A Further Look At The Interannual Variations Of East Asian Trough And Their Impacts On Winter Climate Of China

Using the NCEP/NCAR reanalysis, the observational precipitation and temperature data at160stations of China from1951to2011, the interannual variations of East Asian trough (EAT) along with their impacts on winter climate of China have been investigated in the present paper. A new EAT intensity index (IEAT), EAT position index(PEAT), and EAT trough axis index(TAl) at500hPa in boreal winter have been defined. Our results are summarized as follows:IEAT index depicts the changes of intensity of EAT very well. This index integrates both the geopotential heights in the trough area and the zonal pressure gradient in the western flank of the trough, making the IEAT index a good indicator of the meridional wind between the ridge in geopotential height over Asian continent and the trough system over North West Pacific in the middle troposphere. It is found that the intensity of EAT was relatively weaker before1980’s. The IEAT changes with periodicities of2-3yrs and quasi-4yrs. The variation of EAT intensity in winter may relate to the eastward propagation of the Rossby wave energy along Asian jet from the Mediterranean region to East Asia. The disturbances in westerlies have equivalent barotropic structure.The IEAT has significant correlations with both the rainfall and temperatures in regions east of Tibet Plateau. When the index is positive (negative), EAT is stronger (weaker), inducing the total winter precipitation in most part of East China to be less(more) than normal. Simultaniously, the winter time mean temperature over central China is to be higher(lower) than normal. It is found that the higher surface air temperatures in central China in strong EAT winters are resulted mostly from the diabatic heating anomalies and anomalous dynamic heating due to air subsidence. These results are helpful for us to better understand why and how the winter climate of China along with the EAT intensity change.PEAT index displays the changes of position of EAT in winter in a reasonable way. The index changes with periodicities of2-3yrs and the period longer than lOyrs. The EAT position has shifted eastward in period from1951to2010.TAI index that depicts changes of the tilt of EAT axis in winter shows significantly the quasi-4yrs and quasi-00yrs periodic variations of the EAT. The TAI index has significantly correlates the rainfall in regions of Huang-Huai area and parts of South China. The larger(smaller) the inclination of the trough line, the less(more) precipitation in these areas.The results in the present paper are helpful for us to better understand the EAT variations and the mechanism of climate changes of China.