Data Assimilation Meetings at Reading

Date Meeting type Speakers
12 June 2013 Invited Speaker Stephen Cornford (University of Bristol)
Adaptive mesh modelling of grounding line retreat in West Antarctica
Satellite-based observations suggest that the West Antarctic ice sheet is actively contributing to sea level rise though the dynamic response of it outlet glaciers to ocean warming. Specifically, most of the glaciers are somewhat slowed by the drag of their floating ice shelves, and as these shelves thin the glaciers speed up. That results in both upstream thinning and, potentially, rapid retreat of the grounding line joining the glaciers to their ice shelves. Today, such dramatic dynamics are limited to the Amundsen Sea sector of the ice sheet and, in particular, Pine Island Glacier. Numerical models are needed to assess how these processes may evolve over the coming centuries and whether other sectors of Antarctic will be affected. The modelling of grounding-line migration is, however, technically challenging and we have developed an adaptive-mesh finite volume method which employs sub-kilometer resolution to that end. Unsurprisingly, the model is plagued with unknown parameters, such as the spatially varying stiffness of the ice and the strength of its attachment to the bed, and the present day rate of mass loss underneath the ice shelf. We can go some way to estimating these parameters using conventional optimization and regularization methods to solve the ill-posed problem which relates the model's flow speed to observed flow speed, but there are more observations we could and should make use of. These are typically sparse but perhaps good enough to discriminate between parameter sets that our present optimization problem alone cannot. For example, satellite measurements of surface elevation sample tracks separated by kilometers and years but nonetheless provide a record of grounding line migration and thinning.

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