An indicator of rock bottom for the solar minimum

Solar minimum surprisingly constant

More than half a century of observation yields new discovery


Using more than half a century of observations, Japanese astronomers have discovered that the microwaves coming from the Sun at the minimums of the past five solar cycles have been the same each time, despite large differences in the maximums of the cycles.

Solar microwave observation telescopes in 1957 (top left) and today (bottom left). Fluctuations observed during 60 years of solar microwave monitoring (top right) and the solar microwave spectrum at each solar minimum (bottom right). The background is full solar disk images taken by the X-ray telescope aboard the Hinode satellite. CREDIT NAOJ/Nagoya University/JAXA

In Japan, continuous four-frequency solar microwave observations (1, 2, 3.75 and 9.4 GHz) began in 1957 at the Toyokawa Branch of the Research Institute of Atmospherics, Nagoya University. In 1994 the telescopes were relocated to NAOJ Nobeyama Campus, where they have continued observations up to the present.

A research group led by Masumi Shimojo (Assistant Professor at NAOJ Chile Observatory), including members from Nagoya University, Kyoto University, and Ibaraki University, analyzed the more than 60 years of solar microwave data from these telescopes. They found that microwave intensities and spectra at the minimums of the latest five cycles were the same every time. In contrast, during the periods of maximum solar activity, both the intensity and spectrum varied from cycle to cycle.

Masumi Shimojo explains that,

“Other than sunspot observations, uniform long-term observations are rare in solar astronomy. It is very meaningful to discover a trend extending beyond a single solar cycle. This is an important step in understanding the creation and amplification of solar magnetic fields, which generate sunspots and other solar activity.”

The Sun goes through a cycle of active and quiet periods approximately once every 11 years. This “solar cycle” is often associated with the number of sunspots, but there are other types of solar activity as well. So simply counting the number of sunspots is insufficient to understand the solar activity conditions.

Microwaves are another indicator of solar activity. Microwaves have the advantage that, unlike sunspots, they can be observed on cloudy days. Also, monitoring multiple frequencies of microwaves makes it possible to calculate the relative strength at each frequency (this is called the spectrum).


The paper: Variation of the Solar Microwave Spectrum in the Last Half Century


The total solar fluxes at 1, 2, 3.75, and 9.4 GHz were observed continuously from 1957 to 1994 at Toyokawa, Japan, and from 1994 until now at Nobeyama, Japan, with the current Nobeyama Radio Polarimeters. We examined the multi-frequency and long-term data sets, and found that not only the microwave solar flux but also its monthly standard deviation indicate the long-term variation of solar activity. Furthermore, we found that the microwave spectra at the solar minima of Cycles 20–24 agree with each other. These results show that the average atmospheric structure above the upper chromosphere in the quiet-Sun has not varied for half a century, and suggest that the energy input for atmospheric heating from the sub-photosphere to the corona have not changed in the quiet-Sun despite significantly differing strengths of magnetic activity in the last five solar cycles.

109 thoughts on “An indicator of rock bottom for the solar minimum

  1. This is not new, nor surprising.
    Already Loomis knew this in 1870:
    In fact, there is good evidence that the minima have been constant the last 280 years: and and
    “the EUV flux reaches the same low (but non–zero) value at every sunspot minimum (possibly including Grand Minima), representing an invariant ‘solar magnetic ground state’.”

      • The ground level is not equal in the minimas. Sometimes the minima are long, sometimes short. It’s the same with the Maximas. It is clear: in a sharp frost of 3 days, the sea will not freeze, but with a same frost of 3 weeks. Therefore, those who only stubbornly look at basic conditions in Maximas and Minimas fail to appreciate the greater importance of the temporal extension of the individual phases.

      • It appears to me that there is a slight difference in the minima, i.e. they were slightly above the bottom from 1830-1870.

      • Svalgaard’s take on it is that bodies of water equilibrate quickly. (there should be no difference in temperature between short and long minima)…

    • Just because something is not new or surprising does not mean it has no value or is not worth reporting. We are still testing Einstein’s theories and reporting on them. I would also take issue with the wording that Loomis “knew” about the minimum microwave levels. First, he presented a theory (proposition) that all solar minimums were the same, but did not state it as a fact. Second, there was no way for him to directly observe microwaves. We may know today that sunspots and microwaves are caused by the same underlying phenomena, thus validating Loomis’ theory, but that’s not the same thing as saying that he “knew”.

