The climatological characteristics of photosynthetically active radiation in arid and semi-arid regions of China |
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| Authors: | Bo Hu Yuesi Wang |
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| Institution: | 1. State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
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| Abstract: | Photosynthetically active radiation (Q p ) is a key variable in models of net primary productivity and carbon cycle modelling. The relationship between broadband global solar radiation (R s) and Q p is investigated using 6?years of radiation data collected at 9 sites in arid and semi-arid regions of China. The dependence of Q p /R S on aerosol optical depth (AOD) and water vapour content are also discussed. A simple and efficient all-weather empirically derived model is developed to estimate Q p from R s. The annual average daily Q p in arid and semi-arid areas is 29.9?±?11.7 and 27.3?±?10.1?mol?m-2 d-1, respectively. The highest value (31.9?±?11.3?mol?m-2 d-1) appears at Linze in the arid area. The lowest value (24.3?±?9.7?mol?m-2 d-1) appears at Ansai in the semi-arid area. The results show that the monthly variation of the Q p /R s ratio ranges from 1.69?±?0.19?mol?MJ-1 in Aksu to 1.91?±?0.08?mol?MJ-1 in Fukang. There is a small decreasing trend of the ratio of Q p to R s (PAR fraction) in arid and semi-arid regions because of the recent increase in fine aerosols. A simple and efficient empirically model suit for all-weather condition was developed to estimate Q p from R s. The slope a and intercept b of the regression line between estimated and measured values is close to 1 and zero, respectively. The application of the model to data collected from different locations also results in reasonable estimates of Q p . |
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