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The Role of Atmospheric Processes Associated with Hurricane Olga in the December 2001 Floods in Israel

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  • 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

Over the period from 0000 UTC 3 December to 0000 UTC 5 December 2001, heavy rains fell in northern Israel. Intensity of the rainfall in some areas exceeded 250 mm (24 h)−1. Results of an investigation of the case including back-trajectory evaluations, numerical simulation experiments, and a potential vorticity (PV) analysis are presented. It is demonstrated that the unusual eastern Mediterranean process has been initiated by the formation of a tropical storm that later became Hurricane Olga from 25 to 29 November. The consequent synoptic processes were associated with the development of a large-scale anticyclone to the NE of the tropical storm. Large-scale subsidence in the anticyclone played a central role in the process by leading to a convergence of the moist air masses in a narrow band on the outskirts of the system. The air masses from the area were later transported into the midtroposphere over western Europe. The interaction of these relatively warm and wet air masses with the cold and dry upper-tropospheric air over Europe has led to an intensification of the upper-tropospheric northerly airflow, extrusion of stratospheric air into the upper troposphere, and formation of a PV streamer system over southern Europe. Finally, the positioning and intensity of the PV streamer, as well as the large amounts of air moisture over the Mediterranean region, contributed to the intensity of the 3–5 December 2001 torrential rains over Israel.

Corresponding author address: Dr. Simon O. Krichak, Senior Research Scientist, Department of Geophysics and Planetary Sciences, Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel. Email: shimon@cyclone.tau.ac.il

Abstract

Over the period from 0000 UTC 3 December to 0000 UTC 5 December 2001, heavy rains fell in northern Israel. Intensity of the rainfall in some areas exceeded 250 mm (24 h)−1. Results of an investigation of the case including back-trajectory evaluations, numerical simulation experiments, and a potential vorticity (PV) analysis are presented. It is demonstrated that the unusual eastern Mediterranean process has been initiated by the formation of a tropical storm that later became Hurricane Olga from 25 to 29 November. The consequent synoptic processes were associated with the development of a large-scale anticyclone to the NE of the tropical storm. Large-scale subsidence in the anticyclone played a central role in the process by leading to a convergence of the moist air masses in a narrow band on the outskirts of the system. The air masses from the area were later transported into the midtroposphere over western Europe. The interaction of these relatively warm and wet air masses with the cold and dry upper-tropospheric air over Europe has led to an intensification of the upper-tropospheric northerly airflow, extrusion of stratospheric air into the upper troposphere, and formation of a PV streamer system over southern Europe. Finally, the positioning and intensity of the PV streamer, as well as the large amounts of air moisture over the Mediterranean region, contributed to the intensity of the 3–5 December 2001 torrential rains over Israel.

Corresponding author address: Dr. Simon O. Krichak, Senior Research Scientist, Department of Geophysics and Planetary Sciences, Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel. Email: shimon@cyclone.tau.ac.il

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