Sustained observations of mesoscale and sub-mesoscale surface circulation off the U.S. West Coast

With collaborated research efforts in the regional coastal ocean observing systems (SCCOOS, CeNCOOS, and NANOOS) off the U.S. West Coast (USWC), the nearly completed 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. The HFR surface currents resolve coastal surface ocean variability continuously across scales from sub-mesoscale 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 sub-mesoscale spectra below the observational limits of present-day satellite altimeters.