1998年5月南海夏季风建立的诊断和模拟研究

A Study of Diagnosis and Numerical Simulation Test on the Onset of SCSM in May of 1998

利用NCEP/NCAR高空格点和TBB资料,通过大气热源、水汽汇和准地转位涡方程诊断分析,以及中期数值模拟试验,讨论了南海夏季风建立的中期突变过程物理机制,也讨论了青藏高原的动力和热力作用的影响。研究表明,南海季风建立之前,在孟加拉湾有热带气旋发展,我国华南和南海地区受南下冷空气的锋面系统影响,该两个天气系统产生的降水凝结潜热的作用,增强了从孟加拉湾到南海、西太平洋低纬地区的低层西南气流及高空东风气流,並使200 hPa层上反气旋北跃到22°N附近,导致南海夏季风建立。1998年5月南海夏季风的爆发,主要是前期这两种热源因素共同作用的结果。高原的感热作用加强了四周低层气流向髙原的辐合及髙层气流向外的辐散,从而有利于夏季风建立,但相对于降水凝结潜热作用,影响较小。高原地形动力作用对西风带系统有明显的动力阻滞作用,有利于反气旋北上,但对低纬上下层风场的直接影响不显著。

The summer monsoon over South 1998. Utilizing the NCEP/NCAR grid point and China Sea （ SCSM ） is abrupt settled around 22 May, TBB data, the middle range process of SCSM onset has been diagnostically studied by heat source, moisture sink as well as a simplified quasi-geostrophic potential vorticity equation. By means of the simulation tests of middle range numerical model, the physical mechanism of SCSM onset has been examined further. It has been found that the development of a tropical cyclone over Bay of Bengal and the activity of cold air over south China, South China Sea and western Pacific both play an important role for the onset of SCSM. The release of latent heat associated with them is the most important factor for the intensity of southwesterlies （ easterlies ） at 850 （200 hPa） over South Asia and the movement of anticyclone system to 22°N at 200 hPa over Indo-China peninsula. The onset of SCSM could be considered as a phenomenon to response the variation of those heat sources. The sensible heating over Qinghai-Xizang Plateau could enlarge the convergence （ divergence ） in low （high） level leading to the intensity of SCSM, but the influence is not so obvious as that by above latent heating. The Qinghai-Xizang Plateau displays the dynamic block effect forcing the wave trough of westerlies to weaken and move slow down, which is favorable to the shift northward of 200 hPa anticyclone, but without significant influences on the circulation in low latitudes.