our simulations of the surface mass balance (SMB) of the Greenland ice sheet (GrIS) are compared over the period 1960-2008. Three use a regional climate model to downscale ECMWF reanalysis (ERA-40) and operational analysis data, while the fourth uses the same inputs but an empirical downscaling approach and melt model. These reconstructions have been used in a variety of applications but prior to this study little was known about their consistency with each other and the impact of the downscaling method on the result. The reconstructions are compared to assess the consistency in regional, seasonal and integrated 5MB components and evaluated against a suite of observational data. Three key areas of difference between the models have been identified. Firstly differences in how the ERA-40 reanalysis data are downscaled by the models. Secondly differences in how the 5MB components are calculated. And thirdly differences in the domain, the ice sheet mask used. Total 5MB estimates for the GrIS are in agreement within 34% of the four-model average when a common ice sheet mask is used. When models' native land/ice/sea masks are used this spread increases to 57%. The components of 5MB, with the exception of refreeze, show a similar level of agreement once a common mask is used. Previously noted differences in the models I estimates are partially explained by ice sheet mask differences. Agreement is higher (18% spread) in the accumulation area than the ablation area (38% spread) suggesting relatively high uncertainty in the estimation of ablation processes. Regionally there is less agreement, suggesting spatially compensating errors improve the integrated estimates. Modelled 5MB estimates are compared with in situ observations, gravimetric observations from GRACE and altimetry observations from ICESat. Through the use of a surface density and firn compaction model individual components of 5MB are, indirectly, able to be evaluated against altimetry observation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:633454 |
| Date | January 2013 |
| Creators | Vernon, Christopher L. |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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