Comparison of the Met Office's surface exchange scheme, MOSES, against field observations

Results are presented from a comparison of the Met Office Surface Exchange Scheme (MOSES) with observational data. A stand‐alone version of MOSES is used which can be forced directly with observations rather than model output. The forcing data consist of near‐surface measurements of incident radiation, wind speed, temperature, pressure, humidity and precipitation, and the model output is compared with measured surface fluxes of sensible and latent heat and with soil moisture at several levels below the surface. The dataset spans four years and comes from a grassland site with a shallow water table, the Met Office Research Unit at Cardington in Bedfordshire, UK. The performance of the model is assessed in response to the variation of some key parameters and parametric functions. The model calculation of atmospheric fluxes is found to be robust to variations in the soil thermal properties, and it is shown that there is little overall improvement in model performance as the vegetation height and ratio of scalar to momentum roughness lengths are varied over a range of possible values. The calculation of atmospheric moisture flux and soil‐moisture profile is assessed using two constant subsurface profiles of saturated hydraulic conductivity and one profile which decreases with depth. It is found that the last of these can produce a more physically accurate profile of soil moisture, but with current model tuning this produces less accurate values of atmospheric moisture flux. The model results compare favourably with those of a force–restore model.