FIRST OBSERVATION OF MESOSPHERIC WIND SHEAR AS HIGH AS 330 M S(-1) KM(-1)

Mesospheric wind profiles with an altitude resolution of 25 m have bee n obtained by means of radar tracking of foil chaff clouds. Such exper iments were performed during winter 1990 at Biscarrosse, France (44 de grees N, 1 degrees W). On one flight, a wind shear as high as 330 m s( -1) km(-1) at 87.4 km and a region of dynamical instability between 86 and 88 km was measured. This wind shear is believed to be the largest value ever measured in the mesosphere. The region of dynamical instab ility results from a superposition of two wave motions, and is found t o link well with enhanced turbulence and small-scale wave activity.