ModelE AR5 Simulations: Past Climate Change and Future Climate Predictions
Insolation at Specified Location
This web page produces a numerical table of sunrise, sunset, daily insolation at top of atmosphere, and sunlight-weighted cosine of the zenith angle at a single specified location. The produced table contains data for a single month, or if a month is not provided, data for a single calendar year. Latitude and longitude must be given in degrees and hundredths of degrees, not degrees and minutes. Default location is the Central Park weather station, New York City.
"Insolation" means sunlight received from the Sun at top-of-atmosphere. On a global annual basis, about 57% of insolation is incident on the Earth's surface. Clouds are the main cause of this decrease, but even clear sky will have some reduction. To determine incident sunlight at the surface, click to the "LINE PLOTS" web page, but there data is limited to monthly values on the Model's 4×3 degree resolution grid.
As explained in the file SRERROR.TXT, the Atmosphere-Ocean Model assumes that the Sun is a point source. The columns for daily insolation (sunlight) and mean zenith angle in the produced table continue to use this assumption. The maximum error for this assumption occurs at the poles during the equinoxes where the table's algorithm would indicate no insolation but in reality there should be about x.xx (W/m^2). The columns for sunrise and sunset, however, do consider the radius of the Sun's disk as seen from the Earth (0.267 degrees on average) and atmospheric refraction of sunlight (approximately 0.583 degrees on the horizon). The table should be accurate to within one minute. During equinoxes, points on the equator see about 12 hours and 7 minutes of daylight. The 7 minutes are due to the radius of the Sun's disk and atmospheric refraction.
SRLOCAT.FOR is the Fortran source code of the program used on this web page.
Contact
Please address questions about these AR5 webpages to Dr. Gary Russell.
