南海及周边地区TBB季节内振荡及其与ENSO的联系

文中利用1980～1997年TBB资料,采用小波变换分析方法,对南海及周边地区季节内振荡(ISOs)进行了诊断分析。结果表明:南海及菲律宾以东洋面TBB具有相似的ISOs特征,其年变化表现为单峰型,夏秋季强,冬春季弱,而孟加拉湾地区的ISOs有所不同,呈双峰型,峰值出现5月和11月。南海地区ISOs的周期结构具有复杂性,主要有两个周期段,即以53.8d为峰值的50～70d振荡(ISO1)和以32d为峰值的13～36d振荡(ISO2)。南海地区ISO1的年际变化与周边地区(孟加拉湾、菲律宾以东洋面以及南半球澳大利亚与印度尼西亚之间洋面)ISO1的年变化有显著的正相关,说明这种ISO1的年变化为较大范围的区域现象;而南海地区ISO2的年际变化与周边地区相关性不显著,为局地现象。影响南海地区ISOs的传播具有多向性,ISO1以东传为主,ISO2以西传为主,它们都具有北传的特征。可见,南海地区ISOs既受到来自赤道地区的影响,也受到来自西太平洋和孟加拉湾的影响,同时南海地区局地也可以生成强烈对流活动,从而使得南海地区对流的ISOs变得复杂化。统计结果发现,ENSO与ISO1有密切的联系,但对ISO2的影响不明显。ENSO对ISO1的影响不但表现在南海地区,对孟加拉湾和菲律宾以东洋面上的ISO1有更加明显影响作用,负相关表明ENSO冷事件发生时上述地区ISO1受到压制。可以推测,ENSO通过对热带大气环流(特别是副热带高压)的影响来对南海及周边地区ISO1进行调制。

ISOS OF TBB OVER SCS AND VICINITY AS WELLAS ITS RELATIONSHIP WITH ENSO

Using the TBB data from 1980 to 1997, the intra-seasonal oscillations (ISOs) over the South China Sea (SCS) and surrounding regions were diagnosed with the wavelet analysis. The results show that the ISOs features of TBB over SCS are similar to that over the east of the Philippine, with single peak in summer, but different to that over the Bay of Bagel, with dual peaks in May and November. The periodic structure of the ISOs over SCS is complex and there are two major periods of 50-70 days with peak at 53.8-day (ISO1) and 13-36 days with peak at 32-day (ISO2). The variance of ISO2 is about three times of that of ISO1. Because of the significant positive relationship of ISO1 between SCS and surrounding regions, the inter-annual variations of ISO1 has large-scale characteristics, but that of ISO2 is a local phenomenon. The migrations of ISOs to the SCS take on multi-directions. ISO1 migrates eastward and ISO2 westward and all migrate northward. It indicates the ISOs over SCS can be influenced by the oscillations coming from not only equatorial region, but also west Pacific and the Bay of Bengal. And the local convections generated over SCS also impact the ISOs. So the ISOs of convection over SCS become complex. The statistic results show that the strong (weakening) annual variation of ISO1 is often linked to the cold (warm) phase of ENSO. It is found that ENSO is related with ISO1 more closely than with ISO2. In the warm phase of ENSO, the convections over SCS are weakened. It results in the high TBB values and the weakening ISO1. It suggests that the anomalous tropical atmosphere circulation (for example, the subtropical high over the western Pacific) induced by ENSO can modulate the ISO1 of TBB over SCS.