Guest Post by Willis Eschenbach
In a recent interchange over at Joanne Nova’s always interesting blog, I’d said that the slow changes in the sun have little effect on temperature. Someone asked me, well, what about the cold temperatures during the Maunder and Dalton sunspot minima? And I thought … hey, what about them? I realized that like everyone else, up until now I’ve just accepted the idea of cold temperatures being a result of the solar minima as an article of faith … but I’d never actually looked at the data. And in any case, I thought, what temperature data would we have for the Maunder sunspot minimum, which lasted from 1645 to 1715? So … I went back to the original sources, which as always is a very interesting ride, and I learned a lot.
It turns out that this strong association of sunspot minima and temperature is a fairly recent development. Modern interest in the Maunder sunspot minimum was sparked by John Eddy’s 1976 publication of a paper in Science entitled “The Maunder Minimum”. In that paper, Eddy briefly discusses the question of the relationship between the Maunder sunspot minimum and the global temperature, viz:
The coincidence of Maunder’s “prolonged solar minimum” with the coldest excursion of the “Little Ice Age” has been noted by many who have looked at the possible relations between the sun and terrestrial climate (73). A lasting tree-ring anomaly which spans the same period has been cited as evidence of a concurrent drought in the American Southwest (68, 74). There is also a nearly 1 : 1 agreement in sense and time between major excursions in world temperature (as best they are known) and the earlier excursions of the envelope of solar behavior in the record of 14C, particularly when a 14C lag time is allowed for: the Sporer Minimum of the 16th century is coincident with the other severe temperature dip of the Little Ice Age, and the Grand Maximum coincides with the “medieval Climatic Optimum” of the 11th through 13th centuries (75, 76). These coincidences suggest a possible relationship between the overall envelope of the curve of solar activity and terrestrial climate in which the 11-year solar cycle may be effectively filtered out or simply unrelated to the problem. The mechanism of this solar effect on climate may be the simple one of ponderous long-term changes of small amount in the total radiative output of the sun, or solar constant. These long-term drifts in solar radiation may modulate the envelope of the solar cycle through the solar dynamo to produce the observed long-term trends in solar activity. The continuity, or phase, of the 11-year cycle would be independent of this slow, radiative change, but the amplitude could be controlled by it. According to this interpretation, the cyclic coming and going of sunspots would have little effect on the output of solar radiation, or presumably on weather, but the long-term envelope of sunspot activity carries the indelible signature of slow changes in solar radiation which surely affect our climate (77). [see paper for references]
Now, I have to confess, that all struck me as very weak, with more “suggest” and “maybe” and “could” than I prefer in my science. So I thought I’d look to see where he was getting the temperature data to support his claims. It turns out that he was basing his opinion of the temperature during the Maunder minimum on a climate index from H. H. Lamb, viz:
The Little Ice Age lasted roughly from 1430 to 1850 … if we take H. H. Lamb’s index of Paris London Winter Severity as a global indicator.
After some searching, I found the noted climatologist H. H. Lamb’s England winter severity index in his 1965 paper The Early Medieval Warm Epoch And Its Sequel. He doesn’t give the values for his index, but I digitized his graph. Here are Lamb’s results, showing the winter severity in England. Lower values mean more severe winters.
So let me pose you a small puzzle. Knowing that Eddy is basing his claims about a cold Maunder minimum on Lamb’s winter severity index … where in Lamb’s winter severity index would you say that we would find the Maunder and Dalton minima? …
Figure 1. H.H. Lamb’s index of winter severity in England.
As you can see, there is a reasonable variety in the severity of the winters in England. However, it is not immediately apparent just where in there we might find the Maunder and Dalton minima, although there are several clear possibilities. So to move the discussion along, let me reveal where they are:
Figure 2. As in Figure 1, but with the dates of the Maunder and Dalton minima added.
As we might expect, the Maunder minimum is the coldest part of the record. The Dalton minimum is also cold, but not as cold as the Maunder minimum, again as we’d expect. Both of them have warmer periods both before and after the minima, illustrating the effect of the sun on the … on the … hang on … hmmm, that doesn’t look right … let me check my figures …
…
…
…
… uh-oh
…
…
Well, imagine that. I forgot to divide by the square root of minus one, so I got the dates kinda mixed up, and I put both the Maunder and the Dalton 220 years early … here are the actual dates of the solar minima shown in Lamb’s winter severity index.
