No abstract

During the period 1992-95, nineteen isobaric RAFOS floats, placed in the California Undercurrent at intermediate depths (150-600 m) off Monterey and San Francisco, California, reveal a region of varying width of subsurface, poleward flow adjacent to the continental margin. The float trajectories exhibit three patterns: poleward flow in the undercurrent; reversing, but predominately alongshore, flow adjacent to the continental margin; and, farther offshore, anticyclonic motion accompanied by slow westward drift. Flow continuity of the undercurrent exists between Pt. Reyes and at least Cape Mendocino with an average speed dependent on the float depth. Speeds were variable, but common features were acceleration occurring to the south of Pt. Arena and deceleration to the north of Cape Mendocino. An important mechanism for floats, and water, to enter the ocean interior from the undercurrent is through the formation of submesoscale coherent vortices.

[1] The nearly completed U.S. West Coast (USWC) high-frequency radar (HFR) network provides an unprecedented capability to monitor and understand coastal ocean dynamics and phenomenology through hourly surface current measurements at up to 1 km resolution. The dynamics of the surface currents off the USWC are governed by tides, winds, Coriolis force, low-frequency pressure gradients (less than 0.4 cycles per day (cpd)), and nonlinear interactions of those forces. Alongshore surface currents show poleward propagating signals with phase speeds of O(10) and O(100 to 300) km day −1 and time scales of 2 to 3 weeks. The signals with slow phase speed are only observed in southern California. It is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of Point Conception. The seasonal transition of alongshore surface circulation forced by upwelling-favorable winds and their relaxation is captured in fine detail. Submesoscale eddies, identified using flow geometry, have Rossby numbers of 0.1 to 3, diameters in the range of 10 to 60 km, and persistence for 2 to 12 days. The HFR surface currents resolve coastal surface ocean variability continuously across scales from submesoscale to mesoscale (O(1) km to O(1000) km). Their spectra decay with k −2 at high wave number (less than 100 km) in agreement with theoretical submesoscale spectra below the observational limits of present-day satellite altimeters.

The "Wind Events and Shelf Transport" (WEST) program was an interdisciplinary study of coastal upwelling off northern California in 2000 was comprised of modeling and field observations. The primary goal of WEST was to better describe and understand the competing influences of wind forcing on planktonic productivity in coastal waters. While increased upwelling favorable winds lead to increased nutrient supply, they also result in reduced light exposure due to deeper surface mixed layers and increased advective loss of plankton from coastal waters. The key to understanding high levels of productivity, amidst these competing responses to wind forcing, is the temporal and spatial structure of upwelling. Temporal fluctuations and spatial patterns allow strong upwelling that favors nutrient delivery to be juxtaposed with less energetic conditions that favor stratification and plankton blooms.

Abstract. Observations of transport and currents in