Peculiar temporal structure of the South China Sea summer monsoon

Beijing located at the junction of four major components of the Asian-Australia monsoon system (the Indian, the western North Pacific, the East Asian subtropical, and the Indonesian-Australian monsoons), the monsoon climate over the South China Sea (SCS) exhibits some unique features. Evidences are presented in this paper to reveal and document the following distinctive features in the temporal structure of the SCS summer monsoon: (1) pronounced monsoon singularities in the lower tropospheric monsoon flows which include the pre-onset and withdrawal easterly surges and the southwesterly monsoon bursts at Julian pentad 34-35 (June 15-24) and pentad 46-47 (August 14-23); (2) four prominent subseasonal cycles (alternative occurrences of climatological active and break monsoons); (3) considerably larger year-to-year variations in convective activity on intraseasonal time scale compared to those over the Bay of Bengal and the Philippine Sea; (4) the redness of the climatological mean spectrum of precipitation / deep convection on synoptic to intraseasonal time scales in the central SCS; (5) a remarkable asymmetry in the seasonal transitions between summer and winter monsoons and an extremely abrupt mid-May transition (the outburst of monsoon rain and the sudden switch in the lower troposphere winds from an easterly to a westerly regime); (6) the bi-modal interannual variation of summer monsoon onset (normal and delayed modes). In addition, the monsoon rainfall displays enormous east-west gradient over the central SCS. Possible causes for these features are discussed. A number of specific science questions concerning some of the peculiar features are raised for the forthcoming SCS monsoon experiment to address.