【摘要】 利用NCEP/NCAR候平均再分析资料,对秋冬季节转换前后大气环流特征及高低层季节转换的时间差异进行研究。结果表明:青藏高原表面气温的季节性转变是东亚地区秋冬季节转换的信号,其剧烈的降温将快速引导环流形势向冬季型转变,一定强度的西伯利亚冷高压的建立亦是季节转换的指示器。从秋冬季节转换前后的环流形势对比来看,急流南撤至35°N以南、急流中心稳定移至西太平洋上空、南亚高压反气旋中心退至西太平洋上空时间比较一致,可视为冬季环流建立的标志。通过分析青藏高原及江淮地区表面热通量的变化得知,秋冬季节,青藏高原地面对大气感热及潜热加热的急剧减少,远远超过了净长波辐射加热的增加,这种热量的减少使得离地最近的地面气温出现相应降温,在滞后表面加热突变后2~3候出现季节转换。由于感热的变化主要影响低层,高层对感热变化的响应主要是通过热力适应机制,导致高层的季节转换时间滞后于低层。而江淮流域地区地表潜热加热的急剧减少亦是大气环流改变的一个热力因素,可能是由于潜热加热到达一定的高度通过凝结加热的方式直接影响高层,所以高低层季节转换时间基本一致。更多还原

【Abstract】 The general circulation differences of the transition season between autumn and winter,altogether with the transition time differences at various levels are analyzed by using NCEP/NCAR reanalysis data.The results show that the thermal effect of the Tibetan Plateau is not only the key factor for the onset of East Asian monsoon but also the trigger to the circulation transition from autumn to winter due to its quick decreasing of surface temperature.The southward retreat to the south of 35°N of the East Asian subtropical westerly jet axis(EAWJ) and intensified EAWJ center over the western Pacific Ocean is the signal of the establishment of the winter circulation pattern.Comparison of the surface heat flux between the Tibetan Plateau and Yangtze-Huai River basin indicates that the sharp decreasing of the surface sensible heat flux over the Tibetan Plateau far exceeds the increasing of the net long-wave radiation,which leads to the corresponding dropping of surface air temperature.It is known that the sensible heating mainly works at low level,so the response of high level atmosphere to its change is 2~3 pentad lagged through thermal adapting mechanism.However,the sudden decreasing of latent heat is the main thermal feature for Yangtze-Huai River basin.The effect of the latent heat can reach the atmosphere at high level,which is responsible for the consistency of atmosphere at high level and low level.更多还原