A model of the three-dimensional wind and temperature fields in the 26-month oscillation is presented, based in part on empirical data concerning the temperature behaviour and its relationship to the zonal wind behaviour and in part on theoretical deductions from the thermodynamic energy and continuity equations. The empirical data show that equatorward of 16° latitude highest temperatures precede the west wind maximum by intervals varying from 4–5 months at the 20 mb level to 0–1 months at the 80 mb level. Near the Equator the amplitude of the temperature oscillation is approximately 2°C and varies little with height in the foregoing altitude range. In the subtropics the phase of the temperature cycle is nearly opposite to that at the Equator, lowest temperatures preceding the maximum (relative) westerlies. the amplitude at these latitudes increases from a fraction of a degree at 80 mb to about 1°C at 20 mb. the features of the temperature and zonal wind behaviours are shown to be consistent with the thermal wind relationship. The theoretical results indicate that the vertical velocity has a maximum amplitude of about 0·01 cm sec−1 at the Equator and that the phase of the vertical velocity oscillation reverses near 15° latitude. Maximum subsidence precedes highest temperatures by about one month. Meridional velocities are strongest near 15° latitude where they reach values of 1–2 cm sec−1. Maximum northerly winds follow maximum subsidence by about one-quarter cycle. The observed quasi-biennial oscillation of total ozone amount is shown to be qualitatively consistent with the model, and near the Equator, to be in quantitative agreement with the theoretical results. It is speculated that the 26-month oscillation possesses two superposed modes: a tropical mode characterized by a vertically-propagating wave and a hemispheric mode consisting of a Pole to Equator standing wave. Finally, it is proposed that the oscillation has its origin in a subharmonic response to the annual heating cycle.
R. J. Reed
Quarterly Journal of the Royal Meteorological Society