Figure 3. H.H. Lamb’s England winter severity index, 1100-1950, overlaid with the actual dates of the four solar minima ascribed to that period. Values are decadal averages 1100-1110,1110-1120, etc., and are centered on the decade.
As you can see …
• The cooling during the Wolf minimum is indistinguishable from the two immediately previous episodes of cooling, none of which get much below the overall average.
• The temperature during the Sporer minimum is warmer than the temperature before and after the minimum.
• The coldest and second coldest decades in the record were not associated with solar minima.
• The fastest cooling in the record, from the 1425 decade to the 1435 decade, also was not associated with a solar minimum.
• Contrary to what we’d expect, the Maunder minimum warmed from start to finish.
• The Dalton minimum is unremarkable in any manner other than being warmer than the decade before the start and the decade after the end of the minimum. Oh, and like the Maunder, it also warmed steadily over the period of the minimum.
Urk … that’s what Eddy based his claims on. Not impressed.
Let me digress with a bit of history. I began this solar expedition over a decade ago thinking, along with many others, that as they say, “It’s the sun, stupid!”. I, and many other people, took it as an unquestioned and unexamined “fact” that the small variations of the sun, both the 11-year cycles and the solar minima, had a discernible effect on the temperature. As a result, I spent endless hours investigating things like the barycentric movement of the sun. I went so far as to write a spreadsheet to calculate the barycentric movement for any period of history, and compared those results to the temperatures.
But the more I looked, the less I found. So I started looking at the various papers claiming that the 11-year cycle was visible in various climate datasets … still nothing. To date, I’ve written up and posted the results of my search for the 11-year cycle in global sea levels, the Central England Temperature record, sea surface temperatures, tropospheric temperatures, global surface temperatures, rainfall amounts, the Armagh Observatory temperatures, the Armagh Observatory daily temperature ranges, river flows, individual tidal stations, solar wind, the 10Beryllium ice core data, and some others I’ve forgotten … nothing.
Not one of them shows any significant 11-year cycle.
And now, for the first time I’m looking at temperature effects of the solar minima … and I’m in the same boat. The more I look, the less I find.
However, we do have some actual observational evidence for the time period of the most recent of the minima, the Dalton minimum, because the Berkeley Earth temperature record goes back to 1750. And while the record is fragmentary and based on a small number of stations, it’s the best we have, and it is likely quite good for comparison of nearby decades. In any case, here are those results:
Figure 4. The Berkeley Earth land temperature anomaly data, along with the Dalton minimum.
Once again, the data absolutely doesn’t support the idea of the sun ruling the temperature. IF the sun indeed caused the variations during the Dalton minimum, it first made the temperature rise, then fall, then rise again to where it started … sorry, but that doesn’t look anything like what we’d expect. For example, if the low spot around 1815 is caused by low solar input, then why does the temperature start rising then, and rise steadily until the end of the Dalton minimum, while the solar input is not rising at all?
So once again, I can’t find evidence to support the theory. As a result, I will throw the question open to the adherents of the theory … what, in your estimation, is the one best piece of temperature evidence that shows that the solar minima cause cold spells?
Now, a few caveats. First, I want to enlist your knowledge and wisdom in the search, so please just give me your one best shot. I’m not interested in someone dumping the results of a google search for “Maunder” on my desk. I want to know what YOU think is the very best evidence that solar minima cause global cooling.
Next, don’t bother saying “the Little Ice Age is the best evidence”. Yes, the Maunder occurred during the Little Ice Age (LIA). But the Lamb index says that the temperature warmed from the start of the Maunder until the end. Neither the Maunder’s location, which was quite late in the LIA, nor the warming Lamb shows from the start to the end of the Maunder, support the idea that the sun caused the LIA cooling.
Next, please don’t fall into the trap of considering climate model results as data. The problem, as I have shown in a number of posts, is that the global temperature outputs of the modern crop of climate models are nothing but linear transforms of their inputs. And since the models include solar variations among their inputs, those solar variations will indeed appear in the model outputs. If you think that is evidence for solar forcing of temperature … well, this is not the thread for you. So no climate model results, please.
So … what do you think is the one very best piece of evidence that the solar minima actually do affect the temperature, the evidence that you’d stand behind and defend?
My regards to you all,
w.
