بررسي روابط بين الگوهاي چرخش جوي كلان مقياس نيمكره شمالي با خشكسالي هاي سالانه سيستان و بلوچستان

A Survey on the Relations of the Northern Hemisphere Large Scale Circulation Patterns with Sistan & Baluchestan Annual Droughts

The term "Telecommunication Pattern" refers to a occurence and persistence, large-scale pattern of pressure and circulation anomalies that spans vast geographical areas. Although these patterns typically last for several weeks to several months, they can sometimes be prominent for several consecutive years, thus reflecting an important part of both the interannual and interdecadal variability of the atmospheric circulation. These patterns influence on atmospheric wave, jet streams, rainfalls and storm directions, so most of them cause pneumatic patterns of anomalies which happen coincident on further districts. Many of the telecommunication patterns are also planetary-scale in nature, and span entire ocean basins and continents. Severe droughts are from notable features of hydro-climatology in Sistan & Baluchestan province (South-east of Iran).From a regional perspective, the ongoing drought is the most severe in the past several decades. In this paper we analyzed the relationship between Sistan & Baluchestan droughts and the northern hemisphere circulation patterns that in this paper are described as telecommunication Pattern (TP). Statistical correlations at a-0.01 and a=0.05 levels are calculated for annual Standard Precipitation Index (SPI) of region and major stations and contemporaneous annual telecommunications indices values. Totally in an annual perspective; POL, PDO, NP, NOI, MEI and WHWP have a significant correlation (at least at 0.05 level) with SPl variation. NHTP can be explained over 70% of SPI variance of region. In drought years (SPI<-0.5) TNH and PT explained over 61% of SPI variance. Based on the stepwise multivariate Regression model, the most effective patterns were determined. Also the impact of NHTP on the drought severity and precipitation shortage was evaluated. For example, 1 unit increase in MEI, NO!, POL, NP, PDO and WHWP can increase the annual drought severities by 26, 12.3, 32.5, 24, 16.6 and 7 percent. The regional response to these patterns differ from region to region. The impacts also shown some seasonal variation. Some patterns have effective presence in some season and in some seasons several patterns controlled the climatic conditions of Sistan & Baluchestan.