Six-yr-long time series of winds, waves, and water velocity from a cabled coastal observatory in 12 m of water reveal the separate dependence of the cross-shelf velocity profile on cross-shelf and along-shelf winds, waves, and tides. During small waves, cross-shelf wind is the dominant mechanism driving the cross-shelf circulation after tides and tidal residual motions are removed. The along-shelf wind does not drive a substantial cross-shelf circulation. During offshore winds, the cross-shelf circulation is offshore in the upper water column and onshore in the lower water column, with roughly equal and opposite volume transports in the surface and bottom layers. During onshore winds, the circulation is nearly the reverse. The observed profiles and cross-shelf transport in the surface layer during winter agree with a simple two-dimensional unstratified model of cross-shelf wind stress forcing. The cross-shelf velocity profile is more vertically sheared and the surface layer transport is stronger in summer than in winter for a given offshore wind stress.During large waves, the cross-shelf circulation is no longer roughly symmetric in the wind direction. For onshore winds, the cross-shelf velocity profile is nearly vertically uniform, because the wind-and wavedriven shears cancel; for offshore winds, the profile is strongly vertically sheared because the wind-and wave-driven shears have the same sign. The Lagrangian velocity profile in winter is similar to the part of the Eulerian velocity profile due to cross-shelf wind stress alone, because the contribution of Stokes drift to the Lagrangian velocity approximately cancels the contribution of waves to the Eulerian velocity.

The inner continental shelf, which spans water depths ofa few meters to tens of meters, is a dynamically defined region that lies between the surf zone (where waves break) and the middle continental shelf (where the along-shelf circulation is usually in geostrophic balance). Many types of forcing that are often neglected over the deeper shelf-such as tides, buoyant plumes, surface gravitywaves, and cross-shelfwind stress-drive substantial circulations over the inner shelf. Cross-shelf circulation over the inner shelf has ecological and geophysical consequences: It connects the shore to the open ocean by transporting pollutants, larvae, phytoplankton, nutrients, and sediment. This review of circulation and momentum balances over the inner continental shelf contrasts prior studies, which focused mainly on the roles of along-shelfwind and pressure gradients, with recent understanding of the dominant roles of cross-shelf wind and surface gravity waves.

From January 2014 to August 2016, sea surface temperatures (SSTs) along the Washington, Oregon, and California coasts were significantly warmer than usual, reaching a maximum SST anomaly of 6.2°C off Southern California. This marine heat wave occurred alongside the Gulf of Alaska marine heat wave and resulted in major disturbances in the California Current ecosystem and massive economic impacts. Here we use satellite and blended reanalysis products to report the magnitude, extent, duration, and evolution of SSTs and wind stress anomalies along the West Coast of the continental United States during this event. Nearshore SST anomalies along the entire coast were persistent during the marine heat wave, and only abated seasonally, during spring upwelling‐favorable wind stress. The coastal marine heat wave weakened in July 2016 and disappeared by September 2016.

Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate that wave-driven undertow extends well offshore of the surf zone, over the inner shelves of Martha's Vineyard, Massachusetts, and North Carolina. Theoretical estimates of the wave-driven offshore transport from linear wave theory and observed wave characteristics account for 50% or more of the observed offshore transport variance in water depths between 5 and 12 m, and reproduce the observed dependence on wave height and water depth.During weak winds, wave-driven cross-shelf velocity profiles over the inner shelf have maximum offshore flow (1-6 cm s Ϫ1) and vertical shear near the surface and weak flow and shear in the lower half of the water column. The observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the surf zone. Instead, the vertical structure is similar to the Stokes drift velocity profile but with the opposite direction. This vertical structure is consistent with a dynamical balance between the Coriolis force associated with the offshore flow and an along-shelf "Hasselmann wave stress" due to the influence of the earth's rotation on surface gravity waves. The close agreement between the observed and modeled profiles provides compelling evidence for the importance of the Hasselmann wave stress in forcing oceanic flows. Summer profiles are more vertically sheared than either winter profiles or model profiles, for reasons that remain unclear.

[1] Following relaxations of prevailing upwelling-favorable winds, warm waters from the Santa Barbara Channel propagate poleward around Point Conception and along the south central California coast. We examined characteristics of these relaxation flows, including frontal propagation speed and temperature changes during the warm water arrivals, by using multiyear time series of currents and temperatures from four moorings along the ∼15 m isobath, surface current observations from high-frequency radars, and satellite sea surface temperature images. Propagation speeds of the warm fronts relative to ambient waters ranged from 0.04 to 0.46 m s −1 . As the fronts arrived at the moorings, temperature increases ranged from 0.7°C to 4.2°C. In ensemble averages over many frontal arrivals, alongshore flow speeds increased by 0.1-0.2 m s −1 over the water column during arrivals. Cross-shore flows were onshore near the surface and offshore near the bottom with speeds of 0.02-0.05 m s −1 . This cross-shore flow structure persisted as temperature increased during arrivals and ceased when temperatures stopped increasing. Frontal propagation speeds were correlated with temperature increases at the moorings, consistent with forcing by baroclinic pressure gradients. Compared to other buoyant flows such as from the Chesapeake Bay where density contrasts with ambient waters are 2-3 kg m −3 , these relaxation flows are less buoyant with density contrasts of 0.1-0.9 kg m −3 . Consequently, the propagation of these flows is more affected by bottom friction and the speeds are closer to the "slope-controlled" or "bottom-advected" limit described in theoretical and laboratory work but not well studied in the ocean.Citation: Washburn, L., M. R. Fewings, C. Melton, and C. Gotschalk (2011), The propagating response of coastal circulation due to wind relaxations along the central California coast,