      • Loomis was talking about observations not theory. What he knew was that solar activity was the same at every minimum. Microwaves, EUV, and sunspots are all manifestations of the same underlying phenomenon. That the microwaves specifically are constant at every minimum has been noted by several people including myself long ago, so the claim that the constancy of the flux is new and surprising is not correct.

      • The article did not claim the Japanese results were “new” or “surprising”. Neither did I. So that part of your argument is a straw man. All I said is that this data is useful and worth reporting, even if it only adds to all the other data we have. Stop projecting your own biases onto me.

      • OK, I just noticed the article subheading which claimed the results are new. I didn’t read that before (I usually ignore the subheadings). From what I know, this is not really new, but I didn’t read the entire paper to see if there really was anything new in it.

      • Loomis observed a number of solar minima and saw that solar acitivity was the same at every minimum. I would be interested to know whether he also observed any swans and noted their colour. It can be an interesting journey from observation to knowledge.

        • As Yogi Berra said: “you can observe a lot by just looking”. Loomis did exactly that: looking at the daily variation of the geomagnetic field which had been observed at his time for more than a century [discovered in 1722] and that was known at the time to depend on the sunspot number.

    • Why are you making a big deal of this, Its direct measurement that validates spotty proxy data. Be happy, its what science is all about.

    • This isn’t about “Wow!! We found this new tool method”, or some other eureka moment.

      What this strongly suggests is the microwave readings are superior to and less influenced by observational technique than using using sunspot numbers to track the solar magnetic cycles.

      Sunspots depend on magnetic flux tubes breaking and erupting through the photosphere surface. Those flux tubes may not make it to the surface if the umbral magnetic field strengths continues its decline.

      A Big IF I know, but not impossible to discount – i.e. the Maunder state). The visible sunspots would disappear in that case, but the underlying solar magnetic cycle would still continue, and thus the magnetic heating of corona would continue to modulate the F10.7 readings.

      The one thing that the microwave readings don’t provide is which hemisphere is putting on the show. Visible and UV images though would still discern which hemisphere is the more active.

      • What this strongly suggests is the microwave readings are superior to and less influenced by observational technique than using using sunspot numbers to track the solar magnetic cycles.
        I basically agree, except that the sunspot number [or better: the group number] correlates very well with the microwave flux:
        So for all practical purposes they are equally good, and for times before ~1750 [or some might say 1840] the Group Number is about all we have. And strictly speaking we only have direct measurements of the microwave flux since 1947.

      • My point is not to diss Group Numbers or SSN counting.

        But that the F10.7 value may be all we have if a Maunder state ever arises again (t surely will, but not likely in our lifetime).

        From: M. J. Penn and W. Livingston
        The Astrophysical Journal, 649:L45-L48, 2006 September 20
        Temporal Changes in Sunspot Umbral Magnetic Fields and Temperatures

        A continuation of these trends would produce important changes for the next few solar cycles. The observed distribution of umbral magnetic fields runs from about 1500 through 3500 G, with a median value near 2400 G. If 1500 G represents a true minimum for spot magnetic fields and the field strengths continue to decrease at the rate of 52 G yr-1, then the number of sunspots in the next solar cycle (cycle 24) would be reduced by roughly half, and there would be very few sunspots visible on the disk during cycle 25. It is with this in mind that we eagerly anticipate measurements of sunspot spectra in the next solar cycle.

        That SC 24 sunspot measurements for maximum are now in the history books. 24 was roughly 60% of SC 23. Is that roughly 50%? Probably not close enough. SC 25 will likely have plenty of spots to count in 7 to 8 years from today.

      • As for umbral magnetic field readings, it has always seemed to me pre-selected population from which the measurements are obtained.

        Such that we can only measure the umbral field strength in the visible sunspots (that is the ones that had enough magnetic strength around the flux tubes to break the surface of the photosphere.) Those fluxtubes that didn’t break the surface (likely) had field strengths below 1500. It is a self-selected population. So of course, the measure sunspot umbral field strength will always ride at some level above 1500.

        As an aside, I used to study telomere lengths in T cells. Some of my work involved longitudinal assays (the same people’s telomere length measured at intervals spaced by many years or decades).

        I had to make sure that when I gave lab data talks and quarterly formal presentations, that audience understood that if a younger person had very short telomeres, they were likely lost to follow-up some decades later. That is to say, you cannot measure the telomere lengths of someone who has been dead 10 years on a 20 year follow-up survey. This “you can’t measure dead people’s telomere lengths” fact always meant that telomere length estimates of telomere erosion rates (length decay) was likely biased high.

