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DIURNAL VARIATIONS IN BOUNDARY LAYER WINDS OVER THE SOUTH-CENTRAL UNITED STATES IN SUMMER

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  • 1 Department of Meteorology, University of California, Los Angeles, Calif.
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Abstract

Analysis of 1 week's data in August 1960 shows significant diurnal variations in surface geostrophic wind over the south-central United States. The oscillation in the southerly component (Vg) is driven by the response of the thermal wind to the diurnal temperature cycle over sloping terrain. A smaller oscillation in Ug derives from spatial variations in the amplitude of the diurnal pressure wave. The amplitude of the oscillation in Vg is about 3 to 5 m sec–1 at the surface, decaying exponentially with height to near 0 at 2 km.

Examination of 11 yr of summertime rawinsonde data at Fort Worth, Tex., shows a very regular diurnal variation in boundary layer wind with maximum amplitude of about 3 m sec–1 at 600 m above the ground. This oscillation is forced by periodic variations in both eddy viscosity and geostrophic wind. Using a simplified model of the boundary layer, we obtain solutions for the diurnally periodic wind resulting from “reasonable” variations in eddy viscosity and “observed” variations in geostrophic wind.

Now at the Techniques Development Laboratory, Weather Bureau, ESSA, Silver Spring, Md.

Now at the University of Utah at Salt Lake City

Abstract

Analysis of 1 week's data in August 1960 shows significant diurnal variations in surface geostrophic wind over the south-central United States. The oscillation in the southerly component (Vg) is driven by the response of the thermal wind to the diurnal temperature cycle over sloping terrain. A smaller oscillation in Ug derives from spatial variations in the amplitude of the diurnal pressure wave. The amplitude of the oscillation in Vg is about 3 to 5 m sec–1 at the surface, decaying exponentially with height to near 0 at 2 km.

Examination of 11 yr of summertime rawinsonde data at Fort Worth, Tex., shows a very regular diurnal variation in boundary layer wind with maximum amplitude of about 3 m sec–1 at 600 m above the ground. This oscillation is forced by periodic variations in both eddy viscosity and geostrophic wind. Using a simplified model of the boundary layer, we obtain solutions for the diurnally periodic wind resulting from “reasonable” variations in eddy viscosity and “observed” variations in geostrophic wind.

Now at the Techniques Development Laboratory, Weather Bureau, ESSA, Silver Spring, Md.

Now at the University of Utah at Salt Lake City

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