Scientific Investigations Report 2006–5318
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5318
extrad_dpm.f
Calculates daily solar radiation.
Calculate clear sky solar radiation on horizontal and sloped surfaces for each HRU. The calculations can account for observed solar radiation values that have been interpolated to the HRUs. If no observed data, then use calculated values. The average slope and aspect of a HRU are accounted for in the calculations. Module based on Bauer and Vaccaro (1987).
July, 2004
avelat
Average latitude of basin used for solar radiation calculations, in degrees.
hru_slope
HRU slope in vertical feet/horizontal feet, in percent (0-90). [basin]
hru_aspect
HRU aspect in degrees from north: 0-360, in degrees. [basin]
slrexthz
Solar radiation for horizontal surface for day, in langleys.
slrext
Solar radiation for sloped surface for day, in langleys.
frcdylt
Fraction of day with sun—daylight, in fraction.
hru_solrad
Daily incoming solar radiation for each of the HRUs, in langleys. [grid]
tmaxf
Daily maximum temperature for each of the HRUs, in degrees Fahrenheit. [grid]
tminf
Daily minimum temperature for each of the HRUs, in degrees Fahrenheit. [grid]
The module first checks if there was observed solar radiation that was interpolated to the HRUs and the slope (hru_slope) of the HRU. If there was observed radiation values and the slope is less than 1.0, then calculations are skipped for the HRU. If the slope is greater than 1.0, regardless if there is observed solar radiation, then solar radiation is calculated for a horizontal surface under clear skies, this variable is slrexthz.
If the slope is less than 1 percent, the the solar radiation (hru_solrad) is set set to the calculated value of slrexthz for the case of no observed solar radiation. When the slope of the HRU is greater than 1 the solar radiation is computed based on the HRU’s slope and aspect (hru_aspect), regradless of whether there is observed data.
If there is observed solar radiation, the ratio of solar radiation on sloped surface with an aspect (slrext) to that for a horizontal surface (slrexhz) is calculated and multiplied by the value obtained from grid_met_dpm.f,
hru_solard(i) = hru_solrad(i) * slrext/slrexthz
where
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
hru_solrad is the solar radiation for the a HRU based on calculated and interpolated values, in langleys, and
other variables as define above.
If there is no observed solar radiation, hru_solrad is set equal to slrext—the calculated HRU value based on its slope and aspect.
The actual calculation of solar radiation is based on Kaufman and Weatherred (1982) and has been described and documented in Bauer and Vaccaro (1987) and Leavesley and others (1983). These calculations are invoked in the module by a call to the subroutine extrad. Extrad passes the variables and parameters: julian calendar day (jday), average latitude of the modeled area (avelat), slope (hru_slope), aspect (hru_aspect), solar radiation (slrext or slrexthz), and the fraction of daylight hours (frcdylt).
Last, in order to preserve the calculated value of solar radiation, a MMS function, putvar, is invoked to store the value of solar radiation in the module where it was declared, grid_met_dpm.f.
Bauer, H.H., and Vaccaro, J.J., 1987, Documentation of a deep percolation model for estimating ground-water recharge: U. S. Geological Survey Open-File Report 86-536, 180 p.
Kaufman, M.R., and Weatherred, J.D., 1982, Determination of potential direct beam solar irradiance: Research Paper RM-242, Rocky Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, 23 p.
Leavesley, G.H., Lichty, R.W., Troutman, B.M., and Saindon, L.G., 1983, Precipitation-runoff modeling system--User's manual: U. S. Geological Survey Water-Resources Investigations Report 83-4238, 207 p.
Henry H. Bauer and John J. Vaccaro
U.S. Geological Survey
Washington Water Science Center
934 Broadway, Suite 300
Tacoma, WA 98402
Modified by:
John J. Vaccaro
U.S. Geological Survey
Washington Water Science Center
934 Broadway, Suite 300
Tacoma, WA 98402
Telephone: 253-552-1620
Fax: 253-552-1581
Email: jvaccaro@usgs.gov
U.S.
Department of the Interior | U.S. Geological
Survey
Persistent URL: https://pubs.water.usgs.gov/sir20065318
Page Contact Information: Publications Team
Page Last Modified: Thursday, 01-Dec-2016 19:32:21 EST
