Climatic features of East Asian subtropical summer monsoon trough and its comparison with South China Sea summer monsoon trough

Based on NCEP/NCAR reanalysis data, an investigation has been carried of climatic features of East Asian subtropical summer monsoon trough (sub-trough) and its comparison to South China Sea summer monsoon trough (SCS trough). The results show that the SCS trough is stronger than the sub-trough, whether convergence or convection. The sub-trough extends to higher level and inclines northward with altitude, but the SCS trough is reversed. The SCS trough onsets early and abruptly with the positive relative vorticity appearing suddenly and retreats slowly, but the sub-trough establishes step by step with the positive relative vorticity over Yunnan and Guizhou tableland and Guangxi areas spreading northeastward and withdraws rapidly. It is an obvious indicator that the easterly reverses the westerly during the SCS trough's onset, but the sub-trough establishment is characteristic of the westerly enhancement. The sub-trough has clearly frontal property, but the SCS trough is opposite.