Solar surface rotation: N-S asymmetry and recent speed-up

Posted: February 14, 2015 by tchannon in Solar physics

In Astronomy & Astrophysics this week is an article of interest to some Talkshop readers. The authors are looking at the little understood variation is solar rotation in the context of peculiar change in recent years. Article has been amended with a new figure kindly provided by  L. Zhang showing more detail.

Figure caption: Yearly values of the N-S asymmetry (N-S)/(N+S) of the solar rotation at latitude 17 deg in 1978-2013 for X-ray flares (blue open circles) and for sunspots (red open circles). The blue (red) filled circles denote 11 year running mean values for flares (sunspots).

Figure caption: Yearly values of the N-S asymmetry (N-S)/(N+S) of the solar rotation at latitude 17 deg in 1978-2013 for X-ray flares (blue open circles) and for sunspots (red open circles).
The blue (red) filled circles denote 11 year running mean values for flares (sunspots).

Letter to the Editor

Solar surface rotation: N-S asymmetry and recent speed-up
L. Zhang, K. Mursula and I. Usoskin
A&A 575 L2 (2015)
(open access)

I quote from the abstract

Conclusions. The rotation of both hemispheres has been speeding up at roughly the same rate since the late 1990s, with the southern hemisphere rotating slightly faster than the northern hemisphere. This period coincides with the start of a significant weakening of the solar activity, as observed in sunspots and several other solar, interplanetary, and geomagnetic parameters.

My interest continues in hemispheric variation. As a reminder I unearthed a very strange functional effect from asymmetric treatment[1] the Greenwich/Hathaway sunspot data where the circa 11 year sunspot cycle dropped out leaving circa 45 y and 9 y. Neither is going to be what many call static, curiously though the 45 y shape correlates with some terrestrial data. Whether this means anything is an open question. Done nothing on this recently although Semi did some work with flares, something I’ve never found time to do.

I’m also mindful of reports saying the sun became unipolar during the Maunder minimum.

Both have been mentioned on the Talkshop, not that a quick search finds what I have in mind (I have about 600 articles here). One I had long forgotten did turn up not that it reveal much, from 2010

or this one from 2011

The monopole but not the paper I had in mind

I expect there is more.

Why this is taking place, ah well.

1. difference of hemispheric sine() sunspot area


Original head image.  L. Zhang provided an enhanced image via email: Tim

Post by Tim

  1. scute1133 says:

    Increased surface rotation raises the latitude at which the convective layer and core have the same speed. I’ve always suspected that if they have the same speed, there is no laminar flow and consequent magnetic instability. This allows spent plumes to drop past the tachocline into the core, heat anomalously and rise fast , looping magnetic field with them as they go. These would be nascent sunspot material and perhaps that’s why they start at around 20° N and S- which is where the speeds match.

    If the surface speed is speeding up and the latitude of speed parity is rising, the length of the higher latitude line is shorter. There is therefore less scope for convection plume overshoot into the core, and less scope for sunspots. Hence the quieter sun? Just a thought.

  2. Brillant, the way you keep presenting astro and solar physics. Many thanks.

  3. p.g.sharrow says:

    Increases in the rotation speed of the apparent solar surface may not be actual changes in solar rotation. It may be more akin to movement of the Tropopause cloud deck being moved by upper level jet winds.
    The apparent surface is much like the Earth’s Tropoause where convective/conductive energy exchange gives way to radiative energy. pg

  4. oldbrew says:

    There was a Uranus-Neptune conjunction in 1993, the previous two having been in 1821 (late Dalton minimum) and 1650 (early Maunder minimum).

    Note in figure 2 above the decline in flares and sunspots centred around 1993 +/- a few years, as Uranus was moving past Neptune.

  5. Curious George says:

    Does anybody know why data ends in 2006?

  6. tchannon says:

    Curious Geoge that was the End Of The World.

    No idea, usually a worry on whether there is an agenda.

    A read of the paper suggests why, about flare data

    We studied solar X-ray flares of class-B and higher observed by the NOAA GOES satellites during the period of 1977–2012. Most GOES X-ray flares were identified by simultaneous optical flare observations or by solar X-ray images before 2007. Many X-ray flares since 2008 have no accompanying optical flare, however. Fortunately, the flare location can be identified during the whole time period using the NOAA/USAF sunspot region number. To keep the treatment consistent throughout the entire study period, we used the location of the sunspot region where the flare occurred as the location of the flare. GOES X-ray flare data1 provides the NOAA/USAF sunspot group number where the flare is observed, but no location information for the sunspot groups. The location information of sunspot groups can be retrieved from NOAA/USAF sunspot data2. For sunspots we study the NOAA/USAF sunspot groups for the common period of solar flares.

  7. vukcevic says:

    New ‘Maunder Minimum’ paper published 6 February 2015 (Zolotova et al) extends solar activity correlation and the planetary formula to 1600.

