SEA-LEVEL PRESSURE DEPARTURES IN THE MEDITERRANEAN AND THEIR RELATIONSHIP WITH MONTHLY RAINFALL CONDITIONS IN ISRAEL

Monthly rainfall conditions in Israel were determined, using data from 12 stations, during 30 years (1961-90). The definition of a month to be dry, normal or wet, was done using standardized rainfall totals. Pr essure departures for each of the three rainfall categories for each m onth of the rainy season, were calculated and mapped. Correlation betw een rainfall totals at each of the 12 stations and monthly mean sea le vel pressure at 72 grid points in the area delimited by the 20 degrees W and 50 degrees E meridians and the 20 degrees N and 60 degrees N pa rallels, was performed. For each month, 12 correlation maps were prepa red tone of each station). Similar maps were averaged together to form coherent rainfall regions. At the beginning of the rainy season (Octo ber) the rainfall in Israel is sporadic and spotty without a distincta ble coherent region. At the end of the rainy season (April) the rainfa ll is more widespread, forming a large coherent region covering most o f the country. Dry rainfall conditions in Israel, were found to be cha racterized by positive pressure departures in the eastern Mediterranea n and over Israel and/or by easterly or southerly circulation over the eastern Mediterranean. Wet rainfall conditions in Israel, were found to be characterized by negative pressure departures in the eastern Med iterranean and over Israel and/or by westerly or northerly circulation over the eastern Mediterranean. Moreover, in many cases dry condition s in Israel, were associated with below normal pressure conditions ove r central or western Europe, while wet conditions in Israel, with abov e normal conditions over the same region, thus, reflecting the so-call ed Mediterranean Oscillation. Finally, normal rainfall conditions are characterized by very slight to negligible pressure departures over th e entire Mediterranean and Europe.