The Role of Terrain and Pressure Stresses in Rocky Mountain Lee Cyclones

Abstract The earth–atmosphere exchange of storm absolute dynamic circulation by mountain-induced surface pressure stress and the response of the circulation in a Rocky Mountain Ice cyclone is examined. Surface pressure stresses that transfer horizontal momentum across the earth-atmosphere interface stem from the hydrostatic weight of the atmosphere resting against the inclined surfaces of orography. In a Ice cyclone. mass asymmetries must be combined with terrain variability for net transfer across the interface. Within the storm structure, the acceleration of the dynamic circulation by the pressure gradient force is determined by the line integral of the azimuthally directed components of pressure stress, in effect an angular momentum pressure torque. The pressure torque is compared to the tendencies of specific relative circulation and absolute dynamic circulation in a lee cyclone simulated by the eta model. The mountain-induced pressure torque is found to be negative in the lower layers of the cyclone ...