“96．1”高原暴雪过程湿对称不稳定的诊断分析

利用对“96．1”青藏高原东北部暴雪过程一次较成功模拟的MM4中尺度模式输出资料，根据条件对称不稳定（CSI）的线性和非线性理论判据对这次暴雪过程进行了诊断分析，结果表明，“96．1”暴雪的发生发展过程与条件对称不稳定密切相关，不稳定区位置在M－θc和σ^2垂直剖面图上较其它判据更接近于实际情况。非线性CSI判据的动力学诊断分析指出，“96．1”暴雪是在低空对流不稳定和高空对称不稳定的相互作用下发生发展的，说明非线性对流－对称不稳定是其发展机制。

The Diagnosis of Symmetric Instability of

With the criteria of lin ear and non-linear symmetricinstability,the mechanism of a heavy snowstorm whi ch occurred in the northeast region over Qinghai-Xizang Plateau from 15 to 17 J anuary 1996 (“96.1”) was diagnosed by using two time level output data of a MM 4 mesoscale numerical model which well simulated the developing structure and ev olution of the “96.1” heavy snowstorm.The results show that the location of po sitive value of σ2 is corresponding to that of shear line of the snowstor m; and from the vertical cross section chart of pseudo angular momentum and pote ntial equivalent temperature (M-θe), it can be seen that the region wher e the slope of surface is more vertical than the M is also consistent to th e mo vement of θe the snowstorm.The linear conditional symmetric instability i s a possible explanation for the shear line.The Lagrangian parcel theory was app lied to diagnose the “96.1” snowstorm; and it showed a strong vertical con vection at the l ow level and a slantwise convection at the high level during the snowstorm proce ss.It can be convinced that the convective-symmetric instability is a mechanism of the snowstorm development.And the cusp catastrophe is corresponding to the d evelopement and movement of the shear line;limited comparison lends some support to the hypothesis that non-linear CSI can be a dominant formative mechanism of the snowstorm,though more sophisticated studies are required.