THERMALLY INDUCED FLOW IN VALLEYS WITH TRIBUTARIES .2. RESPONSE TO COOLING

We use the same model as in part I of this paper to study the flow in a main valley with tributaries induced by constant surface cooling switched on at t=0. Nearly all experiments discussed in part I are repeated for the nocturnal situation. By and large we find that the valley flow problem as posed here is linear in that the gross features of night-time flow can be predicted on the basis of the corresponding day-time experiment. An obvious and important exception is the increase of stability during the night in contrast to a decrease during the day. Correspondingly the speed of propagation of valley wind systems is larger during the night and, therefore, tributaries affect the flow in the main valley over larger distances than during the day. In particular, the outflow at the mouth of the main valley is influenced by tributaries more strongly than the inflow during the day. © 1990 Springer-Verlag.