A Preliminary Climatology of the Spectrum of Vertical Velocity Observed by Clear-Air Doppler Radar

Abstract

Multiheight time series of atmospheric vertical velocities in the troposphere and lower stratosphere observed by clear-air Doppler radar are presented at various locations around the world. Frequency spectra of vertical velocities determined from these data sets are compared with the objective of developing a preliminary climatology. We emphasize the nearly universal shape and magnitude of spectra observed during low-wind conditions. These spectra are quite flat for frequencies between the buoyancy and inertial frequencies, and they closely resemble the internal wave spectra observed in the ocean. Spectra observed under strong wind conditions, on the other hand, are greatly enhanced in magnitude, approaching the f^−5/3 spectral slope observed for the spectrum of horizontal motions. Finally, spectra determined from both quiet and active periods at Poker Flat, Alaska, possess spectral slopes and amplitudes intermediate to those spectra determined solely from quiet or active periods at other locations.