[UPDATE] In the comments, someone said that the Central England Temperature record shows the cooling effects of the solar minima … I’m not finding it:
As you can see, there is very little support for the “solar minima cause cool temperatures” hypothesis in the CET. Just as in the Lamb winter severity data and the Berkeley Earth data, during both the Dalton and Maunder minima we see the temperature WARMING for the last part of the solar minimum. IF the cause is in fact a solar slump … then why would the earth warm up while the sun is still slumping? And in particular, in the CET the Dalton minimum ends up quite a bit warmer than it started … how on earth does this support the “solar slump” claim, that at the end of the Dalton minimum it’s warmer than at the start?
The Usual Request: I know this almost never happens, but if you disagree with something that I or someone else has said, please have the common courtesy to QUOTE THEIR EXACT WORDS that you disagree with. This prevents much confusion and misunderstanding.
Data: Eddy’s paper, The Maunder Minimum
Lamb’s paper, The Early Medieval Warm Epoch And Its Sequel
Berkeley Earth, land temperature anomalies
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Oceans (to store) and ocean circulation (to transfer) would seem to be the elephants in the room on decadal temperature variation. My 2 cents worth.
And if you don’t have a reason why sun spots heat the Earth then correlation is not causation and especially poor correlation is not weak causation.
Willis Eschenbach says:
June 23, 2014 at 3:15 pm
Alec Rawls says:
June 23, 2014 at 1:36 pm
“Kirkby’s 2008 survey paper cites a bunch of stuff. …”
… galactic cosmic rays (note the inverted scale; high cosmic ray fluxes are associated with cold temperatures) …
Look at the freakin’ graph … do you see the “high cosmic ray flux” around 1050? Care to point out the “cold temperature” associated with that? And in any case, with five totally different temperature datasets, saying something is “associated with” cold temperatures is a joke.
The cosmic ray ‘data’ is even more of a joke [or even a fraud]. What Kirby shows in Figure two
[reproduced here at the left] http://www.leif.org/research/Kirby-Flaw-GCR-14C.pdf as the cosmic ray flux [blue curve] is NOT the cosmic ray flux, but the flux with the geomagnetic modulation removed. At the right I show the true flux [as given by the 14C data] as the red curve. The large variation [red curve] over the past 200 years is not due to the Sun, but to the Earth’s varying magnetic field. If the real cosmic ray flux was a significant driver then the true flux should be plotted at the left, not the flux with the Earth’s variation removed.
Willis, did any you guys even bother to look at the magnetic field of the earth since it has decreased 10- 15 % since, oh my, since the Industrial Revolution? It should be apparent to you the cross sectional area at the poles is not doubled in field strength but squared. And since magnetic fields are not known to be smoothed, but can be stronger or weaker in places, the burden of proof is on you. I can ask all the questions within reason if you are trying to prove something that is not. Prove to me that it is not the magnetic field of the earth. Prove to me that there isn’t a relationship between the pressure gradient in the solar wind, the compression of the atmosphere (remember as the IPCC told me, a little makes a big difference) which also heats it up, ( they use that technique in the toamack reactor to bring gas to a plasma state, squeezing it by magnetic fields) you know like in a CME, the magnetic fields of other planets, namely Jupiter, as to whether they buck or boost that field strength. Cosmic ray flux is just the tip of the iceberg. Ignoring this will not make it go away, nor calling it an opinion. It’s a system, non linear and chaotic. Looking for precise pieces to this puzzle is ridiculous. It’s too bad you can’t see the relationship between sunspot activity and climate change, I can.
Eliza says:
June 23, 2014 at 3:38 pm
Thanks, Eliza, but I fear that an unexplained and unsupported opinion carries no weight on this scientific website. There are issues with the Berkeley Earth data, to be sure … but you haven’t even begun to show that it is not useful for comparing a few adjacent decades as I have done.
Eliza says:
June 23, 2014 at 3:34 pm
Say what? Each of those three datasets has a definite trend.
w.
Sturgishooper For the 1000 year quasi periodicity see Fig 4 at
http://climatesense-norpag.blogspot.com/2013/10/commonsense-climate-science-and.html
The key uncertainty in climate forecasting is where we are in relation to this 1000 year periodicity .
Looking at the downtrend in solar activity since cycle 22 fig 9 and the temperature trends since 1000AD Fig 3 it would seem more likely than not that we have just passsed the peak and should head down (with some bumps ) for the next 600 years or so.
