Simulating the diurnal temperature range: Results from Phase I(a) of the Project for Intercomparison of Landsurface Parameterisation Schemes (PILPS )

This paper discusses the contribution climate models could make to objectives of the Minimax Workshop in terms of simulating the present-day maximum and minimum daily temperatures. Using atmospheric forcing data generated from a climate model, a series of land surface schemes, participating in the Project for the Intercomparison of Land surface Parameterisation Schemes (PILPS) were run to equilibrium. Atmospheric forcing data for a tropical forest and a grassland grid point were used. Land surface parameters for both locations were provided so that differences in the results would be due to physical differences between the models rather than differences in the surface characterisation. Failures in prescribing all surface parameters identically led to some differences between model simulations. Results were collected at annual, monthly and selected daily time scales for surface temperature, evaporation, sensible heat flux, snow depth and runoff. It was found that there was some agreement between the models in the prediction of annually averaged temperatures with a range, between all the models, of 2.5 K in the case of the tropical forest and 3.8 K for the grassland. Evaporation and sensible heat, averaged over a year, shows less inter-model agreement. Predictions for the tropical forest range from -40 to +50 W m^-2 for the sensible heat flux and +90 to +170 W m^-2 for evaporation. For the grassland, predictions range from -22 to +22 W m^-2 for the sensible heat flux and +25 to +62 W m^-2 for the latent heat flux. However, when results at the diurnal scale were considered, the reasonable agreement in the annually averaged results were not repeated. This is illustrated by comparing the diurnal range in effective temperature simulated by the PILPS models for the days reported.