WMOD00511

• Title: Precipitation Guage Testing on the Wasatch Plateau, Utah, During Early 1993
• Date: 11/1/1993
• State: UT
• Weather Modification - Doc Type: Report

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684

B, SEVRUK AND L ZAHLAVOVA

UH

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H

h

Zo

a = 00

; h; i H ;-1
Uh = UH! log ZO,! tlog r; !

UH

r

....
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- - -(<a- fa>'....
2 --....
-- _::~

H

h

Zo

:;

8
a = ~2: an
1
Uha. = UH \.Iog ~Hlog ~r [1- 0.024<<)

Figure 3. Wind speed profiles for open (top) and partly protected (bottom) gauge sites. The standard measurements of wind speed,
UH, taken at the height, H, above ground are reduced to the level, h, of the precipitation gauge orifice (Uh). using a logarithmic wind
profile and the average vertical angle, :i, of obstacles (see equation (I)).

Figure 3 explains the variables. It shows the difference between the wind profiles for an open exposed
site without obstacles, and a partly protected site where the original logarithmic wind profile is distorted
by houses and trees in the way expressed by Fedorova (1966) in equation (1) using IX.
Equation (I) was derived empirically from monthly values of wind speeds measured simultaneously at
heights of 2 m and between 10 and 20 m at 60 stations situated on flat terrain in different climatic zones
in Russia. It has also been tested with good results in Switzerland for various kinds of terrain (Sevruk, 1988).
Generally, the variables in equation (1), with the exception of roughness length, Zo, and IX are known at
precipitation gauge sites from the direct measurement of wind speed. The value of Zo can be estimated by
rule of thumb as one-eighth of the height of the vegetation cover (crop, turf) surrounding the gauge, or as
equal to 0.03 m for the summer season and between 0,005 and 0.02 m for the winter season, depending on
the conditions of snow cover (Sevruk, 1986b).

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