Effects of Internal Gravity Waves on Energy Budgets and the Vertical Transport of Angular Momentum Over Mountainous Terrain

Abstract

High-resolution pictures obtained with a handheld camera during the earth-orbiting photographic mission of the Apollo 9 spacecraft provided a unique opportunity to map the areal extent of gravity waves over the southwestern United States. The gravity waves were manifested in thin layers of middle- and high-cloud patterns over the rugged terrain of Arizona, Colorado, and New Mexico. Zonal shearing stress gradients in stably stratified air flowing over rugged mountain terrain indicated very large subgrid-scale vertical fluxes of zonal momentum. Maximum stress values of several tens of dynes·cm−2 (10−3 mb) were calculated for the lower tropospheric layers where the air flowed over the high Rocky Mountains of central New Mexico. The vertical fluxes of zonal momentum were directed upward to tropopause levels when extensive areas of gravity waves covered eastern Arizona, New Mexico, and western Texas. The potential energy contained in the wave population attained values through the troposphere as high as 9.3× 105 J·m−2; this potential energy was a substantial part of the atmospheric energy budget. The residual “dissipation” term in the kinetic energy budget indicated a subgrid-scale flux of energy downward from the lower stratosphere concurrent with the upward flux of zonal momentum in the troposphere. Atmospheric turbulence exhibited a maximum during the wave occurrence, diminishing gradually thereafter.