Wind-Driven motion of estuarine plumes.

Abstract

Uses a three dimensional primitive equation model to study the effect of wind forcing on existing estuarine plumes in a coupled, wide estuary/shelf environment. Considers the dynamics of plumes, i.e., the solution to a uniform cross shelf wind forcing (Ekman type drift plus weak coastal jet), and solution subject to alongshore wind forcing (geostrophic current and downwind drift jointly drive a strong coastal jet). Notes the different mechanisms of downwelling and upwelling favourable winds. Three types of ocean basins were studied, 1)uniform depth 15m deep, everywhere, 2)linear seaward slope from 15m to 22.5m at the mouth, and 3) estuary uniformly 15m deep, 15m at the coast increaing to 22.5m at 18km seaward, levelling off further offshore. Surface current and salinity fields therefore vary. Discusses the effect of wind driving and effects of relaxation. Presents the mid estuary vertical features after several days of upwelling and downwelling favourable winds and gives corresponding volume transports. The model shows that while longitudinal winds drive local circulation effectively, alongshore winds do not always drive circulation remotely from the shelf. In particular, upwelling favourable winds over an estuary may enhance the density driven local circulation that the remotely forced signals are too weak to detect. A destratification process is associated with a strengthened S shaped transverse circulation in wide estuaries.