Large-scale atmospheric conditions associated with heavy precipitations in Yasouj

Although precipitation is very important in various aspects of human life but sometimes occurring the heavy precipitations suddenly or in relatively short time have unpleasant effects on human and his life environment. So, more accurate identification of atmosphere circulation patterns mechanism which is effective in occurring this kind precipitations is very important, especially because in recent decades, the climate changes have been resulted in changing the atmosphere patterns and happening climatic anomalies in the most of world regions. At the same time, identification and synoptic and dynamic analysis the systems producing such precipitations can help to forewarning and preparing for encountering them. Therefore, the first step for better use of a region precipitation is sufficient identifying the synoptic and dynamic conditions occurring precipitation in the region. With this approach, this research try to identification circulation patterns producing heavy precipitations and synoptic and dynamic analysis them.

In this research, for identification and analysis the synoptic and dynamic patterns of heavy precipitations on Yasouj, by using environment- circulation approach, the daily precipitation data from 21.3.1987 to 20.3.2014 have been received. On the basis of 95th centile base index, 82 precipitations selected as heavy precipitations among rainfall days. Then, using cluster analysis by “Ward” method four atmosphere thickness patterns between 500-1000 hpa levels have identified. Then, for analysis the precipitations in every thickness pattern, the representative day defined on the basis of correlation coefficient with 95% threshold and in these days, the maps of sea level pressure, atmosphere thickness, frontogenesis for 500 and 1000 hpa levels and moisture flux convergence have been drawn and analyzed for 925 and 1000 hpa levels.

The identified circulation patterns indicated that occurring heavy precipitations on Yasouj resulting from forming and trough settlement on eastern Mediterranean and immigrant low pressures together with the front that flow to Iran. The atmosphere thickness maps explain that falling the cold air from high latitude and encountering with influential moist and warm air from low latitude especially from Persian Gulf and Red Sea have been created the strong baroclinicity region on Iran which play important role in occurring heavy precipitations. Analysis of the frontogenesis function of representative day for atmosphere thickness patterns indicate existing the frontogenesis cores on Yasouj region, too. Analysis the moisture flux convergence function maps in Yasouj indicate existing the maximum core of moisture aggregation in this region. For this reason, cyclonic movement from eastern Mediterranean, Arabian Peninsula and Persian Gulf import the humidity from eastern Mediterranean, Red Sea and Persian Gulf in to studied region.

The results of this research indicate the relatively deep trough settlement with nearly northern- southern axis in eastern Mediterranean between Mediterranean Sea and Aral Lake in the eastern Caspian Sea, which result in occurring heavy precipitations in studied region. Analysis the frontogenesis patterns on Yasouj and it’s around regions, such as Red Sea and Arabian Peninsula. Analysis the effective moisture resources in occurring heavy precipitations of Yasouj indicate the importance and role of eastern Mediterranean, Red Sea and Persian Gulf in supplying the moisture of these precipitations too.