[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.

[1] The influence of the Po plume on the northern Adriatic Sea was observed during two seasons in 2003 under distinct physical forcing regimes. During the winter, the plume was cool, low in both salinity and chlorophyll, but with higher chlorophyll concentrations occurring along the plume boundary. The plume mixed deeply in the water column in response to the strong wind forcing. The northern Adriatic and the Po plume cooled significantly during the observational period, and therefore salinity alone was the best discriminator of water mass variability. In contrast to the strong forcing of the winter period, the late spring was characterized by weak wind forcing, and below-average Po River discharge ($600 m 3 /s) which was about one third of the typical discharge for this period. As in winter, salinity was again the best discriminator of water mass variability. The Po plume advected southward along the Italian coast and in some locations portions of the coastal plume were transferred offshore in filament-like features. However, the one observed filament was quite low in chlorophyll and was quite thin vertically, extending downward less than 5 m from the surface. The spring observations provide a distinct contrast in the effects of the physical forcings of river flow and wind stress from two different seasons. The strong winter forcing resulted in deep mixing of the plume despite its low salinity and buoyancy, whereas the weak summer flow under weak winds resulted in a very shallow plume (<5 m) that was high in chlorophyll.

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Harmful algal bloom (HAB) events threaten human health, living marine resources, and ecosystem health. Their occurrence has increased in frequency, duration, and severity over the last several decades. Preventing, controlling, or mitigating the impacts of HABs requires the development of permanent, operational ocean observing systems that continuously provide the data and information necessary for rapid detection and timely forecasts of changes in ecosystem states. Key elements of such observing systems are observations and modeling that must be efficiently linked via data management and communication networks. Building the observing system begins by integrating existing assets, is followed by incorporation of new technologies and knowledge, and is guided by the data and information needs of decision makers. User needs are particularly important for development of operational forecast models and new sensors for measuring required biological (e.g., HAB species abundance) and chemical (e.g., concentrations of HAB toxins) variables in near real time. This article describes operational observing system requirements for a HAB forecasting system and current efforts by Regional Associations to develop these observing systems for targeted species in their respective regions.