Persistence Of Small Scale Features In The Mesospheric Wind Field

A special series of nine paired ROBIN falling sphere soundings was obtained over a six-hour period on 6 March 1965, as part of an investigation into the small-scale features of the wind field in the upper stratosphere and lower mesosphere. These soundings allow a simultaneous analysis of the temporal and spatial extent of the observed wave-like variations of the zonal wind. In the mesosphere (the altitude interval between 45 and 60 km) such variations are persistent. Individual features are followed throughout the six-hour observation program, and laterally extended. Soundings separated by 50 km show quite good correspondence among gross features. The interpretation of the wind oscillations as evidence of internal waves is considered, and horizontal and vertical wave parameters are determined. Vertical wavelengths are computed to be of the order of 3 km, while horizontal wave lengths are determined to be about 400 km, leading to a horizontal/vertical scale ratio of 120:1. There are also suggestions of horizontal and vertical wave amplitudes of about 5 m/sec and 4 cm/sec, and periods of oscillation of about 13 hours. (Author).

This report presents an analysis of the monthly mean zonal wind and the standard deviation of the zonal wind about the monthly mean. The data are presented in tables and the analyses in time (months)-altitude (30 to 60 kilometers) cross-section as well as profiles for selected levels. The variability of the monthly mean zonal wind, 30 to 60 kilometers, is discussed by individual station. Also, there is a discussion of the altitudinal, latitudinal, monthly, and seasonal variations with a designation of four seasons - winter (dominated by westerlies but with occasional easterlies). November through March; spring transition of westerlies to easterlies, April and May; summer (persistent easterlies), June through August; and fall transition of easterlies to westerlies, September and October.

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