Evaluation of two turbulence parameterization schemes in the Community Climate System Model and their representation of the diurnal cycle

Evaluations of climate models have mostly been focusing on yearly, seasonal and monthly averages. However, the daytime and nighttime planetary boundary layers are in general very dissimilar. To accurately simulate the boundary layer it is therefore also important that the diurnal cycle is well represented. The Community Climate System Model (CCSM) has recently implemented a new boundary layer parameterization scheme: the University of Washington moist turbulence scheme. A previous version of the model, using the Holtslag and Boville parameterization, is retained as an alternative option. Multi-year observations from a number of sites, most of which are part of FLUXNET, are used to evaluate how well the two different parameterization schemes in CCSM manage to simulate the diurnal cycle in the planetary boundary layer. FLUXNET is a global network of micrometeorological tower sites that provides an extensive data source of near-surface parameters and turbulent surface fluxes from various regions of the Earth. The emphasis of our study is on near-surface temperature, wind and turbulent fluxes.