Here, Spot! C’mere, Spot!
By Stephanie Osborn
Written July 4, 2016
A late Happy Independence Day to you all! As I write this, it IS Independence Day. Casa Osborn plans on some good summertime food, and maybe fireworks this evening, if the weather cooperates (storms are expected) and we can fight through the crowds to the display.
So…I’m back, folks. And I’m talking more about the Sun. It’s time for an update, because some slightly unusual stuff has been happening.
According to NOAA’s Space Weather Prediction Center (and per my own observations), the Sun has been unusually quiet for over a month now. In June, there were two periods of zero observed sunspots — a short one of four days that ran from the 3rd through the 6th, and another that started on the 23rd and is continuing (total of 11 days and counting).
More, though the STEREO spacecraft were lagging badly, there seemed to be no real activity on the solar far side, either. The problem is that the two STEREO craft have to be angled to view the far side, in order to get telemetry from them. So there are periods of time when we simply can’t get data from them because they’re BEHIND the Sun as viewed from Earth, and intervals on either side of THAT when we might get data downloaded once in every week. So for this current batch of spotless days, we had a farside image from June 24th, and one from July 2nd, and that was all we had to work with. But of the 3 spot groups STEREO saw on the 24th, none have rotated around to the near side — and the longest interval expected for that was 11 days. It’s the 11th day, and no spots have rotated around. I think it’s safe to say that we went a good part of those 11 days with no sunspots, anywhere on the solar photosphere.
That does seem to be changing, as of last night…maybe. (For whatever it’s worth, astronomical days are counted as beginning at midnight in Greenwich, England. Except it isn’t actually measured at Greenwich anymore; it uses an atomic clock set to what is now called UTC, or Universal Time Coordinated. At any rate, that places it at around 6pm the evening before in the Central time zone.) As of 1:58am CDT 4 July 2016, there is one sunspot group on the farside, another possibly forming, and a teeny-tiny spot group forming near the equator on the nearside, pushing toward the western limb of the solar disk. Boulder has still not given it an official spot number, however, and the Boulder sunspot number (one of two sunspot counts, and the only one that hasn’t been tweaked to try to eliminate certain “inconvenient” periods) still rests at 0. If it holds up and doesn’t immediately deteriorate again, then it’ll get an official group number, and the Boulder number might just go up.
I am thinking it may well be a done deal, however, that the next solar minimum is gonna come early, and be deep. And possibly longish. Will it go into an extended minimum? Well, it’s not supposed to…not yet. Let’s get back to that shortly.
Many of you may have heard of the relatively new model for solar activity, dubbed the double-dynamo model. Since the Sun is a giant ball of rotating plasma — charged particles — this effectively constitutes a current loop. A coil of electrified wire without the wire, if you will. And those generate magnetic fields. Hey presto, the Sun has a magnetic field, and it is, very loosely, bipolar — a bar magnet. But where it gets complicated is that the Sun IS a big ball of plasma — it isn’t a rigid body. Instead, each individual ion is obeying Kepler’s Laws of orbital motion, if we neglect the effects of collisions between ions — of which there are many, so it isn’t negligible by any means. This additional effect would dump us into the realm of magnetohydrodynamics, but is not that pertinent to our current discussion, so I’m not going to unduly complicate the thing and give y’all a headache. Kepler’s Laws are:
- The orbit of a planet is an ellipse with the Sun at one of the two foci. (A circle is a special case of an ellipse, where the foci merge.)
- A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
- The square of the orbital period of an orbiting body is proportional to the cube of the semi-major axis of its orbit.
Now, what that boils down to, for our purposes here, is that the different parts of the Sun do NOT all rotate at the same rate. Unlike Earth, a rigid body all of whose parts sweep out the same angular velocity, the Sun…doesn’t. The volumes around the core rotate at a different speed than the photosphere; the polar regions rotate at a different speed than the equatorial regions. So if we look at the magnetic field lines being generated by that bar magnet, we see a couple things happening. One, that bar magnet can get really, I mean REALLY, distorted. And two, the field lines have a tendency to wrap up and up and up, over and over again, around and around the rotational axis. Over a period of time they can get tightly compressed in some areas, and then magnetic reconnection can occur — the field lines snap and then reattach someplace else. This generates literal but invisible kinks, snarls, and knots in the magnetic field. When these reach the “surface,” or photosphere, they form sunspots. When the reconnects occur in the photosphere, we see flares.
