OBSERVATIONS OF SMALL SCALE WIND SHEARS IN THE MESOSPHERE

Ten wind profiles were measured in summer 1988 in the upper mesosphere over And ya (69°N) with foil chaff. Anew kind of foil chaff was used then, which covers the height range of 103-85 km. The height resolution of the measurement was 25 m. The measured wind shears are observed to have a multi-layered structure whih has three to nine shear layers. The thickness of these shear layers is usually less than 200m. Very large wind shears as high as 40-90 m/s/km are observed and such large shears are present at various heights in the mesosphere. The strong wind shears revealed in a series of five shear profiles have stable and persistent features with a lifetime of at least 2.5 h, an apparent downward motion of 0.4 m/s, and a maximum shear amplitude of 180 m/s/km.