2-Dimensional Simulation of the Convective Snow Band Observed over the Japan Sea: Part 2

Precipitation Mechanism of the Convective Snow Band and the Effects of the Different Parameterizations of Cloud Microphysics on the Convective Snow Cloud

Abstract

   In winter, 1984, snow cloud bands (Sakakibara et al., 1987) were observed over the Japan sea off the coast of Kanazawa (N36.6°, E136.7°). Ikawa et al. (1987) conducted the 2-dimensional numerical simulation of the snow band, using a non-hydrostatic anelastic model with the bulk parameterization of cloud microphysics including both liquid water (cloud water, rain) and solid water (cloud ice, snow, graupel). In Ikawa et al., investigation was focused on the dynamical structure of the convective cloud, especially on its multicellular structure. In this study, a subsequent one to the former studies, cloud-microphysical aspects of the convective cloud are examined.
   Main findings by the comparative sensitivity experiments are as follows:

1. Accretion of supercooled cloud water by snow and graupel (riming) plays a significant role in the precipitation formation of the convective snow cloud.
2. The precipitation amount of the glaciated cloud is much smaller than the mixed cloud.
3. Two types of ice particles, i.e., snow and graupel, have different effects on the convection in the precipitation amount, the coldness and width of the cold dome, the amounts of cloud water and ice particles in the air.
4. “Cold clouds” with both ice particles and liquid water particles incorporated produce a colder and wider cold dome than “warm clouds” with no ice particles incorporated.
5. The precipitation efficiency of “cold clouds” is larger than that of the “warm cloud” with the commonly used autoconversion of cloud water into rain.
6. The basic dynamical structure of the convective cloud, such as long lasting property, upshear tilting of updraft, front-to-back system-relative u-component of the updraft branch, back-to-front system-relative u-component of the downdraft branch, a cold dome at the surface and a warm area above it, is, reproduced in a qualitative sense, in the simulation, not much influenced by the different parameterization methods.
7. The propagation speed of the storm and the transformation from a unicellular storm to a multicellular one are dependent on the parameterization methods.