亚洲夏季风爆发与热源强迫下的热带大气Rossby波

Asian Summer Monsoon Onset and Tropical Atmosphere Rossby Wave Forced by the Heating Source

对南海夏季风爆发前的风场和局地对流凝结加热强迫作用进行了合成分析,表明南海夏季风爆发前局地对流凝结加热作用对与南海夏季风爆发密切相关的低频涡对的产生起着重要作用。然后,从动力学的角度研究了带有外部热源强迫的赤道β平面上的Rossby波,利用Gardner-Morikawa变换和摄动展开方法,得到了热源强迫下描写赤道Rossby的mKdV方程,进而得到了不同热源形式下切变气流中赤道非线性Rossby波的解析解。结果表明,不同类型的热源对赤道Rossby波的结构起着非常重要的作用,同时也为南海夏季风爆发前低频涡对的形成给出了一种动力学解释。

The NCEP/NCAR daily mean wind data at 850 hPa and OLR anomaly data are used. Some composite analyses for the 19 years, data from 1980 - 1998 are made taking the date of South China Sea summer monsoon onset as reference. The wind field and the local convective condensation heating field prior to South China Sea summer monsoon onset are studied based on the composite analyses. It shows that there is a large low value area of OLR in the tropical Indian Ocean during two pentads before the South China Sea summer monsoon onset, that is to say, strong convective activity and a large area of heating source exist in the tropic Indian Ocean. Then about on the 7th day before the South China Sea summer monsoon onset, corresponding to the heating source, a low frequency vortex pair forms in the eastern tropical Indian Ocean. In the following days, the low frequency vortex pair becomes strong and moves to the north along with heating source, the low frequency vortex pair has the trend of developing to the northwest. So the convective condensation has important effect on the vortex pair prior to the South China Sea summer monsoon onset. Then, the nonlinear equatorial Rossby wave with an external heating forcing on a beta-plane has been investigated from dynamic point of view. The mKdV （modified Korteweg-de Vries） equation with an external heating forcing is derived with the Gardner-Morikawa transformation and the perturbation expansion method.And then the periodic structures of equatorial nonlinear Rossby wave under different kinds of external heating forcing are obtained. Combining with the data analysis result of local convection heating before the South China Sea summer monsoon onset, it is found that different kinds of external heating is very important for the equatorial Ross- by wave. With the effect of some special external heating sources, low frequency vortex pair can be found. And this work can also give a dynamic explanation for the low frequency vortex pair before the South China Sea summer monsoon onset.