This is a rather complex dynamo model. And it predicted solar activity…to a point. But recently researchers proposed a double dynamo — one dynamo “located” in the lower regions of the convective layer (the Sun’s “mantle”), and another a little way below the photosphere. More, while they have almost exactly the same period of variation, they don’t have QUITE the same period, and this causes them to go “out of phase” periodically. The model predicts extended minima as a result (which the old, single dynamo model did not). There is support for it in the magnetic data obtained from the Sun by the various space-based solar observing platforms.
The data indicate that we may be in a downward swing from an extended maximum. According to Wikipedia (which in this case lists numerous legitimate astronomy technical journals to support the statement, and I am quite familiar with all of said journals), “Sunspot numbers over the past 11,400 years have been reconstructed using Carbon-14-based dendroclimatology. The level of solar activity beginning in the 1940s is exceptional — the last period of similar magnitude occurred around 9,000 years ago (during the warm Boreal period). The Sun was at a similarly high level of magnetic activity for only ~10% of the past 11,400 years. Almost all earlier high-activity periods were shorter than the present episode.”
We’re also currently on the downward swing from Solar Max toward minimum in Solar Cycle 24. “The [double-dynamo] model predicts that the magnetic wave pairs will become increasingly offset during Cycle 25, which peaks in 2022. Then during Cycle 26, which covers the decade from 2030-2040, the two waves will become exactly out of synch, cancelling one another out. This will cause a significant reduction in solar activity. ‘In cycle 26, the two waves exactly mirror each other, peaking at the same time but in opposite hemispheres of the Sun. We predict that this will lead to the properties of a “Maunder minimum”,’ says Zharkova.”
But the current cycle is starting to diverge even from the 97+%-accurate double-dynamo model; though the model indicates a reduced number, it doesn’t predict a minimum until around 2018-19. But we are already dropping well below all predicted values. The 10.7cm radio flux curve is also slightly below predicted, indicating that at least in some frequencies, solar output is below norms. This could mean a much steeper descent to an earlier Solar Min than forecast… or the Sun could hiccup, and spots will appear again. But the fact that the solar nearside was spotless from June 3-6 (4 days) and again from June 23-July 2 (11 days and counting as I annotate this) is certainly significant. It also yields a mean sunspot number for the entire month of June of just over 16.
[Monthly and yearly sunspot averages: “monthly average” is the mean of the daily means; “yearly average” is the mean of the monthly means.]
What all this means is anybody’s guess and probably watching and waiting is the best thing. However, Dr. J. K. Woosley and I are not convinced that the Sun has only two dynamos; this would not completely account for the complexity seen in the extended sunspot/solar activity record, which extends back (one way and another) for nearly 1000 years. Notable are the nearly back-to-back-to-back extended minima of the Wolf, Spörer, Maunder, and Dalton Minima.
There is decent evidence for additional extended or “Grand” minima, going back many millennia, as I already mentioned. These include, but are not limited to:
- Homeric ~950BC-800BC (possibly continued until as late as 720BC; possibly two overlapping extended minima)
- delta ~410yr or 330yr
- Unnamed 1 ~390BC-330BC
- delta ~980yr
- Unnamed 2 ~650-720AD
- delta ~320yr
- Oort ~1040-1080AD
- delta ~200yr
- Wolf ~1280-1350AD
- delta ~110yr
- Spörer ~1460-1550AD
- delta ~95yr
- Maunder ~1645-1715AD
- delta ~75yr
- Dalton ~1790-1830AD
- delta to present ~186yr
- delta from Dalton to double-dynamo forecast minimum ~210yr
These “Grand” or extended minima can be traced back past 9100BC using various means, for more than 11,000 years of data.
My consideration, upon studying that list: Shouldn’t only 2 dynamos produce much more regular spacing of extended minima?
