Improved station-independent correlations between global radiation and sunshine duration

Abstract

Independent regression fits to Angstrom's relation between sunshine duration and global irradiation have been made for monsoon, pre-monsoon and post-monsoon periods. Long-term data of eight stations situated around 20°N lat in Indea were used to obtain collctives fits for each period separately for stations lying in (1) the zone comprising arid and semi-arid regions and (2) the wet-and-dry zone. The root mean square (r.m.s.) errors are < 3% in each case for the estimation of global irradiance of a month and the maximum error found is 6.3% which is significantly smaller than for previous estimates. The present station independent correlations should give precise estimates of G for locations away from pyranometers in a large part of the Indian subcontinent (Fig. 1). The technique of making collective fits depending on seasons and climatic zones may be applied with advantage to other parts of the world.