Watts Up With That?

August 21st sketch from Catainia Observatory, Italy. Click for a larger image

I had thought I was getting “blown off” by SIDC (Solar Influences Data Center) since I had not heard a response to two emails I sent…that is until today, over a week later. At least it appears they’ll correct the southern hemisphere error. Perhaps Leif can explain to us about the other stations that reported a spot that we haven’t heard about until now. Note, this may be a form letter, since it starts with ”Dear Sir”. I suspect they got a lot of email. I’m convinced though, that 100 plus years ago, this speck would have gone unreported, and thus we now have a non- homogenous sunspot database due to changes in procedures and improvements in instrumentation. That is the most important issue that needs to be addressed. – Anthony

Dear Sir,

Many thanks for your interest in our activities and your feedback. The sunspot data for August have attracted a lot of attention already. More than they deserve maybe, because although it is true that we now have a long period of very low sunspot number, this is not yet something that is going to change the world.

I should first explain that we issue the sunspot index, which is the result of a statistical method applied to data from many stations, at three different  times and with three different ‘qualities’:
1) the Estimated Internationals Sunspot Number (EISN) on a daily basis, with only a few stations and without a consistent recalculation of the K-factor of the stations
2) the Provisional International Sunspot Number on a monthly basis, always on the first of the month in principle before 11am, using an automated procedure with as little manual intervention as possible
3) the Definitive International Sunspot Number on a quarterly basis, when we have received data from all the contribution observatories. In this procedure, manual verification is used to remove inconsistencies, such as indeed the problem of hemispheric distribution that occurred in August.

About the data on August 21-22: indeed, many stations did not report any spots on August 21 and 22. Yet, a not insignificant number of stations DID send us reports of spot observation. This included indeed Catania Observatory, one of our main data providers. However, is it not at all the case that only Catania reported spots. If that were the case, the final outcome would have been zero indeed.

On August 21, a total of 17 stations reported spots (mostly a single spot). On August 22, 14 stations reported spots. This is sufficient to warrant a non-zero sunspot number for those days.

Concerning the hemispheric distribution, there it is obviously physically impossible to distribute the one spot observed over the two hemispheres. However, we received observation reports both in southern and in northern hemisphere, and with an automated procedure such as we
use for the provisional sunspot numbers, it is not evident to decide between north or south location. Combined with low sunspot counts (creating already doubts about whether to select zero or not) and the physically meaningful constraint but that is not obvious to implement statistically that total equals north+south, this sometimes leads to the current result. At the time that we provide the definitive numbers (typically after 3-6 months), based on all observers in the network, manual intervention will be used to determine the best choice for the hemispheric location. (In this instance, this choice will be simple, since only one observer put the spot in the south on August 21, while 2 did so on August 22.)

Kind regards,
Ronald Van der Linden

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