        Similarly, umbral magnetic field is probably biased high.

        • visible sunspots (that is the ones that had enough magnetic strength around the flux tubes to break the surface of the photosphere.)
          Actually, that is not how sunspots are formed. They may originated as flux tubes deep below the surface, but are quickly ‘shredded’ into ‘spaghetti strands’ that are carried to the surface as many [invisible] magnetic discrete flux ‘elements’, that then in the course of a day or so assemble into stronger sunspots becoming visible when the compacted field exceeds 1500 Gauss.
          There are no strong flux tubes ‘breaking’ through the surface.

      • Dr Svaalgard,
        Thanks for that description. My mental picture was incorrect on thinking the tubes remain intact to surface and the 1500 G field is what kept them from spreading out like a drop of oil on the ocean surface.
        But with that I’ll have to go read up where the umbral field gets its energy to assemble the spaghetti strands into a spot.

      • Back in I suggested that we may be missing some of the weaker spots already, and I still think that’s true. However, when I eyeball the mode of the sunspot strength (i.e. the peak of the bell curve distribution) or approximately the 90th percentile at the strong end, it certainly looks to me as though the decline is gone, not hidden.

        In some of the old posts and reports, either Leif or Livingston point out that even if the contrast in visible light makes sunspots disappear, the magnetic signature is still there. Had the decline continued, I imagine there’d be several people trying to identify wannabe sunspots from the magnetic domains.

        At least in your telomere studies, you could identify the lost subjects.

  2. Somebody help me here: are they saying that during the “quiet sun” times there is not much variation in microwave output but during the active times there is varying levels of higher microwave activity?

    If so, doesn’t this show that overall the sun is increasing its warming of the earth?

    • Yes but nobody disagrees on that, just how much its effect is. Those who disregard the sun say that the effect is very small and cannot explain current trends in warming.

  3. lol, solar cycles and MW floor at minima alone are enough to laugh at the standard solar model.

    Because our model of the sun is junk science, we basically have no idea how the sun has effected earth temps\climate over millions of years, except by less reliable than claimed proxies.

  4. what am I saying, there is no standard model, it’s a patchwork quilt of theories that are not connected, like most of astronomy.

    Anything observed that breaks a theory, is ignored and labeled strange and shelved

    • The aa-index is wrongly calibrated before the 1950s [too low] and depends mainly on the magnetic field B in interplanetary space. At minima, when the sunspot related fields go away, B and thus aa depends on the solar polar fields which are a predictor of the next cycle and thus not really a minimum property of the sun.

    • Don’t you dare contradict Lief, everything is known about the Sun for the last 6 Billion years, he told me so about 4 years ago when I questioned his Hubris.

    • All based on media hype. Not science.

      “In plain English, the small change in sunlight reaching the Earth during a new Maunder minimum wouldn’t be enough to reverse climate change. For the technically minded, even a 3 W per m2 change in irradiance corresponds to a radiative forcing of just 0.5 W per m2 (because the Earth is a sphere and not a flat circle), which is less than the radiative forcing produced by anthropogenic greenhouse gases.

  5. In support of Hans-Georg’s November 20, 2017 at 7:38 am above comment.

    It is length of time of the solar minimum that is the issue.

    The fact that the solar minimums for the last four cycles where the same intensity, while the solar maximums for the four cycles in question where different, is interesting, but not relevant to predicting what is going to happen next to the sun.

    The normal solar minimum is 2 to 3 years.

    The past weird unexplained Solar Grand Minimums which all correlated with cold periods in the earth’s climate are of much greater length of time than 2 to 3 years.

    Past grand solar minimums had two durations: 30 to 90 years and greater than 110 years.

    Grand minima and maxima of solar activity: new observational: constraints

    Two different types of grand minima are observed: short (30–90 years) minima of Maunder type and long (>110 years) minima of Spörer type, implying that a deterministic behaviour of
    the dynamo during a grand minimum defines its length. The duration of grand maxima follows an exponential distribution, suggesting that the duration of a grand maximum is determined by a random process.

    A grand minimum is believed to correspond to a special state of the dynamo (Sokoloff 2004; Miyahara et al. 2006), and its very existence poses a challenge for solar dynamo theory. It is noteworthy that dynamo models do not agree how often such episodes occur in the Sun’s history and whether their appearance is regular or random.

