Continental polar outbreaks into the levant and eastern mediterranean

Continental polar outbreaks into the Levant and eastern Mediterranean regions originate in vast continental regions over Asia and Europe, causing respective unique weather conditions - cold, dry, and stable. These north-easterly winds have important environmental implications for agriculture, cold stress, and air pollution, which were the motivation for this study. They are exemplified here by statistical and synoptic study of such events over Israel. Seventy-two days of such outbreaks were observed during 6 years (1983-1988), all of them between October-May associated with different synoptic patterns. The typical duration of these events was of two categories: short events of 1-2 days, and long events of 4-5 days. The latter are the result of 'quasi-stationary' systems whereas the short ones are due to the passage of disturbances over the eastern Mediterranean. The highest frequency is in December, with 28 days (between 1983 and 1988), compared with 13 days in January and 8 days in February. The decrease in frequency towards February can be attributed to changes in the cyclone's trajectories, and to pressure gradient magnitude between the anticyclone over Asia and Turkey and the lower barometric pressure over the Mediterranean. These events have a typical course of pressure increase preceding the outbreak and during its first 2 days, and then a pressure decrease that is mostly accompanied with temperature increase.