Abstract
[1] The long-term development of short-period gravity waves is investigated using the analysis of temperature fluctuations in the mesosphere. The temperature fluctuations are quantified by their standard deviations σ based on data from OH measurements at Wuppertal (51°N, 7°E) and Hohenpeissenberg (48°N, 11°E) obtained from 1994 to 2009 at 87 km altitude. The temperatures are Fourier analyzed in the spectral regime of periods between 3 and 10 min. The resulting oscillation amplitudes correlate very well with the standard deviations. Shortest periods are taken as “ripples” that are indicative of atmospheric instabilities/breaking gravity waves. In consequence the standard deviations are used as proxies for gravity wave activity and dissipation. This data set is analyzed for seasonal, intradecadal, and interdecadal (trend) variations. Seasonal changes show a double peak structure with maxima occurring slightly before circulation turnaround in spring and autumn. This is found to be in close agreement with seasonal variations of turbulent eddy coefficients obtained from WACCM 3.5. The intradecadal variations show close correlations with the zonal wind and the annual amplitude of the mesopause temperature. The long-term trend (16 years) indicates an increase of gravity wave activity of 1.5% per year. Correspondences with dynamical parameters such as zonal wind speed and summer length are discussed.
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