夏季高原大气热源的气候特征以及与高原低涡生成的关系

Climatic Characteristics of Atmospheric Heat Source over the Tibetan Plateau and Its Possible Relationship with the Generation of the Tibetan Plateau Vortex in the Summer

利用NCEP／NCAR再分析资料和基于此再分析资料的高原低涡统计数据集，采用线性趋势、Morlet小波、EOF分解、合成分析等方法，分析了1981-2010年夏季高原大气热源气候特征以及与高原低涡生成的联系。结果表明：夏季高原大气热源平均强度为105Wm-2，随时间有减弱趋势，具有明显的年代际变化，存在显著的准3年周期振荡。高原低涡高发年，高原大气热源强度明显高于气候态，主要表现为高原大气热源的水平分布差异。在低涡高发年，涡度平流的空间分布和大气经向垂直环流结构显示：高原沿东南向西北存在500hPa正涡度平流带，为高原低涡生成提供了有利的涡度场。同时，高原大气热源异常的水平分布促使高原上空产生上升气流，有助于高原上形成低层辐合、气旋式环流，整层上升运动，高层辐散、反气旋式环流的三维流场，促进高原低涡在低层生成，此时高原主体低空为正涡度区。并且，大气热源在垂直方向的变化也影响低涡的生成。最后，根据本文结果和我们前期的相关研究，从热成风原理和高原大气热力适应理论两方面对高原大气热源与高原低涡生成频数的统计结果给出了机理解释。

The NCEP/NCAR reanalysis data and the Tibetan Plateau Vortex （TPV） statistical data from the same data base for the period of 1981 to 2010 have been exploited in this study to analyze the summertime climatic characteristics of atmospheric heat source and its relationship with the generation of TPV. The linear trend analysis, Morlet wavelet, EOF decomposition and composite analysis methods are used. The result shows that the summertime average strength of atmospheric heat source is 105 W m-2 over the TE Moreover, the strength demonstrates a weakening trend that has obvious decadal variations. In particular, a significant periodic oscillation with a cycle of approximate 3 years is detected. In the years of high frequency of TPV, the strength is obviously higher than the climatically averaged value. The main anomaly of heat source is horizontally distributed over the Tibetan Plateau. Analyses of the vorticity advection and the vertical cross section of secondary circulation indicate that a positive vorticity advection from the southeast to the northwest at 500 hPa provides positive vorticity for the TPV over the Tibetan Plateau. At the same time, the Tibetan Plateau behaves as an atmospheric heat source in the summer. It promotes updrafts over the plateau, which are favorable for low-level convergence, high-level divergence, and cyclonic and anticyclonic circulation development. As a result, the generation of the TPV is promoted. Note that positive vorticity is produced above the Tibetan Plateau. Finally, by applying the principle of thermal wind and atmospheric thermal adaptation theory, this study provides a physical explanation for the link of the Tibetan Plateau atmospheric heat sources and the statistical result of the frequency of TPV generation.