VHF Doppler Radar Observations of Vertical Velocities in the Vicinity of the Jet Stream

Abstract

The SOUSY (sounding system) VHF (very high frequency) radar in Germany has been used to make observations of the upper troposphere and lower stratosphere for a number of cases during which the jet stream was overhead, or nearly so. The horizontal and vertical wind components have been calculated from oblique-beam Doppler radial velocities using a velocity-azimuth display (VAD) technique and averaged over periods ranging from 3 h to about 1 day. The vertical wind is found to reverse direction near the height of the maximum horizontal wind in all cases observed, in general agreement with a conceptual model and with other radar measurements. Most commonly, downward vertical motion is observed below the jet-stream wind maximum and upward motion above it for these cases, but in one instance such a circulation has been found to undergo a reversal as the position of the jet shifted. The vertical velocities have magnitudes in excess of 0.5 m s?1. NO minimum critical horizontal wind speed sums to be required in order for the vertical circulation feature to be observed.