Abstract
To examine dynamical effects of mountains on a westerly jet numerical experiments are made using the model developed in Part I. The jet is forced directly in such a way that it is restored to a prescribed equilibrium state, in which it has no vertical shear. The temperature of the atmosphere has a constant lapse rate in the equilibrium state. Three types of mountains are considered. Their scales are of the order of that of the Tibetan Plateau. The first mountain has the smoothest slope at the side boundaries with the average inclination of 4km/20° and the second one has the sides with the slopes of the 4km/5°inclination. The last one has the vertical walls at the sides.
We examine two effects of mountains, that is, the blocking effect on the flow and the streching and shrinking effect of vortex tube over the mountain slopes. The latter effect produces stationary planetary waves coupled with the β-effect. The appearance of these effects depends on the steepness of mountains. The blocking effect is the weakest for the mountain with the smoothest side boundaries and is the strongest for the one with the vertical
walls. On the contrary, the stationary trough in the downstream of the mountain is the weakest for the mountain with the vertical walls and is the strongest for the one with the smoothest side boundaries. The Taylor column effect is important for the blocking of the westerly by the mountains.
Splitting of a westerly jet by the Tibetan Plateau is examined by the model simulation.
When the jet axis is located at the center or at the southern boundary of the mountain, the jet splits into northern and southern branches around the mountain. However, when it is located at the northern boundary, splitting is very weak. The result agrees well qualitatively with the observation of the seasonal change of the westerly jet over the Plateau.
