Detailed data:

Time period 2001 - 2015

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Data from

Data Quality Summary Edition 2.8 (March 27, 2015)

Main values are from Table 4-1, the uncertainty ranges (plus/minus one standard deviation) from Table 4-2.

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Surface:

SW down (clear-sky) = 243.9 (+/-5)

SW up (clear-sky) = 29.7 (+/-3)

LW down (clear-sky) = 316.0 (+/-7)

Surface energy absorbed = 

SW down - SW up + LW down 

= 243.9 - 29.7 + 316.0 = 530.2 W/m2.

TOA:

LW (OLR) = 265.8 W/m2.

530.2 = 2 x 265.8 (– 1.4)

E(SFC, clear) = SW down (clear) - SW up (clear) + LW down (clear) 

= 2OLR(clear)  (-1.4 W/m2)

Spherical area correction factor:

(R_Earth / R_OLR)² = 6371 km / (6371 km + 5.5 km)² = 0.9983

532 W/m2 at Earth's surface = 531.1 W/m2 at the origin of OLR.

Difference: 0.9 W/m2.