A further look at the interannual variations of East Asian trough intensity and their impacts on winter climate of China

Using the NCEP/NCAR rcanalysis data and the observational precipitation and temperature data at the 160 stations of China, the interannual variations of the intensity of East Asian trough(EAT) along with their impacts on winter climate of China have been investigated.A new East Asian trough intensity index(IEAT)at 500 hPa in boreal winter has been defined.The results show that the new index depicts the changes of intensity of EAT very well.This index integrates both the gcopotential height values of the trough area and the tonal pressure gradient in the western flank of the trough,making the IEAT index a good indicator of the averaged meridional wind between the ridge of gcopotential height over Asian continent and the trough system over the western North Pacific in the middle troposphere.It is found that the intensity of EAT was relatively weaker before 1980's.The IEAT changes with periodicitics of 2-3 years nd quasi-4 years.The variation of EAT intensity in winte may relate to the eastward propagation of the Rossby wave energy along the Asian jet from the Mediterranean region to East Asia.The disturbances in the westerlics have an equivalent barotropic structure.The IEAT has significant corrclations with both the rainfall and temperatures in regions cast of the 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.Simultaneously, 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.Thesc results are helpful to better understand why and how the winter climate of China along with the EAT intensity change.