各种非绝热物理过程在中尺度模式中的作用

Roles of Various Diabatic Physical Processes in Mesoscale Models

随着中尺度模式水平分辨率的不断提高，考虑加入尽可能合理的各种非绝热物理过程极为重要。如积云参数化需包括湿下沉气流、中上层的云卷出和非降水性浅对流。显式云物理方案需同时加入含有水相和冰相的预报方程，以计入水负荷、凝结蒸发、冻结融化和凝华升华的影响。本文首先从实测角度介绍上述物理过程在产生中β尺度环流结构的作用，然后通过一些敏感性数值试验来阐述它们如何帮助成功模拟不同的中尺度对流系统。这些物理过程的相对作用取决于网格距大小或可分辨尺度垂直运动的强度。当网格距在２０～５０ｋｍ之间，本文特别强调积云参数化和显式云物理方案的同时使用。最后对各种非绝热物理过程的耦合以及中尺度模式的局限性作了适当讨论。

As the grid resolution continues to increase, it is essential to implement more sophisticated diabatic physical processes into mesoscale numerical weather prediction models. Specifically, cumulus parameterization schemes ought to incorporate the effects of subgrid-scale moist downdrafts, middle to upper-level cloud detrainments and nonprecipitation shallow convection, while explicit cloud physics schemes should contain the prognostic equations for both liquid and solid cloud particles such that the impact of water loading, condensation/evaporation, freezing/melting and sublimation can be included. In this paper, we present first the roles of the above physical processes in generating various meso-β-scale circulations based on observations, and then examine numerical sensitivity experiments to see how they can be succeeded in simulating various types of circulations in mesoscale convective systems (MCSs). The relative importance of the above physical processes in predicting MCSs depends on the gird size or the intensity of resolvable-scale vertical motion. When the grid size falls into the range of 20～50 km, it is strongly recommended to use simultaneously a cumulus parameterization and an explicit cloud physics scheme — the so-called hybrid approach. The coupling of different physical processes in mesoscale models and their limitations are finally discussed.