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Yutaka Izumi

Abstract

The evolution of the low-level temperature and velocity profiles observed at the Cedar Hill tower during the breakdown of a nocturnal inversion and the dissipation of a low-level jet on the morning of 15 March 1961 is presented and discussed. From past studies of low-level temperature variations, the observed evolution of the temperature profile appears to represent a common phenomenon. Its principal characteristics are warming at the upper levels of the tower before sunrise, increased warming at the upper levels immediately after sunrise, cooling in the middle between upper and lower layers of warming after sunrise, and subsequent lifting of the elevated inversion. Subsidence is suggested as the explanation for the upper-level warming. Turbulent mixing appears to play a major role in the breakdown of the inversion and in the dissipation of the low-level jet.

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Yutaka Izumi and Morton Barad

Abstract

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Yutaka Izumi and Henry A. Brown

Abstract

The time and height variations of temperature, wind speed, and moisture content observed at the Cedar Hill tower during the dissipation of a low-level jet on the morning of 14 May 1962 are presented and discussed. Three distinct stages of significant variations occur before sunrise at the upper levels of the tower. The three stages art: 1) a period of an abrupt and simultaneous warming and drying; 2) a period of steady temperature, mixing ratio, and wind speed; and 3) a period of pronounced decreases in temperature and wind speed and a marked increase in mixing ratio that occur progressively later with increasing height. It is proposed that these variations are produced by horizontal and vertical advection and by turbulent mixing.

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Yutaka Izumi and Morton L. Barad

Abstract

Wind tunnel and field experiments have shown that the fast-response three-component sonic anemometer is a highly accurate wind speed sensor. When sonic anemometers were used as reference sensors for wind speed, slower response cup anemometers were found to consistently overestimate the wind speed. Despite measures taken during a field program in Kansas to minimize tower influence on wind measurements, the errors due to the tower effect on the windward side are inferred to be about ±5% of the observed wind speed ratios of cup to sonic anemometers. When the observed speed ratios are compared with the errors due to tower influence, the overspeeding of the cup anemometer is estimated to be about 10% of the reference wind speed.

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Yutaka Izumi and Morton L. Barad

Abstract

The 1428-lt television transmitter tower, located at Cedar Hill, Texas, and instrumented to obtain continuous measurements of wind and temperature at 12 levels from 30 ft to 1420 ft above ground, is proving to be a useful research tool for investigating low-level meteorological phenomena, especially the low-level jet. During the night of 22–23 February 1961, a pronounced low-level jet was recorded. Systematic variations of wind speed and temperature with time and height will be discussed to illustrate the orderly development of the low-level jet, the upward growth of the nocturnal inversion, and the vertical extent of the mixing process within the deepening inversion.

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