热带大气对单一型赤道非对称热源的响应

Response of the Tropical Atmosphere to Isolated Equatorially Asymmetric Heating

本文采用Gill模式得到了热带大气对单一型赤道非对称热源响应的理论解析通解,从理论上完善了单一型赤道非对称热源激发的赤道非对称的大气响应结果。同时在单一型赤道非对称热源的位置、强度及范围变化对大气响应的影响方面做了详细的研究。当热源中心位置北移,北半球气旋强度增加、位置北移,同时赤道辐合气流减弱而越赤道气流增强;当热源强度增强(减弱),热源激发的大气响应整体增强(减弱),但大气分布型不发生变化;当热源范围不断增大(减小)时,北半球气旋强度增强(减弱)、位置西移(东移)、范围增大(减小),同时越赤道气流增强(减弱)。将上述结论应用于分析孟加拉湾地区海温对夏季风爆发影响的研究,指出当孟加拉湾地区经向最大暖海温位于赤道附近时,其两侧表现为Rossby波响应的Gill型气旋环流,而海温暖轴北移后,其南侧激发出有利于季风爆发的越赤道气流,这是Rossby重力混合波对热源响应的结果。这是上述理论结果的一个很好例证,同时也为孟加拉湾夏季风的爆发给出一种动力学解释。

An analysis of the response of the tropical atmosphere to isolated equatorially asymmetric heating is performed using the Gill model General solutions of the Gill model are calculated, and the equatorially asymmetric atmospheric response is examined in detail within the general solutions. Heating strength, location, and extent all have some influence on the atmospheric response. When the center of heating moves northward, the cyclone in the Northern Hemisphere is strengthened and moves northward; at the same time, equatorial convergence weakens and cross-equatorial flow is enhanced. When heating strength increases （decreases）, the atmospheric response forced by the heating is enhanced （weakened）, however, the atmospheric pattern does not vary. When the heating extent increases, the cyclonic strength and extent are enhanced, the cyclone is displaced westward, and cross-equatorial flow is enhanced. The above theoretical conclusions are applied to study of the influence of SST on the onset of monsoons in the Bay of Bengal. When the meridional warmest SST axis （WSSTA） is located at the equator, the Gill pattern appears on either side of the equator; however, when the WSSTA moves northward, cyclonic circulation disappears and cross-equatorial flow is induced south of the WSSTA. This effect represents the response of mixed Rossby-gravity waves to external heat forcing. This work shows the utility of the above analytic approach, and also explains the dynamics responsible for summer monsoon onset in the Bay of Bengal.