Comparison of spatial pattern and mechanism between convexity and gap winds

Abstract

This study uses a numerical model to examine how a convex feature and a gap feature in a mountain range affect the leeward wind field. In the "convexity case", the mountain ridge has a convex feature (viewed from above). In the "gap case", the mountain ridge has a gap. The results show that both cases have local winds at the surface exceeding 8 m s -1 , and both have similar spatial flow-patterns. However, the momentum budgets at the strongwind regions differ between the cases. In the convexity case, the downdrafts are important in the momentum balance, whereas in the gap case, both the downdrafts and the pressure-gradient force are important. Thus, although their spatial patterns of surface wind are similar to each other, their mechanisms for producing a strong local wind differ. Sensitivity experiments of Fr m show that strong-wind appears in both the convexity and gap cases when Fr m is between 0.42 and 1.04. In contrast, when Fr m is 0.21, strong winds only appear in the gap case because the flow can go around the gap. When Fr m exceeds 1.25, strong surface winds appear in the entire leeward plain.