Our resident solar expert, Dr. Leif Svalgaard, sends word of this new discovery.
Stanford solar scientists solve one of the sun’s mysteries
The sun’s magnetic field can play havoc with communications technology. Stanford scientists have now described one of the underlying processes that help form the magnetic field, which could help scientists predict its behavior.
By Bjorn Carey
Stanford solar scientists have solved one of the few remaining fundamental mysteries of how the sun works.
The mechanism, known as meridional flow, works something like a conveyor belt. Magnetic plasma migrates north to south on the sun’s surface, from the equator to the poles, and then cycles into the sun’s interior on its way back to the equator.
The rate and depth beneath the surface of the sun at which this process occurs is critical for predicting the sun’s magnetic and flare activity, but has remained largely unknown until now.
The solar scientists used the Stanford-operated Helioseismic and Magnetic Imager (HMI) – an instrument onboard NASA’s Solar Dynamic Observatory satellite – to track solar waves in much the way seismologists would study seismic movements beneath the surface of the Earth. Every 45 seconds for the past two years, the HMI’s Doppler radar snapped images of plasma waves moving across the sun’s surface.
By identifying patterns of sets of waves, the scientists could recognize how the solar materials move from the sun’s equator toward the poles, and how they return to the equator through the sun’s interior.
“Once we understood how long it takes the wave to pass across the exterior, we determined how fast it moves inside, and thus how deep it goes,” said Junwei Zhao, a senior research scientist at the Hansen Experimental Physics Laboratory at Stanford, and lead author on the paper.
Although solar physicists have long hypothesized such a mechanism, at least in general terms, the new observations redefine solar currents in a few ways. First, the returning currents occur 100,000 kilometers below the surface of the sun, roughly half as deep as suspected. As such, solar materials pass through the interior and return to the equator more quickly than hypothesized.
More startling, Zhao said, is that the equator-ward flow is actually sandwiched between two “layers” of pole-ward currents, a more complicated mechanism than previously thought, and one that could help refine predictions of the sun’s activity.
“Considered together, this means that our previously held beliefs about the solar cycle are not totally accurate, and that we may need to make accommodations,” Zhao said.
For example, some computer models projected that the current solar cycle would be strong, but observations have since showed it is actually much weaker than the previous cycle. This inconsistency could be due to the previously unknown inaccuracies of the meridional circulation mechanism used in the simulations.
Improving the accuracy of simulations, Zhao said, will produce a better picture of fluctuations of the sun’s magnetic field, which can interfere with satellites and communications technology on Earth. The sun’s magnetic field resets every 11 years – the next reset will occur sometime in the next few months – and there is evidence that changes in the meridional flow can influence how the magnetic field evolves during a particular cycle.
“We want to continue monitoring variations of the meridional flow,” he said, “so that we can better predict the next solar cycle, when it will come and how active it will be.”
The report was published in the online edition of The Astrophysical Journal Letters. It was co-authored by three other researchers at the Hansen Experimental Physics Laboratory – senior scientists Rick Bogart and Alexander Kosovichev and research associate Thomas Hartlep – as well as NASA senior scientist Tom Duvall. Phil Scherrer, a professor of physics at Stanford, is the principal investigator of the HMI project and supervised the study.
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Leif adds an excerpt from the paper in an email:
Meridional flow inside the Sun plays an important role in redistributing rotational angular momentum and transporting magnetic flux, and is crucial to our understanding of the strength and duration of sunspot cycles according to flux-transport dynamo theories. At the Sun’s surface and in its shallow interior to at least 30 Mm in depth, the meridional flow is predominantly poleward with a peak speed of approximately 20 m/s.
The poleward plasma flow transports the surface magnetic flux from low latitudes to the polar region, causing the periodic reversals of the global magnetic field, a process important to the prediction of the solar cycles. The speed and variability of the meridional flow also play an important role in determining the strength and duration of the solar cycles, and the unusually long activity minimum at the end of Solar Cycle 23 during 2007–2010 was thought to be associated with an increase of the meridional flow speed during the declining phase of the previous cycle. Therefore, an accurate determination of the meridional flow profile is crucial to our understanding and prediction of solar magnetic activities.
Although the poleward meridional flow at the solar surface and in shallow depths has been well studied, the depth and speed profile of the equatorward return flow, which is expected to exist inside the solar convection zone to meet the mass conservation, largely remains a puzzle. It is generally assumed that the return flow is located near the base of the convection zone, although no convincing evidence had been reported.
