Gravity-wave motions in the mesosphere

Abstract Partial reflection measurements of horizontal winds in the mesosphere and lower thermosphere made at Adelaide (35° S, 138° E) and Townsville (19°S, 147°E) have been spectrally analyzed as functions of frequency and wavenumber. The spectral densities of gravity wave motions observed at 85 km are found to follow a power law relation of the form f−k with k ~ 1.5, where f is the frequency. The functional form of the frequency spectra and the inferred rms amplitudes (~ 30 ms−1) agree well with other reported observations, which suggests there is some ‘universality’ to the gravity wave field in the mesosphere. A vector spectral decomposition of gravity wave wind vs height profiles shows that at least 65% of the vertical energy flux of long period gravity waves is upgoing. The wave number spectra show that the mean vertical wavelength is ~ 12 km, which implies horizontal scales ranging between about 4000 km for the quasi-inertial waves to ~ 50 km for the short period waves. The estimated vertical energy flux at the mesopause is ~ 10−2 Wm−2, a large fraction of which appears to be carried by the short period (

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