Mean and variable flow over the central California continental margin, 1978 1980

Based on two years (July 1978-June 1980) of current meter array measurements and bimonthly STD/XBT transects over the continental margin off central California, the mean California Undercurrent has a jet-like core in excess of 15 cm s ^-1 which is generally confined to the upper 300 m of the water column and to within 30 km of the coast. A comparison of measured current velocities with relative geostrophic velocities suggests, on average, a poleward flow of 10 cm s ^-1 at the reference level, 450 db. The variability is predominantly annual with a maximum poleward flow in May-June. Equatorward flow was suprisingly weak and infrequent in the transect studied. The alongshore flow has characteristic fluctuations of 15 cm s ^-1 on time scales of a few days to weeks. The strongest and most coherent element of variation is the "spring transition", which had different manifestations in the two years observed, perhaps due to differences in the combination of local and remote forcing. The spring transition is characterized by an abrupt decrease in subsurface temperature which is well-correlated with a coastal sea surface temperature (SST) decrease, an upwelling index increase, and a transient reduction or reversal of the poleward flow. The subsurface current and temperature fluctuations are associated with coastal SST and wind fluctuations, and with satellite infra-red imagery patterns and changes.