VHF Doppler Radar Observations of Buoyancy Waves Associated with Thunderstorms

Abstract

The Platteville VHF Doppler radar, located on the Colorado piedmont near Platteville, Colorado, continuously measured the vertical wind velocity during a 12-day period in late July and early August 1981. Measurements were made every 2.5 min on the average with range gates centered at 3.3, 5.7, 8.1, 10.5, 12.9, 15.3, 17.7, and 20.1 km above sea level. Periods of active thunderstorms were identified from the PPI maps from the National Weather Service 10 cm weather radar at Limon, Colorado. When no thunderstorm activity was present, the vertical velocity fluctuations were small and erratic. But a few hours after strong thunderstorm activity began, large quasi-sinusoidal wave trains with periods of about 40 min were observed. Power spectra of the vertical velocity time series showed enhancements at all frequencies during thunderstorm activity, but for periods longer than 30 min the enhancements were larger, particularly for the mid-tropospheric range gates from 5.7 to 12.9 km. Some of the implications of these observations on the relations between thunderstorms and buoyancy waves in the free atmosphere are discussed.