Papers in Meteorology and Geophysics

Based on the snowfall data and the upper-air wind data over the Niigata district for 13 months of cold seasons from 1978 to 1984, the relationship between the snowfall amount and the appearance of tropospheric mid-level jet is examined. The statistical relationship between them is highly significant as a result of chi-square test though the individual correspondence between them is not necessarily found. Statistical analysis indicates that the jet tends to appear over the north of snowfall region nearly at the same instant as snowfall. The vertical structure of the jet in the north-south cross section, which is obtained from averaging strong snowfall cases accompanied by the jets, shows that the jet's horizontal scale is less than four degrees in latitude and the vertical wind profile near the jet has the super-geostrophic characteristic of about 10 m/s.

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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:

Accretion of supercooled cloud water by snow and graupel (riming) plays a significant role in the precipitation formation of the convective snow cloud.
The precipitation amount of the glaciated cloud is much smaller than the mixed cloud.
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.
“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.
The precipitation efficiency of “cold clouds” is larger than that of the “warm cloud” with the commonly used autoconversion of cloud water into rain.
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.
The propagation speed of the storm and the transformation from a unicellular storm to a multicellular one are dependent on the parameterization methods.

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