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D. E. Fitzjarrald

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D. E. Fitzjarrald

Abstract

Measurements during periods of atmospheric free convection have been made using acoustic echo sounders and conventional wind sensors on a meteorological tower. Comparison of data from the two instrument systems shows good agreement. Fourier analysis of the data indicates that the predominant horizontal scales of motion are approximately six times the depth of the convecting layer, in good agreement with laboratory convection experiments.

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D. E. Fitzjarrald

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An experiment has been constructed which yields a vortex flow similar in many respects to atmospheric dust devils. Measurements were made of air velocity and temperature in the vortex core. These results were compared with a theoretical model of the flow, with velocities measured in real dust devils, and with the results of previous researchers who used a non-convective vortex. Observations were made of the different types of vortex flows found in the chamber and their dependence on the controlling parameters.

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D. E. Fitzjarrald

Abstract

An investigation of the dominant horizontal scale of motion in free convection, using data from GATE, principally from the NOAA acoustic sounder, is described. The horizontal scale was seen to vary from two times the depth of the convection layer at high instabilities to six times the depth at low instabilities. Aircraft data indicate the dominance of similar scales of motion. Small-scale humidity fluctuations were found to contribute approximately 30% of the acoustic echo intensity, with the remainder due to fluctuations of temperature.

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D. E. Fitzjarrald

Abstract

A field observation program was conducted at El Mirage, Calif., to investigate some aspects of the interaction between dust devils and their environment. The outputs of sensors designed to measure vertical vorticity were recorded, together with those of cup anemometers. Analysis of the data indicates that there is no correlation between the sense of rotation of the vorticity meter and that of dust devils crossing the observing area.

Tangential velocity, vertical velocity and temperature were determined in 11 dust devils. Maximum vertical velocities were seen to be much less than tangential velocities, indicating that the boundary layer height extended well above the height of measurement.

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