Identifying and tracking cut-off lows effective in Iranian heavy rains

Document Type : Original Article

Authors

1 Shahid Beheshti University of Tehran, Faculty of Earth Sciences, Department of Natural Geography

2 Academic member of RS and GIS Center, Earth Sciences Faculty,Shahid Beheshti University.

3 Professor, Department of Climatology, Faculty of Earth Sciences, Shahid Beheshti University

4 Head of Laboratory, Remote Sensing and GIS Department, Faculty of Earth Sciences, Shahid Beheshti University

5 Lecturer at Payame Noor University, Parand Branch, Tehran

Abstract

In this study, the climatology of cut-off lows systems at the level of 500 hPa of the northern hemisphere effective on heavy rainfall in Iran has been discussed. The ECMWF reanalysis data were used to identify and track cut-off lows that lasted for more than 48 hours in the statistical period of 33 years (1986-2018). For this purpose, geopotential data, orbital wind data, and temperature data at the level of 500 hPa also were used. Identification of cut-off lows systems was performed using the Tibaldi-Multeni algorithm with auto-detection capability. Based on the results, 632 cut-off lows with a lifespan of more than 2 days were identified during the statistical period. The highest frequency of occurrence of this phenomenon was determined during a year (28 events) and the lowest frequency with (10 events). The highest incidence of cut-off lows was in March, January, and October and the lowest incidence was in July. In terms of seasonality, the highest frequency of events was in winter, and spring and the lowest frequency was in summer. The highest percentage of the impact of cut-off lows on heavy rainfall was in the northwest and northeast and the lowest percentage of the impact of cut-off lows on heavy rainfall was in the southeast region of Iran. In total, the share of cut-off lows in heavy rainfall of Iranian study stations was 8.02%, and the northwest region with 8.13% compared to the total amount of heavy rainfall in Iran.

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Researches in Earth Sciences

Articles in Press, Accepted Manuscript
Available Online from 14 February 2023

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