Dynamic analysis of Sudan low-pressure systems and torrents in southwest of Iran

Sudan Systems are low-pressure systems which originate from the Red Sea and their low-pressure isoheights are detectable around south of the Red Sea، Sudan and Ethiopia. The system، in cold seasons passes Ethiopia، Sudan and Red Sea and reaches to west of Iran and results in severe rainfalls in northwest، west and southwest of Iran. In all these synoptic-dynamic systems، low-pressure isobars or low isoheights are considerable. 11 severe storms which happened in southwest of Iran (1998-2008) are selected and using Japanese ReAnalysises data (JRA25)، anomalies of dynamic and thermodynamic indices، 2 days prior to the start of storm and during stormy days have been analyzed. The selected indices in this research are relative vorticity، convergence and divergence، vorticity advection، specific humidity and moisture advection. According to the results of this research and analyzing 6-hourly recorded rainfall amounts، it is understood that in the reference events، before the start of the storm، geopotential height values in the under-studied region decrease and at the time of maximum rainfalls، the geopotential height reaches its lowest values and by end of the storm، the values start increasing.; whereas parameters which are related to convergence and vertical movements، such as relative vorticity، moisture advection، convergence of moisture and specific humidity amounts correspond to the same trend of rainfall from the beginning to the end.