By using the rawinsonde data, upper cloud amount data and objective analysis data for global domain which all were produced by Numerical Prediction Division,JMA and by using daily and mean weather map issUed by JMA an...By using the rawinsonde data, upper cloud amount data and objective analysis data for global domain which all were produced by Numerical Prediction Division,JMA and by using daily and mean weather map issUed by JMA and daily rainfall data over the Huaihe River Basin from China,an observational study to the early summer seasonal change of large-scale circulation over East Asia and its relation to change of the frontal features and environment for the frontal rainfall has been carried out.Following reaults have been obtained:(1) The early summer seasonal change of large-scale circulation was occurred during 20-23 May 1991,which was about 10 days earlier than the normal.During the period the subtropical westerly jet and tropical easterlies abruptly moved northward;(2) The northward movement of the tropical easterlies was not uniform,it was earlier at 100 hpa level and about 24 hrs late at 200 hpa level.The phenomenon was associated with earlier disappearence of the subtropical westerly jet at 100 hpa level;(3)During the seasonal change there were two westerly jets in the upper level and changed their intensity with the time.before 18 May 1991,the southern one was more intense and then changed to more intense for the northern one and disappearence of the southern one,the phenomenon seemed to be appeared as northward movement of the southernjet;(4) A faster temperature(n rising in the upper level over the Tibetan Plateau was associated with the seasonalchange.From the T rising the T maximum moved onto the plateau,changing the T gradient from positive to negahve to the south flank of the plateau,the effect to leduce and disappear the southern westerlies.Also the T rising was associated with change of the frontal features over East Asia;(5) The seasonal change type during 1991 was same as that during 1992 and 1993,but different from that during 1990;(6) The environment for the frontal rainfall was change in the season,the differences were in the baroclinity in upper level and vertical wind speed and direction shear.展开更多
文摘By using the rawinsonde data, upper cloud amount data and objective analysis data for global domain which all were produced by Numerical Prediction Division,JMA and by using daily and mean weather map issUed by JMA and daily rainfall data over the Huaihe River Basin from China,an observational study to the early summer seasonal change of large-scale circulation over East Asia and its relation to change of the frontal features and environment for the frontal rainfall has been carried out.Following reaults have been obtained:(1) The early summer seasonal change of large-scale circulation was occurred during 20-23 May 1991,which was about 10 days earlier than the normal.During the period the subtropical westerly jet and tropical easterlies abruptly moved northward;(2) The northward movement of the tropical easterlies was not uniform,it was earlier at 100 hpa level and about 24 hrs late at 200 hpa level.The phenomenon was associated with earlier disappearence of the subtropical westerly jet at 100 hpa level;(3)During the seasonal change there were two westerly jets in the upper level and changed their intensity with the time.before 18 May 1991,the southern one was more intense and then changed to more intense for the northern one and disappearence of the southern one,the phenomenon seemed to be appeared as northward movement of the southernjet;(4) A faster temperature(n rising in the upper level over the Tibetan Plateau was associated with the seasonalchange.From the T rising the T maximum moved onto the plateau,changing the T gradient from positive to negahve to the south flank of the plateau,the effect to leduce and disappear the southern westerlies.Also the T rising was associated with change of the frontal features over East Asia;(5) The seasonal change type during 1991 was same as that during 1992 and 1993,but different from that during 1990;(6) The environment for the frontal rainfall was change in the season,the differences were in the baroclinity in upper level and vertical wind speed and direction shear.
