Intellectual Merit: This project extend the investigators? work on horizontal convection which refers to the circulation resulting from differential heating along one horizontal boundary of a fluid and is seen as the simplest dynamical element contributing to the oceanic Meridional Overturning Circulation (MOC). The full problem of the MOC is complex and difficult, involving thermal, haline and mechanical forcing. The investigators on this project have been working on understanding single-component horizontal convection, which is commonly viewed as a simplified conceptual model of the MOC. This work, and that of other groups, suggests that the gap between horizontal convection and the MOC is not only quantitative, but also qualitative. The goal of this project is to move from the overly simplified problem of horizontal convection toward the richer dynamical setting of the ocean by conducting further laboratory and numerical experiments. The following hypotheses will be addressed:
1. Deep stratification is largely set by the interaction between the vertical transport of buoyancy in the depth-varying, negatively buoyant plume and the lateral transport due to baroclinic eddies. 2. Kinetic energy dissipation in rotating horizontal convection with and without surface stress occurs primarily in the interior of the flow and is not due to bottom drag. Direct Numerical Simulations indicate that this is true yet ocean circulation simulations with parameterized convection and turbulence suggest otherwise. 3. An input of mechanical energy in the form of a surface stress in opposition to a buoyancy-driven circulation leads to a two-cell circulation, in which the system is no longer governed by classical scaling arguments. 4. Spatial variability of the applied surface stress introduces new dynamical responses and energy pathways. The relative phase between wind and buoyancy forcing is thus important.
Broader Impacts: This renewal project will enable two graduate students to finish their thesis research and acquire skills in laboratory work and computational fluid dynamics. To reach pre-college students, the investigators will continue to contribute to the professional development of high school teachers in the San Diego Unified School District. In partnership with the NSF-funded Center for Ocean Science Education Excellence ? California, they will sponsor a one-day workshop for approximately 25 Earth sciences teachers. The numerical simulations in this project will be used as examples in a seminar class on scientific computing, aimed at introducing graduate students carrying out computational research at the Scripps Institution of Oceanography to the NSF-supported supercomputing facilities.
