Subseasonal dynamical prediction of South China Sea summer monsoon

Abstract

South China Sea (SCS) summer monsoon (SCSSM) is an important component of the Asian monsoon system, of which the onset and intensity exerting critical impacts on surrounding areas. With the Japan Meteorological Agency (JMA) model prediction derived from the S2S project, the predictions of SCSSM, specifically, the annual evolution, onset, and corresponding meteorological variables are investigated with lead times of 1–34 days. The prediction skill on the associated dynamical and thermal background such as wind, vertical motion, pseudo-equivalent potential temperature, and specific humidity decreases with the growing lead times. For the SCS surroundings, the upper- and lower-level circulations are reasonably predicted for lead times of shorter than 3 weeks. Predictions with fair skill on humidity and pseudo-equivalent potential temperature over land area around the northern SCS last for around 4 weeks, better than those over the southern SCS. Predictions on vertical motion and precipitation are reliable within 1 week, while the skill decreases rapidly after 2 weeks. In general, the predictions on the spatial patterns of circulation are relatively poor during the transition period before monsoon onset and are then improved after that. The model capability on predicting the date of monsoon onset decreases with the increasing lead times. Besides, skillful predictions on climate systems such as the tropical vortex pairs over Indian Ocean and the western North Pacific subtropical high are critical for the successful predictions of monsoon onset.