Jennifer D. Mitchell

Small-scale structure observed in-situ during MAC/EPSILON

Abstract We determine in this paper the level of turbulence activity in the middle atmosphere observed during the MAC/EPSILON campaign using different in-situ techniques. The observations show a minimum of turbulence in the height region 75–80 km, with increasing activity below and above. Based upon spectra of density fluctuations covering height intervals of typically 8 km, a unified spectral description is developed. It is shown that the buoyancy scale LB and inner scale l0 of turbulence, as calculated from the power of fluctuations in the inertial subrange, agree with the visually observed breakpoints in the spectra. Spectra of ion density fluctuations are also seen to be consistent with spectral amplitudes predicted by linear saturation theory. The relationship between the level of turbulence in the middle atmosphere and the gravity wave environment in which the turbulence occurs is investigated in detail. Our results suggest that strong turbulence occurs preferentially in or near those phases of the wave motions predicted to be most unstable on the basis of linear gravity wave theory.