    • you are confused about solar minima. A solar minimum is defined as the time between two 11-yr [nominally] sunspot cycles. It usually last a year or two depending on how you define it. A Grand Minimum is a period in which several sunspot cycle of very low amplitude occurs. Usually last half a century, again depending on how you define it.

  6. Long experience suggests that “stupid questions” are rarely stupid. With that in mind follows is my stupid question.

    Is there enough calibration/testing of the microwave sensor array to assure the “floor” is not an instrument response and is actually still detecting a signal? In other words when exposed to lower levels in controlled conditions do they correctly detect or is there a threshold detection value?

  7. While taking few weeks away from blogging I did a bit of graphic ‘doodling’ in order to see if it would be possible to determine what might be the effect if any of a new Solar Grand Minimum in the N. Hemisphere.
    Most of the early temperature records originate from the North Hemisphere the data’s accuracy is superior to that for the global temperature. Since 68% of the global land area is in the Northern Hemisphere and roughly 88 percent of the world’s population lives in the Northern Hemisphere, anticipated consequences from any significant rise or fall in the future temperatures would be more important if based on the North Hemisphere’s rather than if based on the global averaged data.
    To do this I did some numerical (call it ‘numerology’ if you wish) analysis exclusively based on the perceived natural variability.
    In order to get some sense of it, was required to produce a numerical model of what temperatures might be if there is no Grand Solar Minimum in the forthcoming decades.
    When this was ‘achieved’ further three options were considered, with Maunder type minimum starting at beginning of the either of the next three sunspot cycles, SC25, 26 & 27; surprisingly effect is least sever with the SC27’s start.
    Graphic results are shown here, to a degree they are self-explanatory while a verbal description would take far too much space and the reading time patience.
    Periodicity of the multi-Decadal trend line is in the low 60s (years), it has varied in periodicity during last 400+ years (around 65 + & – 5 years). It is assumed that since the multi-Decadal periodic trend was present during the last 100 years that it may continue for another 50-80 years.
    Periodicity of the multi-Centenary trend line is chosen for the best possible correlation with HadCrut4 data (R^2=0.7016).
    Grand Minimum possible effect on the NH temperatures is determined from the CET’s Maunder Minimum results, after scaling down for the hemispheric averaging.
    (Notes: the CET’s multi-Decadal periodicity during MM was in the high 60s, while the multi-Centenary trend periodicity appears to have been constant since 1650).
    If the above numerical hypothesis is a reasonable reflection of the natural variability and the next Grand Minimum starts with SC25 then the science has a good chance to ascertain more accurately the solar contribution to the temperature’s natural variability, but if the next GM is delayed until start of SC27 that opportunity will be lost.

  8. I’ll get to “climates” – but first:

    Leif makes a simple comment that the lead-in to this story used the word “discovered” when it would have been better to have used the word “affirmed.”
    Then a dozen folks act like a starving dog when a bone is being contested. Holy cow!

    Places on Earth have “climates.” Examples include “west coast marine”, Mediterranean (wet winters and dry, warm to hot summers), Continental (or varying sorts), and others.
    Boundaries of these climates were originally established with ecotones, a transition area between two biomes. We live in one with Sagebrush Steppe to the east and Ponderosa Pine forest to the west.
    Local history and various proxies (fire scars and coring of trees, sediments in lakes, and others) indicate this situation has existed for hundreds, even thousands of years after it became established following the last ice advance along the Washington – British Columbia region.
    I’ll let you know when Kudzu covers the Ponderosa and they die.
    If you notice natural growth of Yellow Cedar in Bakersfield, let me know.
    [Minor shifts in ecotone boundaries shall be ignored. There are other things going on – example, fire suppression, age mortality]. [Note #2: I know climate does change — see “ice” above.]

    • John F. Hultquist
      November 20, 2017 at 10:41 am

      Yes, John I quite agree. This childish squabbling over minor points just detracts from useful discussion. It is demeaning to Anthony’s site. Why are peoples’ egos so fragile and in need of silly point scoring?

      Leif, thanks for useful and interesting scientific input on this and other matters of interest ot us all.

      • I am a “lurker” here: gold medalist in engineering half a century ago; highly skeptical about many aspects of so-called “climate science;” very interested in many of the articles and comments; but not knowledgeable enough to understand many of the finer points. WUWT is my main source of information about “climate” and have referred it to many other.

        I agree completely with your comment about nit-picky squabbling and attempts to score points. It’s a real turn-off, and detracts from the value of the site.

