Climate Change With Dry/wet Condition And Its Atmospheric Circulation Anomalies Over The Central Asia

Base on the monthly mean temperature,precipitation and potential evapotranspiration data provided by CRU and the standardized precipitation evapotranspiration data with 12 months scales(SPEI12)from IPE-CSIC during 1901-2015,climatic factors of the nearly 115a are comprehensively analyzed and the spatial-temporal pattern of dry/wet climate change is explored in the Central Asia.Analysis the change characteristics of atmospheric circulation anomalies corresponding to the different period of dry/wet,discussed its possible causes.the results shows that:1.the spatial distribution of annual mean temperature in Central Asia is warmer in the East and West and colder in the Middle,and the whole region shows a significant warming trend and its climate tendency rate is 0.15?(10a)-1.The spatial distribution of annual mean precipitation in Central Asia is more in Central South and less in the East and West,and precipitation in all regions except the Northern Kazakhstan Plain is increasing.The potential evapotranspiration in the whole region is much larger than the precipitation,which is closely related to the topography and the underlying surface,and it is characterized by the large feature in the east and West desert area and the relatively small feature in the Central mountainous region.The dry/wet index(SPEI)considering the water-heat balance shows a weaker trend in the Kazakh plains,which indicates the area becomes slightly dry,while other areas show an increase trend,which indicates the areas become wet.Using the set empirical model decomposition(EEMD),the variation period of SPEI 12 and precipitation are analyzed at different time scales.SPEI 12 has a significant oscillation period of quasi-14a,and the precipitation has a significant oscillation period of quasi-3a and 14a.2.The SPEI 12 is decomposed into six sub-regions using the Rotary Empirical Orthogonal Function(REOF),The dry and wet climate changes in the six subregions show the "Warm-dry to Warm-wet",but the transition time node is different.The sudden change of temperature in the East each of subarea was earlier than the West,the precipitation of West increased significantly earlier than the East,the SPEI 12 mutation time of the West was earlier than the East.3.There are difference in atmospheric circulation corresponding to the dry and wet periods in Central Asia.From the latitudinal circulation,relative to the dry period,the wet period shows that the ridge in the Central Asia-Caspian region and the on the upper and lower reaches have been strength increases in the lower troposphere.High-level troposphere expressed as enhancement of the westerly jet.From the meridional circulation,during the wet period the strong southerly air flow from the low-latitude Arabian Sea to the Central Asia in the lower troposphere is one of the feature of circulation anomalies,This is also one of the sources of water vapor transportation in Central Asia.