MST Radar Observations of Gravity Waves and Turbulence near Thunderstorms

The effect of deep convection on the intensities of gravity waves and turbulence during the summer at White Sands, New Mexico, is investigated using 50-MHz mesosphere–stratosphere–troposphere (MST) radar observations and surface weather reports. Radar data taken at 3-min intervals from the summers of 1991 through 1996 (with occasional gaps of varying length) are used to construct hourly means, medians, and standard deviations of wind speed, spectral width ( ), and backscattered power calibrated as the refractivity turbulence 2 s turb structure constant ( ). The hourly variance of the vertical velocity is used as an indicator of high-frequency 2 2 C s n w gravity wave intensity. Surface observations taken near the radar site are used to identify periods marked by convection at or near the radar. During cases in which no convection is reported, the median hourly is nearly 2 sw constant with altitude (about 0.04 m2 s22 below and 0.03 m2 s22 above the tropopause). Values of , , and 2 2 s C w n are significantly enhanced from no-convection cases to thunderstorm cases. Largest increases are about 12 2 s turb dB relative to the no-convection cases at about 11 km for , about 9.5 km for , and about 7.5 km for 2 2 s s w turb . The relatively lower height for the maximum of is likely due to the influence of humidity advected 2 2 C C n n upward during convection on the mean gradient of the refractive index. The probability density distributions of and near their levels of maximum enhancement are unimodal, with the modes steadily increasing with 2 2 C s n turb increasing proximity of convection. However, the probability density distribution of is bimodal in all instances, 2 sw suggesting that there can be enhanced wave activity even when visible convection is not present and that the presence of a thunderstorm at the station does not necessarily indicate greatly enhanced wave activity.