The Conservative Ratio of Photosynthetically Active to Total Radiation in the Tropics

Abstract

Long-term observations of il, the ratio of PAR to total solar radiation are reported for Dar es Salaam (70S). The records for very clear periods confirm a previously published value for a clear tropical day, viz. i1 = 05 1 + 0 01. For very cloudy skies, i1 was 0.63 + 0.02 in accord with the highest ratios reported outside the tropics. It is concluded that ?I should be regarded as conservative rather than constant, in the tropics as in higher latitudes.