Solar Constant in UV

[Helio]

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".

 

[billslugg]

Very interesting. The effect is probably mitigated somewhat by the fact that such short wavelengths are absorbed very far up in the atmosphere.

 

[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.

 

[billslugg]

Yes, ozone is a good absorber of UV. Chlorine breaks ozone up into O2 which does not absorb UV.

 

[Helio]

Yes, ozone is a good absorber of UV. Chlorine breaks ozone up into O2 which does not absorb UV.

I think O2 will split with UV. See here.

 

[billslugg]

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.