中層大気中の慣性重力波に関する統計的研究

Abstract

An analysis was made of the structure and behaviour of small-scale motions in the stratosphere and lower mesosphere with the aid of meteorological rocket observations over the period of six years from 1977 to 1982, covering the wide range of latitudes.By applying a filter to observed wind data with respect to height, wind fluctuations with characteristic vertical scales close to 10km are separated from large-scale components such as the mean field, planetary waves and tides.From the hodograph analysis it is found that at northern hemisphere stations most of horizontal wind vectors show the clockwise rotation with increasing height while they rotate anti-clockwise in the southern hemisphere. This strongly suggests that the wind fluctuations are due mainly to upward propagating inertia-gravity waves.On the basis of a simplified theory of inertia-gravity waves, the wave-frequency distribution is estimated statistically from the degree of elliptic polarization of holographs, and it is shown that the most predominant values of f/ω (f; the Coriolis parameter, ω; the intrinsic wave frequency) fall into a range of 0.2-0.4. Namely, the typical time scale of these waves is of the order of several hours in middle and high latitudes and of a day in low latitudes.Further discussions are made of the vertical profile of the wave energy density, and it is suggested, from the uniform decay of the wave amplitude with height that the wide spectra of horizontal phase velocities should be taken into account.