I turned to my resident physics expert consultant and sometime beta reader, Dr. J. K. Woosley again. (He and I go all the way back to grad school together, where we worked in the joint Astronomy & Physics Department; we are old and dear friends, adoptive siblings of a sort. And while I do have a degree in physics, sometimes I want a different set of brain cells than mine to corroborate — or disprove — my conclusions. He’s good for that.) So I sent him the double-dynamo paper — not because he hadn’t already read it, but because I suspected he’d need to refresh his memory, and I had it to hand so he didn’t have to hunt for it. And I sent him the papers on the paleoastronomical reconstructions of extended minima…and I asked him for a quick-scan opinion. In other words, “Don’t spend a ton of time running calculations; just give me your educated opinion.” And he replied the next day. (I’m used to most of my replies being the next day; not infrequently I send the queries at 2:00 or 3:00 in the morning! So okay, it’s NOT the next day for the respondent, but it is for me!)
“At the level of a quick skim (all I can afford today), the occurrence of all three extended minima in the last millennium, combined with a current highest-ever solar maximum, do not seem to me to be supported by a two cycle model. I think a three cycle model is the minimum that would be supported, and if I recall correctly, 5 could be supported. Conversely, everything before the Maunder minimum is based on climatological surrogates for sunspot activity (e.g. trapped carbon-14). Determining solar activity trends based on modulation of C-14 production by increased cosmic ray flux during extended minima requires a number of assumptions. Untangling the bias of those assumptions is more than a day’s work for a non-expert.”
Now, all that said, there is evidently no obvious magnetic data to support even one additional dynamo in the model. That doesn’t mean it isn’t there, though — if it has a long enough period, it may be difficult to recognize, for instance. And the current double-dynamo model still misses out on a good 3% of the observations, and doesn’t fully account for the irregularity of the extended minima occurrences.
So my overall conclusion is this: I believe we have not yet managed to fully model the Sun sufficient to accurately predict all of its cyclic behavior. I think that there is at least one additional dynamo hidden in there someplace. And that, in turn, is going to affect the start/stop times of the next extended minimum. To go back to one of the statements I made early in this article, and to which I promised to return: are we about to go into an extended minimum? To this question, I say, “Possibly.” If indeed there are additional dynamos, the onset of the next extended minimum may not wait fifteen more years to start. It is certain that the last three sunspot cycles have been diminishing in intensity; if this trend continues, it may start sooner. If the Sun continues flatlining, as it has in the last month, it may start REALLY soon.
What does that mean for us on Earth? Well, historically and prehistorically, there is a correlation between solar activity and worldwide climate. Solar activity goes up, worldwide temps tend to go up. Solar activity goes down, worldwide temps tend to go down. Slap multiple minima running for half a millennium only a century or less apart, worldwide temps tend to go down a lot. Now, correlation does not necessarily imply causation. But it doesn’t disprove it, either. As I pointed out the last time I visited Sarah’s blog, there are a LOT of very interesting coupling mechanisms between our atmosphere and what’s going on in space, attached to a lot of very complex equilibrium cycles, and we are nowhere close to having modeled all of that yet.
So let me end by saying that I’m not the only astronomer to be thinking about this. One popular science blog specifically asked one of the double-dynamo researchers her opinion on the hyperbolic statements made by the media upon the news release of the model.
“‘We didn’t mention anything about the weather change, but I would have to agree that possibly you can expect it,’ she informed IFLScience…Zharkova compared the Maunder Minimum with the one that her team predicted to occur around 15 years into the future. The next minimum will likely be a little bit shorter than the one in the 17th century, only lasting a maximum of three solar cycles (around 30 years).
“The conditions during this next predicted minimum will still be chilly: ‘It will be cold, but it will not be this ice age when everything is freezing like in the Hollywood films,’ Zharkova chuckled.”
My recommendation? Maybe start stocking up on firewood and long underwear.
It can’t hurt.
 See https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion for more information.
 https://en.wikipedia.org/wiki/Solar_cycle#Cycle_history ; you can go to Wikipedia to obtain the nearly-half-dozen technical article links upon which this statement was based.
 Dr. J. K. Woosley, personal communiqué