[reproduced here at the left] http://www.leif.org/research/Kirby-Flaw-GCR-14C.png
sturgishooper says:
June 23, 2014 at 3:43 pm
My bad, moving a bit too fast, but it makes no difference to my point. My data shows 1694 as the coolest year, but you still need to explain why the temperatures started rising before the sunspots …
w.
Hi Willis. No, I won’t pick one paper and argue with you here rather than at JoNovas. My suggestion was to read them for background knowledge you may not have.
My sole point was clear. There are at least three influences: solar whatever, GHGs, and Earths own natural variations, of which ENSO, PDO, AMO and Arctic ice are evidence (coupled, who knows. I am intrigued by the stadium wave as an equivalent of a phase locked loop oscillator. Anybody with a cell phone owns one). To say that only one factor explains everything is wrong in my view. To say that one of those big three is not a factor at all is equally wrong for the same reasons, again in my view.
Factors meaning on decadal or longer time scales.
Don Easterbrook says:
June 23, 2014 at 1:56 pm
Glad to hear it … are you going to offer a link to the Tony Brown dataset, or is that a secret? Because I’m happy to look AT it, but no way I’m going to look FOR it …
w.
The data used in Figure 4 looks suspect. Perhaps it is reasonable to assume a greater error margin as you move back in time, but the filtered time series also shows larger swings (trends) as you go back in time and that is a sign those trends are noise. There is no reason to expect variations in Earth temperature trends to have reduced significantly over the past 400 years.
Trond Arne Pettersen says:
June 23, 2014 at 2:08 pm
Thanks, Trond. I think that anyone using an 11-year mean on sunspot/TSI data should study my document “Sunny Spots Along the Parana River” until they give up that pernicious averaging practice entirely.
w.
Tonyb says:
June 23, 2014 at 2:14 pm
Tonyb, thanks for your attempt, but dang it, QUOTE WHAT YOU DISAGREE WITH!
Far as I’ve seen, nobody, especially me, has attributed the concept or the identification of the Little Ice Age to either Eddy or Lamb, so you are arguing against a claim that nobody has made.
Folks, it’s more than just a good idea to quote what you disagree with. The mere process of looking for the quote that you remember as being wrong can be very valuable in showing you that you may have misunderstood what someone is saying.
And as a result, it can keep you from making these kind of foolish mistakes attacking a non-existent position …
w.
Willis Eschenbach says:
June 23, 2014 at 3:59 pm
You have not shown that T did start rising before SSN. But even if it did, solar activity isn’t the only variable. However, within margin of error, the correlation with rising & falling T is at worst too close to call.
But if you have in fact compared the average annual T in CET with SSN, I’d appreciate seeing those data & your statistical analysis of correlation.
Motl has analyzed rate of cooling and warming for different periods in CET, although he hasn’t posted cold/hot rankings by ten-year period. He found the fastest cooling of the MM during the 30 years 1666-95 and the fastest warming from 1691 to 1720 (five years out of the MM as usually defined).
http://motls.blogspot.com/2010/01/warming-trends-in-england-from-1659.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+LuboMotlsReferenceFrame+%28Lubos+Motl%27s+reference+frame%29&utm_content=Google+Reader
Tonyb says:
June 23, 2014 at 2:14 pm
Tony, the idea that Mann’s reconstruction is anything but GIGO is laughable. You trying to use it in a scientific paper is a joke. It is well-known that Mann made a foolish newbie math error in that paper, using un-centered principal component analysis that mined for hockeysticks. He also lied about the analysis to a Senate committee, and refused to reveal his data and code despite numerous requests. Finally, he knew before he published it that his results were bogus, as he stashed away inconvenient results in a folder named CENSORED TO 1400 … and you think what he did is science?
Really?
I fear that your failure to deal with or even discuss these issues in your analysis renders your entire approach worse than useless. Sorry to say that, but when you lie down with dogs, you get up with fleas. Since you either can’t see or are unwilling to discuss the glaring and widely discussed problems with the Mann hockeystick analysis, why on earth should I pay even the slightest attention to your opinions on anything?
w.
The solar barycenter affects sunspots and solar magnetic flows, and only affects Earth’s climate incidentally.
Earth’s temperature is regulated by hurricanes, not CO2 or other aerosols. The gradual increase in temperature since the last major advance of ice 11,500 years ago is due to gradual planetary thawing after an anomalous ice dump, not CO2. When oceans get too hot, they make big storms that puncture the upper atmosphere, and transporting huge quantities of moist warm air. The heat radiates into space and the cold moist air falls back to Earth in various forms. The stronger the hurricane is, the greater the heat will be radiated into space and the greater quantity of cold moisture will cover the ground. This is why extreme cold follows extreme warmth.
