Archive for April, 2021

Radiation Amplification Factor RAF in April 2021

April 29, 2021

We had a period of several cloudless, blue sky days at the end of April 2021. So time to redo a calculation of the Radiation Amplification Factor RAF. In short, we want to see how the variation of the Total Ozone Column (TOC) influences the effective UVB radiation at ground level. I wrote several time on this, and usually we found an RAF of approx 1.05 to 1.10.

First here a graph showing the variation of total solar irradiance (blue curve, unit W/m2) and the effective UVB (red curve, unit mMED/h):

First remark that the peak solar irradiance was practically constant; the 24th April was a bit hazy, so it will be left out in the computations. The numbers in the turquoise boxes are the maximum values of the TOC, measured in DU (Dobson Unit) with our Microtops II instrument (serial 5375). Let us first plot the UVBeff versus the TOC: fig. 1 UVBeff versus maximum daily TOC (5 days: 23 and 25 to 28 April 2021)

Clearly the UVBeff values decrease with increasing TOC, as the thicker ozone column filters out more UVB radiation. The empirical relationship is practically linear, and suggests that a dip of 100 DU (a quite substantial thinning of the ozone layer) would cause an increase of effective UVB of about 0.6 MED/h or 1.7 UVI (as 1 MED/h = 25/9 UVI).

The numerical correct definition of the RAF is : UVB = C * TOC**RAF where ** means “at the power of” Taking the natural logarithm gives ln(UVB) = ln(C) +RAF*ln(TOC) or RAF = [ln(UVB – ln(C)]/ln(TOC).

If we have many measurement couples of UVB and TOC, it can be shown (see here) that

RAF = [-ln(UVBi/UVB0)]/[ln(TOCi/TOC0)]

where the index i corresponds to the ith measurement couple, and 0 to that taken as a reference (usually i=0). This is equivalent to say that RAF is the slope of the linear regression line through the scattterplot of -1*ln(UVBi/UVB0) versus ln(TOCi/TOC0).

Here is that plot:

The slope is 1.0461, so the (erythemal) RAF computed from the 5 blue sky days is RAF = 1.0461 ~1.05

This has to be compared to the value RAF = 1.08 in the referenced paper [ref. 1]. Note the excellent R2 = 0.96 of this linear fit.

There is some discussion if TOC should be replaced by TOCslant = TOC/cos(SZA), where SZA is the solar zenith angle. If we do this, the RAF ~ 1.10, close to the previous value; the R2 is somewhat lower with R2=0.91. The SZA is practically constant for the 5 days wuth SZA ~38° .

The RAF = 1.10 value is close to what Jay Herman published in GRL in figure 8 [ref. 2] (red lines added):

Conclusion

These 5 days of cloudless sky give practically the same results for RAF as that found during previous investigations. As a very raw rule of thumb one could keep in mind that a dip of 100 DU yields an increase of at most 2 UVI. The following table resumes the findings of this paper and the references 1 to 5:

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References:

 MASSEN, Francis, 2013: Computing the Radiation Amplification Factor RAF using a sudden
dip in Total Ozone Column measured at Diekirch, Luxembourg (link)

 HERMAN, Jay, 2010: Use of an improved radiation amplification factor to estimate
the effect of total ozone changes on action spectrum weighted irradiances and an instrument response function.
Journal of Geophysical Research, vol.115, 2010 (link)

 MASSEN, Francis, 2014 : RAF revisited (link)

 MASSEN, Francis, 2018: UVI and Total Ozone (link)

Greens for Nuclear Energy

April 8, 2021

We are so used to the absolute rejection of everything related to nuclear energy by the Greens we are familiar with, that this new UK movement comes a bit as a surprise.

Sure, it is their estimation that climate change is an existential threat that underlies their new appreciation of what nuclear as a carbon free energy can do. I can live with that, even if in my opinion there is no climate emergency (read the Clintel declaration).

The Greens for Nuclear Energy home page has a short video that pushes the need for nuclear energy quite far: not only in developing new technologies, but also in keeping in activity running facilities; this is something that would give the German Greens a heart attack!

With Michael Shellenberger, Bill Gates and other well known Greens or former Greens (like Patrick Moore) saying clearly that nuclear energy is a must in a realistic energy mix, will the wind turn ? And how will our EU Greens adapt? Will they change their opinion or stick with their image of a movement that only knows to present a future “to save the planet” made of restrictions in every aspect of life, be it housing, moving, eating or traveling…

You might read this very sober article by Gail H. Marcus in physicsworld (April 2017) “How green is nuclear energy?“, who concludes that “nuclear energy is indeed green, and it offers several other advantages as well. It should, therefore, be considered in this light in decision-making on future energy-supply options”.

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