Summertime Connecticut River Water Pathways and Wind Impacts

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. Plain Language Summary Connecticut River is the primary freshwater source to Long Island Sound. It enters near the sound mouth, where dense continental shelf water intrudes in. The aims are to find out where the summer river waters go and what drives it. In particular, the mild wind impacts on the river water distributions are studied. Simulations with a river water dye pulse show two main pathways simultaneously: in 19days, a third of the river water moves toward the sound head with a near-bottom dense inflow; another third of the river water leaves through the sound mouth at the surface and later on enters onto the shelf. The latter pathway is confirmed by field surface drifter tracks. Three scenarios of wind forcing are tested: a spatial varied wind case, a relatively spatial uniform wind case, and a no-wind case. The results show that winds speedup the up-estuary transport of the river water in central sound. On the continental shelf, winds play a more important role on the estuarine outflow distribution. Results suggest that the spatial varied wind model has better performance on modeling surface drifter tracks. This study gives a clear picture on the summertime Connecticut River water pathways and the related dynamics.