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  • Author or Editor: Marilyn M. Wolfson x
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Marilyn M. Wolfson

Abstract

This report describes in detail the FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) automatic weather station network which is being used in the Terminal Doppler Weather Radar program to assess the radar detectability of wind shear and to help gain an understanding of microburst forcing mechanisms. The weather stations are descended from the PROBE stations originally operated by the Bureau of Reclamation. The current instrumentation has been modified slightly but is largely the same as that originally used as is the hardware structure, but the data collection platforms are entirely new. Each station in the 30-station network transmits 1 min averages of temperature, relative humidity, barometric pressure, wind speed, wind direction and precipitation amounts, as well as peak wind speed, on a single GOES satellite channel.

Performance results from the first 3 yr (1984–86) of mesonet operations are presented. During June and July 1986 the FLOWS network was collocated with the NCAR PAM-II network near Huntsville, Alabama to measure surface data on microbursts as part of the Cooperative Huntsville Meteorological Experiment (COHMEX). A preliminary assessment of the overall performance of the two networks suggests that they performed with comparable accuracy for those meteorological characteristics most important to the detection of microbursts. While differences and discrepancies were noted, none would preclude treating PAM-II and FLOWS data together as if they were generated by a single network.

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Marilyn M. Wolfson and T. Theodore Fujita

Abstract

The effects of obstructions on winds measured by the 30 station FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) mesonet and the 6 station FAA LLWAS (Low Level Wind Shear Alèrt System) near Memphis, TN in 1985 are analyzed. The slowing of surface winds by anemometer site obstructions is a continuing problem for scientific and operational wind shear measurement system This paper considers an improved version of the technique used by Fujita and Wakimoto for compensating the obstruction effects by the use of mathematical models relating the unobstructed wind speed to the measured wind speed and the observed obstructions at each site. Over eight million wind speed measurements gathered over 197 days (15 February–31 August) were used. The effects of obstructions at a particular site were evidenced by a strong negative correlation between the observed wind speed transmission factors and the obstruction angles as measured from panoramic photographs taken of the horizon around each station. The functional relationship between them was modeled as a decaying exponential plus a constant, and an iterative least squares regression technique was used on data from all of the stations at once in deriving the three parameters of the equation. It was found that the first 8° of obstruction have the greatest blockage effects, and that even a 2° or 3° high isolated clump of trees can have a pronounced effect on the measured wind speeds from that direction. The possibility that the transmission factors are scale dependent and time dependent is explored.

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