Equatorial Meridional Flows: Rotationally Induced Circulations

This study examines two-dimensional large-scale atmospheric circulations that are centered over the equator. The influence of terms that contain the Coriolis parameter f % 2V cos U is highlighted in a simple linear inviscid equatorial beta model. Two general types of oscillatory circulations are identified within the y–z plane. In a neutral or stably stratified atmosphere one circulation is expressed in terms of an analytic solution that contains Hermite polynomials, while a second solution is described in terms of a Bessel function. In the more traditional Hermite polynomial solution the influence of f % is small as suggested by scale analysis. Neutral stability provides the only exception. In contrast to these findings, the Bessel solution contains frequencies with semiannual periods that depend entirely on f %"0. This solution describes cross-equatorial flow with a maximum meridional velocity at the equator. Consequently, this indicates that to model the atmosphere it is necessary to include in the model equations all terms containing f %, since they influence oscillatory circulations that describe internal waves with periods that vary from a few days to semiannual.