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

Abstract

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 vr and refractivity turbulence structure constant Cn² 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, vr and Cn² 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.

Detection of Kelvin‐Helmholtz instability with the Indian mesosphere‐stratosphere‐troposphere radar: A case study

“…We are aware that in the offzenith beams the Doppler width could be severely contaminated owing to the shear broadening and the beam-broadening effects. [Klostermeyer andRuster, 1980, 1981;Ruster and Klostermeyer, 1983] or at the mesospheric heights [Vanzandt et al, 1979]. In the present study we have found KHI occurring at 17.7 km, just above the meteorological tropopause.…”

Observations of Kelvin‐Helmholtz instability at a cloud base with the middle and upper atmosphere (MU) and weather radars

“…These features suggest that these structures are strongly turbulent. VanZandt et al [1979] and Rüster [1980, 1981] observed enhanced echo power with off-zenith beams of VHF radars in the environment of KH instabilities. The authors attributed these echoes to turbulence produced by smaller-scale secondary instabilities.…”

“…Mesosphere‐stratosphere‐troposphere (MST) radars can also be used for studying KH instabilities in the atmosphere [e.g., Röttger and Schmidt , 1979; VanZandt et al , 1979; Klostermeyer and Rüster , 1980, 1981; Singh et al , 1999; Yamamoto et al , 2003; Kelley et al , 2005]. The development of frequency domain interferometry (FDI) techniques (using two carrier frequencies or more and devoted to improve the range resolution of the MST radars) allowed direct observations of KH billows [e.g., Chilson et al , 1997, 2003; Luce et al , 2007, 2008].…”

The spectrum of atmospheric velocity fluctuations at 8 km and 86 km

“…Indeed, middle atmospheric dynamics is thought to be strongly affected by upward-propagating, tropospherically-generated internal gravity waves with periods between roughly 5 TM and a few hours (Hines, 1960;Gossard, 1962;Hines and Reddy, 1967;Lindzen, 1981). Radar observations of such waves have been reported by many groups (Rastogi and Woodman, 1974;Rastogi and Bowhill, 1976;Miller et al, 1978;R6ttger et al, 1978;VanZandt et al, 1979;Fukao et al, 1980;. Theoretically, such waves will grow as they propagate upward until they break up by nonlinear processes or are damped out by viscosity (Hodges, 1969;Hines and Reddy, 1967;Lindzen, 1981).…”