一次华北强降雪过程的湿对称不稳定性研究

RESEARCH OF MOIST SYMMETRIC INSTABILITY IN A STRONG SNOWFALL IN NORTH CHINA

运用湿球位涡和倾斜有效位能的概念从条件性对称不稳定（ＣＳＩ）和局地对称不稳定（ＬＳＩ）这两个侧面计算了一次华北强降雪过程的湿对称不稳定的水平分布和垂直分布状况，并比较详细地讨论了湿对称不稳定对１９８６年１１月２２—２３日发生在内蒙古河套地区和林东、林西地区附近的一条狭长的强降雪带的可能作用以及湿对称不稳定与基本气流走向、风垂直切变和水汽的关系，发现：这条降雪带与雪区附近低层的湿球位涡负值区走向大体平行；在降雪带中分别位于呼和浩特、东胜地区和林东、林西地区的强降雪中心有着不同的动力学机制，前者主要为在暖区具有弱的对称不稳定的情形下锋生强迫作用所致，后者则是由明显的湿对称不稳定所致。

he concept of wet bulb potential vorticity and SCAPE (slantwise convective available potential energy) was used to calculate the horizonal and vertical distribution of moist symmetric instability including convective symmetric instability (CSI) and local symmetric instability (LSI) in the process of a storm snowfall in North China. The potential contribution of moist symmetric instability to a narrow storm snowfall belt occuring in the Hetao and Lindong. Linxi region of Inner Mongolia and the relationship between moist symmetric instability and the direction of basic flow, wind shear and moisture were discussed.It was found that the strong snowfall belt is almost parallel with negative value area of wet bulb potential vorticity at low level in the vinicity of snow area. the dynamical mechanism of the strong snowfall centre in the Lindong, Linxi region is different from that in the Hetao region. the former is induced by frontgenetic forcing with weak symmetric instabilities in the warm section of frontal area: the latter is triggered by obious moist symmetric instabilities.