Investigation of Synoptic Conditions coincided with the Occurrence of West and Southwest Floods on March 31 and April 1, 2019

Subject Areas : Sustainable Development

mahdi khazaei ¹ (PhD in Climatology, University of Tehran, Tehran, Iran.*(Corresponding Author))
Amir Hossain nikfal ² (PhD student in Meteorology, Meteorological Institute, Tehran, Iran.)

Received: 2019-08-09 Accepted : 2019-10-02 Published : 2021-02-19

Keywords: Flooding rainfall, west and southwest of the country, Synoptic Systems, moisture sources,

Abstract :

Background and Objective: The purpose of this study is to identify and investigate the synoptic systems that led to the extensive and destructive flood events in the west and southwest of the country on March 31 and April 1, 2019. Method: In order to study the synoptic conditions in coincided with the event of heavy rainfall leading to the floods, in addition to using NOAA18 satellite images, sea level pressure data, sea level specific humidity, geopotential height and omega at pressure level 850, 700 and 500 hPa, Relative humidity pressure  at 700 hPa, U and V component from pressure 1000 to 200 hPa with a resolution of 2.5 ° to 2.5° latitude from the National Center for Environmental Prediction and the National Center for Atmospheric Research (NCEP / NCAR) Received and the maps were plotted. Findings: Existence of a deep cyclone at sea level pressure to 500 hPa pressure from eastern Mediterranean to western of Iran and also the establishment of a subtropical jet stream with meridian direction (southwest - northeast) in the southwest and west of the country and finally the intense vertical shear of horizontal wind from sea level pressure to 200 hPa in the study area, It is known as the main factors of cause of instability in the west and southwest of the country. existence Specific humidity of 14 to 18 g / kg at sea level pressure and relative humidity of 95 to 100% at a pressure of 700 hPa have also been identified as suitable moisture conditions in the study area. Discussion and Conclusion: The results of this study show that on March 31 and April 1, 2019, the atmosphere of the western and southwestern regions of the country in all depths of the troposphere layer experienced severe instability due to the establishment eastern part of a deep cyclone. Above the cyclone mentioned above, located meridional flows of subtropical jet stream which has intensificated the instability to the depth of the tropospheric layer. Also moisture advection from the western Arabian Sea, the Red Sea and the Persian Gulf has caused form cells from thick convective clouds throughout the west and southwest of the country. The heavy rains resulting from these convective clouds have caused severe and extensive floods in this area of the country.

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