The synoptic study of heavy rain fall (200mm or more during 24 hours) over the southern coasts of Caspian Sea due to mean temperature of thickness 1000/500mb, in 2th of October 2001
Subject Areas : Marine PhysicsH. Ardakani 1 , M. Poratashi 2 , M. Kheirandish 3
1 - Faculty of Marine Science and Technology, Islamic Azad University, North Tehran Branch
2 - Faculty of Marine Science and Technology, Islamic Azad University, North Tehran Branch
3 - Faculty of Marine Science and Technology, Islamic Azad University, North Tehran Branch
Keywords: Precipitation, Caspian Sea, Heavy rain fall, Advection, Anticyclone,
Abstract :
The mean annual precipitation over the southern part of Caspian coastal area is around 1000-1500 mm; therefore, this amount of precipitation is very important and is a considerable point of attention. With reference to statistical data, during 30 years (1972-2001), it showed that there were only 10 cases of similar events. We found that, best synoptic patterns for this condition is the mobile cold anticyclones which is moving almost rapidly from Europe and Scandinavia to the north of Black Sea and then moving to the Caspian Sea. These anticyclones have strong cold advection in eastern part and warm advection in the western part and their pressure center are about 1040 mb or more. But those anticyclones are very slow moving or almost stagnant over the area and could not cause these events. The upper-air chart showed that, spatial axis of upper ridge over them is a normal baroclinic condition. The value of cold advection in eastern part of anticyclones computed from 700 mb was -12ºc/12hours, but warm advection in western part of them, were not the same values. Consequently, the month of October is the most effective with compassion of the other months, because, during the summer times (July, August, September). The thermal low over the country frequently extending over the Caspian Sea and SST will increase, so, such patterns with strong cold advection, will cause severe instability over Caspian Sea.