The Geomagnetic Disturbances Of September 1941 - Will We Be Ready When It's Our Time?

The giant, complex sunspot group observed on Sept. 10, 1941.

In September, 1941, one of the most prominent geomagnetic storms in history was triggered by a  mammoth sunspot group of complex geometry. (See image) The monster group, first observed on Sept. 10, 1941,  occurring at low heliographic latitude and at the eastern limb of the Sun. As I noted in previous posts on such large spots, they form via the  gradual assembly of multiple, single flux tubes via convective downdrafts,   ultimately leading to the buoyant emergence of a concentrated magnetic field structure with distinct features (umbra, umbral dots, penumbra).

The multiple flux tube sunspot model was originally advanced by Eugene Parker (Astrophys. J, 1979) from the University of Chicago. A simple sketch showing the geometry of the model is illustrated below:

Where  v _d   represents the downdraft velocity and 'x' is the Wilson depression, denoting the gap between the spot 'surface' and the field -free regions. Parker estimated this to be about 1150 km.  The downdraft velocity, meanwhile, he calculated to be roughly 2 km/sec.

In more detail, the concentration of hundreds of flux elements or tubes at the solar surface prevented the underlying hot solar plasma from reaching the surface.  This also accounted for why sunspots are darker than the surrounding photosphere, because they are some 1500 K cooler,

Observations made over the next week (Sept. 10- 17, 1941)  disclosed the spot group growing even as the solar rotation brought it near the center of the solar disk as seen from Earth. As we know today, this is also the configuration for meridian-centered  CME (coronal mass ejection).  By this stage, the sunspot group was large enough to be seen using the naked eye (using an appropriate filter, of course)

Then at 8h 38m Universal time on Sept. 17th, a spectrohelioscope at the Royal Greenwich Observatory recorded a solar flare above this sunspot group. The instrument detected emissions of ultraviolet and x-ray radiation which - within 8 minutes (the time taken for radiant energy to reach Earth) enhanced the ionization of the Earth's atmosphere causing a sharp perturbation known as a "crochet".

According to a subsequent paper published in The Astrophysical Journal  (July 1, 1958) this is a "relatively minor disturbance of Earth's magnetic field which occurs concurrently with certain flares".  It is associated with dayside perturbations of the geomagnetic field and affects high frequency radio communications. In this respect, it is analogous to a certain class of sudden ionospheric disturbances.

On the basis of daily sunspot numbers supplied by the U.S. Naval Observatory the Dept. of Terrestrial Magnetism at the Carnegie Institution of Washington formally issued a warning to radio operators to expect significant disturbances in ionosopheric and geomagnetic conditions. beginning on September 18th.   This prediction turned out to be accurate so that within 20 hours of the flare a magnetic storm began at 4h 2m UT on Sept. 18th with the arrival of a CME.  The latter abruptly compressed the magnetopause generating a magnetic impulse recorded by observatories around the world.

In addition, a magnetic "superstorm" followed which was intense and of long duration. To fix ideas and perspective at least one magnetic observatory (run by U.S. Coast and Geodetic survey) registered six separate magnetic storms with a "K index" of 9  the most  severe possible. Five occurred over a 24 hour period.

The more direct physical effects followed including spectacular auroral displays as far south as New Mexico with some citizens wondering if an anti-aircraft search battery had been triggered. (Bear in mind the nation was on edge and this was barely three months before Pearl Harbor).  Meanwhile, magnetic activity was found to abruptly increase by 19h 45 m on Sept. 18th and within 5 minutes the Pennsylvania Water and Power Company  recorded uncontrolled voltage variations in transmission lines beginning two hours after the  magnetic storm commenced.

By Sept. 18-19 widespread interference in radio transmission was reported around the world.

The events of September, 1941 are instructive in that they could occur again, say in the next solar cycle. Will we be ready?

At least at that time, as my mother noted (she was then attending  Wisconsin State Teachers' College) the newspapers regularly published brief scientific accounts such as that below *:



This appeared on Sept, 21st, days after the  geomagnetic events, and in The Milwaukee Sentinel.  Though mom was not big on physics or astronomy, she'd save these clippings to be able to use later on, perhaps even to show to her future kids - if she ever got married and had any. (Five years later, she would)  Happily, some ten years later I was the chief beneficiary. Those clippings, along with the associated material in The Book Of Knowledge, drove me to pursue astronomy as a hobby by age 11 and later,  a career in space and solar physics.

Because of these same information- bearing cartoons, citizens  of the 1940s and 50s were generally informed about natural events even if they lacked advanced degrees. Can the same be said of most citizens today? One wonders.

The more critical question is whether we will be prepared when the next severe geomagnetic disturbance and magnetic superstorms erupt.
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Addendum:

*  Of course, in 1941 the basic model of the sunspot was of a magnetic "vortex" or "whirling magnet".  Even Harvard astronomer Donald Menzel in his wonderful monograph, ''Mathematical Physics' (1961, pp. 274-75) asserted: "Observations suggest sunspots are vortices. He then set out to try to quantify this vortex model as a spinning disk with n electrons per cm²  and which rotates with uniform angular velocity..

He obtained:

n =   2 H/   e v _o

where v _o   is the tangential velocity at the periphery of the vortex-disk.. From these basics, Menzel computed:

n =  10 ¹⁵ electrons / cm²

Menzel  then concluded that given the above, "an excess of protons would produce forces 6 x  10 ¹⁵  as great"  and  "a sunspot with such an excess would break up with explosive violence".

He added:

"An excess of one proton per sixty square centimeters on the solar surface would produce sufficient positive potential just to overcome the solar attraction by electrostatic repulsion of an electron"
Thereby concluding "the Sun is practically neutral electrically"

What about the magnetic aspect?

