On the Seasonal Division of Atmospheric General Circulationand Its Abrupt Change. Part III: Climatology
Xue Feng, LinYihua and Zeng Qingcun(Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing100029)
Abstract The seasonal division of atmospheric general circulation and its abrupt change are defined in Part I, an example in an individual year is given in Part II. In this paper (Part III), the results based on NCEP/ NCAR reanalysis data of 1978- 1997 are in general agreement with those of Part II, but it is more distinct and representative. The main results are: (I) On the middle and lower level of the troposphere, the Asian winter monsoon circulation is initiated in the westerlies of high latitudes over Eurasia, the Asian summer monsoon circulation results from the establishment or intensification of several atmospheric centers of action such as the Pacific subtropical high (the subtropical monsoon), Mascarene high and Australian cold high (the tropical monsoon). (2) The seasonal establishment of at-mospheric general circulation is initiated from the stratosphere, the polar regions and some tropical regions at the tropospheric low level start afterwards, then from the above regions and levels, they extend into middle latitudes and develop upwards and downwards respectively, finally, resulting in the seasonal establishment of the whole hemispheric system of atmospheric general circulation. (3) The strongest seasonal abruptness is located in the region between the tropics and sublropics and in the region between high latitudes and the polar region in the stratosphere of both hemispheres, respectively. Besides, the seasonal abruptness from winter to summer is stronger than that from summer to winter. On the other hand, (he seasonal abruptness in the troposphere is much weaker (hun that in the stratosphere, with a maximum center in the subtropical areas from middle level to upper level.