Geophysical fluid turbulence

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The requested funds are for the study of geophysical fluid turbulence employing high-resolution numerical simulations and analytical techniques. It goes without saying that our attempts to understand scientifically the big environmental questions of the day are extremely dependent on numerical models of the atmosphere - ocean - cryosphere - land surface system. Yet these are faced with the enormous complication of the true system. In order to account for all important physical effects, numerical shortcuts have to be made. Most important of these is that the simulated range of length and time scales, as determined by model resolution, is extremely reduced compared to reality. The victim of this brutal simplification is the turbulent mixing of all of the quantities of interest. In order to know anything about the future distributions of such vital things as carbon dioxide, ozone, pollution, etc, one needs to know their sources, their sinks and how the atmosphere-ocean system mixes them. The focus of this research is on the latter with the view that understanding turbulent mixing is a necessary first step to being able to account for it when it is not explicitly resolved. Specifically, the influence of aspects of the atmospheric and oceanic setting, such as rotation and stratification, will continue to be identified. For example, the nonlinear interactions between the resulting wave motion and the vortices, ubiquitous in turbulent flows, will be a primary focus. A number of detailed topics are presented below. They include a heightened focus on the anisotropy of passive tracer mixing, the effect of condensation and evaporation of water in this setting, the change of predictability caused by moisture, the challenging limit of stably-stratified turbulence when rotation is weak (at the heart of mesoscale meteorology and the most difficult limit in boundary-layer turbulence), the breakdown of higher-order balance and the role of small-scale vortex tube stretching in extreme events. The dependence of this work on numerical simulation implies that it is a rapidly-evolving field and research on numerical methods will continue to be undertaken in parallel. My group has been at the forefront of this type of research and has a proven track record of being useful in this regard.