This is a continuation of a recent study on medium range numerical weather prediction utilizing a global spectral model and FGGE/MONEX observations.In the present study the impact of diabatic initialization and steep orography over the monsoon region are examined in a number of medium range numerical prediction experiments.The steep orography is the so-called 'Envelope Orography' which is almost a kilometer higher than the conventional orography over most major global mountain chains. The physical initialization, proposed here, contains a reconstruction of the humidity field such that a close balance between the advective and the radiative forcing is achieved over most of the rain-free areas. Over the tropical rain areas the humidity analysis is structured to a cumulus parameterization scheme of the global spectral model and the observed rain. The initial observations of the rain come from a mix of satellite and surface based observations.The proposed physical initialization recovers a substantial part of the observed rain.Two interesting prediction experiments on tropical cyclogenesis-one on the formation of the onset vortex and the other on the formation of a monsoon depression are described in the context of the physical initialization and steep orography.In both cases realistic forecasts on the medium range time frame are obtained.A realistic track (or motion) of the Arabian Sea onset vortex was obtained with the steeper orography.The storm was noted to move too far inland when a smoothed orography was used. The experiments on the Bay of Bengal depression show a major improvement with the physical initialization. The formation and track up to 6 days is in close agreement with observations.The major result of this study is on the prediction of the time averaged motion field or the stationary components.Results of four medium range prediction experiments from the winter and summer FGGE periods are illustrated.These 7 to 10 day averaged motion fields contain details on many spatial scales, most of these details are reasonably simulated by the prediction.This success in the prediction of the stationary component of the flow field is attributable to the improved physical parameterization in the model.

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Numerical experiments of tropical cyclones are performed using a moving variable grid scheme proposed by Kitade (1979). The formulation for parameterization of cumulus convection is based on the concept of penetrative convection. The physical processes, such as the surface friction, latent and sensible heat supplies from sea surface, eddy dissipation and diffusion, dry convective adjustment and large-scale condensation, are also contained with conventional ways in present model.The initial vortex develops into a mature disturbance in about 2 days. Its structure is similar to that of the tropical cyclone in the real atmosphere and that in numerical experiments performed by many researchers.The simulated tropical cyclone has some asymmetric features due to the variable Coriolis parameter in spite of the adoption of an initial nearly symmetric vortex. Furthermore, the developed tropical cyclone has dynamically unstable regions in the upper layer, which may also contribute to the asymmetry of the simulated vortex.The simulated vortex moves north-north-westward, which is due to the effect of variable Coriolis parameter pointed out by Rossby (1948). The moderate tropical cyclone moves at a speed of about 3 km hour-1 for westward and at about 7 km hour-1 for northward components. The meandering about the mean path occurs with a period of about 25 hours, which seems to be due to the Magnus effect suggested by Yeh (1950).When the sea surface temperature is changed, the path of the vortex center is deviated a little from that in the basic experiment. The deviation is partly explained for the following reason. The strength of vortex is strongly influenced by sea surface temperature.According to Rossby (1948), on the other hand, the northward acceleration due to variable Coriolis parameter increases with the increase of strength of vortex. Therefore the sea surface temperature affects the path of vortex. The variation of speed of vortex movement through its life cycle is also understandable from such point of view. It is confirmed by an experiment with non-uniform sea surface temperature that the asymmetric heating of cumulus convection affects the path of the vortex center.

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The movement of the cyclonic vortex is examined by some numerical experiments of barotropic models. It is confirmed that the northward acceleration of axially symmetric non-divergent vortex on a *-plane is proportional to the scale and the strength of the vortex, which was predicted by Rossby (1948). It is found that the accelerative motion is accompanied by the motion with a nearly constant northward speed. The speed is approximately represented by the relation Cy=0.52*0.6L01.2U00.4 in the range of BL02/U0<0.01, where