Waves and the middle atmosphere wind irregularities

Middle atmosphere wind irregularities with vertical scales less than about 5 km are modeled as gravity shear waves that terminate abruptly on attaining Hedges's condition for overturning, N-2 approximate to 0. A quasi-random spectrum of such waves is constructed, and it reproduces the main features of the winds, including the ragged profiles observed in individual soundings and the short vertical wavelength tail of the wind's power spectrum. Shear analysis of observations reveals that around 100-km altitude the control of instability passes from small-scale internal waves to the tides, a change that probably has some bearing on the position of the turbopause.