Sounding-derived parameters associated with severe hail events in Romania

The present paper analyzes 549 severe weather events reported to the ESWD (European Severe Weather Database) that caused large hail in the territory of Romania. Values of atmospheric instability indices have been analyzed for these episodes using data from Bucharest and Budapest sounding stations. For a period of 140 days with episodes of large hail, 24 instability indices were analyzed to describe the atmospheric conditions of the main daily convective activity. The mean values for most indices characterize an unstable atmospheric environment. Of the indices that measure potential instability, VT (vertical totals index) and TT (totals index) had values that described a conductive atmospheric environment for the development of hailstorms. In addition, the interquartile values of LIV (lifted index using virtual temperature) had values lower than zero. For SWEAT (severe weather threat index) and CAPEV (convective available potential energy index using virtual temperature), only the values in the 75th percentile describe a very unstable environment (according to the literature). Strong linear correlations were registered between several pairs of indices such as CAPEV-LIV and SWEAT-SI that can be used for the operational forecast of hail

Circulation in the troposphere over Europe between 40 and 55 degree North latitude, with special focus on the western direction

This paper aims to be a contribution to the study of the currents in the upper and middle troposphere over Romania, in the context of European temperate zone, as the influence of the relief upon the western predominant influence, under the planetary boundary layer. Processing database from 19 European aerological stations, two in Romania, one in the intra-Carpathian area, Cluj-Napoca and one in the extra-Carpathian area, Bucharest. Romania is situated in the southern half of the European temperate zone. For this latitudinal area of the Europe, was selected a west-east profile, from the Atlantic Ocean to the Dnieper River. Preliminary analysis carried out for a total of just five years, led to the confirmation of the predominance of western circulation characteristic of temperate zones, in the middle and especially in the upper troposphere, but little to counter clearing, of the backward currents in the upper troposphere, tropopause and lower stratosphere eastward and northeastward, prospective currents of the Ferrel Cell circulation model. It was found discontinuous character of these currents and discontinuous character and increasing of the dominant western direction together with the altitude. From the forces acting on the wind direction, west direction was analyzed in correlation with the altitude and morphology of the relief in the case of the lower troposphere, where these parameters are important, also in the middle and upper troposphere was validated the influence of the Coriolis force

THE STATUS OF ATMOSPHERIC INSTABILITY INDICES ASSOCIATED WITH HAIL EVENTS THROUGHOUT MOLDOVA

The lower pressure of water vapor of the outer eastern and south-eastern Carpathians, as well as in Dobrogea, determines within these areas an average annual number of days of under 2 days. In sheltered areas from Bârlad Plateau the average multi-annual value decreases even below 0,5 days. Hail events that affect the territory of Moldova are, in most cases, caused by thunderstorms during May and June (frequency of over 60 %). We had analysed in the present paper a representative number of statistical severe convective events causing hailstorms and material damage between 1990-2013 period. Values of atmospheric instability indices have been analyzed for these episodes as CAPE (Convective available potential energy), SWEAT (severe weather threat), Li (lifted index), KI (K index), TT (total totals) to evaluate their medium range forecast under the hail production conditions. These indicators measure the degree of atmospheric instability providing information about possible occurrence of clouds with large vertical extent. The most powerful correlations have been recorded in the case of parameter LI, for which the daily mean value was used. The status of these indices is assessed for both the days with hail, but also on previous intervals with hail to assess their capacity to forecast this extreme weather phenomenon

PRECURSOR WEATHER CONDITIONS FOR HAIL-EVENT FORECASTING IN THE MOLDAVIA

he present work analysed a statistically representative number of severe convective events which caused hail and material damage during 1990-2015. For these episodes heights of 0oC, -6oC, -10oC and -20oC isotherms were analyzed. In the layers between these four isotherms, the formation and growth of hailstones occur. The height of these isotherms in the period preceding hail is essential in weather forecast of this phenomenon. Lifted index values recorded before hail events are also correlated with height isotherms. The altitudinal differences between the height of -6oC and -20oC isotherm and freezing level which represents intervals of initiation and formation of hail are identified. Not at last the values of the meteorological indices used to forecast the potential formation and hail falling in extracarpathian Moldavia are presented in details