`e' value for earth's atmosphere
[ Follow Ups ] [ Post Followup ] [ Class Discussion Groups ] Posted by James Risbey on September 12, 1997 at 14:11:43:
e factor for Earth's greenhouse effect
In response to the simple mathematical model of the greenhouse effect
showing an amplification factor in temperature of 1.19 for a perfect
longwave absorber (e=1), Neil asked what the e value for Earth's
atmosphere was.
Earth's e value can be derived from the model equation:
T = [ 2I/sigma(2-e) ] ^1/4
given that the earth's average temperature is 288K (15C).
We can rearrange terms in the above equation to yield
e = 2 - 2I/(sigma T^4)
now, I = S/4(1-alpha) = 239W/m2, sigma is the Stefan-Boltzmann
constant (5.67x10^-8), and T = 288K
substituting these values gives:
e = 0.77
so, Earth's atmosphere is a pretty good longwave absorber (i.e. e
value fairly close to 1)