A few things I work on

Have questions about my work? Email me at gregory.leclaire.wagner@gmail.com. See my github for real-time updates on my software projects.

Turbulent surface boundary layers

I am developing models for turbulence in the ocean’s surface boundary layer with ‘optimized’ and uncertainty-quantified parameters. This work is part of the CliMa project.

I presented this poster at Ocean Sciences 2020 in San Diego:

OSM20

The poster shows some recent progress I’ve made comparing different one-dimensional models for turbulence near the surface of the ocean to high-fidelity numerical simulations. We come to the conclusion that one model outperforms another in the narrow context we’ve considered so far, but there’s a lot of work left to do.

Oceananigans.jl

In the course of my work on turbulent boundary layers, I run a lot of large eddy simulations using Oceananigans.jl. Oceananigans.jl is a fast and friendly code for simulating the motion of fluids that I’m helping to develop.

Oceananigans docs

Oceananigans.jl is written in the Julia programming language and runs on CPUs and GPUs.

Surface gravity waves and wave-turbulence interactions

Frothing, whitecapping, undulating surface waves are the top of the ocean surface boundary layer. I work both on the theory of surface wave forcing and momentum transfer between the atmosphere and ocean, and on interactions between surface waves and boundary layer turbulence.

The image below depicts turbulence simulated by Oceananigans.jl. The image shows the turbulent vertical velocity field that develops following the growth of a surface wave field with a wave length of one hundred meters over four hours.

Forced growth

Information about how to produce this image can be found on github, or in our paper’s preprint.

Squeeze dispersion

Squeeze dispersion is a phenomenon by which the dispersion of tracers is enhanced in the presence of fluctuating strain.

The image below illustrates two layers of fluid that are colored green and blue and on which a tracer c has different concentrations. Due to this difference in tracer concentration, the tracer ‘fluxes’ across the fluid between the two layers at the rate F.

Squeezing

Because the flux F is inversely proportional the the thickness of the layer, squeezing and straining increases the tracer flux across the layer on average, all else equal.

Squeeze dispersion can matter in systems where mixing is inherently diffusive, including, for example, the mixing of heat and carbon in the ocean’s abyss. More information about squeeze dispersion is given in our paper that was published in Geophysical Research Letters in 2019.

Internal waves and quasi-geostrophic flow

In a past life I studied the interaction between ‘internal waves’ – giant, deep, slow cousins to surface waves and ‘quasi-geostrophic flow’, or the currents and eddies that comprise the ocean’s weather.

The image below depicts idealized ocean weather (depicted by potential vorticity, Q) and an internal wave field (depicted by the horizontal wave velocity, u) that distort and interact with one another.

Wave-induced flow

The effect of waves on weather are associated with the ‘wave-induced flow’ (depicted by its speed, |∇χ|) — mean currents associated with the ‘nonlinearity’ of the wave field.

FourierFlows.jl

FourierFlows.jl is julia software that solves fluid dynamics problems on CPUs and GPUs. I develop FourierFlows.jl with Navid Constantinou.