In a mountainous region,the surface slope,orientation (i.e.aspect),and surrounding terrains have a strong impact on the surface SW radiation.Taiwan is a subtropical island with complex terrains.The Central Mountain Range extends from north to south of the island.There are numerous rivers with deep valleys emanating from central mountain regions to reach the east and west coasts within a short distance.The island is mostly hills and mountains.Topographic impact on the surface solar (or shortwave,SW) radiation was investigated using a 40-m high resolution digital topographic data and a radiative transfer model.With applications to the complex terrain of Taiwan,we found that the spatial variation of the surface SW radiation has a strong diurnal cycle.We developed a parameterization of the topographic impact on the surface SW radiation that scales the SW radiation computed for a flat surface without shading by surrounding terrains.The scaling is separately applied to the direct and diffuse radiation.It is applicable to all clear,aerosol-laden,and cloudy conditions and to all spatial resolutions with ix >40 m.