A methodology to estimate annual transboundary atmospheric transport is proposed, taking into account different background meteorological conditions. For this purpose, the 850 hPa synoptic-scale atmospheric circulation over the area examined was classified on a daily basis into 14 distinct synoptic types, using a database for an extended period of 40 years. The corresponding frequency of appearance of the synoptic types for a normal year was calculated. For selected days representing the synoptic types during this year, the inflow-outflow fluxes of NOx and SO2 were estimated through a balancing box with the aid of a MEMO/TRAPPA modelling system. According to the proposed method, the total inflow-outflow fluxes were calculated using the lateral fluxes for each representative day, being weighted by the annual relative frequency of appearance of the synoptic scale weather types. It was demonstrated that this approach provides similar results to the intensive method based on day-by-day calculations. Furthermore, this approach is easier to use, since it is based on the simulations of selected days, and it allows the investigation of the influence of different types of atmospheric circulation on the inflow-outflow budget. Copyright © 2003 Royal Meteorological Society.

The synoptic scale atmospheric circulation prevailing during hail days in Northern Greece is examined for a period of 26 years (1976-2001) during the warm season. The initial objective of this classification scheme is to serve as a predictive tool for hail forecasting and permit a specification of greater or lesser hail risk, within the forecast activities of the Greek National Hail Suppression Program. The atmospheric circulation was classified into seven synoptic types and their frequency distribution was examined on an annual and monthly basis. Southwesterly flow (SW) and Shortwave trough (SWT) appear to be the most conducive synoptic types for hailstorm activity. Furthermore, the thermodynamic environment favoring the hailstorm development and evolution was examined using selected instability indices. The frequency distribution of the instability indices for a period of 11 years (1991-2001) in association with the synoptic types demonstrated their performance as a forecasting aid for thunderstorm activity to occur in a given synoptic environment.

The horizontal and vertical distributions of volatile organic compounds (VOCs) and ozone (O3) concentrations within the lower troposphere over the greater Athens area. Greece, under sea-breeze conditions were studied. Furthermore, an attempt was made to explain the dynamic and chemical mechanisms responsible for the formation of these distributions. Measurements were collected using a specially instrumented Falcon 20-E5 research aircraft, ground-based meteorological instrumentation, and a network of air quality monitoring stations within the context of the Scientific Training and Access to Aircraft for Atmospheric Research Throughout Europe (STAAARTE) 1997 experimental campaign. Relatively high ozone values (55-100 ppbv) were identified within the first 300-400 m above ground, and significantly reduced values were found over the depth of the atmospheric boundary layer. High values of VOC concentrations [150-350 ppbCarbon (C)] were observed near the ground as well as within the first 300 400 m above ground. At higher altitudes, of 1400-1600 m, VOC concentrations remained relatively high (100-200 ppbC). It was demonstrated that the sea-breeze circulation plays a major role in the formation of the above-mentioned concentration levels and that chemical transformations explain specific characteristics.