My thanks to Astrophysicist Ian Wilson for flagging up this new paper from Zhang, Mursula and Usoskin. This sheds some light on the periodic changes in the rate of rotation of the latitudinal bands on the solar surface, and the correlated changes in the number, size and hemispheric location of sunspots. It turns out there is an anticorrelation between the two solar hemispheres. In other words, when rotation rates are high in the north, along with sunspot roduction, they are lower in the south, and vise versa. There are nuances that modify this relationship, and this leaves scope for further study. The periodicity is given as 80-90 years, and this frequency is potentially linked to planetary periods such as the Double inner solar system cycle, the half Jose cycle and Uranus’ orbital period, which falls in the middle of the range.
Consistent Long-term variation in the hemispheric asymmetry of solar rotation
Context.
Solar active longitudes and their rotation have been studied for a long time using various forms of solar activity. However, the results on the long-term evolution of rotation rates and the hemispheric asymmetry obtained by earlier authors differ significantly from each other. Aims. We aim to find a consistent result on the long-term migration of active longitudes of sunspots in 1877−2008 separately for the two hemispheres.
Methods.
We used a dynamic, differentially rotating reference system to determine the best-fit values of the differential rotation parameters of active longitudes for each year in 1877−2008. With these parameters we determined the momentary rotation rates at the reference latitude of 17◦and calculated the non-axisymmetries of active longitudes. We repeated this with five different fit intervals and two weighting methods and compared the results.
Results.
The evolution of solar surface rotation in each hemisphere suggests a quasi-periodicity of about 80−90 years. The long-term variations of solar rotation in the northern and southern hemisphere have a close anti-correlation, leading to a significant 80−90-year quasi-periodicity in the north-south asymmetry of solar rotation. The north-south asymmetry of solar rotation is found to have an inverse relationship with the area of large sunspots. The latitudinal contrast of differential rotation is also found to be anti-correlated with the sunspot area. Different fit and weight methods yield similar results.
Conclusions.
Our results give strong evidence for the anti-correlation of the rotation of the two solar hemispheres. The long-term oscillation of solar rotation suggests that a systematic interchange of angular momentum takes place between the two hemispheres at a period of about 80−90 years
Tallbloke's Talkshop 
Lots in here, including fitting with off blog discussions which go on between various parties.
The paper is not so much an answer as food for thought on further investigation of a difficult problem.
Tim, agreed. Our own investigations have revealed things not picked up on in this paper. It does provide a useful well researched basis for advancing our stuff alongside though. Kudos to the authors for investigating.
One important speculation/conclusion from the paper is:
“The long-term oscillation of solar rotation suggests that a systematic interchange of angular momentum takes place between the two hemispheres at a period of about 80−90 years.”
This may hint at a mechanism that is responsible for long-term changes in the Sun’s rotation rate.
At least its compatible with the possibility of an external planetary (gravitational/tidal/magnetic-hydrodynamic) driving mechanism.
Ian, yes. I still like Ray Tomes hypothesis of the solar core being dragged up and down relative to the Sun’s outer layers by a differential gravitational effect caused by relativistic consideration of the energy/matter gradient from the centre of the Sun outwards. That would produce a ‘pumping’ effect which would translate into meridional and thence latitudinal flow rate changes, with anticorrelation beteen the hemispheres, just as observed by Zhang et al.
It’s one of those hindsight no-brainers. You have 1 & 1. Then during a long awaited free moment, you realize something terribly simple: If you put them together you should find 2. They looked. Indeed they found 2.
The authors have found another way to show what was elegantly shown here:
Pulkkinen, P.J.; Brooke, J.; Pelt, J.; & Tuominen, I. (1999). Long-term variation of sunspot latitudes. Astronomy and Astrophysics 341, L43-L46.
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1999A%26A…341L..43P&defaultprint=YES&filetype=.pdf
Only 1 other piece of info is needed to see the equivalence.
The solar asymmetry literature & related discussion is burdened by enduring misunderstandings. There has been a general failure to appreciate and understand the comparative differences – including mathematical properties – of the great variety of asymmetry metrics. As a result, interpretation has suffered. People get into intractable arguments because they’re talking about different things without realizing it. Sober attention to nuances is due.
