冬季青藏高原大气热状况分析Ⅰ:气候平均

An analysis of the diabatic heating characteristic of atmosphere over the Tibetan Plateau in winter Ⅰ: Climatology

中文关键词:  冬季,青藏高原, 非绝热加热, 冷热源, 再分析资料

英文关键词:Winter, Tibetan Plateau, Diabatic heating, Heat sources and sinks, Reanalysis data

中文摘要:

      通过诊断3套再分析资料的非绝热加热场，研究冬季青藏高原上空大气的热力特征。结果表明，与夏季为强热源的特征不同，冬季高原上空不是欧亚大陆上最强的冷源中心。冬季高原上空整体是偏弱的冷源，在高原西侧及东南地区上空甚至出现非绝热加热正值区，这一分析对以往研究提出的高原是冷源的特性给出了修正。各种非绝热加热分量的诊断表明，冬季高原上空这种总的非绝热加热分布主要是由于高原主体的长波辐射冷却较周边地区弱，以及西侧至东南地区凝结潜热释放造成的。为了说明再分析的非绝热加热资料对冬季高原上空大气的这种热力特征描述的可信性，文中还利用了地表辐射能量、TRMM及PREC/L降水、垂直速度等资料进一步辅助分析，证实了由于高原位势较高造成大气整层温度偏低，向外长波辐射偏少，以及高原地势的隆起造成局地较强的上升运动，高原西侧至东南角降水大值区潜热偏大，最终造成高原上空总非绝热加热负值偏小。最后理想高原隆起的水球试验结果说明，冬季，高原的存在减弱了陆地上空的冷却效应，因而其上为弱冷源，再次证实了资料分析的结果。

英文摘要:

      The atmospheric diabatic heating over the Tibetan Plateau (TP) during winter was analyzed using the 3 kinds of reanalysis data. The results indicate that the TP in winter is not the strongest center of the heat sink in Eurasia, in contrast to the characteristic in summer as a strong heat source. On the whole, the atmosphere over the TP acts as a weaker heat sink, and there exist a region of positive diabatic heating near the western and southeastern TP. This analysis is a revision to the previous notion that the TP is a heat sink during winter. The diagnoses of the various diabatic heating components explain that this heating characteristic over the TP in winter is mainly due to the weaker longwave radiative cooling than that over the surrounding land area and latent heating near the western and southeastern TP. To further confirm the above results derived from reanalysis data, the surface radiation budget (SRB) data，the precipitation rates and vertical velocity reanalysis data from the TRMM and PREC/L are also used for diagnosis, which approve that negative total heating over the TP is weaker as a result of reduced outgoing longwave radiation at the top of the atmosphere due to lower air temperature over the TP and intensified condensation latent heating associated with more precipitation and ascending motion over the western and southeastern TP. Finally, the results of numerical experiments with idealised TP support the above results, that is, the existence of the TP weakens the cooling effect of land, and the atmosphere over the TP is a weaker heat sink during winter.