The Role of Soil Moisture in Land-Atmosphere Interactions

Abstract

Soil moisture plays a crucial role in land-atmosphere interactions through its ability to divide the incoming radiation into latent heating and sensible heating. Accurate modelling of soil moisture could significantly improve numerical weather prediction, but observational data is difficult to obtain. In this research, the Tiled ECMWF Scheme for Surface Exchanges over Land (TESSEL) is coupled to Whiffle’s large eddy simulation model called GRASP and the behaviour of this system is explored. It is concluded that TESSEL is highly sensitive to initial conditions of soil moisture and soil parameters. In 6 months of model runs, rain-soil moisture coupling improves the model results through increased latent heating. Differentiation between soil types in Cabauw and Gilze-Rijen also increases the model skills, concluded from decreased biases and increased correlations with observations of surface fluxes, temperature, humidity and wind speed. This effect is strongest in summer and also influences wind speed and cloud formation. In a radiation fog case study, initialization with atmospheric observations produced a fog layer close to observations in depth, with the dissipation delayed by an hour. For this model set-up, it is recommended to permanently add differentiation between soil types, so that the initial soil moisture matches the soil parameters. Some improvements made to TESSEL should be added such as the conductivity formulation, the bare soil evaporation and the addition of surface run-off. In future research the behaviour of the system during heavy rainfall could be studied, as well as the influence of open boundary conditions and the use of other data sources for initialization.