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Solar Radiation at Top of Atmosphere

There are four tasks to be accomplished to calculate solar radiation at the top of the atmosphere for a given year:
1. determine Earth's orbital parameters which are the eccentricity of the orbit, the obliquity, and the longitude of perihelion;
2. determine time of vernal equinox to be used by future Atmosphere-Ocean Model simulations;
3. determine time integrated insolation at any latitude and longitude on Earth;
4. determine sun's strength or radiation output.

Read questions, answers and comments about insolation.

The file SRTERMS.TXT contains the definition of terms used in calculating insolation. The file SRERROR.TXT lists the approximations that are used by the Atmosphere-Ocean Model. Simulations C089, C090, C091, C092, C093 and C094 assume the constant orbital parameters of 2000 AD, that the tropical year is exactly 365 days, that Vernal Equinox occurs on March 21, hour 0, and that the solar constant is fixed at 1367 W/mē.


The following links allow the user to produce tables and graphs of insolation and solar behavior:
Produce a table of sunrise, sunset, and daily insolation as a function of latitude, longitude, year, and month.
Produce a table of monthly latitude insolation for a whole year.


The following programs were used to calculate insolation for the six simulations (C089 through C094) of this web site.
ORBPARold.SUB Calculates the three orbital parameters as a function of year. The values are based on Andre Berger's 1978 solution.
ORBITold.SUB Calculates the distance to the sun and the Earth's declination angle as a function of time of year and the orbital parameters.
COSZ0.SUB Calculates the Model's time integrated zentih angle at each grid cell on the Earth as a function of the declination angle and the time interval of the day. This subroutine can return two output arrays, the zenith angle weighted by time and the zenith angle weighted by sunlight.


Future versions of the Atmosphere-Ocean Model will use more up-to-date versions of these subroutines:
ORBPAR.SUB More terms and slightly improved precision for the orbital parameters of the Earth compared with ORBPARold.SUB.
ORBIT.SUB Sun location and Equation of Time are additional outputs compared with ORBITold.SUB.

GEN INFO LINE PLOTS MODEL DATA UNIX MODEL CODE PEOPLE SUNLIGHT
STATISTICS COLOR PLOTS OBSERVA PC MODEL DOC PUBLICA TIDES and MOON
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Curator: Gary L. Russell . . . . . 2004/10/22/11:32:50