The conservative ratio of photosynthetically active to total radiation in the tropics.
Abstract
Long-term observations of eta , the ratio of PAR to total solar radiation, are reported for Dar es Salaam (7 deg S.). The records for very clear periods confirm a previously published value for a clear tropical day, viz. eta = 0.51 plus or minus 0.01. For very cloudy skies eta was 0.63 plus or minus 0.02, in accord with the highest ratios reported outside the tropics. It is concluded that eta should be regarded as conservative rather than constant in the tropics, as in higher latitudes.