Astronomers know that the Sun exhibits an 11-year average sunspot cycle. This means that every eleven years - on average, sunspot numbers reach a peak. This period of increased activity, known as the solar maximum, is also a potentially perilous time for Earth, which gets bombarded by solar storms that can disrupt communications, damage power infrastructure, harm some living creatures (including astronauts) and send satellites plummeting toward the planet.
From a distance, the Sun may seem calm and steady. But zoom in, and our home star is actually in a perpetual state of flux, transforming over time from a uniform sea of fire to a chaotic jumble of volatile plasma and back again in a recurring cycle. In the lead-up to each gargantuan reversal, the Sun amps up its activity: belching out fiery blobs of plasma, growing dark planet-size spots and emitting streams of powerful radiation.
Superimposed on the 11-year cycle is a 22-year cycle, for reversal of magnetic polarities to occur in the "leading" spot. The 22-year cycle means that 22 years must elapse before leader spots again have negative polarities at sunspot maximum. In the intervening, or 11-year maximum, the leader spots will all have positive polarity. Of course, the frequency of sunspots in different (and succeeding) cycles is subject to change. In the diagram below such variations in sunspot numbers are shown over time from 1750, occurring as cycles:
These two complementary aspects and effects (defined as a and w dynamos) are illustrated below:
Note the expansion and
direction of the reference field line for the w- effect, and conversely the compressed nature and
field line directions for the a- effect. Given below are the four primary equations pertaining to
magnetic induction :
Within these equations lies the key to why the level of eruptions and disruptions of a given cycle may vary from a prior one. In particular, the azimuthal component of the magnetic induction (B j) and the poloidal component , or B p = (Br , B j) = Ñ X A, where A is the vector potential, may determine the degree of magnetic twist. This in turn can determine the level of activity for the cycle.
Sunspots themselves are formed when strong magnetic fields rise up from the convection zone, a region beneath the photosphere that transfer energy from the interior of the Sun to its surface. At the surface, the magnetic fields concentrate into bundles of flux elements or tubes, which prevent the hot rising plasma from reaching the surface.
When two such large (and magnetically complex) spots come into close proximity there is the potential for what is called "polarity intrusion" and ensuing explosive eruptions, e.g. when magnetic vector magnetographs detect this sort of aspect:
The important point to note is that as the deformation progresses the magnetic gradient dramatically increases. The magnetic gradient is written simply as:
grad B = [+B N - (-B N)] / x
where the numerator denotes the difference in the normal components of the magnetic field B N (between opposite polarities (+, -) of the active region as measured by vector magnetograph and the denominator denotes the linear (x) scale separation between them. As x decreases, as it will deform the neutral line whereupon the gradient spikes and this signals probable flare conditions, namely for a d -class sunspot given it is most likely to feature such gradient change.
A number of solar physicists now believe the next cycle will see such indices and hence be exceptional in violent eruptions, to the extent of disrupting electronic communications and possible even power grids. Also, originally most solar physicists believed the current cycle would peak in 2025, however this may not be so. A bumper crop of sunspots, solar storms (as well as auroral substorms) suggest the maximum may arrive by the end of this year at the earliest. Many also warn we earthlings are poorly prepared for the worst (X-ray flare, and CME outbursts).
See Also:
10 signs the Sun is gearing up for its explosive peak — the solar maximum
And:
New Solar Research Confirms Why Delta Sunspots Are More Flare Worthy Than Other Magnetic Classes
And:
And:
Ensemble Modeling of Coronal Mass Ejections - A Superior Means Of Prediction? The Jury Is Still Out
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