Analysis of monthly average daily global radiation and monthly average sunshine duration at two tropical locations

The monthly average daily totals of global solar radiation on a horizontal surface at Madras (13°0′N, 80°11′E) and Kodaikanal (10°14′N, 77°28′E) during the period 1983–1987 have been processed, analysed and presented. The regression coefficients, a and b, of Ångstrom linear type correlations for the monthly mean daily global solar radiation have been determined for these two locations. A comparison of average global radiation and sunshine duration obtained here (5 years) with long term data (more than 15 years) shows that a minimum of 5 years is sufficient to obtain average values for radiation, whereas the same does not hold true for the duration of sunshine.