The study on the mechanism of SSTA in the Pacific Ocean affecting the onset of summer monsoon in the South China Sea——Numerical experiments

A 9-layer 15-wave global spectral model of general circulation is used to study the effects of SSTA in various parts of the tropical Pacific Ckean so as to reveal the role of the former in the timing of onset of the South China Sea summer monsoon.It is shown in the numerical experiment that positive (negative) anomalies of the westem Pacific SST can weaken (strengthen) the subtropical high in the western Pacific; positive (negative) anomalies of the central Pacific SST can weaken (deepen) the TUTT over that part of the ocean; positive (negative) anomalies of the eastern Pacific SST can result in anti-cyclonic (cyclonic) changes in the upper-level circulation off either side of the equator in the eastern Pacific and the subtropical high strengthens (weakens) in the western Pacific.Either of the SSTA in the western and the eastern Pacific can have significant effect on the variation of the subtropical high intensity and thus on the onset timing of the southwesterly monsoon in the South China Sea, with the effect of the latter being more pronounced.The positive (negative) SSTA in the western Pacific usually occurs with the negative(positive) SSTA in the central Pacific, making suitable for general circulation conditions for early (late) onset of SCS summer moonsoon.The above pattern of SSTA is an important impacting factor on onset of SCS summer monsoon.