Global Dynamics Approach to Gap Leaping and Loop Current Systems

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Loop currents, such as those in the Gulf of Mexico or South China Sea, represent an important part of the ocean circulation. Linking the coastal and open ocean, they affect regional climate and ecosystems through the transport of nutrients, species and heat, with more direct influence on human population through the transport of pollutants and influence on hurricane intensity. It is well known that the Loop Current dominates the upper 1km of circulation in the Gulf of Mexico and is likely a major driver of the deep circulation. Despite its importance, little is understood about the dynamics of loop currents in real ocean situations. Laboratory experiments and idealized numerics (conducted by PI and his collaborators) have recently confirmed the existence of multiple steady states and hysteresis in loop current systems, as well as provided a framework under which these complex dynamics might be understood. That is, the global dynamics of loop current systems appear to be governed by a cusp catastrophe geometry of solutions. The objective of this work is to experimentally and theoretically expand the Cusp formulation of gap-leaping boundary currents toward more realistic oceanographic scenarios, so that such global dynamical systems understanding can be more broadly applied to actual oceanographic systems. This will be accomplished through a combination of rotating table laboratory experiments and theoretical considerations. The results of this research will better inform decision makers about the effects of climate change and other environmental stressors on semi-enclosed basins. The confirmation and systematic extension of the multiple states hypothesis (cusp catastrophe framework) in realistic ocean conditions will impact a wide range of fields. In the Gulf of Mexico, hurricane intensity may be predicted more accurately if loop currents are modeled correctly. It will also provide a means for ?bringing ocean education inland? with at least one graduate student and one undergraduate student participating directly in this project, but more generally it will help establish an inland hub for oceanographic education, thus exposing a largely unrepresented population to ocean science. The project will also serve to assist in the professional development of junior faculty PI, and the dissemination of results will present a unique approach to fundamental geophysical fluid dynamic interaction.The cusp catastrophe perspective follows from a dynamical systems interpretation of the Loop Current (which in this case represents a global dynamical systems approach to Gulf of Mexico circulation). It has been shown that when the control parameters of inertia (current strength) and vorticity constraints (which physically relate to sea level, wind forcing, stratification and topography) are varied, the loop current systems undergoes global bifurcations. By tracing the Loop Current state on the catastrophe surface, transitions between a looping state, a non-looping state and a periodic eddy shedding state can be understood in a logical and predictable way. The cusp catastrophe represents a fundamentally different way of thinking about Loop Current dynamics. Traditional studies of the Loop Current have focused on quantification/identification of frontal eddy formation and propagation, barotropic and baroclinic instability development, and other local dynamical features. The cusp catastrophe formulation suggests that these local dynamics are merely symptoms of a global system bifurcation. An important consequence of this theory is that semi-enclosed basins are likely to exhibit extreme sensitivity to subtle climate shifting. It should be noted that the cusp catastrophe follows from a balance between inertia and vorticity constraints which are prevalent throughout the entire ocean system, suggesting the results of this study are broadly applicable.