Summertime Connecticut River Water Pathways and Wind Impacts

Abstract

Long Island Sound is a large macrotidal estuary. Connecticut River as the primary freshwater source enters near the sound's mouth. The summertime pathways of river water under low discharge and mild wind conditions are studied through both numerical simulations with a passive dye pulse and field surface drifter observations. Within the 19-day modeling analysis period a third of the river dye pulse remains in the eastern sound; another third of the pulse moves up-estuary with the near-bottom dense inflow into the central and western sound with a spring-neap tidal modulation; and another third leaves the sound with the near-surface outflow toward the continental shelf through Block Island Sound. The latter pathway is confirmed by field surface drifter tracks. Three scenarios of wind forcing are tested: a WRF-ROMS Coupled case, a NARR data forcing case, and a No-Wind case. The results show though that the sound is tidal mixing dominated, mild winds still alter the position and strength of the estuarine exchange flow, and either enhances by the cross-estuary winds or lateral straining. On the shelf, winds play a more important role on the fresher estuarine water distribution. The sensitivities of circulation, salinity, and numerical drifter tracks to different atmospheric forcings also are studied. The results suggest that the coupled model has better performance to simulate surface drifter tracks.