Predicting the outcome of inertial instability in ocean currents and eddies

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

Inertial instability of a vortex can rapidly intensify radial velocity gradients, triggering an instability that then tears the vortex apart. Eventually the flow equilibrates as a set of new stable vortices. This process often proceeds through a strong turbulent phase that on the surface, might seem to preclude any possibility of predicting the final state. However, based on absolute angular momentum conservation, it is possible to deduce rules that show exactly how inertial instability acting alone would transform any unstable barotropic flow. Stabilization of inertial instability ultimately requires reducing potential vorticity to zero in the initially unstable region. Previous work has resulted in simple rules for angular momentum mixing which can be used to predict how an unstable barotropic vortex will evolve. This project will extend these results to: include the combined effects of inertial and barotropic instabilities, and to account for stratified flows. A method will be devised to predict the effect of the turbulent breakdown due to inertial instability and the subsequent production of meanders and vortices due to barotropic instability. The approaches will involve a new method in which small incremental changes in the velocity field are linked with changes in the shape of the isopycnals in a way that mimics the natural progression of the instability. The goal is to be able to predict the ultimate fate of any inertially unstable velocity profile, barotropic or baroclinic. This will include how many vortices will emerge from the instability, what their vorticity profiles will look like, how much energy they will carry away, and how much energy will be dissipated in the process. Intellectual Merit: This work will improve understanding of the role that inertial instability plays in production, transformation and maintenance of oceanic currents and eddies. The methods being developed here are new and fundamental. They should be applicable to any branch of rotating fluid dynamics. Broader Impacts: Results obtained through this research can have an important impact on the development of ocean models. Small-scale instabilities are not resolved in ocean models, but their role in developing and maintaining large-scale currents is very important. By studying these instabilities, their effects can be predicted, and could lead to parameterizations for ocean models. Improvement in ocean modeling can have an important impact on climate research because of the essential role that the ocean plays in controlling the climate.