Measuring and modelling photosynthetically active radiation in Tibet Plateau during April-October

Abstract Based on the measured data of spectral solar radiation in Lhasa, Tibet from 15 April to 15 October 1994, the ratio of photosynthetically active radiation (PAR) to solar global radiation was presented, i.e. ηPAR=0.439±0.014, and 1 J energy of PAR is equivalent to 4.43 μmol quantum. In the climatological estimation of Tibet Plateau, following equations can be used to estimate the daily total PAR energy flux density QPAR (MJ m−2 per day) and daily total PAR photo flux density UPAR(mol photon m−2 per day): Q PAR =(0.3914+0.0190 ln E ∗ ) Q U PAR =(1.7339+0.0842 ln E ∗ ) Q Here, Q (MJ m−2 per day) is the daily global radiation. E*=E P0/P, E (hpa) is the water vapor pressure at site, P0(hpa) is the standard atmosphere pressure at sea level, P (hpa) is the atmosphere pressure at site.

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