The representation of snow in land surface schemes: Results from PILPS 2(d)

Twenty-one land surface schemes (LSSs) performed simulations forced by 18 y r of observed meteorological data from a grassland catchment at Valdai. Rus sia, as part of the Project for the Intercomparison of Land-Surface Paramet erization Schemes (PILPS) Phase 2(d). In this paper the authors examine the simulation of snow. In comparison with observations, the models are able t o capture the broad features of the snow regime on both an intra- and inter annual basis. However, weaknesses in the simulations exist, and early seaso n ablation events are a significant source of model scatter. Over the 18-yr simulation, systematic differences between the models' snow simulations ar e evident and reveal specific aspects of snow model parameterization and de sign as being responsible. Vapor exchange at the snow surface varies widely among the models, ranging from a large net loss to a small net source for the snow season. Snow albedo, fractional snow cover, and their interplay ha ve a large effect on energy available for ablation, with differences among models most evident at low snow depths. The incorporation of the snowpack w ithin an LSS structure affects the method by which snow accesses, as well a s utilizes, available energy for ablation. The sensitivity of some models t o longwave radiation, the dominant winter radiative flux, is partly due to a stability-induced feedback and the differing abilities of models to excha nge turbulent energy with the atmosphere. Results presented in this paper s uggest where weaknesses in macroscale snow modeling lie and where both theo retical and observational work should he focused to address these weaknesse s.