Title: Corrections for Sunshine Duration Models under Rugged Terrain Conditions
Abstract:It was found that there exist systematic errors in models for calculating sunshine duration based on theoretical analyses in that these models do not account for the fact that the sunshine percentage ...It was found that there exist systematic errors in models for calculating sunshine duration based on theoretical analyses in that these models do not account for the fact that the sunshine percentage is calculated from the astronomical sunshine duration. In this paper, the author investigated the variability in the systematic errors through testing the model outputs with measurements from plain, hilly and mountainous areas. The characteristics of the systematic errors from the model are: 1) the error in winter is generally greater than that in summer; and 2) the error in mountainous areas is greater than that over flatland. A corrected model for calculating sunshine duration was subsequently proposed to eliminate the systematic errors. The corrected model was implemented through correcting the sunshine percentage involved in the original mode, i.e., the ratio of actual sunshine duration to astronomical sunshine duration. By multiplying a coefficient, the sunshine percentage in the original model was converted into the actual sunshine percentage in the corrected model, i.e., the ratio of actual sunshine duration to geographical sunshine duration. The coefficient is equal to the ratio of the astronomical sunshine duration over the geographical sunshine duration. By this way, the sunshine percentage in the corrected model is much more than that in the original model. This method has the capability to remove the systematic errors. To calculate the geographical sunshine duration, a day can be divided into several equal time steps. After judging whether each period is shadowed by surrounding terrains, the geographical sunshine duration is eventually derived by summation of sunshine duration at each time step not shadowed. Therefore, the actual sunshine duration under rugged terrain conditions can be determined by the proposed method. The shorter the time step partitioned, the more accurate the results would be obtained. Given the time cost and efficiency in calculation, the time step can, however, not be very short. In addition, the author illustrated the error in the correction model, indicating that there is no systematic error in the corrected model. The overall error of the corrected model could be attributed to non-uniform sky conditions and DEM resolution. The magnitude of the error is closely related to the distance from the monitoring stations to the calculation sites and weather systems. Based on the comparison between the corrected model-based outputs and the measurements, it was demonstrated that the corrected model can basically meet meteorological operation and practical applications under current weather station networks.Read More
Publication Year: 2010
Publication Date: 2010-01-01
Language: en
Type: article
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