A numerical study of deep three-dimensional mountain waves over the Southern Andes and Drake Passage

The atmospheric component of the Navy's Coupled Ocean-Atmospheric Mesoscale Prediction System (COAMPS) has been applied over the Southern Andes and the Drake Passage to examine the launching, propagation, and breakdown of mountain waves during the period of the austral winter 2009. The simulations show that the deep westerly jet aloft associated with the polar low inhibits breakdown of mountain waves in the troposphere and lower stratosphere. In several simulations, mountain waves are present over the eastern slope of the Andes in the troposphere, with phase lines nearly oriented parallel to the Andes ridge, and in the lower stratosphere (i.e., between 15-25 km above MSL), the waves extend southeastward, almost across the Drake Passage (i.e., ~1000 km away from the wave source). The three-dimensional characteristics of the simulated waves and the underlying dynamics are further investigated using linear analytical tools. The model diagnosis and theoretical analysis indicate that the horizontal propagation of mountain waves to the southeast of the Andes in the lower stratosphere are induced by strong lateral wind shears and the curvature of the westerly jet associated with the polar-vortex.