The role of a longshore pressure gradient in Pacific Northwest coastal dynamics.

Abstract

The investigation of the role of the seasonal barotropic longshore pressure gradient in the coastal dynamics of the Pacific Northwest is reported. Values of seasonal longshore pressure gradient were included in the two-dimensional, time dependent, baroclinic finite difference model of Hamilton and Rattray as an external force. Three important features of the mean circulation are discussed: the anomalously strong southward flow that follows the spring transition, the well documented northward undercurrent (the California Undercurrent) that exists along most of the West Coast in summer, and a southward undercurrent (denoted as the Washington Undercurrent) which the model predicts and observations substantiate for the Pacific Northwest slope during winter. Also the results show that bottom stress is significant in the mid shelf region during both winter and spring and the assumption that offshore transport in the surface layer is balanced by onshore transport in the inviscid interior is shown to be invalid except during the summer. (from authors' abstract)