Research

My research is centered on polar ocean dynamics, with a recent focus on ice-ocean interactions from the mesoscale to microscale near and around ice shelf cavities and fjords in Greenland and Antarctica. Please also see the Movies page for some visualizations of recent work.

Completed Work

(6) Roles of Geometry and Standing Eddies in Mediating Fjord-Shelf Exchange

A key feature of high resolution fjord simulations that emerges when realistic fjord bathymetries are used are standing eddies. We discovered the existence of these eddies using high-resolution MITgcm fjord simulations, which used datafrom the NASA OMG (Oceans Melting Greenland) observations. This builds on the understanding of fjord recirculation from idealized theories in projects (1),(2), and (4) by concentrating the vorticity dynamics to a series of standing eddies, which have the potential to amplify glacial melt rates.

(5) Improved Parameterizations of Vertical Ice-Ocean Interfaces.

Currently, the momentum, heat, and salt fluxes at vertical boundaries between ocean and ice faces (glaciers and icebergs) is poorly represented and leads to order of magnitude discrepancies in melt at the warmest glaciers. I used Large Eddy Simulations and Direct Numerical Simulations to better understand the dynamics at these boundary layers.

(4) Linking Overturning, Recirculation, and Melt in Glacial Fjords

Glacial fjords are long, narrow, and deep inlets that connect glaciers to the open ocean. These glacial fjords exist around the margins of Greenland, West Antarctica, Alaska, and other regions, and collectively contribute a significant source of ice discharge into the ocean. Over the past two decades, tidewater glaciers in Greenland have accelerated, which can lead to sea level rise, and there is growing evidence that this acceleration is caused by deep warm water currents that flow into the fjords from the open ocean. These warm water currents have the potential to melt the submarine sides of glaciers, causing them to retreat over time. The dynamics of warm water delivery to the glacier face, particularly its interaction with fjord circulation, are presently poorly understood.

(3) Dynamics of Eddies Generated by Sea Ice Leads

I co-supervised Kaylie Cohanim, who was an undergraduate researcher at UCLA. Kaylie used an idealized MITgcm configuration to study submesoscale eddy generation beneath sea ice leads.

(2) Geometric Constraints on Glacial Fjord-Shelf Exchange

The oceanic connections between tidewater glaciers and continental shelf waters are modulated and controlled by geometrically complex fjords. These fjords exhibit both overturning circulations and horizontal recirculations, driven by a combination of water mass transformation at the head of the fjord, variability on the continental shelf, and atmospheric forcing. However, it remains unclear which geometric and forcing parameters are the most important in exerting control on the overturning and horizontal recirculation.

(1) Sill-Influenced Circulation in Ice Shelf Cavities

This work was highlighted on the UCLA physical sciences division website: www.physicalsciences.ucla.edu/spotlight-ken-zhao/

There are vast cavities forming beneath some of the fastest melting ice shelves in West Antarctica and northern Greenland. One notable example is the Pine Island Glacier in West Antarctica. The Pine Island Glacier has a tall bathymetric sill or “bump” in the seafloor that holds back relatively warm (by a few degrees) water from the open ocean. This work seeks to understand how the height of the bump holds back open ocean, warm water from melting the glaciers in these regions.

Current Work

(7) Ice-Ocean Boundary Layers

I am using Direct Numerical Simulations to understand and guide observations at LeConte Glacier, Alaska and provide improved parameterizations of melting glaciers and icebergs. This work aims to provide a physical understanding of convective and shear ice-ocean boundary layers and how melt plumes may achieve a much stronger melt rate due to interaction between horizontal currents with the buoyancy-driven plume dynamics. These ideas will be tested and confirmed in upcoming field campaigns in Alaska. As part of this work, I am contributing to the deployment and development of instrumented platforms.

(8) The Influence of sub-Ice Shelf Channels on Melt

I am co-supervising Sarah Villhauer, who is an undergraduate researcher at UCLA. Sarah is using idealized models of sub ice-shelf channels to study the role of geometry on the circulations within these channels and their role in driving melt.

(9) Submesoscale Eddies beneath Antarctic sea ice

I am co-supervising Jennifer Kosty, who is an undergraduate researcher at UCLA. Jennifer is using seal and Argo data to find and analyze submesoscale eddies below sea ice around Antarctica.

(10) Energy Balance in the Shallow Water Equations

I am investigating the mean-eddy decomposition of the kinetic and potential energy balance relations in isopycnal coordinates. The differences between the energetics in isopycnal and z-coordinate systems are important to the interpretation of results using such models.

(11) Mechanisms of Barotropic Oceanic Zonal Jet Formation

Satellite altimetric observations and numerical simulations of the extra-tropical and mid-latitude oceans reveal the presence of weak zonal jets, embedded in a field of Rossby waves and mesoscale eddies. The precise mechanisms of jet formation, their interplay with waves and eddies — even their existence as distinct entities — remains a topic of debate. Here we revisit this problem through the lens of freely-evolving periodic shallow water quasi-geostrophic simulations, initialized with both wave and random-field initial conditions.