What Forcing Mechanisms Affect the Interannual Sea Level Co-Variability Between the Northeast and Southeast Coasts of the United States?

Abstract

Interannual sea-level variations between the United States (U.S.) Northeast and Southeast Coasts separated by Cape Hatteras are significantly less correlated than those within their respective sectors, but the cause is poorly understood. Here we investigate atmospheric forcing mechanisms that affect the interannual sea-level co-variability between these two sectors using an adjoint reconstruction and decomposition approach in the framework of Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate. We compare modeled and observed sea-level changes at representative locations in each sector: Nantucket Island, Massachusetts for the Northeast and Charleston, South Carolina for the Southeast. The adjoint reconstruction and decomposition approach used in this work allows for identification and quantification of the causal mechanisms responsible for observed coastal sea-level variability. Coherent sea-level variations in Nantucket and Charleston arise from nearshore wind stress anomalies north of Cape Hatteras and buoyancy forcing, especially from the subpolar North Atlantic, while offshore wind stress anomalies, in contrast, reduce co-variability. Offshore wind stress contributes much more to interannual sea-level variation at Charleston than at Nantucket, causing incoherent sea level variations between the two locations. Buoyancy forcing anomalies south of Charleston, including over the Florida shelf, the Gulf of Mexico, and the Caribbean Sea, also reduce co-variability because they induce sea-level responses at Charleston but not Nantucket. However, the relative impact of buoyancy forcing on interannual sea-level co-variability between the two sectors is much smaller than that of offshore wind stress.