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There are two ways in which this can be achieved; either take an existing set of model initial files (the ICM*INI* files) and interpolate pressure to the surface, or run the model and adjust the orography and pressure whilst the model is running to prevent a sudden 'shock'.

Also see

ECMWF took part in the 2012 Dynamical Core Model Intercomparison Project (DCMIP). More information can be found here: https://www.earthsystemcog.org/projects/dcmip-2012/

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