On the Land Surface–Atmosphere Coupling and Its Impact in a Single-Column Atmospheric Model

Abstract

Abstract Three versions of the single-column European Centre for Medium-Range Weather Forecasts–Hamburg (ECHAM4) climate model are compared that differ either in the technique of the numerical coupling between land surface and atmosphere or the physical parameterization of the land surface processes. The standard ECHAM4 model utilizes a semi-implicit coupling technique between land surface and atmosphere in a way in which energy at the land surface–atmosphere interface is not conserved. This is a major deficiency. Two new model versions were developed: ECHAM4/IMPL and ECHAM4/SECHIBA. They incorporate an implicit coupling technique that conserves energy. ECHAM4 and ECHAM4/IMPL are identical with respect to all physical parameterizations they apply; the only difference is the coupling. In ECHAM4/SECHIBA, the ECHAM land surface scheme was replaced by SECHIBA (Schematisation des Echanges Hydriques a l’Interface entre la Biosphere et l’Atmosphere). The intercomparison of one-dimensional versions of these three...