Numerical investigation with a physically based regional interpolator for off-line downscaling of GCMs: FIZR

Abstract

The model is physically based and it requires outputs from a previous GCM integration. The methodology is based upon the premise that much of 'small-scale' variability is often the result of surface forcings rather than small-scale dynamical effects. Following on this consideration, the present work seeks to address the question of regional climate diagnostics by combining precomputed GCM atmospheric large-scale transports of momentum, heat, and moisture, called 'the dynamics', with recomputed GCM subgrid-scale parameterized effect, called 'the physics', including an additional mesoscale forcing term that is parameterized in terms of large-scale flow resolved by GCM coupled with fine-scale geophysical surface fields. This combination is integrated in a prognostic mode on a high-resolution grid over a chosen limited area of the earth. This is an original one-way nesting technique and it offers major advantages over simpler techniques used to interpolate GCM outputs down to finer scales. The model is nicknamed FIZR: FIZ serves to remind that the model is physically based, and R stands for regional.