The continuous Doppler observations by the Helioseismic and Magnetic Imager onboard the recently launched Solar Dynamics Observatory mission (SDO) allow us to measure and detect the long-sought equatorward flow. Our analysis, which takes into account the systematic center-to-limb effect that was recently found in the local helioseismology analysis techniques, gives a two-dimensional cross-section picture of the meridional flow inside the nearly entire solar convection zone, and reveals a double-cell circulation with the equatorward flow located near the middle of the convection zone.
Figure 1 shows the new picture suggested by the HMI data.
This new picture of the solar interior meridional circulation differs substantially from the previously widely believed picture of a single-cell circulation with the equatorward flow near the bottom of the convection zone [the Conveyor Belt Model]. Through removing a systematic center-to-limb effect that was only recently identified, our analysis corrects and improves the previous solar interior meridional flow profile given by Giles (1999) using a similar analysis procedure.
The new meridional circulation profile poses a challenge to the flux-transport dynamo models, but provides more physical constraints to these models creating a new opportunity to further understand how magnetic field is generated and how magnetic flux is transported inside the Sun. Past dynamo simulations have already demonstrated that a meridional circulation profile with multiple cells might not be able to reproduce the butterfly diagram and the phase relationship between the toroidal and poloidal fields as observed, unless the dynamo model was reconsidered. However, on the other hand, solar convection simulations have shown the possibility of multi-cell circulation with a shallow equatorward flow (e.g.,Miesch et al. 2006; Guerrero et al. 2013), demonstrating that our analysis results are reasonable.
Moreover, a recent dynamo simulation, with the double-cell meridional circulation profile incorporated, showed that the solar magnetic properties could be robustly reproduced after taking into consideration of turbulent pumping, turbulent diffusivity, and other factors (Pipin & Kosovichev 2013). All these studies, together with our observational results, suggest a rethinking of how the solar magnetic flux is generated and transported inside the Sun.
Abstract: http://iopscience.iop.org/2041-8205/774/2/L29
pdf here: http://www.leif.org/EOS/ApJL-2013-Meridional-Flow.pdf
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From Leif Svalgaard on August 29, 2013 at 7:47 pm:
Would it have helped if I had said IN the Sun? It’s obvious then the mass overhead does matter. From a plane bisecting the Sun, the mass “overhead” does matter as at the center it will cancel out the gravitational force of the mass “underneath”. Move the plane outwards along a radius, up until you clear the Sun, the solar mass overhead still matters as its gravitational force will be partially counteracting that of the solar mass underneath.
And Newton proved it doesn’t matter? It has been awhile since I got my BA in Physics, that did not get used. Perhaps I forgot it. Got a link to an explanatory text?
kadaka (KD Knoebel) says:
August 29, 2013 at 8:47 pm
Got a link to an explanatory text?
http://en.wikipedia.org/wiki/Shell_theorem
For the lovers of Geomagnetic Cycles:
Previously when researching the Earth’s core, I found new research showing it rotated far slower than previously thought, hardly turning at all.
Now the researchers have done it again, and found something even more improbable, variable speed.
http://phys.org/news/2013-05-earth-center-sync.html
Lately the Sun’s magnetic field has decreased, while the inner core has dramatically sped up.
Faster rotation 1970’s and 1990’s, slowed down in 1980’s, and also apparently was slow in the 2000’s.
Who’s going to be the first to claim a tie to the approximately 11-yr sunspot cycle?
Who already has these rotational speed changes clearly visible in their already-published graphs and charts?
There does not seem to be a good reason not to suppose that there are one or more zones circulating below the first two. I wondered about the impact of the speed estimate under the surface if this is the case. There is only so much stirring energy from rotation. Perhaps it is distributed over a greater depth. The sun is full of surprises.
I look forward to an estimation of the activity of the next two cycles based on this new understanding because I will probably be around long enough to see them. I will keep watch.
kadaka (KD Knoebel) says:
August 29, 2013 at 9:06 pm
Lately the Sun’s magnetic field has decreased, while the inner core has dramatically sped up.
Faster rotation 1970′s and 1990′s, slowed down in 1980′s, and also apparently was slow in the 2000′s. Who’s going to be the first to claim a tie to the approximately 11-yr sunspot cycle?
Who already has these rotational speed changes clearly visible in their already-published graphs and charts?
The 1970s solar activity was lower than that of the 2000s.
