Modelling and estimation of photosynthetically active incident radiation based on global irradiance in Indian latitudes

Photosynthetically active radiation (PAR) as a component of solar radiation plays a major role in different applications dealing with plant canopies, biomass production and microalgae growth. The amount of PAR energy depends upon location, time of the year and atmospheric conditions. Understanding the PAR and its availability is very essential for modelling biological growth system. The objective of this study is to estimate PAR for latitudes ranging from 9° to 34° and for the entire year based on hourly and monthly average of the daily global radiation (Hg). Based on the estimated data, a power regression model showing the relationship between PAR and Hg is presented for six Indian latitudes. The ratios of hourly sum of PAR to Hg and monthly average of hourly global radiations (Ig) vary smoothly with significant seasonal variations and are influenced by several other local climatic conditions. The power regression equation between PAR and Hg obtained are as follows: (a) For 9° latitude, PAR = 0.040 (Hg)0.924, R2 = 0.970, (b) 14° latitude, PAR = 0.029 (Hg)0.952, R2 = 0.894, (c) 19° latitude, PAR = 0.256 (Hg)0.748, R2 = 0.721, (d) 24° latitude, PAR = 0.159 (Hg)0.775, R2 = 0.896, (e) 29° latitude, PAR = 0.052 (Hg)0.886, R2 = 0.830 and (f) 34° latitude, PAR = 0.016 (Hg)1.013, R2 = 0.768.