Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Solar spectral irradiance at earth's TOA

  1. Jul 11, 2010 #1
    (just tried general astronomy board but no luck)

    I'm trying to reproduce a plot of Sun's black-body behavior like this one:
    Problem is, after I convert the black-body radiance to irradiance, its curve is way too high as compared with measurement. The measurement data is taken from:
    http://rredc.nrel.gov/solar/spectra/.../ASTMG173.html [Broken]

    The top of atmosphere (TOA) irradiance at Earth's distance is obtained in the following way:
    radiance (W/m^2/nm/Sr) L=2*h*c^2/(lamda^5*exp(h*c/(kB*lamda*T)-1))
    c=3e8 m/s (speed of light)
    h=6.625e-34 Joul Second (Planck's)
    kB=1.38e-23 Joul/Kelvin (Boltzman's)
    omega=pi*r_sun^2/D_sun_earth^2 (Sun disk solid angle as seen from Earth)
    r_sun=6.96e8 m (Sun's radius)
    D_sun_earth=1.496e11 m (1AU)
    Finally irradiance is E=L*omega (W/m^2/nm) (and one needs to multiply 1e9 to be in nm)

    My curve is roughly twice above the measurement, so if I do:
    I can get something close to the picture in the wiki link. This 67-deg is roughly Earth's spin inclination. However I really doubt multiplying cos(67-deg) makes sense, as we are talking about TOA irradiance, not anywhere on Earth surface.

    What I'm missing here?

    Last edited by a moderator: May 4, 2017
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted

Similar Threads - Solar spectral irradiance Date
Will solar output decrease Dec 28, 2017
Aurora colors in a bottle Jun 9, 2017
Enormous solar storms Oct 29, 2015
How much energy is in the solar wind plus Feb 6, 2011