资源环境科技发展态势分析平台

The interdecadal changes in the frequency of tropical cyclone (TC) genesis in the western North Pacific (WNP) were examined for the epoch 1979-2013. There was an interdecadal increase in the frequency of TC genesis in the WNP in May during 1999-2013 than during 1979-1998, and such changes differed from those occurring between June and December. This interdecadal change is attributed to the early onset of the South China Sea summer monsoon (SCSSM) during 1999-2013, when the southwesterly winds spread eastwards and the monsoon trough (MT) moved into the WNP earlier. The MT favoured enhanced convection and anomalous low-level cyclonic vorticity, facilitating more TC genesis. During 1979-1998, in contrast, the onset of the SCSSM was delayed and the MT was confined to the west of the South China Sea. As a result, weakened convection and anomalous anticyclonic low-level vorticity are observed over the WNP, facilitating less TC genesis.