MST Radar Observations of a Saturated Gravity Wave Spectrum

Abstract

We present vertical wavenumber spectra of mesoscale wind fluctuations using data observed in the troposphere, lower stratosphere and mesosphere by the MU radar at 35°N in Japan in October 1986 and June 1987, as well as lower stratospheric spectra obtained by the Arecibo UHF radar at 18°N in Puerto Rico in June 1983. These spectra are much more homogeneous than previously available spectra since all of the data were observed by the same radar technique, the data in the different atmospheric regions were taken essentially simultaneously, and all of the spectra were analyzed using very similar methods. In the large-wavenumber ranges of the observed spectra, the asymptomatic slopes and amplitudes agree well with the saturated gravity wave spectral model developed by Dewan and Good (1986) and Smith et al. (1987), which has a slope of ?3 and a spectral amplitude proportional to the buoyancy frequency squared. The good agreement between the model spectrum and the observed spectra from different altitudes, different reasons, and two different stations located at 35° and 18°N suggests that the model is essentially correct, in spite of the heuristic nature of some of its assumptions. The spectral densities of the zonal and meridional components are similar at large wavenumbers, while the meridional spectrum has larger energy density at small wavenumbers where the spectrum is not saturated. The dominant vertical scales of the gravity wave field in the mesosphere, lower stratosphere, and troposphere are estimated to be >10 km, 2.2 to 3.3 km, and ≥3.3 km in october and ≥4.5 km in June, respectively, consistent with determinations from previous studies.