Radar/Balloon Measurement of Vertical Air Motions Between the Surface and 15 km

Abstract

An estimate of the vertical wind component up to an altitude of 15 km is derived from FPS-16 radar/Jimsphere ascent-rate measurements. The method involves removing ascent-rate profile variations which are not associated with vertical air motions. Radar noise errors are evaluated by comparing simultaneous measurements by two radars of a single balloon ascent. Radar noise is shown to be a high-frequency phenomenon which can be substantially reduced by smoothing. Ascent-rate profiles are smoothed to reduce the rms noise error to less than 5 cm sec?1. The vertical resolution of the smoothed profiles is ?250 m. The contributions of buoyancy and drag to the vertical component of balloon motion are estimated and removed from the smoothed ascent-rate profile. The residual profile contains perturbation amplitudes of up to 40 cm sec?1. The hypothesis that this profile represents the vertical wind component is supported by evidence that several other potential causes of ascent-rate variations are insignificant. It is concluded that useful estimates of sub-synoptic variations in the vertical wind component in clear air below 15 km can be derived from FPS-16 radar/Jimsphere ascent-rate measurements.