In the present study numerical experiments of a tropical squall line, which was observed on 22 Feb 1993 during TOGA COARE, were performed with Meteorological Research Institute Nonhydrostatic Model. Our main focuses are on resolution dependence (dx=1.25-7.5km) and the impacts of ice microphysics.

In contrast to smooth evolution of a storm-scale (O(100km)) structure in a control (dx=1.25km) case, cellular motion of the grid-scale (with smaller vertical scale than control) dominated in coarse-resolution cases, and the development of the squall line was significantly delayed (especially for dx > 4km). The deficiency was most significant in weakness of a cold pool and an underestimate of the deviation of area averaged moisture by the squall line, though that of horizontal velocity tended to be comparable or overestimated. These imply that an explicit treatment for a coarse resolution fails to represent organization of convection that is closely related to precipitation processes, while spontaneous cellular motion may cause significant momentum transport.

The impact of ice microphysics is investigated by comparison with the case without including them. The difference was especially notable in the vertical profile of pressure deviation. With ice microphysics, low-pressure deviation extended deeper and more highly concentrated around the leading edge. It modified horizontal velocity fields and distribution of cloud and heating. More of the results from sensitivity tests on parameters and formulations concerning ice microphysics will be discussed.