利用2.5层海洋模式分析了北太平洋副热带逆流（STCC）区波长在450-840km之间的长Rossby波的动力特性。不考虑耗散时，STOC区域的长Rossby波是中性波，其快模态的周期是88-110d，相速度为0。06-0.09m/s，群速度几乎与相速度相同。弱耗散作用使长Rosssby波为弱衰减波，但几乎不影响其相速度与频率。观测的STCC区海平面高度 （SSH）的准90d振荡对应长Rossby波的第一斜压模，“快”模态的波动振幅是“慢”模态的约5倍。准90d振荡存在的3个必要条件是：（1）第2层向西平均流取值为0.02-0.04m/s；（2）2个活动层的厚度超过480m；（3）第2层的密度σθ介于24.8-26.8之间。正因为北太平洋STCC区满足这3个条件，才在该海域出现SSH的准90 d振荡。海面热通量的变化对快模态长Rossby波的传播特性影响不大，但对慢模态的传播特性有一定的影响。

Based on the Sverdrup relation, using climatological wind stress data, the basin scale Sverdrup transport in the South China Sea(SCS) is calculated and the basic seasonal features of the Sverdrup circulation are obtained. A comparison of these calculated features with observations proves that the wind-driven circulation in the SCS is very important for the formation of the SCS upper oceanic circulation in winter, summer and fall. It is shown that the non-uniform sea surface wind is one of the causes to form multi circulation centers in the basin of the SCS. The westward current at 18

Seasonal and intraseasonal variability of thermocline and relative surface height in the central South China Sea (SCS) are investigated using time series data of temperature from three buoys and sea surface height anomalydata from TOPEX/POSEIDON and ERS-1/ERS-2 satellites(T/P-ERS) from Feb. 1998 through Mar. 1999. We found that the thermocline becomesde eper and thinner in winter, owing to a great loss of the heat on the sea surface. This feature is more evident in the northern than the southern part of the central SCS. The intraseasonal variation of the thermocline ismain ly controlled by the geostrophic vorticity and is out-of-phase with sea surface height (SSH). Furthermore, we find a double-thermocline phenomenon occurs in the SCS: In spring, owing to maximum net downward heat flux at the surface, with the new the rmocline appearing above 80m and the old thermocline keeping under 80m deep.