Concurrent Thermal Effect Of Tibetan Plateau And Iranian Plateau On Boreal Summertime South Aisan High And Rainfall In China

Tibetan Plateau(TP)and Iranian Plateau(IP)are closely related to the climate change in their downstream regions.Research of concurrent springtime thermal effect of TP and IP on the climate in the subsequent seasons can improve our understanding about the mechanisms of climate variabilities over East Asia and helps to predict interannual climate variation in China and prevent us from meteorological disaster.Spatial and temporal distribution characteristics of surface heat fluxes over both Tibetan Plateau and Iranian Plateau in boreal spring and summer and their relationships are thoroughly examined in this study by using ERA-interim reanalysis data.Additionally,their concurrent effect on summertime South Aisan High(SAH)and rainfall in the middle and lower reaches of the Yangtze River is revealed.The results show that the basic spatial and temporal characteristics of surface heat fluxes over TP and IP are different in spring and summer,and surface heat fluxes in specific regions of these two plateaus exhibit different characteristics at interannual and interdecadal time scales.Over TP,surface sensible heat flux(SH)in the western part is stronger than that in the eastern part during spring and summer,whereas the spatial distribution of surface latent heat flux(LH)is opposite with larger values in the eastern part.SH peaks in spring and exceeds LH before summer,but LH is larger than SH in summer.On the interannual time scale,SH is negatively correlated with LH in western TP during spring and summer,and SH anomalies over western TP can persist from spring to summer.On the interdecadal time scale,there is a significant difference in surface heat fluxes between eastern and western parts of TP.Springtime(summertime)SH over eastern TP exhibits a significant decreasing trend and experienced an interdecadal change in 1998(2001),switching from positive to negative anomaly.However,springtime SH over western TP exhibits a significant increasing trend and experienced a negative-to-positive interdecadal change in 2003.The LH over eastern TP displays a significant decreasing trend only in spring and exhibited a positive-to-negative interdecadal change in 2003.The LH over western TP exhibits a significant decreasing trend in both spring and summer and experienced an interdecadal change at the beginning of the 21 st century,switching from positive to negative anomaly.Over IP,both SH and LH are uniformly distributed during spring and summer.SH peaks in summer,LH is strong in spring but weak in summer,and it is smaller than SH all year round.SH over IP is stronger than SH over TP in each season.On the interannual time scale,spring and summer SH(LH)anomalies over the entire IP are uniformly positive or negative.There is a significant negativecorrelation between SH and LH over IP.SH and LH anomalies over IP can persist for a long period about three months.A significant difference is found in the interdecadal variability of surface heat flux between northern and southern parts of IP.Spring and summer SH(LH)over northern IP exhibits a significant increasing(decreasing)trend and experienced an interdecadal shift at the end of the 20 th century,when the anomaly of SH(LH)switched from negative(positive)to positive(negative).There is no significant trend in SH and LH over southern IP during spring and summer.However,SH over southern IP in spring and summer experienced a negative-to-positive interdecadal change,while springtime LH experienced a positive-to-negative interdecadal change at the end of the 20 th century.The relationship between surface heat fluxes over these two Plateaus is as follows: SH over IP is positively correlated with SH over western TP and is negatively correlated with SH over eastern TP in spring;LH over IP is positively correlated with LH over eastern TP in spring;SH over IP in the spring is negatively correlated with SH over eastern TP in the subsequent summer.Concurrent thermal effect of Tibetan Plateau and Iranian Plateau on general atmospheric circulation over East Aisa is analyzed in each month.In boreal spring,Northwest-southeast shift on June SAH closely relates to the concurrent thermal effect which characterise negative correlation of SH over TP and IP in May,due to the release of latent heat of condensation over northern India.Indian summer monsoon(ISM)is stronger(weaker)and SAH shifts to northwest(southeast)when IP is warmer(cooler)and TP is cooler(warmer)in May,strengthing(weaking)the release of latent heat of condensation over northern India.The anomalous variation of SAH sustains from June to July,causing a stronger(weaker)ISM and a stronger(weaker)EASM which bring more(less)rainfall in northern India and less(more)rainfall in the middle and lower reaches of the Yangtze River.