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Observations of Thunderstorm Reflectivities and Doppler Velocities Measured at VHF and UHF

M. F. LarsenDepartment of Physics and Astronomy, Clemson University, Clemson, SC 29631

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J. RöttgerEISCAT Scientific Association, S-98127 Kiruna, Sweden

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Abstract

We compare observations of thunderstorms made with two radars operating at different wavelengths of 70 cm and 5.67 m. The first set of observations was made with the UHF radar at the Arecibo Observatory in Puerto Rico, and the second was made with the Max-Planck-Institut für Aeronomie VHF radar in the Harz Mountains in West Germany. Both sets of observations show large echo strengths during periods of convective activity. We show, based on the observational data and calculations, that precipitation completely dominates the UHF signals. In fact, a sensitive UHF radar such as at the Arecibo facility is a good tool for investigating cloud droplet distributions in the upper parts of the clouds. The signal at VHF has contributions from both precipitation and the turbulent scatter, and the two contributions can easily be separated since the droplet fall velocity and the updraft velocity are different, except for the smallest drop sizes. Our results show that VHF and UHF are potentially a good combination of frequencies for cloud physics research.

Abstract

We compare observations of thunderstorms made with two radars operating at different wavelengths of 70 cm and 5.67 m. The first set of observations was made with the UHF radar at the Arecibo Observatory in Puerto Rico, and the second was made with the Max-Planck-Institut für Aeronomie VHF radar in the Harz Mountains in West Germany. Both sets of observations show large echo strengths during periods of convective activity. We show, based on the observational data and calculations, that precipitation completely dominates the UHF signals. In fact, a sensitive UHF radar such as at the Arecibo facility is a good tool for investigating cloud droplet distributions in the upper parts of the clouds. The signal at VHF has contributions from both precipitation and the turbulent scatter, and the two contributions can easily be separated since the droplet fall velocity and the updraft velocity are different, except for the smallest drop sizes. Our results show that VHF and UHF are potentially a good combination of frequencies for cloud physics research.

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