Couple of days ago someone mentioned TSI variation significantly varies during earth orbit, no news in this, it did though trip me having another look at SORCE data, see if I agreed with the figure.
For some reason I decided to look more closely whereupon something which had never occurred to me popped out, obvious in hindsight.
The lunar orbit modulates sun-earth distance too which leads to an idea.
Since this is such a precise signal can it be demodulated out of earth data and therefore give a useful measure of earth TSI sensitivity for the earth dataset being used. I don’t know whether this has been done or how feasible it is.
I am using the daily SORCE data, runs from Feb 2003.
The dataset includes values at earth distance and at 1AU
This examination is looking closely at the earth distance data.
Figure 2 show raw SORCE and with earth orbit one year subtracted, no surprises.
Figure 3 shows the second stage of subtracting out earth orbit, plot is offset zero now. Blue trace is red trace figure 2.
Figure 4 blue trace is figure 3 red trace. This is close to the SORCE 1AU data, note the detail, the fast wave. That is lunar.
Figure 5 subtracts out the lunar signal, shown separately to scale. Software here says it is 29.49 days assuming 365.2422 days per year. (we are into la-la land trying to get numbers exact)
Question is whether that can be unearthed from terrestrial data. Reported as 0.102595 watts/sqm rms, which is tiny, nevertheless synchronous working is the most extreme.
Figure 1 shows the final result of subtracting out earth and lunar data, plus an approximation to the underlying slow variation. the extrapolation is very uncertain but I’ve shown it anyway.
There is a disagreement between the result and the official 1AU values, too little to be concerned about. I note a long pattern in the residual, perhaps from earth orbit perturbations.
Given the TSI has an extreme crest factor there are a number of crocodiles lurking to do with handling data, just the kind of thing which messes up inadequate instrumentation. CF is most known in the mains power field but is general.
Sorry about the poor post format, WordPress is being awkward as usual with unknown CSS fighting default HTML and secret specials. Only practical way to put images right there is tables, another cantankerous item. If your browser misrenders awkwardly please speak up, see what I can do.
Post by Tim Channon