“96.1”高原暴雪过程三维条件性对称不稳定的数值研究

Numerical Study on Three-Dimensional Conditionally Symmetric Instability of "96.1" Snowstorm Event

利用“96 .1”青藏高原东北部暴雪过程的较成功的中尺度模拟的输出资料 ,用非纬向非平行基流中的对称不稳定模式 ,对“96 .1”暴雪发生发展过程的动力学机制进行了三维基流中二维非线性对称不稳定数值模拟试验。结果表明 ,ψ场和w场的三维配置与切变线的演变过程相当一致 ,说明用三维基流中二维非线性对称不稳定可能能较好地描述SI在切变线东伸南移过程中所起的作用。

Using the output data of a MM4 mesoscale numerical model which fairly well simulated the developing structure and the evolution of the '96.1' snowstorm event over Qinghai Xizang Plateau, a nonlinear and non zonally non parallel basic flow symmetric instability (SI) models and simulation system were developed to validate the possible effect of conditional symmetric instability (CSI) on the formation of the snowstorm process, the results showed that in a developing model of two dimensional nonlinear SI in a three dimensional basic flow with proper parameters, the use of localized perturbation of streamfunction or potential temperature resulted in circulations forming which slant to south with height in y-z cross section by symmetric instability and are vertical in the along front direction by nonlinear transversal wave instability, have samilar results as in literatures . These circulations were tilted in the horizontal plain relative to y coordinate, and the three dimensional disposition in the fields of the streamfunction and vertical velocity is consistent with the evolution of the '96.1' snowstorm, that means the two dimensional nonlinear symmetric instability in three dimensional basic flow is a possible explanation for the organization of the '96.1' snowstorm.