Mean upwelling velocities on the Oregon continental shelf during Summer 1973

Abstract

Mean vertical velocities for a 56-day period during Summer 1973 are estimated from consideration of the heat balance and mass conservation at a mid-shelf location in the coastal waters off Oregon. In the heat balance, vertical velocity is required to carry cold water upward predominantly to balance horizontal advection of warm water toward the coast by onshore velocities below 20 m depth. In the conservation of mass, vertical velocity is required to transport water upward to balance the onshore transport below 20 m. The two sets of vertical velocities at four depths agree within 0.2 × 10 −2 cm s −1, which is less than their estimated errors. The upward velocities are found to increase from 0.3 × 10 −2 cm s −1 at 87.5m to 1.6 × 10 −2 cm s −1 at 30 m depth. These vertical velocities are as large as those estimated previously during upwelling events of a few days duration. Because they are time-averages over almost two months, these mean vertical velocities are likely to be more important than the event-scale vertical velocities in the coastal circulation. Comparisons of observed onshore and offshore transports with the wind-driven offshore transport predicted by simple models suggests that the coastal circulation is a factor of 3 larger than that predicted from observed local winds.