STUDY OF ACOUSTIC-GRAVITY WAVE SPECTRA IN THE ATMOSPHERE USING MESOSPHERE-STRATOSPHERE- TROPOSPHERE RADAR (PROPAGATION, UNIVERSAL SPECTRUM).

摘要

Current research indicates that acoustic-gravity waves can greatly influence the large-scale dynamics of the middle atmosphere. The morphology and structure of the atmospheric processes which cause this phenomenon can be better understood by the study of acoustic-gravity wave spectra. In order to use the meso-scale wind fluctuation data measured by MST radars to investigate such spectra, it is necessary to apply the relation between the observed wind fluctuation spectrum and the wave spectrum. The correct relationship is quantitatively derived in this study, based on acoustic-gravity wave theory and radar observation principle. Theoretical spectra are computed for a vertically and azimuthally symmetric wave model and also for a more general asymmetric model. Examples are given to show how the theoretical results can be used to interpret the one-dimensional observational data as well as to derive parameters for the model wave spectrum. The Doppler shift produced by the presence of a horizontal background wind is also examined since it leads to a redistribution of power in the observed frequency spectrum. The model is also generalized in order to determine the conditions for which the extended radar beam-width can affect the observed spectrum. An interpretation is further made of a two-dimensional observed spectrum by comparison to the two-dimensional model spectrum. The theoretical results are used to propose additional tests for the consistency of the acoustic-gravity wave model for atmospheric wind fluctuations.