资源环境科技发展态势分析平台

This study contributes to an improved understanding of Central Southwest Asia (CSWA) wintertime (November-April) precipitation by analyzing the dominant spatial-temporal modes of the regional winter precipitation and examining their relationship with global sea surface temperature (SST) and large-scale atmospheric circulation fields, for 1950/51-2014/15. Empirical orthogonal function (EOF) analysis results show that the first mode (EOF-1) of winter precipitation is characterized by a mono-sign pattern, with significant links to El Nino-Southern Oscillation (ENSO). EOF-2 displays a north-south dipole related to the latitudinal shift in the jet stream position, while the west-east dipole in EOF-3 appears to be influenced by the thermal contrast between the equatorial regions and higher latitudes. Further, we focus on the interdecadal change of connection between wintertime ENSO and EOF-1 observed around the early 1980s. The relationship is weak during 1950/51-1983/84 (P1), but strong and statistically significant in 1984/85-2014/15 (P2). In P1, without the ENSO signal, EOF-1 related atmospheric circulation anomalies are confined mainly over the mid- to high-latitudes of the Northern Hemisphere, associated with the extratropical East Atlantic-Western Russia (EA-WR) teleconnection. In P2, however, a close connection to the tropical Pacific is observed that includes a pronounced SST expression similar to that of ENSO. As a result of the increased relationship between ENSO and EOF-1 in P2, the regional impact of EA-WR observed over CSWA in P1 is linearly superimposed by the anomalous hemispheric-wide atmospheric response forced by the ENSO conditions in the Pacific.