A MULTIPLE SOUNDING TECHNIQUE FOR THE STUDY OF GRAVITY-WAVES

Radiosondes released in rapid succession, with a time separation of a few minutes, were launched during a field experiment in central Wales, U.K. to study orographic gravity waves. Rate of ascent fluctuations were used to infer the existence of vertical-velocity fluctuations associated with orographic gravity waves, and differences between consecutive ascents provided information on the steadiness and phase-line slope of the waves. The potential of the multiple sounding technique is examined here and an analysis strategy proposed. Three triple-sounding cases from the field experiment are used to illustrate the strengths and weaknesses of the technique. In one case it was possible to estimate a phase-line tilt with height and this, combined with the inferred vertical-velocity amplitude, allowed the estimation of the vertical momentum flux. It is suggested that the near-simultaneous release of between three and five sondes upstream of mountainous terrain could provide a useful method for calculating the vertical flux of momentum due to gravity waves.