      • I rather enjoy the free-for-all. It can be a learning experience for all sides – especially for those who are initially unacquainted with the issue under debate.

    • Solar cycles are nominally 11 years long, but in reality stretch about 16-17 years from before the first sunspot of a cycle shows up and continuing a couple of years after the last spot has died away. Thus cycles overlap by several years.

  9. In Japan, continuous four-frequency solar microwave observations (1, 2, 3.75 and 9.4 GHz)

    It’s odd that these folks are talking about frequencies, when I can’t recall hearing about anything other than the 10.7 cm wavelength everyone else uses. (Leif, why 10.7? I’ve never seen that explained.)

    Here’s a handy table.

    Freq  cm
    1.00  30.0
    2.00  15.0
    2.80  10.7
    3.75   8.0
    9.40   3.2
    • Covington [who discovered that the Sun was emitting microwaves] used surplus military radio equipment [after WWII]. It just so happened that it was tuned to a frequency od 2800 MHz or 10.7 cm. By lucky coincidence that wavelength is where the microwave emission has a local maximum.

    • I figured it might be that simple. I also expect that the Japanese equipment is also “what was available.” Perhaps if they realized they’d still be at it 50 years later they would have gone looking for a 10.7 cm rig to round out the collection.

  10. Solar cycle minima are clearly unequal. Silso has this interesting graph on Number of spotless days vs. Solar Cycle amplitude.

    If the number of spotless days can change by a factor of 5 between different minima, it is absurd to maintain that their level of activity is the same, even if it is the same on any spotless day. Clearly a day with spots on average has a higher activity than a day without spots.

    By the way this graph supports that solar activity on average has increased over the past 200 years, peaking in the second half of the 20th century.

    • A little knowledge is a dangerous thing. Observations show that on days where solar activity has died away, the sun always emits the same microwave flux [and EUV flux] causing the same ionospheric electric currents. That this flux is not zero is the important aspect of the finding. The number of spots and groups during a minimum year is so small that they only increase the microwave and EUV flux a tiny amount as you can easily see from the graph in the post. The number of spotless days is a very poor indicator of solar activity and the solar magnetic field. As usual, the question is always ‘how much more’? and that excess is very small and completely insignificant.
      And if you had included the 18th century in your graph you would have seen that there has been no trend the last 300 years. E.g.
      Your selective omission of inconvenient data is the oldest trick in the book.
      That is the important fact that should be heeded.

      • Ask SILSO about extending that graph. Perhaps they don’t have the earlier daily data.

        And regardless what happened in the 18th century, it is clear that since early 19th century long term activity increased.

        Whether a 5 time difference in the number of spotless days constitutes or not an insignificant difference in terms of activity, you are entitled to your opinion obviously.

        I don’t believe you that having 1000 days of no spots is the same as having 200. And the graph shows clearly that there is some relationship between the level of activity of a cycle and the number of spotless days in its minimum, as the number of spotless days is essentially as drawing an envelop to the sunspot activity graph, so they are clearly related.

        • Perhaps they don’t have the earlier daily data.
          In fact they don’t

          And regardless what happened in the 18th century, it is clear that since early 19th century long term activity increased.
          And that since the early 20th century as well, after a strong decline since the 1870s. The fact is that solar activity reached about the same level in every century. That is the ‘long-term’ level.

          Whether a 5 time difference in the number of spotless days constitutes or not an insignificant difference in terms of activity,
          The number of spotless days is a poor measure of [inverse] activity. What is important is the actual activity on the days with spots. For example, the minimum year 2008 had 265 spotless days with an average F10.7 flux of 68 and 101 days with spots and an average F10.7 flux of 71.

          • In fact they don’t

            So you asked me to do a graph for which there is no data. A very nice way of arguing in a debate.

            The number of spotless days is an statistical measure of a difference in the Sun. The Sun cannot be in the same state when it produces 200 susnpot-free days that when it produces 1000. As you don’t know everything that happens in the Sun, and you don’t know the effect that every change in the Sun has on the Earth, your claim that this difference doesn’t matter is empty.

            The difference between solar minima exists. We do not know of any effect that this difference might have on the Earth, but we cannot rule out such effect, as the level of our knowledge is inadequate.

