Observations of the Flow Field near the Nose of a Buoyant Coastal Current*

Abstract

Abstract Low-salinity water from Chesapeake Bay forms an intermittent buoyant gravity current that propagates more than 100 km southward along the coast. During five events when wind and surface gravity-wave forcing were weak, the buoyant coastal current 90 km south of Chesapeake Bay was less than 5 km wide, was 5–10 m thick, and propagated alongshore at ∼50 cm s−1. The density decreased 2–3 kg m−3 over a few hundred meters at the nose of the buoyant coastal current, which was located about 1 km offshore in ∼8 m of water. Water up to 4 km ahead of the advancing nose was displaced southward and offshore (maximum velocities near the nose of 20 and 10 cm s−1, respectively). The southward alongshore current increased abruptly to ∼50 cm s−1 at the nose and continued to increase to a supercritical maximum of ∼70 cm s−1 about 1 km behind the nose. An onshore flow of between 5 and 15 cm s−1, which extended at least 5 km behind the nose, supplied buoyant water to the onshore region of weak, subcritical alongshore ...