Simulating tropical bare soil surface temperature using the force-restore method
The force-restore (FR) method is a simple and efficient approximation procedure that can be used for predicting soil thermal characteristics such as ground heat flux and the surface temperature. It uses a prognostic energy-balance equation and the response to a periodic heating caused by diurnal variation of the solar radiation. Several variants of the FR method exist and have been developed and tested for the high latitude regions, but is rare for the tropical areas. In this particular study, a force-restore (FR) model is adapted to simulate bare soil surface temperature and other thermal properties at an experimental site a (tropical location) chosen inside the Teaching and Research Farm of Obafemi Awolowo University Ile-Ife, Nigeria (7.55oN, 4.56oE). In the model, the surface energy balance equation used does not contain the latent heat flux term. Thus it was assumed that evaporation/condensation processes at the surface was neglected. The relative contributions of the imposed initial conditions; deep ground temperature, soil thermal characteristics, surface temperature, and cloud cover fractions, were used to investigate the performance of the FR model. The numerical simulations of the energy fluxes and surface temperature were then compared with the observed field data. The FR method worked quite well for estimating the diurnal variation of bare (dry) soil surface temperature within a range of ± 2.0oC from actual values. On clear and relatively dry days, the simulated net radiative flux attained a maximum value of (420± 10)Wm-2 at about 1400hrs local time. It was found that the bare soil surface temperature depends essentially on the soil thermal properties, deep soil temperature and the cloud cover fractions. The result of this study is found useful for agrometeorological purposes particularly for predicting the soil surface temperature and frost conditions.