  8. Andrew McRae says:

    On a completely unrelated note… those with the stomach for the math and a penchant for predicting blocking events around the arctic (and the infamous Polar Vortex??) may get something out of this recent paper: “An early warning indicator for atmospheric blocking events using transfer operators”
    No idea how useful that is but some Talkshoppers might be interested.

  9. tchannon says:

    What a brilliant rendering Michele.

    I tend to be fascinated by Esher etc., looks across at calendar, morphing scene of mixed reality by some artist I’ve never heard of. Was much the same with eg. Ansel Adams, not a particularly good photographer, the key was darkroom alteration to get inside what printing can do and a high level of what is photographed. Good example is the picket fence gap, you join with the image, no longer a wall.

    A key part as shown of the egg is the liquid reaching beyond the frame. If the whole had been framed, different picture.

  10. tchannon says:

    Looks an important spot Andrew McRae since this is a huge problem for weather forecasting. Looks to me to check some right boxes too on how they are doing it, without me knowing any detail of their working, fits with other things I know about.

    In a vague sense this is chaotic modal, which is more or less weather. Probably extends to cyclic what some are claiming is climate change.

    Could be an article, bit too dry as is.

  11. ren says:

    “To summarize, we find that both solar hemispheres have increased their rotation rate since the late 1990s until recent years. Moreover, the increase rate is fairly similar in the two hemispheres, so that the hemispheric asymmetry in rotation rates has been roughly constant, with the southern rotation being slightly faster. This period of recent solar speed-up coincides with

    the decline of the Modern Maximum (a period of exceptionally high activity during most of the twentieth century), which is evidenced by the overall reduction of sunspot activity, vanishing of small sunspots, decreasing solar wind density and magnetic field, etc. We also note that similar albeit shorter and less significant periods of both hemispheres speeding up were only found during the two lowest solar cycles 12 and 14 at the turn of the nineteenth and twentieth century. These results strongly suggest that, at least momentarily, there can be and, in fact, there currently is a negative correlation between the solar surface rotation rate and sunspot activity. The causes of these results can be found in the interaction between the solar differential rotation and the magnetic field. Simulations (Brun, 2004) have shown that low Maxwell stresses in weak magnetic fields lead to a high rotation rate at low latitudes where sunspots appear.”

  12. Sparks says:

    I’m in a bit of a rush and I’ve just seen this so a short note.. I’ve been building a 3d computer model to simulate the suns polar field reversals, one thing that is very clear is when the suns polar fields N+S are rotating around the sun at a faster rate, activity increases UV, X-rays sunspot number it all increases. And when the suns polar fields are rotating slower activity decreases, and slower rotating polar fields produce longer solar minimums between solar cycles.. the timing of each solar cycle can be replicated using the degree of rotation of the polar fields.. the limits of how much the suns polar field reversal can slow down produces one danger I noticed in particular, when the polar rotation slows too much the N+S fields can be rotating toward earth for longer periods of time, it basically means if the systems slow down as a result to solar activity, the strength of the suns polar field does not, so there is a danger during these periods of lethal doses of radiation from slower moving solar polar fields as they cross earth.

  13. Liyun says:

    Sorry Curious Geoge, we didn’t describe Fig.2 clearly. The data in fig.2 are 11 year running mean values for data 1977-2012, starting from 1983 and ending in 2006. We should have also presented the original yearly values without smoothing. I can present a figure with original yearly values and 11year smoothed values.

  14. tallbloke says:

    Liyun: Thanks very much for commenting here. It would be great to see the higher resolution annual data.

  15. Liyun says:

    I sent the updated figure of Fig.2 to Tim. Hope that he will add it here ASAP. 🙂

    Figure caption: Yearly values of the N-S asymmetry (N-S)/(N+S) of the solar rotation at latitude 17 deg in 1978-2013 for X-ray flares (blue open circles) and for sunspots (red open circles). The blue (red) filled circles denote 11 year running mean values for flares (sunspots).

    Figure caption: Yearly values of the N-S asymmetry (N-S)/(N+S) of the solar rotation at latitude 17 deg in 1978-2013 for X-ray flares (blue open circles) and for sunspots (red open circles).
    The blue (red) filled circles denote 11 year running mean values for flares (sunspots).

  16. tchannon says:

    Thank you Liyan, added to article and your comment.

  17. oldbrew says:

    TC: note when the red dots cross the centre bar in the graphic above, then look at this…coincidence?

  18. tchannon says:

    This is when there was a solar change, the start of cycle 23, the point where I have suggested the far UV changed and I pointed out it is when Arctic ice seemed to change. The ice data is poor, long story written elsewhere, not that anyone took notice. Whole ice thing is vague.

    The old article linked above shows the 1995/6 ssn is between cycles, are blurred one into the other anyway. Cycle 23 is probably a double cycle, hence the oddness eg. 2005

    There are various north/south complementary variations.
    A novel one is the LoD effect which I think is inertial phase linked to polar ice whereas others think it is atmospheric wind driven. One of these has a feasible phase relationship for cause and effect, the other is coherent.

    Afraid I am in no position to do much, computers are in limbo.