Solar Constant in UV

The total output of the Sun is very constant. It only varies by about 0.1%. It's even called the "Solar Constant", and rightfully so.

But, this is only a total energy difference, not what happens across the spectrum.

Would you believe that in the UV (Ultra Violet) the variation is a lot more than 0.1%? At 121.5 nm (UVC) the variation is over 74%! Data available here. [I used 20 years of daily data.]

But the energy level is tiny at that wavelength, fortunately. The question, nevertheless, is whether or not that large swing in strength somehow acts on sensitive molecules that have a larger effect on the climate? Don't ask me, but it helps to know not to get stuck on the 0.1% "constant".
 
Last edited:
Nov 19, 2021
476
216
560
Very interesting. The effect is probably mitigated somewhat by the fact that such short wavelengths are absorbed very far up in the atmosphere.
 
  • Like
Reactions: Helio
Very interesting. The effect is probably mitigated somewhat by the fact that such short wavelengths are absorbed very far up in the atmosphere.
Yes. 95% of the UV that does reach the surface is the less brutal UVA. No UVC, fortunately, reaches the surface.

Ozone and O2 seem to be affected by all UV.
 
Nov 19, 2021
476
216
560
Yes, UV can split O2 as well. In fact, all diatomic molecules have some tiny, tiny portion that are split spontaneously, no outside energy needed.
 
  • Like
Reactions: Helio

ASK THE COMMUNITY

Latest posts