东亚季风指数及其与大尺度热力环流年际变化关系

EAST ASIAN MONSOON INDEX AND ITS INTER-ANNUAL RELATIONSHIP WITH LARGESCA-LE THERMAL DYNAMIC CIRCULATION

中文关键词:  季风指数  Walker环流  ENSO  年际变化

英文关键词:Monsoon index  Walker circulation  ENSO  Interannual variability

中文摘要:

      将东西向海平面气压差与低纬度高、低层纬向风切变相结合,定义了东亚季风指数,该季风指数较好地反映了东亚冬、夏季风变化.其中,夏季风指数年际异常对西太平洋副热带高压南北位置变化和长江中下游旱涝具有较强的反映能力.分析表明:东亚夏季风年际变化与印度洋-西太平洋上空反Walker环流及夏季越赤道南北半球间的季风环流呈显著正相关关系.在强、弱异常东亚夏季风年份,异常的Walker环流在西太平洋上的辐合(辐散)中心在垂直方向不重合,高层(200hPa)速度势与东亚夏季风显著相关区域位于西北太平洋上,该异常环流的高层的辐合(辐散)通过改变低层空气质量而影响夏季500hPa西北太平洋副热带高压.采用SVD分析进一步发现:与海温耦合的异常Walker环流在西太平洋上空的上升支表现出南北半球关于赤道非对称结构,亚澳季风区受该异常Walker环流控制.因而,东亚季风与热带海气相互作用可直接通过这种纬向非对称的Walker环流发生联系.

英文摘要:

      A new East Asian monsoon index is developed for land-sea between zonal and meridional thermal difference in terms of East Asian zonal sea-level pressure contrast combined with high and low-level zonal wind shear at low latitudes.The index-shown seasonal and interannual variation of summer monso n goes well with the western Pacific subtropical high (WPSH) ridge and better reflect the drought/flood in the middle-low reaches of Yangtze river.Results show that the summer monsoon bears significant anti-correlation relationship with the anti-Walker circulation over Indian and western Pacific oceans and the cross-equatorial monso on circulation in Asia.The convergence and divergence center of anomalous Walker circulation over western Pacific ocean at low and high level is not vertical superimposed in stronger and weaker summer monsoon year.The pronounced correlation region between velocity potential at 200hPa level and summer monsoon index is over western North Pacific,thereby the anomalous zonal circulation can affect the WPSH at 500 hPa by virtue of its convergence anomaly.The Walker circulation coupled with SSTA exhibis a meridional asymmetrical character over Australian and Asian monsoon regions on the basis of SVD,there exists directly connection between East Asian monsoon and air-sea interaction in the framework of such circulation.