与水平风切变强度不均匀相联系的CISK惯性重力波

在虚拟高度坐标系中, 用一个简单的线性模式初步研究了水平风切变强度不均匀分布对长江流域梅雨锋附近贯穿整个对流层的深厚惯性重力波发生发展的影响。结果表明:水平风切变强度不均匀对CISK惯性重力波不稳定有重要作用。在一般干的层结大气中, 实际可能出现再强的水平风切变的影响也难以使惯性重力波变得不稳定; 只有在积云对流潜热参与, 原为弱稳定条件下, 水平风切变强度不均匀能促使低空急流北侧不稳定扰动的发生发展。而水平风切变强度不均匀对不稳定贡献最大的区域是梅雨锋南侧的急流轴附近。

CISK Inertia-gravitational Wave Related to Horizontal Wind Shear Intensity Nonhomogeneous

In the Meiyu season most of the severe MCSs (mesoscale convective systems) with torrential rain may form, develop, move and regenerate down-stream along such Meiyu front in the Yangtze River basin. The kind of wave disturbance most relevant to these activities of MCSs is not only likely the deep mesoscale inertia-gravitational waves in company with the macroscopic cumulus cloud ensemble heating (inertia-gravitational wave CISK briefly), but also that relates to horizontal wind shear and wind shear intensity nonhomogeneous. The so called Meiyu front in Yangtze River basin is actually an equivalent barotropic zone wherein the horizontal thermal gradient is negligibly weak and rather the humidity gradient is very strong particularly in the lower troposphere. A three-dimensional linear model in a dimensionless pseudo-height (Z ≡-ln (p/p₀)) coordinates with a simple parameterized cumulus heating expression is most suitable to be applied to discuss the deep mesoscale disturbances analytically in Yangtze River basin. The behaviors and the weather influences of the CISK inertia-gravitational wave relating to horizontal wind shear instability near Meiyu front on the MCSs activities over Yangtze River basin are investigated. The results show that the horizontal wind shear and horizontal wind shear intensity nonhomogeneous characters have the important influences on the instability of CISK inertia-gravitational wave. In the dry stratified atmosphere without cumulus heating, practically in almost all cases, the effect of horizontal wind shear and its horizontal nonhomogeneous characters can not make the inertia-gravitational waves instable. And only in the nearly CISK situation and the weak stability condition, the horizontal wind shear and its horizontal nonhomogeneous characters have a positive contribution to the instability of the wave disturbances. Such additional instability is mainly attributing to the second order derivative of basic flow in meridional direction. So the most favorable instable location is near the low-level jet stream on the south of the Meiyu front where the MCSs are likely most active. It does not mean that the instability and dispersion of the inertia-gravitational wave-CISK are the only mechanism of the genesis of the MCSs. Other mechanisms, including the dry inertial-gravitational wave in some stable-stratification atmospheric layer, may also lead to the MCSs development.