AN EVALUATION OF CERTAIN FORMS OF MOMENTUM TRANSFER IN THE 26-MONTH OSCILLATION

Abstract

The fundamental equations are linearized by the method of small perturbations for the conditions of hydrostatic equilibrium and geostrophic balance of meridional forces. In a first case, Fickian momentum diffusion is used; in a second case, a shear- and latitude-dependent eddy viscosity is used. A wave solution for the zonal wind oscillation, having in meridional profile the shape of a probability curve, is substituted in the equation of zonal motion. This procedure leads first to conditions on parameters, next to a solution for the meridional wind, and, through the remaining perturbation equations, finally to solutions for the remaining perturbation quantities. The temperature perturbation follows from the thermal wind equation and has the same probability curve shape in meridional profile as does the zonal wind disturbance. The conditions on parameters and the resulting solutions show that the assumed forms of eddy diffusion of momentum cannot under any circumstance account for momentum changes in the non-attenuating layer (above about 25 km.), but may, to the extent that mean vertical motion over the equator is negligible, be applied at the levels where the oscillation attenuates downward (below about 25 km.). In this case air drifts equatorward during westerlies and poleward during easterlies, and the oscillation consists of downward-propagating cells in meridional cross-section.