Simulated Tropical Cyclogenesis Climate By Regional Climate Model With Different Resolutions Over The Northwestern Pacific

The TC genesis over the Northwestern Pacific during1949to2010was analyzed using the best track data of CMA-STI. The results show as follow. The TC often generate in5°N-25°N,110°N-170°N. The South China Sea, east to Philippine Islands and Mariana Islands around are the most frequent area of TC genesis. The TC genesis number increase during1949to1974and increase observably during1975to1994. But the mean number during1975to1994is less than it during1949to1974. The TC genesis number decrease indistinctively during1995to2010. and the mean number is less than it during1975to1994. Most TC generate during July to October. The most TC generate in August and the least generate in February. The variation of TC genesis number has a period of2to4years and a period of6to8years. The period of2to4is significant during1968to1976and the period of6to8years appears in1957-1979. The TC number has one sudden increase and two sudden decreases and the turnings happen in the late1950s,in the mid1970s and in the mid1990s.After knowing the features of TC genesis over the Northwestern Pacific, the TC genesis number, the TC genesis position and the variation of TC genesis number over the Northwestern Pacific during2000to2009are simulated by Regional Climate Model Version3.1(RegCM3) with15km,30km,45km and60km resolution to examine the capability of RegCM3on TC genesis simulation over the Northwestern Pacific. The results show that, the capability of RegCM3on TC genesis simulation over the Northwestern Pacific is influenced by resolution. And resolution increasing can not always leads to the improvement of simulation result. The RegCM3with30km resolution has the best capability on TC genesis number and its variation simulation. The capability of RegCM3with45km resolution is a little worse than the RegCM3with30km resolution. The RegCM3with60km resolution has the best capability on TC genesis position simulation. The RegCM3with15km resolution has the worst capability on TC genesis number, TC genesis position and the variation of TC genesis number simulation.Compared with other models, more active southwest monsoon, weaker subtropical high, higher relative humidity in mid-and-low troposphere, stronger 850hPa relative vorticity and weaker vertical wind shear in summer simulated by RegCM3with60km resolution are beneficial to the addition of TC genesis number and the improvement of TC genesis position.Compared with other models,weaker southwestem monsoon over the South China Sea and stronger subtropical high over the West Pacific summer simulated by RegCM3with15km resolution hinder the development of convection then reduce the TC genesis number and increase the position simulation error.Compared with other models, southwestern monsoon over the South China Sea, subtropical high over the West Pacific and850hPa relative virticity in summer simulated by RegCM3with30km and45km resolution are beneficial to the addition of TC genesis number. And these are the reasons why the simulation resuIts of different resolution models are different.The vortices simulated by30km,45km and60km resolution model can merge and it lead to the TC generate.The vortices simulated by15km resolution model can not merge for the small scale of the vortices and the far distance between them.It may reduce the TC genesis number. Much dry air involves in wet air before TC genesis and then reduces the water vapor and condensation latent heat release in mid-and-low troposphere. It may also reduce the TC genesis rumber.