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

• Published in: Journal of geophysical research. Oceans Vol. 129; no. 1
• Main Authors: Wang, Ou, Lee, Tong, Frederikse, Thomas, Ponte, Rui M., Fenty, Ian, Fukumori, Ichiro, Hamlington, Benjamin D.
• Format: Journal Article
• Language: English
• Published: 01.01.2024
• Subjects: adjoint sensitivity; buoyancy forcing; ECCO; forcing mechanism; sea level; wind stress
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2023JC019873

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. Plain Language Summary The magnitude of year‐to‐year sea‐level variations along the East Coast of the United States (U.S.) can be comparable to that of global mean sea‐level rise over a few decades. These year‐to‐year sea‐level variations contribute to more frequent nuisance floods that affect coastal communities. Year‐to‐year sea‐level variations between the U.S. Northeast and Southeast Coasts separated by Cape Hatteras are significantly less correlated than those within the respective sectors. Understanding causal mechanisms affecting the coherence of year‐to‐year sea‐level variations in the two sectors would help improve sea‐level predictions. Our study attributes year‐to‐year sea‐level variations at Charleston and Nantucket, proxy locations for the U.S. Southeast and Northeast Coasts, to wind and buoyancy forcing (air‐sea heat exchange and precipitation/evaporation at sea surface that both affect seawater buoyancy). We find that nearshore winds north of Cape Hatteras and buoyancy forcing both cause coherent year‐to‐year sea‐level variations between Nantucket and Charleston. Offshore winds affect much more year‐to‐year sea‐level variation at Charleston than that at Nantucket. Offshore winds are the major factor causing less correlated year‐to‐year sea‐level variations between Nantucket and Charleston. Warming/cooling of water south of Charleston affects sea‐level variations at Charleston, but not at Nantucket. However, this effect is smaller than that of the offshore wind. Key Points Nearshore winds north of Cape Hatteras and buoyancy forcing cause coherent interannual sea‐level variations between Nantucket and Charleston Offshore winds contribute much more to interannual sea‐level variation at Charleston than to that at Nantucket Offshore winds are the major factor causing incoherent interannual sea‐level variations between Nantucket and Charleston