Atmospherically Forced Eddies in the Northeast Pacific

Abstract

In the northeast Pacific eddies are observed in the salinity and, to a lesser extent, in the thermal anomalies. In particular, a pronounced eddy is frequently observed a few hundred kilometers west of Sitka, Alaska, latitude 57°N. This paper investigates a possible mechanism for the production of such eddies. The northeast Pacific ocean is approximated by a quarter-plane region, and a continuously stratified, inviscid linear model is used to study the reflections of wind-driven perturbations by the two boundaries. In the model the perturbations take the form of planetary waves, and by choosing a forcing function which is sinusoidal in time the problem reduces to solving the forced Helmholtz equation in a quarter-plane region. From the solution to this equation, the perturbation density field is derived. In general, it consists of a large number of eddies which result from the superposition of multiply reflected planetary waves. It is found that tilting the quarter-plane from the north-south direction alters the shape of the eddies in the perturbation density field. Furthermore, when the quarter-plane is not rotated the eddies are aligned parallel to the boundary representing the Alaskan peninsula-Aleutian Island chain. As the quarter-plane is tilted, the axis of alignment of the eddies rotates toward the boundary representing the Alaskan-British Columbia coastline.