Graduate Student / Postdoc Seminar
Observing, quantifying and parameterizing macroscale turbulence in Earth's ocean
Speaker: Shafer Smith, Courant Institute, New York University
Location: Warren Weaver Hall 1302
Date: Friday, February 21, 2025, 1 p.m.
Synopsis:
Earth's ocean is `turbulent' across nearly all its scales, ranging from isotropic turbulence at the millimeter Kolmogorov scale, to highly anisotropic macroscale vortices with lateral scales that peak at a few hundred kilometers. Compared to the ocean's average depth of five kilometers, these vortices are like pancakes, taking on a very different character from the turbulence at the microscale. Macroscale turbulent flows account for a significant fraction of the ocean's kinetic energy, and play a leading role in the uptake and transport of heat and tracers like carbon and oxygen. The measurement, quantification, and representation of macroscale turbulence in global ocean circulation models is essential to achieve high fidelity climate simulations. Each of these tasks is enormously challenging.
The ocean is barely penetrable by light, so that even 50 years into the satellite era, and with thousands of autonomous drifting measurement devices, it is sparsely observed at depths past a few tens of meters. Observing from space provides an unprecedented global view, but even these measurements are limited to lateral scales of kilometers, and require us to use incomplete mathematical models to infer what happens below the surface. The world's largest supercomputers can now simulate the global ocean down to lateral scales coincident with the lower bound of satellite observations, but only for a few years of model time. It remains in the realm of hero simulations, far from what's necessary to achieve ensemble statistics. Thus for climate simulations, the effects of unresolved macroscale turbulence must be parameterized. Finally, even with a very high-resolution simulation, with unlimited access to the temporal and spatial scales that characterize macroscale turbulence, measuring their effects on the larger-scale flow is a surprisingly challenging task mathematically.
I will give a flavor of each of these major problems, highlighting current progress and interesting mathematical approaches and problems along the way.