Links Between The South Asian High And Southern Hemisphere Climate

The summer South Asian High(SAH)is the main large-scale circulation system in the upper troposphere of the Eurasian continent,Moreover,the SAH is significantly affected by the thermal effects of the Tibetan-Iran plateau,the summer South Asian High has a broad impact on Asian climate and global climate.The paper utilizes1979-2014 monthly mean the European Centre for Medium-Range Weather Forecasts(ECMWF)reanalysis dataset,Average geopotential heights in the central area(25°N-40°N?40°E-110°E)were used to examine time variation characteristics of the SAH.Then the correlation between the Tibetan Tropospheric(400-200 h Pa)Temperature(TTT)and the SAH intensity index is analyzed.Based on the South Asia high index,the circulation characteristics and the causes of the climate system in Eurasia and the southern hemisphere are discussed.The methods used are composed analysis method and correlation coefficient method.The main observation areas are the middle and low latitudes of the Indian Ocean and the Antarctic sea ice area.The following conclusions are drawn:(1)Although there was a significant interannual variation in the SAH in the Northern summer of 1979-2014,no trend of the fluctuation was found.There was a close relationship between the South Asian high in summer and the temperature of the upper and middle troposphere on the Tibetan Plateau.(2)On an interannual scale,the height field and temperature field of the upper troposphere at the middle-low latitudes between Eurasia and the southern Indian Ocean show a quasi symmetrical structure with the tropical axis.The quasi symmetrical structure is closely related to the SAH: When the SAH increases,At the middle-lower latitudes between Eurasia and southern Indian Ocean,the temperature in the upper middle troposphere increases and is distributed zonally.The reverse is true.The quasi symmetrical structure is closely related to the abnormal meridional and vertical circulation: When the SAH increases,the sinking branch of the Hadley circulation in the Eurasian region of the northern hemisphere is weakened by the circulation cell,it is strengthened in the Indian Ocean region of the southern hemisphere.As a result,The meridional and vertical circulations at the middle-low latitudes between Eurasia and the southern Indian Ocean might be an imperative medium for the interaction between the northern and southern hemispheres,which plays an important role in the transmission of heat and energy in the Eurasian continent and the southern Indian Ocean.(3)The SAH is closely related to Antarctic sea ice,There was a significant positively correlated with the Ross sea ice,However,There was a significant negatively correlated with the Weddell sea ice.When the SAH increases,When the SAH is strong,there are abnormal southerly winds blowing over the Ross sea,which blow cold air to the middle and high latitudes of the Southern Hemisphere,and increase sea ice.However,In the weddell sea,abnormal northerly winds blow warm air at mid-latitude toward the polar regions,reducing sea ice.(4)The SAH is closely related to the Southern hemisphere westerly jet and the circumpolar easterly jet,There was a significant positively correlated with the Southern hemisphere westerly jet,However,There was a significant negatively correlated with the circumpolar easterly jet.When the SAH increases,the Southern hemisphere westerly jet extend northward,The strength of the circumpolar easterly jet weakened.At the middle-high latitudes of the southern hemisphere,In the correlation between the SAH and meridional wind,a wave chain structure of "negative-positive-negative-negative-positive" is presented.Therefore,this paper preliminarily speculated that the abnormal signal of South Asia high from Eurasia to the southern Indian Ocean at the middle-low latitudes spreads outward in the form of Rossby wave train.Along the westerly jet to the southern hemisphere at the middle-high latitudes,thus causing the dynamic mechanism of the change of many meteorological elements in Antarctica.