A new sub-grid surface mass balance model for continental-scale ice-sheet modelling: validation and glacial inception
Abstract
To investigate ice sheet evolution over the time scale of a glacial cycle, 3D Glacial Systems Models (GSMs) need to be run at grid resolutions (10 to 50 km) that do not resolve individual mountains. This will introduce to-date unquantified errors in sub-grid transport, accumulation and ablation for regions of rough topography during glacial advance and retreat. The extent to which these errors may account for the ongoing inability for GSMs to capture the inferred high rate of ice mass accumulation during glacial inception is unclear. Local climate and therefore surface mass-balance is sensitive to the terrain characteristics in a given grid cell. In the past, synthetic hypsometric curves, a cumulative distribution function of the surface elevation, computed using minimum, maximum and median elevation have been used in GSMs to describe the variability of these processes. However, past analyses with this approach still underestimate inferred ice volume during last glacial inception and the results obtained using this method have not been subject to detailed uncertainty analysis. Previous approaches have not addressed topographic characteristics such as the non-proportionality of the terrain slope to the hypsometric curve elevation variation, the ice draining out of the region at different elevation, or the ice flowing in lower elevations through valleys of different width. To address these limitations, we use a 1 km resolution digital elevation model to compute each local hypsometric curve and to determine local parameters to represent the hypsometric levels' slopes, widths and the percentage of every level draining outside each GSM grid-cell. 1D mass-transport for the sub-grid model is computed with the shallow ice approximation. We test this new sub-grid model for a conceptual case and on different regions of the Rocky Mountains, by comparing results against simulations produced by the 3D Ice Sheet System Model (ISSM) run at 1 km grid resolution. We also present ensemble results for North America to quantify the impact and remaining parametric uncertainties of this sub-grid model on glacial inception.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.C53B0580L
- Keywords:
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- 0798 CRYOSPHERE Modeling;
- 0762 CRYOSPHERE Mass balance 0764 Energy balance;
- 0726 CRYOSPHERE Ice sheets;
- 0776 CRYOSPHERE Glaciology