Effects And Mechanism Of Arctic Sea Ice On Extreme Climate Events On The Qinghai-Tibet Plateau In Winter

Based on the daily temperature data of Tibet Plateau stations from 1980 to 2018,CPC global daily precipitation data,Hadley Center monthly sea ice data and ERA5 reanalysis data,this research analyzes the temporal and spatial variation characteristics of Arctic sea ice and extreme cold events and extreme precipitation on the Tibet Plateau,and reveals the influence and possible mechanism of Arctic sea ice on extreme weather on the plateau.The main conclusions are as follows:(1)The variability of Arctic sea ice has significant temporal and spatial characteristics.The climate variability of Barents Kara Sea is the most significant,followed by Laptev Sea,Beaufort Sea and Norwegian Sea in marginal areas;The Extreme Cold Events(ECEs)in winter on the Tibet Plateau mainly exhibits the same spatial variation and interannual variability across the whole region,while the distribution of Extreme Precipitation(EP)has obvious East-West differences.The west is the region with the most extreme precipitation.(2)The ECEs in the Tibet Plateau is mainly affected by two wave trains from the polar region regulated by sea ice,which are independent of each other.The southern wave train is controlled by the sea ice in the Beaufort Sea.It initiates in the Norwegian Sea,and then passes through the North Atlantic Ocean,the Arabian Sea,and the Bay of Bengal along the subtropical westerly jet stream.It enters the TP from the south and brings warm,humid air from the oceans.By contrast,the northern wave train is controlled by the sea ice in the Laptev Sea.It originates from the Barents and Kara seas,passes through Lake Baikal,and enters the TP from the north,bringing dry and cold air.(3)The EP in the western plateau has a significant negative correlation with the sea ice in the whole region in autumn on an interannual scale.On the interdecadal scale,there is a significant negative correlation with the sea ice in the Barents Kara Sea in winter.The decadal mutation point of both was in 2002.The decrease of sea ice in the Barents Sea Kara Sea caused the "+-+-+" potential height wave train anomaly over the Barents Sea-Western Europe-Northern Africa-western plateau-southeast plateau.There is a significant negative geopotential height anomaly in the west of the plateau.The southwest wind along the outer edge of the cyclonic circulation is easy to bring water vapor over the Indian Ocean and has a strong dynamic uplift,;In the southeast of the plateau,the positive geopotential height is abnormal,and the southwest wind along the eastern edge can also bring some water vapor,but it is mainly subsidence movement,which can not create favorable dynamic background conditions for precipitation.Therefore,the extreme precipitation variability in the southeast of the plateau is less than that in the West.