Investigation of the relationship between vorticity fluctuations and precipitation in northwest of Iran (Case study: Sardasht station)

Positive and negative vorticity in the westerly winds wave cause changes in the type of precipitation. The purpose of this study is to investigate the relationship between vorticity fluctuations and precipitation in Sardasht region. First, daily precipitation data were obtained from Sardasht synoptic station and after statistical analysis of the data, synoptic maps of Sea level pressure (SLP), 500 millibar Geopotential height (HGT), omega and vorticity for representative days were extracted and analyzed using GAREDS software. The results indicate the creation of a front at surface in all SLP maps at Sardasht station. Also in the HGT map, the study area is located in the PVA section of the west wind troughs, which has created unstable conditions at the level of 500 millibar and has caused the rise of humidity. At sea level, the most important sources of moisture that strengthened the front and rainfall at the station were the Black Sea, the Mediterranean and the Caspian Sea. The direction of wind at sea level was northeast-southwest and in the upper level was west, southwest and northwest. Most of the day, we see the dominance of a cyclonic system in the region, which has occurred due to the creation of unstable conditions by the front. On omega map, all days are unstable and negative omega cores are formed in Sardasht station. The vorticity map shows the effect of positive vorticity in this station, which has caused precipitation, especially liquid precipitation in the area.