Examination of various techniques for measuring wind velocities using clear-air radars, with emphasis on vertical wind measurements

Abstract

In this work, I examine various techniques for measuring wind velocities using clear-air radars. Special emphasis has been given to the vertical wind measurements. All the observations were obtained in the lower atmosphere (below 20 km) using the Jicamarca 50 MHz radar system near Lima, Peru. I have concentrated my efforts on: (a) examining: different radar techniques for horizontal wind estimation, (b) improving the understanding of angle-of-arrival radar measurements, and (c) comparing a number of techniques for the measurement of the vertical wind velocities. I have measured horizontal wind velocities by a variety of both time- and frequency-domain spaced antenna (SA) techniques. Comparisons of these techniques for both zonal and meridional components have been carried out in a statistical sense. Two sets of data were analyzed under both "quiet" (low wind, low variability) and "active" (high wind, high variability) conditions. I have found that the simpler techniques that assume horizontally isotropic scattering compare well with the more complicated full correlation analysis techniques. Briefly, while all SA techniques give essentially the same horizontal wind direction, considerable discrepancies are apparent in the wind speed, particularly above 15 km. With regard to technique comparisons for vertical velocity, two types of measurement techniques using a concurrent data set are compared. Both Zenith (i.e., using a vertically-directed single beam) techniques and spaced antenna (SA) techniques are compared using a concurrent 5-day data set obtained with a special configuration of the Jicamarca 50 MHz radar antenna. Two separate Zenith techniques are implemented using different antenna beam-widths (a 0.85º and a 3º beam-width). Different SA approaches are also implemented using a: "quasi" Doppler beam swinging (DBS) approach and four "classical" SA approaches. "Classical" SA approaches make use of horizontal wind and AOA measurements to get 'corrected' vertical velocities. Statistical results are presented for both quiet and active conditions.