For those readers of this blog that follow the monthly update of Solar Cycle 24, things are about to change. For the better I think, but until the final report is released, we wont know for sure. Sunspot Index and Long-term Solar Observations (SILSO) a part of the World Data Center has issued a Sunspot Bulletin that says:”
Warning of Major Data Change
Over the past 4 years a community effort has been carried out to revise entirely the historical sunspot number series. A good overview of the analyses and identified corrections is provided in the recent review paper: Clette, F., Svalgaard, L., Vaquero, J.M., Cliver, E. W.,”Revisiting the Sunspot Number. A 400-Year Perspective on the Solar Cycle”, Space Science Reviews, Volume 186, Issue 1-4, pp. 35-103.
Now that the new data series has been finalized, we are about to replace the original version of our sunspot data by an entirely new data set on July 1st. On this occasion, we decided to simultaneously introduce changes in several conventions in the data themselves and also in the distributed data files.
Numbers will change and that will cause some confusion, I would imagine. Since this has been announced, many are concerned about losing the “raw data” fearing something like the temperature fiddling the CAGW people regularly do. We are being assured that the raw data will be retained. But the raw data is really questionable, and that is the motivation for the revision of the historical data.
As many of you know, several Sunspot readings are being reported now. The International Smoothed Sunspot Number has been the Sunspot number that has attempted to keep the present readings in touch with the early readings, some of which began in the 17th Century. Matching the “then” and the “now” has been complicated.
The telescopes available for many years were not anywhere as powerful as those we enjoy today. So Sunspots that were not really visible for many years of Sunspot record taking are now obvious. Over the years, someone in Zurich or Brussels or Locarno or where ever have provided the generally accepted numbers. Over the years, the different directors responsible for this have devised systems for counting the numbers. Should one count a spot that had no umbra? What was a cluster worth? Different scaling factors were used. What does one count when more are visible than that of prior years? For years the official scope (80mm, 4-f00t Fraunhoffer refractor) used to see the spots had to be duplicate of the one used by R Wolf, beginning in the mid 19th century. The team has been working on normalizing these inconsistencies. And as you go back in time to include the 18th century, the records are somewhat spotty.
I have read a draft of the report to be issued effective 1 July 2015. This is what the draft report says about Modern Maximum and Solar Cycle 24, two sensitive topics for many viewers:
- Still, although the levels of activity were not exceptional except maybe for cycle 19, the particularly long sequence of strong cycles in the late 20th remains a noteworthy episode. Indeed, the 400-year sunspot record and one of its by products, the number of spotless days, show that such a tight sequence of 5 strong cycles over 6 successive cycles (from 17 to 22, except 20), which we can call the “Modern Maximum”, is still unique over at least the last four centuries.
- However, based on the abundant sunspot data from recent years, recent statistics indicate that a substantial change in the sunspot population occurred during cycle 23 and continues into the current cycle 24. This change is reflected by a 30% decrease of the average number of sunspots per group. This recent and well-documented evolution is concomitant with parallel changes in other solar proxies and suggests that in different regimes of activities, the mutual relation between solar reference indices and proxies may vary. ………………. This also warns us that many standard proxies used nowadays and mostly based on the last 3 to 5 cycles may not be valid for earlier times and should not be simply extrapolated.
Ultimately, switching to F10.7cm solar flux maybe the best way to look at Solar Activity. But the F10.7 measurements have only limited history; it has been measured consistently since 1947.
I am looking forward to the changes.
Ps: Wrote this yesterday, but before I published it, we lost power in a storm. When I finally got through to PECO they said they would have us back on line on Thursday 25 June at 11 pm. Fortunately, the power came on about 2:30 am this morning, 24 June.
Thank you for your persistence and the elegant reply to a very complicated subject!
Thank you Walktall!!!!
The older raw data is questionable, but that is not the reason for the revision. The reason for the revisions is that the tally methodology has been applied inconsistently to the raw data over time.
The idea of this recalibration is to bring internal consistency back into to the whole record. It’s been known for decades the counts were not internally consistent. This fixes that. The biggest corrections come with data after the 1940s and before the 1890s, according to Dr. Leif Svalgaard of Stanford, who has spearheaded the revision.
Svalgaard has a new paper suggesting a correlation between the group number and F10.7:
Click to access Building-a-Relative-Sunspot-Number.pdf
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