Andrew Wells

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Andrew Wells

Associate Professor

I am an Associate Professor in Physical Climate Science.

I am interested in fluid mechanics and thermodynamics, motivated by geophysical processes. My work uses mathematical and numerical methods to develop theoretical models, informed by analogue laboratory experiments. Current research areas include the physics of sea ice, interaction of ice sheets and glaciers with the ocean, and turbulent buoyancy-driven fluid flow.

Our research considers fluid mechanical and thermodynamic processes that underly geophysical and climatic phenomena, with particular emphasis on the interactions of ice and oceans in the polar regions. Recent areas of interest include understanding the growth of sea ice, and melting of large glacial ice shelves and icebergs.

Sea Ice in the Arctic and Antarctic

More than 20 million square kilometres of ocean freezes over each year during the Arctic and Antarctic winters as part of the seasonal waxing and waning of the sea ice cover. You can find an animation of the evolving sea-ice cover between 1978 and 2006 at The Cryosphere Today website, where the colour scale shows the fraction of ice coverage or "ice concentration" at each point in the image.

The evolving sea ice cover can have important consequences for the climate. For an indication of some potential consequences see this BBC news article and video feature.

One are of our research focuses on the early stages of ice growth each year. As ocean water freezes its salt separates from the relatively pure ice crystals, with the resulting sea ice comprising of salty brine trapped within a porous matrix of ice crystals (much like water in a sponge). As the sea ice grows further this dense salty water drains from the ice and sinks, helping to maintain the thermohaline circulation of the ocean.

We are developing numerical and theoretical models to describe how quickly this salty water drains from the ice and the resulting structure of the remaining ice matrix. This work will improve our understanding of the interaction of sea ice with both the oceans and atmosphere. As an interesting spin off, our simulations also provide insight into industrial solidification processes such as the casting of metal turbine blades, where the same solidification and fluid flow processes are in action and control material microstructure.

Another recent area of interest is heat transfer in melt ponds, which are puddles of water that collect on the surface of Arctic sea ice during summer melt. Melt ponds play a key role in the ice-albedo feedback, with incoming sunlight absorbed in the ponds rather than being reflected off bare ice. Motivated by recent observations of melt ponds on Arctic sea ice, we are using numerical simulations and theory to study the fate of the heat absorbed in melt ponds. The internal heating leads to convective flow, which plays a key role in determining how much of the heat is lost back up into the atmosphere, versus going down into the ice to contribute to melt (see Movie of simulated convection in a radiatively heated melt pond).

Melting Ice Shelves and Icebergs

In many places the vast polar ice sheets flow off the land, creating ice shelves that float in the ocean or fracture to form icebergs. Floating ice shelves can be many hundreds of kilometres in length and extend thousands of metres below the ocean surface. Melting at the base of an ice shelf creates fresh, buoyant meltwater currents that rise along the underside of the ice and generate ocean circulations (much like warm air rising next to a household radiator). This convection also enhances the supply of heat to the ice, promoting further melting.

I have developed models to describe this convection process on the vast scale of ice shelves and large tabular icebergs, helping to improve predictions of ice shelf melting. This has implications for ocean currents and the stability of the polar ice sheets.