冬季西伯利亚高压动力结构的研究

本文研究了冬季西伯利亚高压建立时期的动力结构。研究得到,在高压建立前期,对流层中以正涡度为主。低层和高层有弱的辐合,中层是辐散;相应在700hPa以下是上升,以上是下沉。但当反气旋发展时,高层为正涡度和辐合气流,低层为负涡度和辐散气流,整层为下沉运动。这表明对流层中、上层的强质量辐合是导致西伯利亚高压发展的一个重要因子。涡度方程的诊断表明,西伯利亚高压区负涡度的出现和加强是对流层中、上层负涡度平流和低层散度项的作用。 另外,西伯利亚高压热平衡计算表明,对流层有深厚的冷却层(热汇)。这种非绝热冷却将在对流层中导致深厚的下沉运动,从而引起中高层的辐合,低层的辐散,有利于高压的加强。因而西伯利亚高压是在动力和热力因子共同作用下形成的。

A STUDY OF DYNAMIC STRUCTURES OF THE SIBERIAN HIGH IN WINTER

The present paper has studied the dynamic structures of the Siberian high during it's build-up. It has been found that at the initial stage of formation of the Siberian high, the positive vorticity dominates the region of the high in the troposphere. There is convergence at low-level and high-level, respectively, with divergence in between. Correspondingly, there is the upward motion in the layer below 700 hPa and downward motion above 700 hPa. At the mature stage of the high, the significant negative vorticity and strong divergent airflows are observed in the lower and middle troposphere while there are the positive vorticity and convergent airflows in the upper troposphere. The downward motion occurs in the whole layer of the troposphere. This fact shows that the strong mass convergence in the middle and upper troposphere is a major factor leading to the development of the Siberian high. The diagnostic analysis made by the use of the vorticity equation further indicates that the generation and intensificanon of the negative vorticity in the high troposphere mainly result from the effects of the advection of the negative vorticity in the middle and upper troposprere, whereas at low-level the divergence term(divergence) is the major factor for the generation of the negative vortieity. On the other hand, the heat budget of the Siberian high has revealed a deep layer of cooling, thus inducing the downward motion in the troposphere and then convergence at mid and high levels and divergence at low-level. This condition is favorable for the enhancement of the high. Therefore, the build-up of the Siberian high results from the combined effects of dynamic and thermal factors.