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Title: An improved Ångström-type model for estimating solar radiation over the Tibetan Plateau

item LIU, JUNIGDON - Chinese Academy Of Sciences
item PAN, TAO - Chinese Academy Of Sciences
item CHEN, DELIANG - Lund University
item ZHOU, XIUJI - Chinese Academy Of Sciences
item YU, QIANG - University Of Technology Sydney
item Flerchinger, Gerald
item LIU, DELI - Chinese Academy Of Sciences
item LIU, YUJIE - Chinese Academy Of Sciences
item LINDERHOLM, HANS - Lund University
item DU, JUN - Chinese Academy Of Sciences
item WU, DINGGRONG - Chinese Academy Of Sciences
item SHEN, YANBO - Chinese Academy Of Sciences

Submitted to: Energies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2017
Publication Date: 7/1/2017
Citation: Liu, J., Pan, T., Chen, D., Zhou, X., Yu, Q., Flerchinger, G.N., Liu, D., Liu, Y., Linderholm, H., Du, J., Wu, D., Shen, Y. 2017. An improved Ångström-type model for estimating solar radiation over the Tibetan Plateau. Applied Energy. 10:892. doi: 10.3390/en10070892.

Interpretive Summary: The intensity of solar radiation is critical input to many ecological and hydrological models, but it is not commonly measured at most meteorological stations. Several algorithms for estimating solar radiation were tested using data from 15 meteorological stations across the Tibetan Plateau, representing a wide range in elevation and meteorological conditions. Two of the better algorithms were selected and used for mapping the distribution of solar radiation across the Tibetan Plateau. These data are available for use in ecological and hydrological studies in the area.

Technical Abstract: Sunshine- and temperature-based empirical models are widely used for solar radiation estimation over the world, but the coefficients of the models are mostly site-dependent. The coefficients are expected to vary more under complex terrain conditions than under flat terrains. To test this hypothesis, solar radiation data from 15 stations over the Tibetan Plateau (TP) and also adjacent regions were collected and analyzed to validate the applicability of different models. Calibration indicates that the sunshine-based models perform better than the temperature-based ones. The highly rated sunshine-based Angstrom model and temperature-based Bristow model were then selected for further analysis. Models were evaluated based on simply averaging the coefficients from all stations versus calibrating a common set of coefficients for all stations. The Angstrom-type models perform much better than the Bristow-type models with average Nash-Sutcliffe Efficiencies (NSE) of 0.826 for the Angstrom-type methods for both approaches, and 0.444 and 0.555 for the Bristow-type approaches. Models based on linearly regressing coefficients with geographically-based parameters perform very poorly with average NSE value of 0.422 for the Angstrom-type model and -1.111 for the Bristow-type model. A simple universal model using the Angstrom model was then developed using the altitude and water vapor pressure as the leading factors accounting for the coefficient variations between stations. The universal model is able to accurately predict the coefficients at all the stations, and performs the best among all models with an average NSE value of 0.856. Based on the gridded water vapor pressure and sunshine percentage interpolated by the ANUSPLIN method, the spatial distribution of annual mean daily solar radiation was estimated with the universal model. The overall spatial pattern of the solar radiation indicates an increasing trend in radiation from east to west, with a high centre of solar radiation on southwest TP ranging from 20 to 24 MJ·m-2day-1. The overall pattern of the solar radiation was validated point by point at different radiation stations, together with an independent measurement.