The outer core is effectively a superconductor and does not allow any magnetic fields to penetrate more than a few meters into the outer core, thus screening the inner core from any external magnetic forces.
kadaka (KD Knoebel) says:
August 29, 2013 at 9:06 pm
<i.Lately the Sun’s magnetic field has decreased, while the inner core has dramatically sped up.
http://www.leif.org/research/Geomagnetic-Earth.png shows how changing external magnetic fields propagate into the Earth and stop and when they meet the outer core [there diminishing wiggles].
Re: Leif Svalgaard on August 29, 2013 at 8:55 pm:
Got it. The infinitely thin spherical shells “overhead”, thinking spherically instead of planar, will exert zero net gravitational force on the object within the Sun. Only the remaining sphere underneath will be exerting gravitational force, easily calculable as a point mass at that radius.
So this has mostly been a frame of reference argument?
Well, thanks for the shell theorem info, that explained it.
kadaka (KD Knoebel) says:
August 29, 2013 at 9:29 pm
So this has mostly been a frame of reference argument?
No, a lack of understanding the physics argument…
Leif-
Thank you.
Does this provide any insight into the Livingston and Penn Effect or the possibility of a coming minima, or both?
A short article explaining key points along with solar cross section diagram: http://en.wikipedia.org/wiki/Solar_core
The core radius is 22% of the solar radius, but is only 1% of solar volume. There has to be some inner convection, otherwise He buildup in the core would stop H fusion.
I love threads like this!
From Leif Svalgaard on August 29, 2013 at 9:29 pm:
Hey, I know better than to expect them to propagate inward much. Mainly because the mantle material is basically like thick asphalt loaded with magnetic materials. Just as asphalt is used for sound dampening (you’ll likely find pads of it under your car’s carpeting), any physical movement of the magnetic materials will be dampened, sapping energy.
Please advise if I’m in error about that.
From Leif Svalgaard on August 29, 2013 at 9:17 pm:
Which takes care of the rest.
Except now people may think there’s a “superconducting motor” for our planet’s core, thus it doesn’t need as much energy to speed up and slow down as otherwise… People are funny that way.
Eric Gisin says:
August 29, 2013 at 9:50 pm
<i.There has to be some inner convection, otherwise He buildup in the core would stop H fusion.
I don’t think so. If fusion is throttled a bit because of less fuel, the core would contract and the temperature would go up. The fusion is extremely temperature dependent so even a tiny increase in temperature is enough to compensate for the slightly lower concentration of H. Convection is only possible if [roughly] the pressure gradient is smaller than the density gradient and in the solar core it is not, so the core is stable.
kadaka (KD Knoebel) says:
August 29, 2013 at 10:00 pm
Except now people may think there’s a “superconducting motor” for our planet’s core, thus it doesn’t need as much energy to speed up and slow down as otherwise… People are funny that way.
Most people are reasonable. But there is always a small number who is total nuts and will believe anything or peddle anything. We have a good sampling here on WUWT, so expect some of them to come out of the woodwork.
People have asked about the influence on the dynamo theory of the double cell. Here is a paper that discusses this http://arxiv.org/pdf/1302.0943v2.pdf The main conclusion is “The mean-field dynamo model that includes the subsurface rotational shear layer and the double-cell (in radius) meridional circulation, indicated by the recent helioseismology results, can reproduce the solar magnetic cycles in the form of the time-latitude “butterfly” diagrams. The double-cell circulation affects the distribution of the magnetic field with radius in the convection zone, increasing the field concentration to the convection zone boundaries, and in the middle of the convection zone where the two cells converge. The latter effect can lead to a non-monotonic profile of the amplitude of the large-scale poloidal magnetic field in response to an increase of the circulation speed. The models qualitatively explains the observed synchronization between the polar magnetic field strength and the sunspot number”
Brad says:
August 29, 2013 at 9:38 pm
Does this provide any insight into the Livingston and Penn Effect or the possibility of a coming minima, or both?
I don’t think so [but don’t know, of course]. I think the L&P effect is rather a surface phenomenon.
From Leif Svalgaard on August 29, 2013 at 9:32 pm:
Now come on, we both know sometimes the physics just doesn’t become clear without the proper frame of reference.
http://xkcd.com/123/
Lief, I would like to ask you a couple of questions, the atmosphere on planets seems to be governed by chaos with strange attractors that give some harmony in the chaos. Examples are the big red spot on Jupiter the black spot on Neptune and the strange but constant hexagon cloud on pole of Saturn. The red spot and the dark spot as are many other features on planets always at 19.5 north or south latitude.
