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Can a VHF Doppler Radar Provide Synoptic Wind Data? A Comparison of 30 Days of Radar and Radiosonde Data

Miguel Folkmar LarsenSchool of Electrical Engineering, Cornell University, Ithaca, NY 14853

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Abstract

A number of experiments have shown that UHF and VHF Doppler radars can make “clear air” wind measurements in the troposphere and lower stratosphere, even in the presence of clouds and precipitation. Past comparisons of radar and rawinsonde profiles for a single day have shown good agreement between the two within the limitations imposed by the spatial separation between the two measurements. However, the accuracy of the measurement does not insure that the data are synoptically significant. A comparison of 30 days of radiosonde geopotential height and wind data and radar data from Alaska was carried out to determine the applicability of the radar data to synoptic meteorology.

Rawinsonde and radar wind time series at six heights between 3.79 and 14.79 km altitude were compared and the rms differences calculated. The two independent wind measurements were also compared to the geostrophic wind obtained from the geopotential height fields generated by applying the Cressman objectives analysis scheme to data from five radiosonde stations surrounding the radar site. The two independent wind measurements were most similar with a difference of 3–4 m s−1. The radar and balloon winds both differed from the geostrophic winds by 5–6 m s−1. The rms differences decreased when the radar winds were averaged over longer time intervals. The cross correlation between the measured and geostrophic winds was found to be ∼0.75 and essentially independent of height over the altitude range studied.

Abstract

A number of experiments have shown that UHF and VHF Doppler radars can make “clear air” wind measurements in the troposphere and lower stratosphere, even in the presence of clouds and precipitation. Past comparisons of radar and rawinsonde profiles for a single day have shown good agreement between the two within the limitations imposed by the spatial separation between the two measurements. However, the accuracy of the measurement does not insure that the data are synoptically significant. A comparison of 30 days of radiosonde geopotential height and wind data and radar data from Alaska was carried out to determine the applicability of the radar data to synoptic meteorology.

Rawinsonde and radar wind time series at six heights between 3.79 and 14.79 km altitude were compared and the rms differences calculated. The two independent wind measurements were also compared to the geostrophic wind obtained from the geopotential height fields generated by applying the Cressman objectives analysis scheme to data from five radiosonde stations surrounding the radar site. The two independent wind measurements were most similar with a difference of 3–4 m s−1. The radar and balloon winds both differed from the geostrophic winds by 5–6 m s−1. The rms differences decreased when the radar winds were averaged over longer time intervals. The cross correlation between the measured and geostrophic winds was found to be ∼0.75 and essentially independent of height over the altitude range studied.

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