthly variations, classification of tracks according to their origin domain, dynamic and kinematic characteristics, and trend analysis. The dataset used is the 1962–2001, 2.58 3 2.58, 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). The identification and tracking of the cyclones was performed with the aid of the Melbourne University algorithm. It was verified that considerable intermonthly variations of track density occur in the eastern Mediterranean, consistent with previous studies for the entire Mediterranean, while further interesting new features have been revealed. The classification of the tracks according to their origin domain reveals that the vast majority originate within the examined area itself, mainly in the Cyprus area and the southeastern Aegean Sea, while the tracks that originate elsewhere most frequently enter from the west. Deeper cyclones follow the southwest track originating from the area between Algeria and the Atlas Mountains. A greater size characterizes the westerly tracks (southwest, northwest, and west), while the northwest tracks propagate faster over the study area. A negative trend of the track frequency was found on an annual basis that can be mostly attributed to the winter months, being associated with variations in the baroclinicity. This negative trend is more prominent for the westerly and northeasterly tracks, as well as for those originating in the northern part of the examined area.

A case of abrupt and significant increase of surface ozone was examined, which is recorded during the night of October 9th, 2003, over the area of the Thriassion Plain - Greece, being accompanied by the occurrence of a wind outbreak during the same period. As this increase cannot be explained by the ordinary diurnal evolution of tropospheric ozone concentration, the possibility of downward stratospheric ozone transport was investigated. It was indeed found that the case is associated with tropopause folding and subsequent stratospheric air intrusion in the upper troposphere over Greece. With the aid of mesoscale modeling, being also supported by the hydraulic theory, it was found that the intense wind outbreak is associated with the development of disturbances in the lee side of the neighbouring mountain ranges. These disturbances contribute to the free troposphere - atmospheric boundary layer interaction, facilitating the transportation of stratospheric air close to the surface, thus resulting to the observed tropospheric ozone increase. © 2010 Gebrüder Borntraeger, Berlin, Stuttgart.

In this study, an updated and extended climatology of cyclonic tracks affecting the eastern Mediterranean region is presented, in order to better understand the Mediterranean climate and its changes. This climatology includes intermonthly variations, classification of tracks according to their origin domain, dynamic and kinematic characteristics, and trend analysis. The dataset used is the 1962-2001, 2.5° × 2.5°, 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). The identification and tracking of the cyclones was performed with the aid of the Melbourne University algorithm. It was verified that considerable intermonthly variations of track density occur in the eastern Mediterranean, consistent with previous studies for the entire Mediterranean, while further interesting new features have been revealed. The classification of the tracks according to their origin domain reveals that the vast majority originate within the examined area itself, mainly in the Cyprus area and the southeastern Aegean Sea, while the tracks that originate elsewhere most frequently enter from the west. Deeper cyclones follow the southwest track originating from the area between Algeria and the Atlas Mountains. A greater size characterizes the westerly tracks (southwest, northwest, and west), while the northwest tracks propagate faster over the study area. A negative trend of the track frequency was found on an annual basis that can be mostly attributed to the winter months, being associated with variations in the baroclinicity. This negative trend is more prominent for the westerly and northeasterly tracks, as well as for those originating in the northern part of the examined area. © 2010 American Meteorological Society.

The objective of this study is to investigate the linkage of large-scale upper air circulation over the greater European area with intense precipitation events over Eastern Mediterranean and then to estimate potential changes in the atmospheric patterns in the future, under global warming conditions. For this purpose, results from the regional climate model HadRM3P and Global Circulation Model HadAM3P have been used for the present period 1960-1990 (control run) and the future period 2070-2100 based on the B2a IPCC emission scenario. For the identification of the precipitation extremes the Simple Daily Intensity Index (SDII) was employed. Our analysis has shown a notable relation of extreme events with the East Atlantic and Scandinavia teleconnection patterns, as well as the Eastern Mediterranean Pattern (EMP) during the wet period. In the future, similar patterns are found, with different magnitude and position, following the projected changes in atmospheric circulation over Europe.

The relationship of prolonged dry spells in Eastern Mediterranean with large-scale surface and upper circulation is investigated on seasonal basis with the aid of the Singular-Value Decomposition Analysis (SVDA) for the period 1958-2000. The study was based on daily precipitation data of 56 stations, evenly distributed over Eastern Mediterranean region. Extreme dry spells are defined using the CDD index (maximum number of consecutive dry days). It was found that teleconnection patterns centered over Northern Atlantic and northern Europe seem to affect the duration of the longest dry spells over the Eastern Mediterranean, while surface synoptic scale systems in Northern Africa play a substantial role. The SVDA results compare well with the corresponding results of Canonical Correlation Analysis (CCA), mainly for the surface circulation during winter and summer. © Springer-Verlag 2009.

The objective of this study is to investigate the relationship of orography over Greece with prolonged dry spells, as represented by the maximum number consecutive dry days (CDD index) during an extremely dry summer. For this purpose a simulation experiment was conducted with the aid of the regional climate model RegCM3.1 using a spatial resolution of 10 km. It was shown that a significant precipitation regime formed over the mountainous areas of continental Greece and Crete during this dry summer, due to orographically forced precipitation, consequently influencing the length of dry spells. Furthermore, the CDD appears spatial variations over the maritime areas, despite the zero or insignificant precipitation. The sensitivity test that was performed with the elimination of orography demonstrated the important role that orography plays in the distribution of CDD, since significant lengthening of extreme dry spells was found over the mountainous areas. © Author(s) 2010.