Equatorially trapped waves and the generation of the Somali Current

A three-dimensional numerical model is used to study and compare two previously proposed theories for the development of the Somali Current. The rapid propagation of internal planetary waves at the equator provides a means whereby a baroclinic western boundary current can be established quickly, even by remote winds. This theory, first developed for the linear case by Lighthill, is studied numerically and extended to the nonlinear case. Local winds, parallel to the western boundary, and the accompanying Ekman suction, also produce a western boundary current, although different in spatial and temporal characteristics from the above. Comparison with observations indicates that local driving is dominant during the establishment of the current. Remote forcing may produce significant alterations in the flow later. In the nonlinear cases, horizontal shearing instability produces eddy-like features in the western boundary current similar to those observed.