Accounting for the Solar Flares and Events In Solar Active Region 2017

The X-1 class flare (extreme upper right) that erupted on March 29, likely in a quadripolar sunspot group.

By now, most solar researchers are aware of the events associated with Active Region 2017 last month. Most remarkable was a major (X-1) class flare that erupted on March 29th, starting at 17:35 UT, peaking at 17:48 UT and ending at 17:54.  The area of impact on Earth affected large portions of its sunlit side especially at the sub-solar point. The flare was geo-effective, with high frequency radio communications blacked out for over an hour.  Other events associated with the flare also occurred, including:

- A 10 cm radio burst  with a peak of 360 solar flux units (SFU) from 17:45-17:48

- A Type II radio burst was observed at 17:53  with an estimated velocity of 508 km/sec.

In addition the region has been replete with M class flares (the x-ray scale is ascending from C to M to X) and the characteristic of the region is that it contains a delta class sunspot group. This is a category of group I've posted on previously, in conjunction with my own research.  Much of this focused on the events associated with this delta class group - which I photographed on 11/4/ 80 at its maximal extent:
The group itself marked the return of McMath plage region 17181, and first appeared on the sun's east limb on Oct. 30, 1980 with an area of 70 millionths of a solar hemisphere (msh). In other words, the area increased more than a factor 20 within a span of five days. By 1st November, the group was in the complex delta class, which is determined by the presence of mixed magnetic polarities in the same region. (The active region itself was given the designation AR2776).

Most conspicuous in the course of the group's evolution was the leader spot's pronounced, elliptical penumbra (outermost, lighter sector). This appeared to fragment from Nov. 6 which may have led to a steady decrease in total group area from that date. The emergence of a defined vortical structure in the penumbra occurred thereafter and was accentuated by the formation of a "light bridge" within the penumbra.

At issue, however, was whether it was indeed the delta morphology that led to the high flare occurrence, or something else.  Note that the qualifying entry to the delta class is umbrae - dark central  regions - separated by less than two degrees within one penumbra having opposite polarity. This condition leads to what we describe as a steep magnetic gradient, viz.

grad B = [+B_n - (-B_n)] / x

where the numerator denotes the difference in the normal components of the photospheric magnetic field (between opposite polarities of the active region) as measured by vector magnetograph, and the denominator is the scale separation (x) between them. In several iterations of the Solar-Terrestrial Workshops and Predictions Proceedings, it has been noted that when grad B exceeds  0.1 Gauss/km then a flare is 96% probable within 24 hrs.  Alas, it is not possible to forecast the specific x-ray class.

 Subsequent investigations I conducted disclosed it was more likely the presence of a magnetic multi-pole in a delta class spot that gave rise to large flares such as the one observed on March, 29 this year.


In the diagram shown, such a multipole sunspot model is depicted such that the most intense magnetic field locus is centered in the largest sunspot and is "line-tied" , i.e. it represents the anchored ‘foot’ of one magnetic arch with the other foot connected to a 2nd polarity (minor spot) executing proper motion around it.   In this case the dipole undergoes an approximate 28 degree proper motion over time interval (t2  - t1) during which the (-) polarity footpoint is displaced from a1 to a2.  Treating the region as localized in the complex plane (note the defined Re axis) it is possible to do extensive analysis of motions, shears, and behavior of the respective poles and spots. Such analyses are too comprehensive to go into here, in a blog post, but are described in my book, Selective Analyses in Solar Flare Plasma Dynamics - also available as an E-book.

Of special interest for really large, energetic solar flares are quadripolar sunspots. In one quadri-polar  analysis by Somov et al (Solar Phys., 1998) a series of magnetic charges was specified as:

(+B) <-> e (N)

(-C) <-> e (S)

+A <-> e (n)

-A <-> e (s)

Where the capital letters on the left denoted the identified loop foot points and the  'e' identifiers on the right specified the respective magnetic "charges"  or polarity centers. By establishing a "characteristic dynamic length"  ℓ  for the region, the researchers were able to use Poisson statistics to predict what the average flare production would be over time.

Much more work remains to be done, and plausibly we won't really have a major breakthrough until we can get a high resolution solar optical telescope. This would be of the type that had originally been planned in the 1980s (SOT-1),  designed as a "Hubble version" of a solar telescope dedicated entirely to fine-resolution optical observing but also equipped with:  a tunable filtergraph, a system of state of the art spectrographs, and a photometric filtergraph. All would be contained in a single housing called the 'Focal Plane Instrument Package'. This SOT-1  would have been able to resolve coronal and other structures to within 0.1 arcsec or better, and deliver spectacular real time photometric and spectrographic imagery and information.

 The SOT-1 was scrapped by the budget cutters because they believed mounting a "Star Wars" missile defense system was more important (never mind physicists later showed this program was useless, your classic 'white elephant').

Maybe the budget obsessive nitwits - who always seem to be able to find money for more wars or giving $1b to the Ukraine- will wake up when a large CME strikes and knocks out our power grids. At least one hopes they will, but who knows?