First results with the Adelaide VHF radar: spaced antenna studies of tropospheric winds

Abstract

The first results from a VHF radar of the ST type located at Buckland Park near Adelaide, Australia (35°S, 138°E), are presented. The radar is designed to be versatile and can be used to measure velocities in the lower atmosphere using both the spaced antenna (SA) and Doppler beam-swinging (DBS) techniques. Here studies of irregularities and motions made with the spaced antenna technique are discussed. It is shown that the scale of the diffraction pattern formed by the backscattered radiation varies with altitude, with the mean pattern scale being smaller in the troposphere than in the stratosphere. The observations are consistent with the backscattered energy decreasing as a function of off-vertical angle by 1.5 dB per degree in the troposphere and by about 2.8 dB per degree in the lower stratosphere. An intercomparison of zonal velocities measured with the SA and DBS methods shows good agreement. In May and August 1984 an extensive comparison was made between the velocities measured by the SA method and winds determined from over 80 balloon-borne radiosondes released from Adelaide Airport, situated some 36 km to the south of the radar. The velocities were compared on a statistical basis and showed excellent agreement, although the SA speeds tended to be 1–2 m s −1 smaller in magnitude than the radiosonde velocities. Overall, the rms differences between the two sets of measurements was only 3–4ms −1 throughout the troposphere, a result which is consistent with the random errors inherent in each technique, as well as the spatial separation between the radar and balloon observations. The utility of the SA method for meteorological observations is illustrated by a study of both the horizontal and vertical wind fields during the passage of a cold front made in November 1984. The high time resolution available with the radar allows detailed studies of the development of the pre-frontal jet, the wind convergence into the front and associated vertical motions.