Analysis of photosynthetic photon flux density and its parameterization in Northern China
2008
Xia, X. | Li, Z. | Wang, P. | Cribb, M. | Chen, H. | Zhao, Y.
The relationship between broadband global solar radiation (R S) and photosynthetic photon flux density (Q P) is investigated using 2 year's worth of radiation data collected at a site in northern China. These data are used to determine the temporal and monthly variability of the ratio Q P/R S and its dependence on aerosol optical depth (AOD) and the column-integrated water vapor content. A simple and efficient all-weather empirically derived model is proposed to estimate Q P from R S. Results reveal that the monthly variation of the ratio Q P/R S ranges from 1.87EMJ⁻¹ in January to 2.08EMJ⁻¹ in July with an annual mean value of 1.96EMJ⁻¹. Large day-to-day variations in aerosol loading resulted in large variations in Q P/R S. Under cloudless conditions, aerosols lead to a reduction of about 0.14EMJ⁻¹ in Q P/R S per unit increase of AOD at 500nm. The ratio Q P/R S increases from about 1.82EMJ⁻¹ to about 1.97EMJ⁻¹ when the water vapor content increases from 2 to 10mm, with the effect diminishing for higher values of water vapor content. The simple all-weather empirically derived model estimates instantaneous Q P with high accuracy at the site where the model is developed. The mean bias error is close to zero and root mean square error is 3.8%, respectively. Application of the model to data collected from different locations also results in reasonable estimates of Q P.
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