Subtidal Frequency Fluctuations in Coastal Sea Level in the Mid and South Atlantic Bights: A Prognostic For Coastal Flooding


  • Gerald S. Janowitz
  • Leonard J. Pietrafesa


Sea-level change, coastal flooding, shelf dynamics, Ekman pumping


An analytical model is used to determine spatial and temporal variations in coastal sea level. The model is developed for subtidal frequency motions in the viscous parameter regime, where advection of relative vorticity can be neglected with respect to production of relative vorticity by bottom Ekman layer pumping. The latter is then balanced by the topographically induced vertical velocity. The effects of the atmospheric wind stress on coastal sea level are assessed; and it is found that an upwelling (downwelling) favorable wind stress causes a continual drop (rise) in coastal sea level downstream from an initial cross-shelf location, with modifying effects of cross-shelf profile and initial location on the downstream variation in coastal sea level also being important. The model is applied over the Mid Atlantic Bight from Woods Hole, Massachusetts to Cape Hatteras, North Carolina and then to Charleston, South Carolina. Reasonable agreement exists between observations and model results which suggests that a predictive capability has been established; dimensionless mean squared errors range from 0.122 to 0.294 with a mean of 0.181 over the six test cases. The model can be driven by several days of forecast winds to determine the timing of coastal flooding, with linear superposition of location specific predicted astronomical tides onto the subtidal frequency model predictions.