Use of the VAD technique and measurements of momentum flux in the stratosphere at Aercibo, part 4.3A

The Arecibo 430-MHz radar was used in the velocity-azimuth display (VAD) mode to obtain radial velocity measurements at 16 azimuth directions from which the three-dimensional wind field and momentum flux can be calculated. The radar was operated on a nearly continuous basis for a seven-day period in May of 1982 and the elapsed time between start and finish of a VAD scan was approximately 35 minutes. Radial velocities were measured in the upper troposphere and lower stratosphere (6-24 km) with at height resolution of 150 meters at a zenith angle of 15 deg. Vertical and horizontal velocities are calculated from the sums and differences, respectively, of radial velocity pairs, i.e., at azimuth directions AZ and AZ + 180 degrees. Momentum flux at a particular azimuth is calculated by taking the difference between the square of radial velocities at AZ and AZ + 180 degrees. It should be noted that measurements of radial velocity pairs are not simultaneous but are time delayed by approximately 15-25 minutes. This period, the time required to rotate the antenna feed and take measurements at AZ and AZ + 180 deg, effectively limits sampling of velocities and momentum fluxes to longer period gravity waves and planetary waves.