厄尔尼诺事件的成因与预报

Causes and forecasts of El Nio Events

为研究ElNi no事件的形成机理、建立其统计学预报模式,该文提出"拓展伴随模态分析"的新方法并将其应用于实测月平均SLP(或1000毫巴位势高度)和SST距平资料。分析结果表明:中高纬度高压移动所形成的异常热带亚澳大陆桥高压、北太平洋涛动的中纬度低压和构成南方涛动的异常海洋低压三者之间的相互作用是ElNi no事件演变过程中的决定因素;其形成和前发展阶段主要是大气驱动海洋,异常东亚或中亚高压与后二者的结合诱发东部型Ni no事件而异常西亚、南印度洋或南澳大陆高压与后二者的结合诱发中部型ElNi no事件;其后发展和消亡阶段主要是海洋驱动大气,在异常南、北太平洋中纬度海洋低压和亚澳大陆桥高压共同作用下形成的、以热带西太平洋为中心的钳型异常低温水舌牵引着上方的钳型异常海面高压向东北延伸使得阿留申低压回归原处,向东南延伸使得南方涛动的海洋低压减弱变性并造成了ElNi no事件的衰亡。其预报结果为:2003年将是一个正常偏冷年份。

Extended associate pattern analysis is proposed to analyse the combined observed datasets of sea surface temperature (SST) and sea level pressure (SLP) or geopotential hight at 1000 hPa (GH1000) over the Pacific and related seas. The results clearly show all the processes of El Nio events, starting, developing and ending during an eighteen month period. It is concluded that the Asia Australia land bridge formed by positive SLP anomaly moving from higher latitudes, negative SLP anomaly of the North Pacific Oscillation and negative SLP anomaly of Southern Oscillation (SO) over middle latitudes are the major causes for El Nio onset. Basically, during its early stage the ocean is forced by the atmosphere, while during its late stage the atmosphere is forced by the ocean. It is shown by forecast that 2003 would be a colder than normal year.