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.
