Oceanic variability off the Central California coast

Mesoscale variability off the Central California coast is strongly influenced by coastal upwelling and related processes. Off Point Sur, there is significant space-time variability in oceanic properties over periods of days and distances of several tens of km. However, the internal density field, averaged over space ( similar to 120 km alongshore) and time ( similar to 18 days), reveals the expected characteristics of a coastal upwelling regime, including an equatorward surface jet 25-40 km offshore and weaker poleward flow below 150 and within 20 km of the coast. Upper ocean circulation is strongly influenced by the bathymetry offshore to water depths of at least 1000 m. Based upon repeated horizontal grids of oceanographic stations, horizontal correlation scales for temperature are of the order of 30 km in the upper 100 m; therefore, a horizontal sampling rate of similar to 10 km is desirable. Vertical correlation scales for temperature are of the order of 100 m; therefore, a vertical sampling rate of similar to 10 m is desirable. Similarly, there are indications of a temporal correlation scale of a few weeks; therefore, a temporal sampling rate of several days is desirable. Empirical Orthogonal Functions (EOFs) in the cross-shore vertical plane suggest the influence of coastally-trapped motions within 40 km of the coast, with an intense alongshore, near-surface, transient coastal jet located similar to 20 km offshore. Sudden spring transitions to coastal upwelling conditions are often pronounced in coastal temperature records, and they may precede the offshore migration of the major upwelling front by at least a month. The spring transitions occur over a period of about a week. In 1980, the spring transition propagated poleward along the California coast at a speed of similar to 64 km day super(-) super(1) . During spring and summer, movement of a coastal upwelling front, often located 15-50 km offshore, is a major contributor to crossshore variability. The upwelling front meanders with an alongshore scale of similar to 80 km, a time scale of 30-40 days, and an amplitude scale of 10 km r.m.s., based upon satellite IR imagery. The alongshore mean position of the major upwelling front migrates offshore during spring and summer. Offshore displacement of the front may be caused by Ekman transport over periods of days to weeks, and by Rossby wave dispersion over longer periods. During summer, a time-dependent offshore scale based on Rossby wave dynamics was