MEDITERRANEAN CYCLONES TRACKS IN EUROPE WITH SPECIAL VIEW OVER ROMANIA (1985-2015)

Abstract

Mediterranean cyclones (MCs) affect not only the countries neighboring the Mediterranean basin, but also the weather conditions in regions that are not in direct contact with the Mediterranean basin such as Central, Eastern and South-Eastern Europe, including Romania. They are associated, in general, with extreme weather events. This study considered data over a 30-yr. period (December 1, 1986 – November 30, 2015). For MCs identification and their track tracing, the mean sea level pressure, 500 hPa geopotential heights, 500-1000 hPa relative topography and 850 hPa pseudo-equivalent potential temperature were employed. The European spatial domain was delimited as 30°-60° N latitude and as 20° V - 45 ° E longitude. To select those cyclones influencing the weather in Romania a square-shaped area whose external limits are located about 500 km from the center of Romania was used. For tracing the trajectory, the low-pressure center position at every 6 hours was considered. Frequency of occurence and track density were analyzed considering two temporal approaches: i. for the entire period and for three 10-yr subperiods; ii. the annual and seasonal scale for the entire period. For track density, the anomalies for each 10-yr sub-period and for each season were calculated. The main findings of this study are: the most exposed area to MCs are central and eastern Mediterranean regions, 43.39% of the cyclones generated in the Mediterranean basin crossed the region of Romania; seasonally, the highest occurrence frequency is specific to winter and the lowest to summer; no significant changes in the annual or seasonal occurrence was detected; during the second 10-yr sub-period weak to moderate positive anomalies were detected, whereas during the first and the last ones, positive and negative anomalies were found depending on the season and region; seasonal average position of the MCs tracks revealed the largest shift from one sub-period to another in winter and the smallest in autumn.