Atmospheric Gravity Waves from Winds and Storms

Abstract

Atmospheric gravity waves were explored on the leeward side of the north-south trending Continental Divide in Colorado by using an array of electronic microbarographs and recording anemometers. Observations of low-velocity gravity waves in a two-to-three octave region for wave periods of 3?24 min were made. These waves are apparently caused by locally generated signals from upper tropospheric winds, jet streams, weather fronts, thunderstorms, and severe weather, with shear the principal mechanism. Lee waves and moderate-to-severe turbulence were frequently observed in conjunction with the appearance of gravity waves generated at mountain-top level. A unique wave source is identified due to the interaction of down-slope winds on the leeward side of a mountain and an inversion-layer boundary. Weather fronts on some occasions seem to provide a passive boundary layer for the production of waves, but in other cases they may actively generate waves. Readings on summer thunderstorms indicate that an early arrival in the gravity-wave train is an exponential pressure pulse, or gust, resulting from a downward-accelerating air parcel within the storm cell as it reaches maturity. An anemometer was found to be an essential companion tool to the microbarograph for a full understanding of the wave phenomena. Detailed weather information from the Denver station of the National Weather Service near the recording sites was used to supplement the basic data.