A preliminary analysis of disturbance tracks over the Mediterranean basin

The Mediterranean basin experiences considerable cyclone activity mostly during fall, winter and spring and diminished activity during summer. In this study we present results of synoptic disturbance track analysis for two contrasting winter months and two, near average, summer months over the eastern Mediterranean. The surface and 500 hPa disturbance tracks were subjectively analyzed from two points of view. First, looking at tracks of conventionally defined cyclone centers (eddies) based on actual pressure and height distribution and second, looking at tracks of transient cyclonic disturbances (TRADs), defined as centers of negative deviations from the time mean. The second type of analysis demonstrated a considerable increase in the number of detectable tracks. Over the Mediterranean and vicinity the ratio between the number of surface TRAD tracks to cyclone tracks is, about 2, whereas at 500 hPa the ratio is much higher, about 5. However, the average life span of transient disturbances was only slightly longer than that of conventional cyclones (mainly at 500 hPa). At the surface and at 500 hPa about 50% of the cyclone tracks coincided to a certain extent with TRAD tracks. In summer, when conventional analysis over the eastern Mediterranean yields mostly quasi-stationary low pressure centers associated with the Persian Gulf Trough, we detected clear signs of transient disturbances. Some interpretations of the differences between cyclones and TRADs in terms of weather in the eastern Mediterranean are also made.