亚洲季风变动与大气正压/斜压运动动能变化的气候特征

The variations of Asian monsoon as revealed by the variations of kinetic energy of barotropic/baroclinic modes of the wind field

使用 NCEP/NCAR 40年 ( 1 95 8～ 1 997年 )月平均再分析资料 ,通过动力学诊断研究了大气斜压 /正压运动动能的变化及其相互转换 ,分析了亚洲季风变动与这两种动能变化的联系。指出 :季风区大气运动动能的组成和变化具有独特的特征。冬季风时期 ,大气斜压运动动能与正压运动动能具有正相关线性关系 ,斜压运动动能向正压运动动能转换 ;春、秋季无论是东亚还是印度季风区斜压运动动能与正压运动动能之间的转换都处于极小值 ,只是印度季风区始终是斜压动能向正压动能转换 ,而东亚季风区则出现正压动能向斜压动能的转换。夏季风时期季风区以斜压运动动能为主 ,而中、高纬度地区一直以正压运动动能为主。由冬至夏季风区正压动能减少并在盛夏达到极小值。春夏转换时期季风区斜压运动动能和转换因子曲线的随时间的变化位相与夏季风建立的位相同步 。

WT5BZ]By using the monthly mean data from NCEP/NCAR 40 reanalysis(1958~1997),analyzed are the time evolutions of Asian monsoon by diagnosing the variations of kinetic energy of both the barotropic and the baroclinic modes of the wind field in terms of the atmospheric dynamic equations in the present article. It is found that there exist different features of the kinetic energy variations associated with barotropic and baroclinic components of airflow between monsoon and non monsoon regions. The time evolution of baroclinic kinetic energy is well linearly correlated with that of barotropic one in mosoon area during boreal winter.At the same time, there occurs the conversion of kinetic energy from baroclinic mode to barotropic one. The conversion of kinetic energy reaches their minimums with positive value in the Indian monsoon area and the negative in the east Asia during both spring and fall seasons. The kinetic energy of baroclinic winds is the major contributor to the total kinetic energy in monsoon areas during summertime whereas the kinetic energy of barotropic winds is the major part in middle and high latitudes. In monsoon areas, the magnitude of kinetic energy of barotropic mode decreases and eventually reaches the minimum from winter to summer. The kinetic energy of baroclinic mode as well as the kinetic energy conversions from baroclincic to barotropic mode changes in phase with the progresses of summer Asian monsoon. But the variations of these kinetic energy components in the east Asia are lagging to those in the Indian monsoon region.