一次夏季西南低涡形成机理的数值试验

本文用一个适合于高原地区的简化流体动力学模式,对一次夏季西南低涡的形成进行了多种数值试验。控制试验结果表明,西南低涡形成的位置在高原东侧地形高度3000m附近,与实况基本吻合,降水区分布比较合理。对不同物理过程进行试验表明,动力过程对西南涡的形成起了基本作用,但单纯的动力过程不能使西南涡维持下去。潜热加热对西南涡的维持发展有重要影响。感热加热作用较小。 青藏高原地形对西南涡的形成有决定性影响。模式地形高度削减一半,模拟的西南涡形成位置比实况偏西偏南;去掉地形后,700hPa为一热低压,位于青藏高原内部。

NUMERICAL EXPERIMENT ON THE FORMATION MECHANISM OF A SW VORTEX IN SUMMER

The formation mechanisms of a SW vortex were investigated with numerical experiments using a simplified hydrodynamic meso-scale model suitable to Qinghai-Xizang Plateau in this paper. The results of control experiment show that the vortex forms over the eastern flank of the Plateau near 3000 m contour, and is consistent with the observed. The distribution of rainfall zone is also reasonable. Based on different model experiments, it is found that the dynamic process is essential for formation of the SW vortex and that the latent heating plays an important role in its maintenance and development. Without the releasing of latent heating the vortex would tend to degenerate. Sensible heating has just a little function in the vortex formation. The Qinghai-Xizang Plateau exerts significant effect on formation of the SW vortex. When the model orography height is reduced by half, the simulated SW vortex is located to the southwest of that in the control experiment. The experiment without orography reproduces a heat low at 700 hPa in the east part of the Plateau only.