Zonally Asymmetric Variation Of Summer Asian Sub-tropical Upper-tropospheric Jet And Its Possible Association With North Atlantic SSTA And Eurasian Land Surface Thermal Anomaly

Applied the ERA-Interim re-analysis data in an empirical orthogonal function(EOF)decomposition of the summer zonal wind anomaly in the sub-tropical at 200hPa over Asia,we extract the zonally asymmetric spatial distribution of summer Asian subtropical upper-tropospheric jet stream,it reflects the out-of phase change of meridional displacements of jets over West Asia and East Asia.The related circulation and possible external forcing factors are diagnosed by statistical methods,it reveals that certain connection exists between the zonally asymmetric variation and North Atlantic sea surface temperature and Eurasian land surface thermal anomaly.The main conclusions are as follows:(1)The first mode describes the meridional displacement of position of ASWJ which presents the zonally symmetric distribution.The second mode describes the zonally asymmetric distribution of the summer jet over East and West Asia,which has a close connection with jet over West Asia and East Asia,it reflects the out-of phase change of meridional displacemens of jets over West Asia and East Asia.(2)The wave train propagating from North Atlantic to Eurasia and the four circulation anomaly centers over Eurasia are two important features associated with zonally asymmetric variation.The starting point of the anomalous wave train is located over the North Atlantic and is respectively transmitted to the high latitudes and lower latitudes of Eurasia.The anomalous anticyclonic circulation around east European Plain and anomalous cyclonic circulation around Balkhash Lake related to the wave train could affect West Asian jet.In addition,the East Asian jet correlated well with the anomalous cyclonic circulation to the north of Lake Baikal and anomalous anticyclonic circulation to the south of Lake Baikal.(3)The relationship between the sea surface temperature and the zonal asymmetry variation in the North Atlantic was explored.As the first pattern of North Atlantic SSTA in spring and summer,the SSTA tripole pattern can stimulate a wave train which will affect the downstream circulation and climate.There is a seasonal change in the wave train,and in summer it coincides with the consistent anomalous circulation centers with zonally asymmetric variation.(4)The anomalous circulation center over Eurasia corresponds to the key area of soil moisture.The soil moisture in each area can reflect the characteristics of the zonally asymmetric variation,but there are regional differences in the influence of soil moisture.This regional difference also exists in the land surface thermal anomaly and the local circulation configuration.(5)Besides,the zonally asymmetry variation of summer Asian sub-tropical upper-tropospheric westerly jet appeared the decadal turning in the 60s and 90s of the last century,which is consistent with the multi-decadal oscillation of the North Atlantic(AMO).AMO may modulate the interdecadal variations of zonally asymmetric variation and soil moisture in Eurasia.