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Geodetic Zone Weights Information


CERES Ed2.6 and higher products use geodetically weighting to compute global means. This spherical Earth assumption gives the well-known So/4 expression for mean solar irradiance, where So is the instantaneous solar irradiance at the TOA. When a more careful calculation is made by assuming the Earth is an oblate spheroid instead of a sphere, and the annual cycle in the Earth's declination angle and the Earth-sun distance are taken into account, the division factor becomes 4.0034 instead of 4. Consequently, the mean solar irradiance for geodetic weighting is ~1361/4.0034 = 340.0 W/m2, compared to 1361/4 = 340.3 W/m2 for spherical weighting.

Spherical earth zonal weighting uses the sin(lat1 lat2), where lat1 and lat2 are the boundaries of the zone geodetic weighting assumes an oblate spheroid, with the equatorial radius = 6378.137 km, and the polar radius = 6356.752 km.

A FORTRAN program used to calculate a global mean from zonal means given that the Earth is not a true sphere is provided here.

The CERES geodetic 1.0-deg zonal weights are provided here.

From the National Geospatial-Intelligence Agency, http://earth-info.nga.mil/GandG/coordsys/csatfaq/math.html link to external site


δA = Cpδy
δy = δφ
360
CM
CM = 2πRM
RM = α(1 − ε 2)
ω3
ε = [ƒ(2 − ƒ)] 1/2
δy = 2π
360
α(1 − ε 2)
ω3
δφ
CP = 2πRP
Rp = acosφ
ω
Cp = 2π acosφ
ω
δA = 2π acosφ
ω
2π
360
α(1 − ε 2)
ω3
δφ
δA = 4π2 α2(1 − ε2)
360
cosφ
ω4
δφ
ω = (1 − ε2 sin2 φ) 1/2
ω4 = (1 − ε2 sin2 φ) 2
δA = 4π2 α2(1 − ε2)
360
cosφ
(1 − ε2 sin2 φ) 2
δφ
ωt = cosφ
(1 − ε2 sin2 φ) 2

cosφ
(1 − ε2 sin2 φ) 2

CERES Data Product Information

 
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Page Last Modified: 10/16/2017 11:04:36 EST
Site Last Modified: 11/07/2017 17:18:43 EST