ABSTRACT: Solar radiation is the principal and fundamental energy for many physical, chemical and biological processes. However, it is measured at a very limited number of meteorological stations in the world. Estimation of solar radiation from measured meteorological variables offers an important alternative in absence of measured solar radiation. In this work, 20 developed models using measured meteorological variables are explored to estimate monthly average daily solar radiation at 13 stations in Yangtze River Basin in China. Two scenarios are considered. When sunshine duration is available, monthly average daily atmospheric water vapor pressure, relative humidity and precipitation do not contribute to the improvement in estimation accuracy of the sunshine-based models. It is therefore unnecessary to take them into account, and the newly developed model 6 is proposed and can provide a good method for the estimation of monthly average daily solar radiation in the study area. If sunshine duration is not available, inclusion of monthly average daily atmospheric water vapor pressure, relative humidity and multiplication maximum by minimum ambient temperatures can significantly improve the estimation accuracy of the temperature-based models. While monthly average daily precipitation does not contribute to the improvement in estimation accuracy. And model 20 is proposed and it is more applicable in area with larger ambient temperature range.

Abstract: There are many correlations developed to predict incident solar radiation at a given location developed based on geographical and meteorological parameters. However, all correlations depend on accurate measurement and availability of weather data such as sunshine duration, cloud cover, relative humidity, maximum and minimum temperatures etc, which essentially is a costly exercise in terms of equipment and labour. Sri Lanka being a tropical island of latitudinal change of only 30 along the length of the country, the meteorological factors govern the amount of incident radiation. Considering the cloud formation and wind patterns over Sri Lanka as well as the seasonal rainfall patterns, it can be observed that the mean number of rainy days can be used to predict the monthly average daily global radiation which can be used for calculations in solar related activities conveniently.

Abstract Measurements of photosynthetically active radiation (PAR), which are indispensable for simulating plant growth and productivity, are generally very scarce. This study aimed to compare two extrapolation and one interpolation methods for estimating daily PAR reaching the earth surface within the Poyang Lake national nature reserve, China. The daily global solar radiation records at Nanchang meteorological station and daily sunshine duration measurements at nine meteorological stations around Poyang Lake were obtained to achieve the objective. Two extrapolation methods of PARs using recorded and estimated global solar radiation at Nanchang station and three stations (Yongxiu, Xingzi and Duchang) near the nature reserve were carried out, respectively, and a spatial interpolation method combining triangulated irregular network (TIN) and inverse distance weighting (IDW) was implemented to estimate daily PAR. The performance evaluation of the three methods using the PARs measured at Dahuchi Conservation Station (day number of measurement = 105 days) revealed that: (1) the spatial interpolation method achieved the best PAR estimation (R 2 = 0.89, s.e. = 0.99, F = 830.02, P < 0.001); (2) the extrapolation method from Nanchang station obtained an unbiased result (R 2 = 0.88, s.e. = 0.99, F = 745.29, P < 0.001); however, (3) the extrapolation methods from Yongxiu, Xingzi and Duchang stations were not suitable for this specific site for their biased estimations. Considering the assumptions and principles supporting the extrapolation and interpolation methods, the authors conclude that the spatial interpolation method produces more reliable results than the extrapolation methods and holds the greatest potential in all tested methods, and more PAR measurements should be recorded to evaluate the seasonal, yearly and spatial stabilities of these models for their application to the whole nature reserve of Poyang Lake.

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Since air temperature records are readily available around the world, the models based on air temperature for estimating solar radiation have been widely accepted. In this paper, a new model based on Hargreaves and Samani (HS) method for estimating monthly average daily global solar radiation is proposed. With statistical error tests, the performance of the newmodel is validated by comparing with the HS model and its two modifications (Samani model and Chen model) against the measured data at 65 meteorological stations in China. Results show that the new model is more accurate and robust than the HS, Samani, and Chen models in all climatic regions, especially in the humid regions. Hence, the new model can be recommended for estimating solar radiation in areas where only air temperature data are available in China. 1.

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e (annual mean) equalling 1.6 MJ m2 day1 and MBE being all tested methods. Where there were no reliable estimates of the www.elsevier.com/locate/agrformet Agricultural and Forest Meteorology 131 (2005) 54–76 § The nomenclature of the paper tries to follow the original one used by the authors of the tested methods.