Enhanced stratification in the lower Chesapeake Bay following northeasterly winds

Density data from a lower Chesapeake Bay transect obtained after two northe asterly wind events were used to describe the effects of these events on th e density field in the lower estuary. The first northeaster occurred in ear ly August 1995 and the second northeaster was related to the passage of hur ricane Felix off the lower bay in mid-August 1995. The latter northeaster p rolonged a period of persistent winds from the N and NE that began in early August and caused storm surges of similar magnitude to the former northeas ter. The salinity fields observed after the early August event suggested en croachment of coastal waters into the lower bay as reflected by high salini ties throughout the transect. Two days after weakening of the winds related to Felix, the density distribution across the lower bay showed strongly st ratified conditions. This behavior suggested that the inflow of coastal wat er into the lower bay and the wind mixing related to Felix combined to prod uce a vertically uniform density gradient perpendicular to the bay entrance that relaxed after the winds weakened. This weakening of the winds coincid ed with neap tidal currents, which were not energetic enough to maintain ve rtical homogeneity and must have allowed the self-adjustment of the density gradient and the seaward advection of relatively buoyant waters near the s urface. These mechanisms were illustrated with simplified numerical experim ents. The findings of this study are used to propose the hypothesis that, i n general, enhanced stratification and flushing in the lower bay will ensue the relaxation of a northeasterly wind event, provided that this relaxatio n coincides with a weak friction regime, i.e., neap tides. (C) 1998 Publish ed by Elsevier Science Ltd. All rights reserved.