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Faculty Profile

Zhan Su

Earth, Atmospheric and Planetary Physics
Assistant Professor


Welcome to the Department of Physics Dr. Su. Your PhD is in Oceans Physics from the California Institute of Technology. Can you tell us about your research?

My research aims to apply mathematical and modeling techniques to study ocean fluid dynamics, mainly the theoretical part, such as ocean turbulence, as well as the associated climate effects. Due to the essentially nonlinear and stochastic nature of these processes, I need to develop sophisticated quantitative models or statistical methods to study them, as well as using big datasets.

My PhD work is mainly about the theory of ocean deep convection and mesoscale eddies. I found that a special type of ocean convection, called thermobaric convection, can occur very abruptly and strongly. Within a few days, the ocean column can be totally mixed due to such convection, which impacts ocean tracer transports and the global ocean circulation. I have developed a theory of the energetics of such convection that helps to understand and quantify such convection.

I also worked on ocean mesoscale eddies (at scales of roughly 50-200 km). The ocean is full of mesoscale eddies and these mesoscale eddies account for the majority of oceanic kinetic energy. An important energy source for these mesoscale eddies comes from the release of Available Potential Energy (APE) through Baroclinic instability. My research better characterizes the general relations between APE and Eddy Kinetic Energy (EKE).

Why did you choose to study the oceans?

I liked the courses of mechanics, physics and applied mathematics, when I was in undergraduate school. When I started my graduate studies at Caltech, after trying a few very different projects, it seems that ocean fluid dynamics captured my interests the most. I felt that I could apply my skills of applied mathematics in such research, including the skills of modeling, theory, and big data analysis. Also, I liked the fact that ocean motions are so stochastic; but the physics behind them is so beautiful and organized.

You did your post-doctoral fellowship at NASA and Caltech. What did you work on during that time?

I worked on the modeling and analysis of ocean submesoscale turbulence (at scales of 0.1-10km), by taking advantage of the powerful supercomputer and their datasets at NASA. Also, I studied the dynamics behind the trend of Antarctic sea ice. Both are exciting.

It must have been really cool to work with NASA, what was your favorite part of the experience?

NASA provided lots of resources for computing and it was a lot of fun to handle ~5 petabytes of big datasets. Also, they have an excellent animation group that can make very beautiful movies based on the datasets you provide. The collaborations with experts there was very helpful as well

You also spent time as a post-doctoral researcher at MIT. What did you work on during that time?

I used machine learning, including neural network and random forests algorithms, to parameterize the ocean turbulent heat flux.

What are your research plans at the University of Toronto?

I will focus on the research of ocean fluid dynamics, including large-scale ocean circulation, ocean turbulence, and ocean-ice-atmosphere interaction, as well as the resulting effects on the climate. Specifically, by taking advantage of the current quick improvement of computing power and more datasets from observations, I believe it is a time that we can make lots of progress in this field.

Can you tell us about your YouTube movie The Turbulent Gulf Stream that we are sharing with our readers below?

This movie shows our simulated ocean turbulence at the North Atlantic at a very high resolution (~2 km resolution). The quantity shown is relative vorticity, a measure of the spin of fluid parcels, that emphasizes the turbulent nature of ocean motions across a broad range of scales. We find that such fast-rotating turbulent motions are crucial to transport physical and biogeochemical tracers (e.g. heat, carbon), and power the large-scale ocean circulation, which impact on the global climate.

The turbulent Gulf Stream

What are you most excited about being in Toronto?

In addition to the research at the University of Toronto, I am also very excited about the food in Toronto. It seems so convenient to get the diversity of food of any country in Toronto.