The cold spells, such as this past winter, are caused by changes in the electrostatic and electromagnetic forces holding the polar atmosphere into place. Low solar output (not just sunspot activity) results in upper polar atmosphere over Greenland falling to the troposphere and giving cold winters in the Eastern US. It has nothing to do with the amount of heat leaving the Sun.
Changes in the electrostatic and electromagnetic activity of the Earth at the planetary scale also affects the intensity and path of the jet streams, ocean currents, and cloud formation.
Willis
You referenced the relation between Sunspot minima and temperature as being a relatively modern idea dating to 1976 .
I was merely pointing out that the lia ( and the sunspot association that was the point of the article) dates back to way before this time.
I am not agreeing or disagreeing with anything else, merely that eddy was the latest in a long line of correspondents.
As regards the association between sunspots and low temperatures, whilst there appears to be a correlation at times, there appears to be limited correlation at other times, when it would have been expected, according to the theory. As an example the sporer from 1500 to 1550 appears to have been rather warm. The 1450 to1500 sporer period however appears to have been rather cold.
Tonyb
Rud Istvan says:
June 23, 2014 at 3:59 pm
Fine, Rud. Then go back to Jo’s. If you don’t want to reveal your evidence, then you’re of no interest to me. Why should I talk science with someone who won’t take a stand and defend it with evidence?
Regarding discussing things with you at Jo’s, as I told Jo and David, I’m not doing anything further at JoNova until she and David publish all of the hidden data, code, equations, model, out-of-sample testing, and the rest of the stuff she’s refused to reveal to date. That kind of withholding and doling out of data and results isn’t my idea of science, so I said over there that I’m out of their game until she decides to stop faffing around and to act in a transparent and scientific fashion by publishing everything.
w.
Does anyone here know or have a suspicion as to what caused the Little Ice Age?
Steve from Rockwood says:
June 23, 2014 at 4:01 pm
Thanks, Steve, an interesting observation. First, recall what I said, viz:
Second, the greater variation is not a sign of greater “noise” as you claim. Instead, it is the inevitable result of using a smaller number of stations which are located in a smaller geographical area. Both of those will lead to greater variance in the signal … but that doesn’t make it “noise”. It is still the real average of real data.
And yes, I’d love to have better data … but it’s what we have.
Regards,
w.
Jimbo says:
June 23, 2014 at 4:36 pm
In my opinion, lots of folks have suspicions, but nobody knows. I’ve never seen an explanation that’s held water for either why we went into the LIA (long before the Maunder minimum) or why we’ve been gradually warming ever since then.
w.
Willis
The long slow thaw was not a polemic. It was a serious study using measured language and incorporating thousands of references that examined the period to 1538 and used as a guide the studies of both Mann and lamb. I make it quite clear there, and in various other articles that I do not agree with Mann. He does not begin to reflect natural variability and I have said this numerous times here and elsewhere over the past five years.
Whatever our personal opinions of him and his science he remains far more credible than you or I and consequently we have to deal with that in our own way. I choose to do it in a measured way and you will have a different approach.
Tonyb
Gee what totally convinced me, the killer fact – so to speak was that in the ‘decade 1425 to1435 ‘Global Temps’ declined at their fastest rate on record. I mean at that point for me the science was settled.
Huh?
Wa?
In 1593!!!! Galileo Galilei invented a rudimentary water thermoscope, which for the first time, allowed temperature variations to be measured.
Darn!
(You know I’m beginning to think that Willis is actually parodying ‘Climate Scientists’ who seem to be able to hang the grandest theories on the flimsiest of data.)
By the way I was down at the beach for a paddle just then and I noticed that the ‘Pacific Ocean’ was warmer than it usually is at this time of year.
rishrac says:
June 23, 2014 at 4:24 pm
Thanks, rishrac. I hate to say it, but clearly you have a deep fundamental misunderstanding of science. In science, nothing can every be proven. So asking me to prove something is meaningless.
In addition, you misunderstand the burden of proof. For example, if you think that the earth’s magnetic field strength or the magnetic field strength of Jupiter affects the climate, then it is your job to come up with the detailed theory and the evidence for that claim. And you may be right about the magnetic fields, there’s lots we don’t know about the climate.
