Mahamood khosravi Sistan va Bluchestan University-ZAHEDAN-IRAN Khosravi_mh@yahoo.com

Abstract

The El Nino-Southern Oscillation(ENSO) exerts a profound influnce on global weather and climate patterns. A great deal of time and effort have been spent investigating the phenomenon with benefits in terms of economics public safety and the environment. In this paper we studied ENSO signals and impacts on precipitation and other related elements during summer and autumn.In order to study the relationships between precipitation over the region , Enso and other ciculation patterns specially NAO and AO several long term climate data set were obtained. This documents include 23 stations precipitation data and Climate Diagnostic Center(CDC)Reanalaysed data and plots. This data covers both surface and multiple-level of atmoshere over the region.Additionally simultaneous correlation and principal statistical and component analysis was used with the reanalysis data to study teleconnectivity between ENSO ,NAO,AO and other telconnections patterns.The results suggested that precipitation significently correlated with ENSO in autumn and its amount in ENSO warm phases(El Nino)greater than cold and netural phases. Summer precipitation and moisture increases in cold phases (La Nina)and we find a meaningful Correlation between All Indian Summer Monsoon Rainfall(AISMR) , summer precipitaion in Region and NINO3-4 Index. The summural rainfall enhansed in La Nina years (inverse autumn).This results confirmed by statistical analaysis and hypothesis tests. Culmnar precipitable water ,Outgoing Long Radiation(OLR),Jet streams intensity and tracks and some of the synoptic aspects was study in this paper and results shows some anomalies between cold and warm phases. We found also some spatial variation in response to the ENSO signals between southern coastal regions (south and south east of Bluchestan) and other parts of region.In strong El Nino events (for example 1997-98 and1982-83) great positive anomaly occurred with southward changes in Jet streams and stormtracks .Some stations like Chahbehar and Bandar abbas recived more than 200% of their normal autumnal precipitation . Enso cold phases usually trend to result in drier than usual autumn and sever droughts occurred over the region in these phases. The ENSO cycle is highly nonstationary. Each El Nino has its own characteristics. It is more meaningful to investigate the evolution of ENSO event by event. Case studies are also desirable for revealing the differences from case to case, which are valuable for understanding the nature and cause of the deviations from a composite scenario.