The intellectual merits of this work involve clarification of the unique dynamics near oceanic boundaries and quantification of their effects on essential oceanic processes like boundary stress, mesoscale dissipation and diapycnal mixing followed by adiabatic isopycnal dispersion. The primary unsolved dynamical problem of physical oceanography involves the 'dissipative' closure of western boundary currents, which is the primary focus of this project.
The problem of Topographic Control of the Gulf Stream with particular application to its separation is being addressed. This project is built on the hypothesis that boundaries exert fundamental controls on the ocean circulation in general and the Gulf Stream in particular. These processes are poorly represented or absent from current climate models. The main focus of the proposed research is on sub-inertial excitation of inertia-gravity waves and activation of the sub-mesoscale by boundary processes, with a view towards their potential vorticity and lateral stress implications. The driving hypothesis is that these processes dominate Gulf Stream separation and downstream development. This is a critical aspect of ocean circulation that all current models struggle with, regardless of resolution. The result is the introduction of strong biases in the model North Atlantic that is likely to affect climate projection on the decadal time scale. Observations also suggest an important role for topography in promoting mixing.
Broader impacts: Preparing for climate change is the most pressing problem currently facing society. This project is addressing a significant shortcoming of the oceanic component of coupled climate models. The mesoscale and boundary currents are the dominant kinematic features of the ocean and are controlled in all existing models by parameterizations. This project is designed to build into these parameterizations physically based models of boundary interactions, thereby enhancing the fidelity of climate prediction and eliminating a major bias found in current ocean circulation models. Since the new parameterizations will be implemented in the Community Climate System Model, they will be widely available to the general climate community.
Improving climate change models NSF: Type I - Collaborative Research: Topographic Control of the Gulf Stream (University of California, Los Angeles) Type I - Collaborative Research: Topographic Control of the Gulf Stream (Florida State University) Type I - Collaborative Research: Topographic Control of the Gulf Stream (University Corporation for Atmospheric Research) State: California, Colorado, Florida Congressional Districts: California District 30, Colorado District 02, Florida District 02 Research Areas: Earth & Environment The Gulf Stream is a warm, surface ocean current that carries a large amount of heat from the tropics to polar regions in the Atlantic (see figure). However, many current models have an incorrect position for the Gulf Stream, compared to measurements, as it moves away from the U.S. Eastern Seaboard and flows toward Europe. This error causes them to depict inaccurate warming of the atmosphere under the middle-latitude storm tracks. NSF-funded researchers have developed a technique to remove the positioning error, at least in regional models of the Atlantic and potentially in global models. Collaborators at University of California at Los Angles, Florida State University, and the National Center for Atmospheric Research have shown how the Gulf Stream path and strength are sensitive to the details of the model depiction of the ocean bottom shape. This is a subtle problem both because the topography is not well known and because the flow near topography can be quite complex. In demonstrating the model's sensitivity to topography, the researchers proposed alternative depictions that reduce model error. As a result the warm water flowing northward at the surface follows a more realistic path and more accurately represents the heat exchange with the overlying atmosphere. Ultimately, this advance could lead to more accurate global circulation and climate models. Such models may reduce prediction errors of future climate.
