南亚和东亚热带夏季风分界域变化

Changes of the Boundary Between the South Asian and East Asian Tropical Summer Monsoon Subsystems

利用1948—2012年NCEP/NCAR逐日再分析风场资料,对亚洲两个热带夏季风子系统（南亚夏季风和东亚热带夏季风）边界进行划分。根据所得出的边界提出了亚洲两大热带夏季风子系统分界域的观点,定义偏向指数来确定两大热带夏季风子系统边界的偏向;通过对比,确定出边界在纬向上的变动较大的区域,并以确定的变动较大的纬度区域来研究亚洲两大热带夏季风分界域的变化规律;最后通过边界指标刻画出季风强度的变化情况,分析其关键环流特征。选取涡度作为边界的确定指标,边界的变动可以分为东部型、中部型、西部型。根据边界的振幅情况选取10°-17.5°N作为主要研究区域,由边界指标定义的夏季风指数得出,亚洲两大热带夏季风子系统强度的一致性变化占主导地位,其次为反相变化。

NCEP/NCAR 65-year daily reanalysis wind data are used to divide the boundary of the two tropical Asian summer monsoon subsystems（the South Asian summer monsoon and the East Asian Tropical summer monsoon）.According to the boundary derived from the wind data,it＇s concluded that both of the Asian summer monsoons have their own control domain.A deviation index is defined which can describe changes of two Asian tropical summer monsoon subsystems＇ boundary,positive value means that the boundary of two tropical Asian summer monsoon subsystems is further east,while the negative value means their boundary is further west.Then comparative study is carried out to check out which area of the boundary changes larger.The area with intense changes is further investigated to study the change regulation of two Asian tropical summer monsoon subsystems.At last,a monsoon strength index is designed which can describe the strength change of Asian tropical summer monsoon.According to the latitude of vorticity minimum value,and the boundary deviation index between the decadal changes,results show the boundary change is either eastern,central or western.When the pattern of the central changes to the pattern of western,there is a mutation passing the test of 0.01 level.The low,medium and high layers of the three boundary categories are also quite different.And then,10°—17.5°N area can be chosen as the main study area according to the oscillation amplitude.By using the boundary deviation to define the two Asian Tropical Summer monsoon indexes,it＇s found that consistent change happens more than reversed phase change for the strength of two summer monsoons.And the meridional wind anomaly field of four kinds of strength type from the Bay of Bengal to the South China Sea reflect the four anomaly situations：＇＋-＇,＇- ＋＇,＇--＇,and ＇＋ ＋＇.