Forcing of cross-shelf plumes on a wide continental shelf

Analysis of satellite imagery of the Carolinas continental shelf (the US East Coast) shows frequent occurrences of cross-shelf buoyant plumes under upwelling winds. Forcing conditions for fifteen representative events spanning 2017 through early 2020 are analyzed. The buoyancy forcing is represented as an estuarine Richardson number accounting for freshwater discharge and its tidal mixing. The wind forcing is represented as the low-passed alongshore wind stress component, the wind stress magnitude and its standard deviation. Forcing elements are averaged over three days preceding the event. Three cross-shelf plume patterns emerge: the separated plume, when a single streak of buoyant water spreads offshore (an archetypical cross-shelf plume structure), the curving-back plume turning against the wind at some offshore distance, and the multi-lobe plume partially trapped by the coast, with more than one streaks protruding offshore. The latter two regimes represent a low-wind and a strong-wind limit of cross-shelf plumes, respectively.