Analysis of Dynamic Indices of Torrents in Karun Basin

In this research large scale dynamic and thermodynamic anomalies during storm events resulted from cyclogenesis in the Mediterranean Sea and Sudan low-pressure systems، are investigated. 5 severe storms that happened in KarunBasin (1998-2008) were selected and using Japanese Re-analysis data (JRA25)، anomalies of dynamic and thermodynamic indices، 2 days prior to the start of the storm until the end of the storm were analyzed. The selected indices in this research are potential vorticity، convergence and divergence، vertical velocity، absolute vorticity advection، specific humidity، moisture flux، potential temperature and equivalent potential temperature. According to the results and comparing 6-hourly recorded rainfall amounts، it was found out that in the reference events، before the start of the storm، geopotential height values، in the under-study region decreased and at the time of maximum rainfalls، the geopotential height reached to its lowest values and by end of the storm، the values started increasing، whereas parameters related to convergence and vertical movements، such as potential vorticity، vorticity advection، moisture flux، convergence of moisture and specific humidity amounts corresponded to the same trend of rainfall from the beginning to the end. It is obvious that none of these indices can individually cause the occurrence of a storm، but by analyzing trends and regressions، it seems that there are meaningful relationships between geopotential height، moisture advection and potential vorticity and rainfall amounts which can be used in forecasting future rainfall events. To verify the results obtained from the reference events، 2 days without rainfall at least 2 days before and after the selected days، were also selected and studied. The results verify considerable changes of the selected dynamic and thermodynamic indices during stormy days compared to the days without any rainfall in the region.