          • as the level of our knowledge is inadequate.
            “If you don’t know anything, everything is possible”
            Arguing on the basis of ignorance is not very fruitful.
            What we do know is that at every solar minimum the Sun enters a sort of magnetic ground state with only a tiny residual component of activity. What we call a ‘spotless day’ is determined by the instruments with which we measure solar activity. If we used telescopes with a higher resolution we would see fewer spotless days, in the limit there would be none. An example is the activity today:
            which is classified as ‘spotless’ but still has some weak active regions.
            The microwave flux [and the magnetic flux] is much better at picking up the real activity and it not limited by the inability of the the [small] telescopes to see the very small spots. What the microwave observations show is that there are no really ‘spotless’ days. The limit set by our choice of telescope does not apply to the actual measure of the Sun.

      • Ask SILSO about extending that graph. Perhaps they don’t have the earlier daily data.

        And regardless what happened in the 18th century, it is clear that since early 19th century long term activity increased.

        Why don’t you ask them? The scientists I’ve asked about various things have almost always responded well. Especially Bob Carter, he was a good guy.

        It’s clear to me that since the late 18th and mid 19th century, we’ve been in a long term decline. Ditto mid 20th century. Good tasting cherries! More importantly, this is a great time to be studying the sun. It’s doing interesting stuff and we have some very good tools.

    • You (and others) have lost the track. The claim is that at solar minima, microwave emission reach the same level as the do at other minima. Hans-Georg above, noted “Sometimes the minima are long, sometimes short,” essentially the same thing as the number of spotless days.

      Neither the Japanese nor Leif are claiming that one minimum has the same duration as another. You’ve noted the number of spotless days varies, so did we all while waiting for the start of SC24. Every little sunspeck seemed to get its own WUWT post.

      BTW, have you noticed we’ve had 82 spotless days this year?

      • I do not dispute the claim of the Japanese researchers and I do not count spotless days. Silso does that.

        Leif appears to believe that there are no significant differences between different minima. I disagree, and not convinced by his arguments. His belief rests on his assumption of what is significant and what is not, as some measurements show very significant differences.

        And clearly I don’t need you to tell me in the comments section of an internet blog whether what I say is out of track or not. That’s your opinion, and as such worthless to all that do not share it.

  11. The claims that solar minima are so similar depends on how you look at it.

    Using monthly F10.7cm solar microwave flux data, the largest yearly difference during the solar min is 5.3 sfu, not large, but important. The extended low solar flux of the last deeper solar minimum brought TSI to a very low level and with little variation. More shallow minimums with more frequent sunspot activity have had more TSI volatility than during the 2008-9 minimum.

    Solar minimums during the modern maximum in sunspot activity were on the whole shorter and with significantly fewer spotless days to go along with their overall higher sunspot cycle maximums:

      • You may never have heard about ‘statistical significance’.
        The R-square value for the Group Number [since 1700 because before we don’t really know what the values should be] is 0.000774 and the trend is 0.000936+/-0.001896, thus not different from zero. For the Sunspot number R-square is 0.0176, also not significant, i.e. less than 2% of the change the last 218 years is due to any trend. In both cases the statement that “there has been no significant trend the last 300 [actually 318] years” is borne out by the data we have.

    • Long solar cycles are associated with weak cycles for the next cycle, and short cycles are associated with the next being strong. The decline of a long cycle lends itself to a long minimum and lots of spotless days, e.g. the SC 23/34 minimum that dragged on and on and on….

      Again, the only similarity claimed in the post is that the microwave levels are similar during all minima. This does not imply that all minima are same, they differ in many ways, as you note, but trying to include the microwave flux doesn’t provide much insight.

  12. Leif
    As a matter of interest, how far do you think we off the solar minimum?
    And have you a prediction for the next solar max yet?
    Regards Ian

  13. lsvalgaard November 20, 2017 at 7:48 am
    Has been noted several times before. Not new.

    I agree.

    Possibly Lief could comment on findings by several other authors that indicate the constancy recorded minimums may be telling us that the variable being recorded is not capturing the full range of solar activity because the data is truncated at the same low level.

    The estimated solar modulation potential (phi) has been estimated by Steinhilber, Beer, and Frohlich as well as many other others they have cited.

    Total solar irradiance during the Holocene, F. Steinhilber, J. Beer, and C. Frohlich

    Caballero-Lopez et al., 2004 and McCracken, 2007 have related phi to the the strength of the open solar magnetic field.

  14. This minimum value of solar activity could be correct but 50 years is a small amount of time given the period of the event we are measuring even a few hundred years is a small amount of time.The true pattern of the change in solar minimum might only become clear over thousands of years.

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