My questions , could the cyclical behaviour of the sun be it chasing its strange attractors and if so finding them would give a good insight into its antics.
Secondly as on the planets are there any of the solar activity centered around 19.5 latitude north or south. I understand that these are odd questions but if you have any information it would be received with thanks.
kadaka (KD Knoebel) says:
August 29, 2013 at 10:13 pm
Now come on, we both know sometimes the physics just doesn’t become clear without the proper frame of reference.
Knowing the proper frame is understanding of the physics.
wayne Job says:
August 29, 2013 at 10:14 pm
My questions , could the cyclical behaviour of the sun be it chasing its strange attractors and if so finding them would give a good insight into its antics.
I don’t think so as the sun exhibits both deterministic and random behavior at the same time. Random is not the same as chaotic, and I don’t think the sun is chaotic as a whole.
Secondly as on the planets are there any of the solar activity centered around 19.5 latitude north or south. I understand that these are odd questions but if you have any information it would be received with thanks.
There does not seem to be anything special on the sun about 19.5 latitude.
From Leif Svalgaard on August 29, 2013 at 10:26 pm:
Bingo!
I noticed in Fig 1 the flows were oriented perfectly north-south. However, angular momentum (i.e. conservation of a.m.) would alter the flow, and produce a lateral component, unless somehow the energy is bled off in another process. Using the Mark I lipid-ion computer, I’m trying to create my own flow model. Wouldn’t the flow likely be somewhat like a screw? Although perhaps there would not be even one complete turn from the equator to near the pole. I imagine then the flow might dive under and follow almost the same track back to the equator, offset to some degree because of the change in depth.
Hey, if it’s a bad idea, don’t complain to me about it, ya get whatcha paid for.
Leif, look on the bright side. You don’t have the guy we’re not to bring up and his iron core sun junk. No Maya apocalyptic pole shift, rotation reversal nutters show up anymore. Remember the guy Red something, Red Dawn or Red Day? You blew a gasket at the mods for that one.
These Solar threads are still more entertaining than fight night on Mexican TV but overall they have improved a lot. And you still make wuwt so good.
SvP says
I will admit to wrong,if the sun is either much more active then I expect or if the sun is quiet and
the temperatures fail to go down.
Henry says
temps are falling
http://www.woodfortrees.org/plot/hadcrut4gl/from:1987/to:2014/plot/hadcrut4gl/from:2002/to:2014/trend/plot/hadcrut3gl/from:1987/to:2014/plot/hadcrut3gl/from:2002/to:2014/trend/plot/rss/from:1987/to:2014/plot/rss/from:2002/to:2014/trend/plot/hadsst2gl/from:1987/to:2014/plot/hadsst2gl/from:2002/to:2014/trend/plot/hadcrut4gl/from:1987/to:2002/trend/plot/hadcrut3gl/from:1987/to:2002/trend/plot/hadsst2gl/from:1987/to:2002/trend/plot/rss/from:1987/to:2002/trend
I however, I do fear that there is already large scale fiddling going on, trying to hide the decline.
temps are have fallen at least 0.17 since 2002 of my own data set so there is already a discrepancy. Ignoring the exact sequence of sunspots, over time, I find an average of
75 during a warming period (1950-1995)
and an average of
63 during a cooling period (1904-1950)
hence we are now in a cooling period.,….
(1995-2039)
So the theory of the sun causing certain climate patterns/cycles at regular intervals firmly stands.
That there must be an angular momentum cranking the sun up or down a bit seems the most likely explanation of all the data that has so far been collected by me.
http://blogs.24.com/henryp/2013/04/29/the-climate-is-changing/
As the end of the month is approaching, the current sunspot numbers are still low side (SIDC non-smoothed is likely to be around 65).
http://www.vukcevic.talktalk.net/SSN.htm
Polar fields have finally fully reversed, the SC24 max is not far off http://www.vukcevic.talktalk.net/LFC6.htm
It looks as the SC24 will not be multi-peaks cycle as SC14 or as low as SC5
http://www.vukcevic.talktalk.net/SC24-14-5.htm
“Steven Mosher says:
August 29, 2013 at 11:01 am
Stupid questions exists. folks, you’ve just seen three of them”
The only stupid questions in my experience are the ones not asked.