This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
The atmospheric forcing of marginal-sea overflows will be investigated. The main motivation is the need to develop better parameterizations of marginal sea outflows of all scales and also from observations of the Nordic Seas overflows showing considerable interannual variability of transport and water temperature, possibly linked to the North Atlantic Oscillation (NAO). The observed variations would be difficult to explain using standard hydraulics models alone, but could be captured in models that combine atmospheric forcing, hydraulic processes and a consideration of the circulation in the marginal sea. As a first step, a new analytic model for a marginal sea outflow that includes atmospheric forcing and time dependence will be developed. The model will predict the lower layer outflow properties of the two-layer exchange given the forcing and the upper layer inflow temperature and salinity. It should be applicable to marginal seas and straits of scales varying from the Med/Gibraltar systems to the Nordic Seas and should be superior to existing parameterizations used in some general circulation models. A hierarchy numerical modeling simulations using both idealized and realistic bathymetry will be conducted to examine the impacts of atmospheric forcing, such as NAO, on the overflow, and to identify mechanisms responsible for the timing and amplitude of observed changes of the overflow. The numerical modeling component will be focused on the Nordic overflows. The hypothesis that the atmospheric forcing over the Nordic Seas is the primary cause for interannual Nordic Seas overflow variability will tested. Alternative ways of monitoring the deep overflows will also be investigated. The ultimate goal is to understand how the overflow and the Atlantic Meridional Overturning Circulation (AMOC) respond to a changing climate.
Intellectual Merit: This study will advance our understanding of the Nordic Seas overflow and its responses to climate forcing, provide a climate-responsive marginal-sea boundary condition (MSBC) that is more advanced than the Price-Yang version used in several climate models, help understand AMOC variability in model simulations, and help improve the predictability of AMOC's responses to a changing climate.
Broader Impacts: The Nordic Seas region is an important player in the global ocean climate puzzle. A better understanding of the response of the deep outflows to changing forcing will ultimately help predict the global effects of warming, glacier melt, and other environmental changes in the Nordic regions. In terms of outreach activities, investigator Pratt has given presentations to high school students at a local school (Cape Cod Academy). The subject material of this project (marginal seas, overflows, and the abyssal circulation) should be fascinating to students of that age and we plan to go back into the classroom and talk about it. Plans are coordinated through Cathy Cetta, assistant headmaster and teacher at CCA. Investigator Pratt also plans to build on the educational impact of his text book by developing online aids such as additional homework exercises and movies.
This project is a contribution to the Atlantic Meridional Overturning Circulation research theme under the U.S. CLIVAR (CLImate VARiability and predictability) Program.
