Observational Evidence of a Saturated Gravity Wave Spectrum in the Troposphere and Lower Stratosphere

Abstract

Radial velocity and temperature data obtained at the MU Radar Observatory during October and November 1986 are used to examine the character of the motion spectrum in the troposphere and lower stratosphere. It is found that the spectrum is dominated by low-frequency gravity waves with an upward sense of propagation in the lower stratosphere and both upward and downward propagation in the troposphere. Vertical wavenumber spectra of velocity and temperature are used to examine the consistency of the motion spectrum with the saturated spectrum of gravity waves proposed by Smith et al. Results indicate excellent agreement of the observed and predicted velocity and temperature spectra in both amplitude and slope. Vertical wavenumber spectra in area-preserving form reveal a dominant vertical wavelength of ∼2.5 km, systematic variations in energy density and the dominant vertical scale with time, and consistency between the temporal variations of velocity and temperature variance. Taken together, our results provide strong support both for the view that velocity and temperature fluctuations are due primarily to internal gravity waves and for the saturated spectrum theory and its imposed constraints on wave amplitudes and spectral shape.