There’s too much more to say, so the sensible thing to do is delay until sufficient time is available (definitely not this week).
However: I’ll try to make time tomorrow to clear up (via illustration) one very important, truly die-hard misunderstanding about sunspot area asymmetry.
Quote : “Our results give strong evidence for the anti-correlation of the rotation of the two solar hemispheres”
http://link.springer.com/article/10.1007%2FBF00157550
In the solar minimum maunder, sunspots rotated faster near the equator by 3 or 4%, and the differential rotation between 0 and ±20° latitude was enhanced by about a factor 3″
What we deduce ?
Michele: Good question!
The evolution of solar surface rotation in each hemisphere suggests a quasi-periodicity of about 80−90 years
If we are to believe Wikipedia, the average solar cycle length from 1755-2008 was 10.6 years, well below the often-quoted average of 11 years or slightly more.
http://en.wikipedia.org/wiki/List_of_solar_cycles
Maybe a long-term correction is due?
So simple it may seem vacuous:
N+S Sunspot Area |N-S|
If the implications aren’t immediately obvious, I can suggest thinking it through carefully.
Now that the worst of the work week has settled down, I’ve had a chance to look more carefully at Zhang, Mursula, & Usoskin (2013). Here’s what I conclude:
Pulkkinen, Brooke, Pelt, & Tuominen (1999) illustrated a very stimulating & interesting result, but Zhang, Mursula, & Usoskin’s (2013) extrapolation of that pioneering result (which they don’t even cite) to another variable is neither sensible nor justified since the assumptions built into their equation 5 fail even the simplest diagnostics.
I hope readers will consider the preceding carefully rather than take my word for it.
—
A separate note — here’s something I came across yesterday:
Cho, I.-H.; Kwak, Y.-S.; Chang, H.-Y.; Cho, K.-S.; Park, Y.-D.; & Choi, H.-S. (2011). Dependence of GCRs influx on the Solar north-south asymmetry.
Click to access 1103.4255v1.pdf
“[…] observed GCR influxes […] are more suppressed when the solar activity in the southern hemisphere is dominant compared with when the solar activity in the northern hemisphere is dominant. Its reduction rates […] are all larger than those of the suppression due to other factors including the solar polarity effect on the GCR influx. […] It is found that suppressions due to the solar North-South asymmetry as well as the solar polarity are significant and yet the suppressions associated with the former are larger and more significant.”
Thanks Paul, important paper!
TB & Others,
It’s not only the heliographic & heliomagnetic asymmetry, but also the multipolar asymmetry — e.g. dipole-octopole. An example I summarized last week:
multidecadal heliosphere structure, solar cycle deceleration, & terrestrial climate
Basically it’s anything that can change the shape (including waviness & coning) of the heliosphere & the heliospheric current sheet (HCS). The different types of asymmetry are manifest in different metrics. A taxonomy needs to be mapped out to facilitate clearer comparative awareness.
I actually heard a mainstream news report today linking the deep, deep unknowns of dark matter & energy to all of this. They interviewed a prof who emphasized that cosmic ray flux (CRF) measurements are now being recognized as key clues about the elusive fundamental nature of dark matter & energy.
I have to confess my ignorance about this:
I hadn’t realized that cosmic ray variations inform about dark matter & energy.
________________
Flat Earth anyone??
Let’s keep the context in mind:
Only 40 years ago physicists were “surprised” at the discovery of the HCS.
They hadn’t even imagined that such a thing existed and it’s the biggest thing in the solar system – bigger than the sun.
Creepy to say the least – on a deeply & genuinely visceral level.
Hiroko Miyahara: Solar Activity and Climate
vimeo.com/30119927
appears WP has scrambled that link somehow — try this…
also see:
Click to access 2k_Miyahara_SORCE_brief.pdf
…and her other work.
Her common sense interpreting stats is refreshing and — to be frank — reassuring about the capacity of the true intellectual forerunners of the human race.