Reversed Phase Change of the Temperature in the Upper and Lower Troposphere over the Tibetan Plateau in Summer and Its Relationships to Precipitation and Atmospheric Circulation under the Background of Global Warming
Using linear-trend estimates, empirical orthogonal function (EOF) analysis, correlation and composite analysis, the vertical variation of temperature in the troposphere over the Tibetan Plateau in summer and its relationships to precipitation and atmospheric circulation are examined, based on monthly NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data and precipitation data from 596 stations in China. The characteristics of the vertical variation of temperature reveal that the temperature in the lower to middle-upper troposphere over the Tibetan Plateau in summer shows a significant warming trend since 1971, while the temperature in the high troposphere shows a significant cooling trend. In terms of interannual and interdecadal the temperature in the lower to middle-upper troposphere and the high troposphere are negatively correlated, and all have the cycles of 2-4 and 8-13 years. The first EOF mode of the vertical temperature anomaly averaged along 27.5°N-40°N over the Tibetan Plateau in summer shows a reversed phase change of an increase in the lower to middle-upper troposphere and a decrease in the high troposphere. Its time coefficient shows a long-term positive trend, and there is abrupt change in 1978 and 1994. The relationships between the interannual and interdecadal reversed phase change of temperature, i.e., an increase in the lower to middle-upper troposphere and a decrease in the high troposphere over the Tibetan Plateau in summer, and precipitation in China in summer, are explored. When the temperature over the Tibetan Plateau increases in the lower to middle-upper troposphere and decreases in the high troposphere, summer rainfall in China shows a southern type pattern, in which more precipitation in the regions south of the Yangtze River and southern China and less precipitation in the northeast of China are the main distributional characteristics. In addition, less precipitation occurs in the local areas of the Yangtze River Basin and some areas of northwestern China, while more precipitation occurs in the local areas of the eastern part of North China, the central and eastern regions of the Tibetan Plateau, and northwest Xinjiang. The abnormal interdecadal distribution of precipitation is more significant than the interannual distribution. Analysis of the circulation reveals that when the temperature over the Tibetan Plateau increases in the lower to middle-upper troposphere and decreases in the high troposphere, there is abnormally high pressure in middle and high latitude regions of East Asia, while in middle and low latitude areas there is abnormally low pressure. Meanwhile, a relatively significant relationship is found between circulation and precipitation.