Radiation in the British uplands.
An analysis was made of recent observations of solar radiation receipt in upland areas and the longer term data on h of bright sunshine. Estimates were made of the means and spatial variabilities of these quantities in upland regions of UK. There was a decrease in solar radiation receipt, with increasing alt., of 2.5-3 MJ/m2 day km. This was due to increased cloud cover and was probably more dependent on regional mean alt. than on the alt. of the station. The altitudinal gradient of sunshine duration was 1.3 h/day km. Given the uncertainties in the relationship between sunshine and solar radiation, this value was consistent with the observed gradient of solar radiation. In cloudless conditions, solar radiation increased by approx. 15%/1000 m; this was the value which would be expected theoretically from the scattering of solar radiation by aerosol and water vapour. Above 1000 m the land was frequently above the level of the cloud tops, at least in the summer, so that solar radiation receipt was as much as 35% greater on the summit of Cairngorm, Scotland (alt. 1245 m).