Turbulent Thermal-Wind-Driven Coastal Upwelling: Current Observations and Dynamics

Abstract A remarkably consistent Lagrangian upwelling circulation at monthly and longer time scales is observed in a 17-yr series of current profiles 12 m water on the southern New England inner shelf. The strongest summer, with magnitude ∼1 cm s −1 , which flushes shelf ∼2.5 days. average winter about one-half summer circulation, but larger month-to-month variations driven, part, by cross-shelf wind stresses. persistent not wind-driven; it driven buoyancy force associated less-dense near coast. density gradient primarily due to temperature when strong surface heating warms shallower nearshore more than deeper offshore water, salinity winter, caused fresher In absence turbulent stresses, would be geostrophic, thermal-wind balance vertical shear along-shelf current. However, stresses over attributable tidal currents stress cause partial breakdown that releases force, drives circulation. presence has profound impact exchange across this Many shelves are characterized gradients lighter coast, suggesting thermal-wind-driven coastal may broadly important mechanism. Significance Statement shallow off England. This traditional wind-driven upwelling; instead, forced (density) gradients, released water. wave forcing weak, portion continental few Consequently, buoyancy-driven for cooling provides reliable mechanism exchange.