An evaluation of the role of hurricane Olga (2001) in an extreme rainy event in Israel using dynamic tropopause maps |
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| Authors: | S O Krichak P Alpert M Dayan |
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| Institution: | (1) Department of Geophysics and Planetary Sciences, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel |
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| Abstract: | Summary During the period from end of November to early December 2001, a sequence of extremely intense synoptic developments occurred
over the area from the Atlantic to Mediterranean. These included the formation of hurricane Olga, an intensification of the
Icelandic Low, strengthening of the subtropical westerly jet stream (STJ) over North Africa, formation of the Red Sea Trough
(RST) and Cyprus Low cyclones, which resulted in torrential rains in Israel on December 4–5. The evolution of the synoptic
processes over a large area from the Atlantic to Western Europe and the Mediterranean region during November 25–December 2
is investigated here with the help of dynamic tropopause patterns calculated based on reanalysis data. It is shown that the
chain of extreme weather events was triggered by the acceleration of a coherent tropopause disturbance (CTD) over the Labrador
Sea. Two branches of the process may be distinguished, southern and northern. The southern one was associated with the transformation
of a tropical storm into hurricane Olga, strengthening of the STJ and eventually the formation of the RST cyclone. The RST
contributed to the intensification of the transport of moist air masses from equatorial Africa to the Mediterranean region.
The northern branch was determined by an eastward drift of the CTD, moist air mass transport from the area of the hurricane
to the North Atlantic and the European-Mediterranean region, strengthening of the Icelandic Low and formation of an upper
troposphere potential vorticity-streamer system over western Scandinavia. Displacement of the streamer to the Mediterranean
region and its interaction with the RST system played a major role in the development of the powerful Cyprus Low cyclone over
the northeastern Mediterranean region. |
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