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Grid ENabled Integrated Earth system model |
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Earth System Modelling
The following components will be integrated in various realisations of the GENIE model. All components are comparable to, or significant advances over, most existing intermediate complexity models.
(a) Energy-moisture balance atmosphere: A standard 2-D diffusive model of atmospheric heat and moisture transport, incorporating radiation and bulk transfer formulae for air-sea and air-land surface fluxes of heat and moisture (Weaver et al. 2001) will be used in the "GENIE-Trainer".
(b) 3-D Ocean: A 3-D, non-eddy-resolving, frictional geostrophic model (Edwards et al 1998, Edwards and Shepherd in press) will be used throughout. This allows much longer time-steps than a conventional ocean GCM by neglecting acceleration and momentum transport, to obtain the large-scale, long-term circulation only. More than 5 man-years of effort have been invested in developing this model.
(c) 3-D Atmosphere: A 3-D, non-transient-eddy-resolving, stationary wave model (Valdes & Hoskins 1989) will be used in "GENIE-Mini" and "GENIE-Whole". This uses the same equation set as in a conventional atmospheric GCM but allows a much longer time-step (~1 month rather than 30 minutes), by parameterising baroclinic instability.
(d) Land surface, hydrology and biogeochemistry: A simplified version of the MOSES land-surface scheme (Cox et al. 1999), already developed by P. M. Cox of the Hadley Centre, will be used in "GENIE-Mini". This allows a longer time step than full MOSES (~12 hours rather than 30 minutes) by excluding fast processes (e.g. canopy interception). The 'TRIFFID' model from the Hadley GCM will be used to capture vegetation dynamics and their effect on land surface properties. CEH Wallingford will isolate the source codes, help define the coupling to the atmosphere and runoff to the ocean, and add meta-data. Next, carbon and nitrogen cycling will be switched on and biogeochemical coupling to the atmosphere and ocean included. Finally, a fully 'traceable' (to the GCM) land-surface scheme will be developed for "GENIE-Whole". This will retain all MOSES processes but explicitly time-average to achieve a fast version with a long time-step.
(e) Sea-ice: A 2-D sea-ice model, incorporating standard thermodynamics (Hibler 1979) and elastic-viscous-plastic dynamics (Hunke and Dukowicz 1997) will be included in "GENIE-Mini" and "GENIE-Whole".
(f) Ocean biogeochemistry: Existing representations of marine carbon and nutrient (phosphate, silicic acid, and iron) cycling (Ridgwell 2001) that have been successfully applied to questions of past (Watson et al. 2000) and future carbon cycle behaviour, will be integrated into the 3-D ocean model by UEA.
(g) Marine sediments: A model of the interaction of the deep-sea geochemical sedimentary reservoir with the overlying ocean will be included in "GENIE-Whole". This will be derived from an existing representation of opal diagenesis developed at UEA (Ridgwell 2001) and from standard schemes for dissolution of calcium carbonate and remineralisation of organic matter. It will enable GENIE to capture the 'slow' (>1kyr) response of the ocean carbon cycle to perturbation, and facilitate model testing by comparing predicted sediment core records with actual records. UEA will define the asynchronous coupling of the sediments to the ocean, and add meta-data to the component code.
(h) Ice sheets: An existing ice sheet model (Payne 1999) will be applied to simulate glacial maximum ice sheets and deglaciation in "GENIE-Whole". It will operate at finer spatial scales (currently scaleable over a range 20-100+ km grid cells), but longer (decadal) time steps than other components. It now includes fast ice flow and can be used to study large-scale surging, important in phenomena such as Heinrich events. Bristol will first develop a stand-alone simulation of full glaciation. Then the atmosphere (and ocean) will be coupled in an asynchronous fashion and the coupled model implemented at coarse resolution to aid mass-balance parameterisation. Spatial and temporal changes in ice-sheet extent and thickness, surface albedo, topographic blocking effects on atmospheric circulation, and the output of freshwater to the ocean will all be simulated. Finally, the model will be implemented at finer resolution to capture the flow physics more accurately.