Poleward flow in the California Current System

Abstract

In the California Current System, poleward flow has been observed at different levels and in different seasons. In winter, there is broad poleward flow at the surface along most of the coast along Washington, Oregon, and northern California. During the upwelling season, in spring and summer, there is a narrow, inshore poleward surface current which appears off northern California whenever upwelling-favorable winds weaken; off southern and central California, this inshore poleward flow seems to persist through most of the upwelling season. During the upwelling season, there is also subsurface poleward flow, both near the bottom over much of the continental shelf and at depths of a few hundred meters along the upper continental slope. Whether and how these “branches” of poleward flow are related to each other is still unknown. We have some ideas of how the surface poleward flows are driven, but still very little information on the continuity and the driving of the subsurface undercurrents. In this note, we shall summarize briefly the main characteristics of each of these “branches,” and present some recent observations of the California Undercurrent in the CODE region near San Francisco.