The Influence Of Thermal Conditions In The Qinghai-Tibet Plateau On Precipitation In The East Asia-West Pacific Subtropical Region

Using the observation data of 160 stations in China,two sets of global monthly average precipitation data,ERA-Interim reanalysis data from 1979 to 2016 and the Community Climate System Model version 3(CCSM3),this study investigates the relationship between the thermal condition of the Tibetan Plateau and the precipitation in the subtropical East Asian-West Pacific during boreal summer,and its associated physical mechanisms.The conclusions in this dissertation are as follows:(1)The summertime Tibetan tropospheric temperature has obvious interannual and interdecadal variations,and in the past 38 years,the tropospheric temperature in the Tibetan Plateau has gradually increased,whose heating rate is 0.22 °C/10 a.The summertime TTT index is positively correlated with the tropospheric temperature over the Tibetan Plateau and its surrounding areas,which is able to appropriately represent the tropospheric temperature over the Tibetan Plateau.In addition,this index is also related to the surface sensible heat of the Tibetan Plateau.The Tibetan Plateau surface heating has a certain influence on the tropospheric temperature.(2)On the interannual time scale,the summertime Tibetan tropospheric temperature is positively correlated with the precipitation in the northern part of China and the subtropical western North Pacific region,but negatively correlated with the precipitation in the Yangtze River basin of China and the southern part of Japan and its adjacent region.When the summertime Tibetan tropospheric temperature is high,there is higher than normal precipitation occurs over the northern part of China and the subtropical western North Pacific zone,and precipitation in the Yangtze River Basin and southern Japan and its adjacent region is less,and vice versa.Anomalous precipitation in the East Asia-West Pacific subtropical region is characterized by a “positive-negative-positive” distribution in the latitude from west to east.(3)When the summertime Tibetan tropospheric temperature is high,the South Asia High over the mid-upper troposphere from the western Tibetan Plateau to the eastern part of Japan,is anomalous strong and deep.In the lower troposphere,the anomalous anticyclonic circulation dominates over the Yangtze River basin in China to the southern part of Japan,combined with the anomalous subsidence movement and anomalous water vapor divergence in this area,so that the precipitation in this area is anomalous low.The western North Pacific subtropical zone and the mid-high latitudes of the Pacific are controlled by a pair of significant cyclone and anticyclone.Under the guidance of the anomalous cyclone and anticyclone,winds generated by the anomalous circulation converge in the eastern parts of the western Pacific subtropical zone that makes water vapor convergent abnormally,which finally results an anomalous convergent rising movement.The process illuminates above creates considerable water vapor and proper dynamic conditions for the occurrence of precipitation,which is conducive to the increase of precipitation in the central and eastern parts of the western Pacific subtropical zone.(4)Observation and numerical simulation further show the physical processes of the Tibetan Plateau thermal conditions affecting the atmospheric circulation in the East Asia-West Pacific subtropical region.When the Tibetan Plateau is heated too strongly,the tropospheric temperature above it increases,the troposphere in the northern part of the Tibetan has an anomalous upward movement.This anomalous upward airflow gradually shifts northward with height,and then spreads eastward along the anomalous westerly airflow to the Japanese region in the mid-to-high latitudes,finally sink to the south of Japan.Affected by the anomalous subsidence movement,anomalous anticyclone occurred in the lower part of southern Japan,and anomalous southerly winds in northern part of China and the anomalous northerly winds in the south part of western Pacific Ocean and the corresponding anomalous cyclone and anticyclonic circulation coupling structures in the western Pacific,ultimately affecting the precipitation in the East Asia-Northwest Pacific subtropical region.