When you do come up with your detailed theory and your supporting evidence, I encourage you strongly to write it up and send it to Anthony, so that everyone can see if they can find fault with your logic or your data or your code or your evidence. If nobody can find fault with it, then it gets provisionally accepted as valid until the day someone may eventually find something that supercedes it.
But your idea that it’s up to me to “prove” that your vague, detail-free, physical mechanism free, evidence-free claims are untrue?
Sorry … that’s not how science works.
Since I can’t show a negative (i.e. that the 11-year sunspot cycle doesn’t affect the climate), what I’m doing is showing in as many climate datasets as possible that there is no significant effect. But no, I can’t prove that. All I can do is stack up contrary evidence.
w.
Jimbo says:
June 23, 2014 at 4:36 pm
I suspect the same causes as of the prior centennial- or sub-millennial-scale cool spells which follow and precede warm phases of interglacials, which may well be the same as during glacials.
For the post-Optimum Holocene, to wit, the Greek Dark Ages, Dark Ages and Little Ice Age Cold Periods, for example.
Willis, you are not your usual self today. I must say, your somewhat snide ( in my view) reply to TonyB just above proves it. Anybody who is following these debates knows what ClimateReason is trying to do through painstaking original historical research. His website explains it in detail.
Understand natural variability back behind CET. And anybody who has bothered to read his fascinating posts (mostly at CE) would know he is as much or more critical of Mann’s hockey stick than Steve MacIntrye. And, in my opinion, with better popular arguments against the Mannian erasure of natural variability. Not everybody gets white noise/red noise and all that fancy statistical math. Everybody gets blizzards, rains, heat waves that caused crop failures, and such.
Calm down, and stop swinging so wildly at ‘friends’ like Tony, Don Easterbrook, etc.
Unfortunately for you, those wild swings are unlikely to be ‘disappeared’ as they probably would at SkS, RC, or other Warmunist sites.
IMO, Lassen has not been shown false:
http://www.tmgnow.com/repository/solar/lassen1.html
Excerpt:
Long-term Variations in Solar Activity
and their Apparent Effect on the Earth’s Climate
K.Lassen
Danish Meteorological Institute, Solar-Terrestrial Physics Division,
Lyngbyvej,100, DK-2100 Copenhagen (2), Denmark
Abstract
The varying length of the 11-year cycle has been found to be strongly correlated with longterm variations of the northern hemisphere land surface air temperature since the beginning of systematic temperature variations from a global network, i. e. during the past 130 years. Although direct temperature observations before this interval are scarce, it has been possible to extend the correlation back to the 16th century due to the existence of a series of proxy temperature data published by Groveman and Landsberg in 1979. Reliable sunspot data do not exist before 1750, but we have been able to derive epochs of minimum sunspot activity from auroral observations back to 1500 and combine them with the direct observations to a homogeneous series.
Comparison of the extended solar activity record with the temperature series confirms the high correlation between solar activity and northern hemisphere land surface air temperature and shows that the relationship has existed through the whole 500-year interval for which reliable data exist.
A corresponding influence of solar activity has been demonstrated in other climatic parameters. Thus, both the date of arrival of spring in the Yangtze River Valley as deduced from phenological data and the extent of the sea-ice in the Atlantic sector of the Arctic sea have been shown to be correlated with the length of the sunspot cycle during the last 450 years.
Conclusion
70-90 years oscillations in global mean temperature are correlated with corresponding oscillations in solar activity. Whereas the solar influence is obvious in the data from the last four centuries, signatures of human activity are not yet distinguishable in the observations.
Introduction
Variations in the activity of the Sun greatly influence the physics of the upper atmosphere. Thus, magnetic disturbances, occurrence of auroras at low latitudes, sporadic ionization above -80 km altitude, and – as a consequence of the latter – reduced quality of shortwave radio transmissions all appear to follow the approximately 11-year soler activity cycle. This cycle is most distinctly seen in two observed parameters: the sun- spot number and the 10,7 cm radiation. For analytical purposes the intensity of the 10,7 cm radiation may be the best suited, but it has the drawback that observations were first initiated in the 1950s. For studies involving longer data series the only usable directly observed signature of solar activity is the varying number of sunspots. This has been subject of observation through several hundred years and may be regarded as reliable since 1750 (Eddy, 1976). The sunspot number, generally denoted R, is highly correlated with the 10,7 cm flux.