Buoyancy waves in the troposphere: Doppler radar observations and a theoretical model

On 15‐16 April 1976 a polar‐front jet stream with northward winds as large as 70 m/s passed over Colorado. Profiles of the radial component of the velocity v r and refractivity turbulence structure constant C n ² were observed by the Sunset VHF pulsed Doppler radar, near Boulder, CO, from near the ground up to about 15km, with 67s time resolution and lkm height resolution. While the jet stream was overhead, v r and C n ² fluctuated continuously with time scales from a few minutes up to hours. On several occasions coherent wave trains with periods ranging from 4 to 8 minutes were observed. The corresponding pressure perturbations at the ground were measured by a nearby microbarograph array. One of these events is discussed here. These observations are compared with the results of a linear stability analysis of the background wind and temperature profiles. The theoretical predictions of the period, wavelength, and phase speed, and the corresponding height variations of the phase and amplitude of the perturbation velocity along the radar beam all agree well with the observations. This agreement demonstrates that (1) the short‐period waves were generated by shear instability on the bottom of the jet stream and (2) linear theory can adequately describe many features of buoyancy waves generated by dynamic instability.