Investigation of Atmospheric Turbulence

Citation

MacCready, Paul Beattie (1952) Investigation of Atmospheric Turbulence. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/F8AR-VH67. https://resolver.caltech.edu/CaltechETD:etd-11032003-104542

Abstract

Satisfactory measurement techniques were developed which overcame the four principal experimental problems arising in the investigation of atmospheric turbulence. 1) The data are made reproducible for statistical analyses by recording them on a portable magnetic tape recorder. 2) Measurements at elevations up to several hundred meters are made feasible by the use of a multi-cable tethering system for a balloon which supports the measuring devices. 3) and 4) The problems of measuring wind velocity fluctuations over broad ranges (frequencies between 0 and 50 cycles per second, and magnitudes between 1/4 and 20 meters per second) are solved by using hot wire anemometers together with non-linear amplifiers. The statistical analysis of recordings made under various meteorological conditions indicates that Kolmogoroff's similarity hypothesis, concerning the isotropy of turbulence in a certain inertial sub-range of eddy sizes, is directly applicable to eddies of sizes ranging from under 10 cm. to dimensions larger than the elevation of measurement. Over this range the "2/3 law" holds for the autocorrelation coefficient and the "-5/3 law" holds for the energy spectrum, within the accuracy of the measurements. The large eddy limit of the range of the "2/3 law" appears to be considerably extended by strong thermal instability. Heat flux measurements from the correlation between temperature and vertical velocity agree reasonably with the heat flux measured with heat meters. At 70 cm. under moderate wind conditions over half the heat flux is due to eddies of periods less than two seconds. Momentum flux measurements from velocity correlations were inconclusive.

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