Talk by Ed Bueler, University of Alaska – Niels Bohr Institute - University of Copenhagen

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Talk by Ed Bueler, University of Alaska

Talk by Ed Bueler, Dept of Mathematics and Statistics and Geophysical Institute, University of Alaska, Fairbanks

abstract: 

Polythermal conditions are found on small valley glaciers and near the bases of ice sheets.  Models employing conventional temperature-based "cold-ice" methods do not account for the latent heat stored as liquid water within temperate ice, so such schemes are not energy-conserving as temperate ice appears or disappears with changing conditions. 

Accurate time-dependent calculations of basal melt rates, in particular, which are critical for constraining basal hydrology and bed resistance in fast flow situations, are strongly dependent on conserving energy in the polythermal ice near the base of ice sheets, even when only a small ice sheet volume fraction is temperate ice. 

Fortunately, temperature and water content are functions of a single enthalpy variable, which can serve as the energy state variable in the model.  A small enthalpy change in cold ice reflects a change in temperature, while a small enthalpy change in temperate ice is a change in water content. 

An enthalpy formulation is a relatively-straightforward replacement for a temperature-based conservation of energy scheme in any thermomechanically-coupled ice sheet flow model.  We describe the implementation in the Parallel Ice Sheet Model, and compare model results for the Greenland ice sheet.

This is joint work with Andreas Aschwanden and Heinz Blatter.