Predicting Incoming Radiation from Long-Term Temperature and Sunshine Records in Britain

Solar radiation is the primary energy source for plants, and governs the land surface energy balance and evapotranspiration. However, solar radiation is recorded at relatively few meteorological stations. Where radiation measurements are not available, they must be estimated from more readily available variables. Measurements of global solar radiation at 18 locations in Britain were compared against estimates from two models based on temperature, and one model based on sunshine hours, using data from U.K. Meteorological Office stations. Preliminary analysis shows that agreement between measured and predicted monthly radiation is close in all three methods when using published parameter values. Agreement is increased when model parameters are fitted to the observations. However, much of the variation is explained simply by the annual cycle in incident radiation at the top of the atmosphere. The relative merits of each method in explaining the residual variation are discussed.