Mesoscale Wind and Temperature Fields Related to an Occurrence of Moderate Turbulence Measured in the Stratosphere Above Death Valley

Abstract

A specially instrumented NASA B-57B Canberra, capable of measuring turbulence velocities, winds and temperatures, flew several data runs on 26 March 1975 at 13 km altitude, east of the Sierra Nevada mountains of California. An area of light to moderate clear air turbulence extended for 120 km and contained zones of more intense turbulence. One zone, 10?20 km wide, occurred in a warm region centered over Death Valley. Significant variations of meteorological parameters included a wind shift of 13 m s?1 and 40° in 7 km, temperature changes of 3.5?5°C in 0.02 to 0.12 km, and variations in the mean vertical turbulence velocity of 3?4 m s?1 over distances of 15?25 km. The turbulence apparently originated after atmospheric waves had formed along show interfaces where low-velocity stratospheric air descended into a region of strong winds above Death Valley. The waves were amplified and broke down into turbulence when large vertical shear reduced the Richardson number below the critical value.