On the spectrum of atmospheric velocity fluctuations seen by MST/ST radar and their interpretation

Abstract

We consider the observations of the spectrum of atmospheric motions over the range of periods from a few minutes to many hours that have been made with ST/MST radars in the past 5 years. This range of periods includes the periods associated with buoyancy waves and the scale of atmospheric motions often referred to by meteorologists as the mesoscale. We consider the spectra of both horizontal and vertical velocities and examine their interpretation in terms of buoyancy wave theory and turbulence theory. To help in interpreting these spectra we present some recently determined aircraft wavenumber spectra. It is found that radar and aircraft horizontal wind spectra are in reasonable accord with expectations from quasi two‐dimensional turbulence theory. The vertical velocity spectra are believed to be due to waves. Comparison of the energy levels and shapes of the horizontal and vertical velocity spectra are not consistent with existing models of internal wave spectra. However, it is possible that these inconsistencies arise from Doppler‐shifting effects that are not taken into account in existing internal wave models. Nevertheless, we stress that all the observations we have examined support the hypothesis that quasi two‐dimensional turbulence coexists with a nearly universal spectrum of buoyancy waves. Copyright 1985 by the American Geophysical Union.