An energy balance model for prediction of surface temperatures.

Typ: Rapport
Serie: RMK 63
Författare: Alexandersson, Hans., Gollvik, Stefan, Meuller, Lars


From the winter season 1988/89 and onwards an energy balance model has been used to estimate surface temperatures within a weather seivice system for the road authorities in "Östergötlands" and "Göteborg-Bohuslän" in Sweden. It is based on a simplified form of the energy balance equation at the surface and a numerical model with ten layers in the ground or road. In the road seivice system manually given forecasts of clouds and wind are used as input into the model. The initial values of surface temperatures are obtained on-line from the road stations involved. Forecasts of surface temperatures have been made for up to five hours and give significantly better results than e.g. perstistency or linear trend forecasts.

The model has also been generalized to run directly on model output clouds an winds and to give forecasts for a large area. As starting values we then use screen temperatures analysed in a grid net with a resolution of about 20 km covering Scandinavia. Initial surface temperatures are obtained through extrapolation to the ground. Through a relaxation formula forecasted surface temperatures are then transformed back to screen level. The temperature forecasts obtained in this way seem to be much better than the LAM-model gives where the daily amplitude is too small.

This latter model is henceforth called the objective system while the former is called the road seivice system. The two aystems have large parts in common. Differing parts are indicated in section headings ant text.