Regional Mountain Torque Estimates over the Rocky Mountains in Lee Cyclones

Abstract The zonal mountain pressure torque across a portion of the Rocky Mountains is estimated for three lee cyclones simulated with the National Centers for Environmental Prediction’s Eta model. The relative importance of the mountain torque to the regional balance of atmospheric angular momentum is examined through the use of a momentum budget. The magnitude of the regional mountain torque is generally greater than that of the tendency of atmospheric angular momentum, and the torque’s negative sign at all times in all cases examined indicates the transfer of angular momentum from the atmosphere to the earth. The average mountain torque associated with the strongest lee cyclone is found to be the same magnitude and sign as the tendency of global atmospheric angular momentum during the time frame of the simulation, and the cyclone is concurrent with the maximum negative tendency observed during the month. Estimates of the friction torque suggest that this force also transfers momentum to the earth over ...