太平洋海温异常对南海西南季风建立早晚的影响——数值模拟研究

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

利用9层15波全球大气环流谱模式研究了太平洋海温异常对南海西南季风建立早晚的影响作用.结果表明:西-中太平洋海温异常数值试验结果最能反映出南海西南季风爆发早、晚年4～5月份大气环流的差异特征.数值试验结果显示:西太平洋海温正(负)异常可导致西太平洋副高减弱(加强);中太平洋海温正(负)异常主要使得中太平洋上空的洋中槽减弱(加深);东太平洋海温正(负)异常可造成东太平洋赤道两侧高层环流产生反气旋性(气旋性)变化,孟加拉湾-南海-西太平洋热带地区出现东风(西风)异常,西太副高加强(减弱).可见西太平洋海温异常和东太平洋海温异常都可以对副高强弱变化产生明显影响,从而对南海西南季风建立早晚产生影响,只不过西太平洋海温异常的影响作用更为显著.西太平洋正(负)海温异常与中太平洋负(正)海温异常经常是同时出现的,其激发出的与向东传的Kelvin波和向西传的行星波相联系的环流异常为南海季风建立早(晚)提供有利的条件,因而这一海温分布型是影响南海西南季风建立早晚的重要影响因子.

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 Ocean 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 western 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 monsoon. The above pattern of SSTA is an important impacting factor on onset of SCS summer monsoon.