The aim of the present paper is to investigate the formation mechanism of a convergent cloud band which appears east of the Korea Peninsula over the western Japan Sea under northwesterly winter monsoon.Numerical experiments with different surface conditions reveal that the land-sea contrast of thermal property between the Peninsula and the Japan Sea plays the leading role in the formation of the convergent cloud band. Less transformation over the cold land causes a mesoscale high pressure in the lower troposphere with its center at the southeast end of the Peninsula and a convergence zone forms over sea at the eastern margin of it. The convergence zone makes cumulus convections active and organized into a band. In addition, blocking effect of the mountains north of Korea acts to intensify the convergence zone.

Three schemes for nonhydrostatic models with orography incorporated, consisting of an-elastic (AE), elastic horizontally and vertically implicit (E-HI-VI) and elastic horizontally explicit, vertically implicit (E-HE-VI), are compared in their formulation and performance.If sound waves are damped enough in the elastic models, the results of these schemes are similar, in spite of the use of the flux form of the advection term in AE. Efficient damping methods of sound waves are examined, and a linear analysis is made of their stability, where both sound and gravity waves are taken into account simultaneously.An iterative application of a direct method for solving the elliptic equation of pressure needed for the AE and some E-HI-VI schemes appears to be accurate. One application of a direct method increased the central processing unit (CPU) time by about 15%, which is comparable to the CPU time required for a small time step integration of the E-HE-VI scheme.For the E-HI-VI scheme, a partially implicit method was found to need no iteration in solving the pressure equation for the case of a low or moderate mountain, since the erroneous forcing at the boundary is practically negligible. However, for the case of a high and steep mountain, the method needs iteration to get rid of the erroneous forcing at the boundary which is no longer negligible. This method is found to be unstable for the case of a very steep mountain.

The evolution process and fine structure of a long-lived M*CS(meso-*-scale convective system) in the subtropical East Asia was studied for 14-15 July 1979 using Geostationary Meteorological Satellite IR observation and radar observation data. This M*CS was generated in the Baiu frontal zone under the influence of a weak shortwave trough and developed into a weak Baiu frontal depression. The M*CS consisted of a few M*CSs (meso-*-scale convective systems). The evolution and propagation of the M*CS were related to both development and displacement of M*CSs. The successive generation of M*CSs over the western coast of Kyushu (western part of Japan) indicated the orographic influence on the formation of convection. The successive development of M*CSs to the west of the preexisting one over Kyushu resulted in the slow moving of the M*CS over Kyushu. The environmental conditions for development of M*CS and the strong response in the upper-level wind field to M*CSs are also discussed.

In order to study the Yamaji-kaze-a typical downslope wind found in Japan, the two-dimensional flow over an asymmetric mountain is simulated by use of a non-hydrostatic model. The Yamajikaze front and the reversed wind behind the front-characteristic features of the Yamaji-kaze-are explained in terms of the internal hydraulic jump and its associated circulation.Numerical experiments for a homogeneous atmosphere show that the behavior of the internal hydraulic jump is significantly affected by the inverse Froude number and the shape of the mountain. When the inverse Froude number is large, a quasi-steady state solution such that the hydraulic jump remains on the lee side of mountain is obtained, with the associated reversed flow being generated just behind the hydraulic jump. In the case of the Yamaji-kaze, the asymmetry of the Shikoku Mountains and the blocking effect of the Chugoku Mountains impede the propagation of the Yamaji-kaze front and allow the reversed wind to occur more readily.For the case of the Yamaji-kaze observed on 21 April 1987, a notable inversion layer was found at a level near the mountaintop. It is confirmed, by numerical experiments of a heterogeneous atmosphere with the observed thermal stratification, that the surface wind strengthens in the presence of the inversion when compared to that without the inversion. Development and propagation of an internal hydraulic jump are qualitatively simulated under the observed thermal stratification and timechanging wind profile. On the basis of the experimental results a conceptual model of the Yamaji-kaze is proposed.

Observations are given for the foehn event which occurred in the Abashiri-Ohmu area (N44.3, E143.5), Hokkaido, northern Japan, on 12 May 1975. A numerical investigation is made of the foehn, using a 2-dimensional nonhydrostatic model.The foehn is well simulated, even without any diabatic heating in the presence of an inversion layer below 900hPa. This foehn is confirmed to be dynamically induced, and is an unsteady, highly nonlinear phenomenon. It is accompanied by an atmospheric bore (a shock-like disturbance propagating upstream) and an internal hydraulic jump (a shock-like disturbance propagating downstream), but no wave breaking (wave induced critical layer). The foehn of a homogeneous fluid (with constant mean velocity U and constant Brunt-Vaisala frequency N) is also simulated. It is accompanied by wave breaking and hydraulic jump, but no bore.A foehn index (a non-dimensionalized potential temperature rise on the lee slope) is introduced, and its dependence on the inverse Froude number (Nh/U) is examined for the 4-layered fluid of the Abashiri-Ohmu case and the homogeneous fluid. The critical mountain height for the occurrence of the foehn is found to be lower in the presence of an inversion layer below 900hPa than in the absence of an inversion layer.In addition, the foehn event in the Abashiri-Ohmu area is compared with that of the European Alps (Hoinka, 1985).