Modelling topographic influences on the radiation balance

The aim of this project is the accurate prediction of the spatial distribution of local surface temperatures in mountainous terrain, what is in particular of interest for a detailed winter surface energy balance for avalanche formation and road surface condition prediction. It is found that a detailed surface radiation balance is essential. Thus considering complex terrain with a spatial resolution of tens of meters or below topographic shading, single and multiple reflections at surrounding terrain surfaces and atmospheric backscattering should be taken into account. Especially the influence of multiple reflections on the netto incoming shortwave radiation becomes most important in the presence of large fluctuations in surface albedo values, which may be of order of 90 % for partly snow covered domains. But the implementation of such a detailed radiation transfer normally results in high memory requirements at least for relatively large model domains with local resolutions.

As solution a common approach (using sky and terrain view factors) is to be implemented in the radiation balance model of the modular model system Alpine3D. Further investigations are dedicated to measurements of single radiation components, to model evaluations, to modelling patterns on artificial digital height models as well as to the influence on road surface temperatures.

Multiple reflections in complex topography (N.Helbig).