Abstract:
Based on surface radiation balance data and daily meteorological observations collected at 19 radiation stations in China from 1993 to 2012, the applicability of seven empirical methods for the estimation of surface effective radiation (including Brunt model, Penman modified model, Bepлянд model, FAO24 modified model, FAO56-PM model, Deng Genyun model, and Tong Hongliang model) was assessed and a revised method applicable to China was established by re-fitting the formula using new observational data. The iterative solution method and the multivariate regression analysis method with the minimum root mean square error (RMSE) was used as the objective function in the revised method. Results showed that the effective radiation over China was underestimated by all the above seven models. The mean absolute percentage error (MAPE) and RMSE derived from the Tong Hongliang model was 27.0% and 24.5 W/m2 respectively, which are less than those from the other six models. Thereby the Tong Hongliang model was the best among the seven models for estimating the effective radiation over China, followed by the Penman modified model and the Deng Genyun model. The FAO56-PM model was not applicable to China due to its low accuracy. For individual stations, the accuracy of the Deng Genyun model was the highest in the eastern plain area while the Tong Hongliang model was suitable for the plateau area because it includes the altitude correction in the atmospheric moisture calculation. Correlation analysis indicated that the water vapor pressure was the most critical factor affecting the estimated error of the effective radiation. Therefore, the regional models were established for the eastern and western areas respectively based on geographical distribution of the water vapor pressure. The RMSE calculated by the revised models, which were developed based on observations, for entire China and for the eastern and western areas were 20.8 and 21.4 W/m2 respectively. Results of the new models were more accurate than that of the seven models mentioned above. Furthermore, the regional model produced smaller errors than the model for entire China at most of the stations, indicating that it is necessary to distinguish the eastern and western areas in the development of new methods for determination of effective radiation. The western regional model was obviously more accurate than Deng Genyun model in the western area and the eastern regional model was obviously more accurate than Tong Hongliang model in the eastern area. Therefore the regional models developed in this study were recommended as the standard climatology models for calculation of the effective radiation over China.