Author
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Meek, David |
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Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/10/1997 Publication Date: N/A Citation: N/A Interpretive Summary: The estimation of maximum possible clear day solar radiation at any location and date is important in many scientific fields including agricultural engineering, civil engineering, crop physiology, ecology, hydrology, meteorology, physics, and soil science. In agronomy, interested parties range from modelers to managers working in environmental or hydrological problems or resource management. Two previously published models were modified and shown to work well for estimating solar radiation. Methodology to extract and to utilize long-term and publicly available information to run the models was developed in the process. Data for these input factors are available for hundreds of locations throughout the United States and in some other countries. So the simple models can be implemented at any place on any day in the year to provide estimates of maximum possible solar radiation. Uses of this information range from checking weather station data to irrigation scheduling. Technical Abstract: The estimation of maximum possible daily solar radiation is important in many applied sciences. This study develops and evaluates climatic extreme based modifications of two broadband shortwave irradiance models for the purpose of estimating a dynamic upper boundary for global solar radiation at any given location. Climatic component models were developed for five rural locations in the central United States. Each site had long-term records of daily global solar radiation data available. Aerosol optical depth, precipitable water, and surface albedo were the input variables. Input data were obtained from nationally available databases. For each site, precipitable water and aerosol optical depth daily data were used to develop annual trends in the climatic lows and normals for each variable. The normals were based on median daily values. Nonlinear weighted least squares regression analyses were used to develop the interpolating curves. To evaluate the broadband models, the maximum daily solar radiation values for a given day from the entire period of record for each site and day in the year were selected. In either broadband model, the use of the climatic normals in each input variable either interpolated or under-estimated the selected radiometer data. The use of the climatic lows, however, did yield a reasonable upper boundary for the selected minima curves for each turbidity variable were generally significantly different throughout the year from the climatic normals. The models were most sensitive to aerosol optical depth. Although it is more sensitive to input variation and it is somewhat less conservative, the simpler of the two broadband models is adequate for most applications. While results are site specific, the methodology is general. |
