Mountain Torques in the Global Angular Momentum Balance

Abstract

Based on recently published mean maps, the torques upon the atmosphere owing to pressure differences between the west and east faces of mountain ranges are computed for the whole earth, for four midseason months. Considering the year as a whole, mountain torques are eastward in high and low latitudes, and westward in middle latitudes. Individual mountain complexes have mixed effects; the greatest drain of momentum is by the relatively low mountains of eastern Siberia while the average effect of the Himalayas is small. The momentum drain by the Andes is greatest in summer, while in winter their influence is overcome by the eastward torque of Africa. Seasonal variations are greatest near latitudes 15°, where in the winter of each hemisphere there is an eastward pressure torque that reverses to westward in summer. Relative to frictional torques, mountain torques are greatest in middle northern latitudes in April and July, when they approach the same magnitude.