FURTHER STUDY OF A SATURATED GRAVITY-WAVE SPECTRUM IN THE MESOSPHERE

Mesospheric wind profiles with a height resolution of 25 m derived from five foil chaff experiments performed during the last salvo of the MAC/SINE (Middle Atmosphere Cooperation/Summer in Northern Europe) campaign in the summer of 1987 at Andoya Rocket Range, in Northern Norway (69-degrees-17'N, 16-degrees-01'E), allow us to study the character of the motion spectrum in the mesosphere. The wind data have shown that (1) the average slope of the five vertical wave number spectra was -3.0 +/- 0.2 for wavelengths in the range from 6.4 km to 100 m; (2) a dominant vertical wavelength of more than 6.4km was found; and (3) there was good agreement between the observed spectrum and the saturated spectrum presented by Dewan and Good (1986) and Smith et al. (1987). In this paper, we further show that (1) very large wind shears, as high as 50-90 m s-1 km-1, are observed to be present at various heights (such large shears yield Richardson numbers smaller than 0.25, suggesting that the saturated gravity wave spectrum is associated with the shear instabilities); and (2) when the Richardson number profile is compared with the altitude profile of the mesosphere-stratosphere-troposphere (MST) radar (SOUSY) echo power, the low Richardson numbers are observed in the region of most intense backscatter. It is suggested from our measurements that the enhanced echo power is linked to wave saturation processes.