Asian Summer Monsoon Onset and Tropical Atmosphere Rossby Wave Forced by the Heating Source
亚洲夏季风爆发与热源强迫下的热带大气Rossby波

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 Rossby 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.