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利用 NCEP/NCAR再分析资料 ,通过对 El Nino与 La Nina发生前与发展初期低层风场的合成分析 ,发现在赤道中东太平洋增暖当年的春季与夏季 ,赤道西太平洋存在两次显著的西风局地 ( 1 40°E～ 1 80 )增强过程。其原因并不仅仅在于印度洋的西风异常东移 ,更在于南北半球的经向风在该地区强烈辐合 ,造成局地气压梯度增强 ,促进西风加强并向东爆发 ;同时由于地球自转效应的作用 ,来自北半球的东北风到达赤道附近后转西北风 ,南半球的东南风转西南风 ,直接加强了西风的强度。对比分析南北半球经向风的作用表明 ,南半球东南风的强度与位置更稳定 ,对赤道西风两次增幅过程的贡献更大。这支南半球的经向气流来自高纬极区 ,与中高纬度气压场异常有直接的关系。
Based on the NCEP / NCAR reanalysis data and the composite analysis of the low-level wind fields before and during El Nino and La Nina, it is found that there are two significant westerlies in the equatorial western Pacific over the spring and summer of the equatorial Pacific Ground (1 40 ° E ~ 1 80) to enhance the process. The reason is not only that the westerly anomaly eastward in the Indian Ocean is moving eastward, but also that the meridional winds in the northern and southern hemispheres are intensively converged in the region, resulting in an increase in the pressure gradient at the local boundary to promote westerly strengthening and an eastward eruption. At the same time, due to the Earth’s rotation effect , The northeasterly winds from the northern hemisphere reached the equator and then moved northwestward. The southeasterly winds of the south hemisphere turned southwest winds, which directly strengthened the intensity of westerlies. A comparative analysis of the meridional wind in the northern and southern hemispheres shows that the strength and location of the southeasterly wind in the southern hemisphere are more stable and contribute more to the two amplitudes of the equatorial westerly winds. The meridional airstream in the southern hemisphere comes from the high latitude polar region, which is directly related to the abnormal atmospheric pressure field in the middle and high latitudes.