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James B. Harrington
Thomas R. Heddinghaus


Power spectra of mesoscale eddies with periods ranging from 10 min to 8 hr were computed for the months of January and July from three years of surface wind data obtained at Columbia, Mo. To educe the degree of determinism in the spectra, their variability with time of year, time of day, wind speed and direction, and with the presence or absence of thunderstorms was measured.

Diurnal spectra for January and July were found to be similar. A comparison of semidiurnal daytime and nighttime spectra showed that the former contained considerably more energy than the latter and that the difference was greater in July than in January. The eddy energy was shown to increase by a factor of approximately 7 at night in the presence of thunderstorms. No effect of wind direction could be found.

Over a large portion of the lower mesoscale range the diurnal power spectra followed a −1 law, similar to that for “wall turbulence” in the layer of strong shear in the boundary layer over a flat plate.

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