The Spatial Variation of Long‐term Mean Global Radiation in Finland

In this study, detailed spatial analyses of the long-term mean global radiation in Finland were made using both directly measured and indirectly estimated radiation values. The interpolation on to a 10 km ×10 km grid was done using the kriging interpolation method, which can take external forcing, such as the altitude, into account in the interpolation. The time period used was 1961–1990. When inaccuracies due to indirect estimation methods and due to the interpolation method were taken into account the error of the interpolated radiation value at any randomly selected grid-point was found to be less than 5 per cent for most months. During winter the spatial distribution of global radiation was clearly dependent on latitude, the higher latitudes receiving less radiation than the southern parts, and during summer the spatial distribution of global radiation was determined by the variation of cloudiness.