"No alignment of the individual atom magnets could possibly be maintained in the presence of the turbulent motion and high temperatures existing on and in the Sun, The effect is undoubtedly electrical..."

One can only marvel at how our understanding of sunspots has progressed since Menzel's book.

See also:

http://brane-space.blogspot.com/2015/02/a-new-model-for-magnetic-substorms.html

Solar Flares May Have Helped Originate Organic Basis For Life On Earth

One of the major reasons that I became interested in solar flares was on account of their pervasive terrestrial effects, including: capacity to adversely affect navigation controls on aircraft, ability to erode much of the then ozone layer, release of high energy particles and x-rays to knock out satellites and ability to disrupt telecommunications.

Those research efforts paid off in exposing novel ways to score flare frequency as well as to forecast geo-effective events such as sudden ionospheric disturbances (SIDs).  My work also exposed new aspects of solar physics, specifically the conditions for solar flares to develop near magnetically complex solar active regions if the right morphology was present, e.g.


http://brane-space.blogspot.com/2014/06/quantifying-solar-loop-oscillations.html


Now, new research has revealed that solar flares may not always have been the deleterious phenomena we behold, but actually sparked the first ingredients for Earth life. Researchers at NASA, according to a report in EOS: Earth & Space Science News (July 1), have discovered that when the Sun was about a half billion years old (it is 4.5 billion yrs now) large solar flares could have changed the chemistry of Earth's atmosphere.  These flares, btw, would have dwarfed even the largest flares on record today - including the one that knocked out the Ottawa power grid in 1989.

Specifically, the work --led  by Vladirmir  Airapetian- proposed that bombardment of Earth by high energy particles at the time might have triggered existing inorganic molecules to form organic ones (considered the precursors to life). One of the other molecules that could have formed at the time is a potent Greenhouse gas, methane (CH4).

The authors, based at NASA's Greenbelt, MD  Goddard Space Flight center, published their work in Nature Geoscience:   http://bit.ly/super-flares-life


also noting how the Earth could have been a warm and hospitable place given the Sun was significantly less luminous than today, in spite of the large solar flares 

If their findings are confirmed, it would help illuminate the long-  standing mystery of how the original spark set off the chain leading to organic molecules, as illustrated in the Miller-Urey experiment.

The Miller -Urey experiment basically applied an electrical discharge to a chemical brew resembling the Earth’s primitive reducing atmosphere. This brew included ammonia and methane, as well as hydrogen and water vapor. The effect of the discharge transformed the mix into a diverse yield of organic compounds. These included amino acids, as well as substances such as formic acid and urea that normally occur in living organisms.

The very fact so many organic compounds could arise is remarkable in itself, given the vast number of possible compounds that might have emerged. And while it is true that the discharge didn’t produce actual living cells, there is no reason – given enough time,- that a primitive pre-biotic cell in the distant past could not have emerged given the building blocks left behind.

Thus, if validated, the Airapetian et al solar flare ("super flare")  finding also affects how researchers assess the prospects for life on assorted exoplanets - especially those orbiting young, active stars.

Establishing A Physics Identity

Front cover of my 400+ page thesis, and me (ca. 1981) recording magnetic classifications of sunspots, estimating their areas using a solar graticule.

In a recent issue of Physics Today (May, p. 47) we learn ('Developing Physics Identities') of the various tracks to establishing a "physics identity".  The one that most caught my attention was "When you have your own ideas and your own project. Basically you're working on something not having been spurred by someone else telling you to do it."

After passing two 3-hour physics qualifying exams for the M. Sc. degree,  I was asked by my adviser whether I needed "ideas for the thesis". I told him 'no, thanks', as I had already been working on a problem of my own for the past two years. This concerned how one might use morphological and magnetic features of sunspots to predict geo-effective events, specifically flares that incepted sudden ionospheric disturbances or SIDs.  Thus, my thesis was born, leading to no fewer than six published papers in peer-reviewed journals- twice as many as any other staff members in the time.

The title of the thesis became: 'Can Sunspot Morphology Be Used To Predict The Occurrence of SID Flares?'  and had been subsequently advanced for  Ph.D. submission at my advisor's request after the publication of the first 3 papers. Exemption from the oral exam followed but the conferral of the Ph..D.  was delayed by one outside examiner (from Sweden) to "enable further observational work via the Solar Optical Telescope" (Not the Hinode one!).

Alas, after 1 1/2 years the SOT was terminated in the NASA budget under GOP pressure - and with Reagan's military expenditures already reaching $1. 7 trillion, leaving the Ph.D. stillborn. See e.g.

http://brane-space.blogspot.com/2011/06/telescope-that-never-was.html

An M.Phil. (Master of Philosophy) higher research degree, next thing to a Doctor of Philosophy or Ph.D.,  was awarded instead.  This despite the fact my thesis had produced no fewer than five papers based on original work and insights. And at 401 pages (including 68 pages of Appendices) the thesis was more substantial than most doctoral dissertations - and with more published papers engendered.

The strategic basis and motivation for my work was originally published in a paper appearing in The Journal Of the Royal Astronomical Society of Canada, e.g.


http://adsabs.harvard.edu/full/1983JRASC..77..203S

The stand-alone authorship is especially important because it discloses the person's ability to write a full scientific paper on his own, and have it published professionally. This proof alone qualified me for Full Membership  (as opposed to 'Associate') in the American Astronomical Society, despite not having the Ph.D. (My 2011 monograph, 'Selected Analyses in Solar Flare Plasma Dynamics' is the equivalent of the doctoral dissertation that never was, i.e. had the thesis been so accepted without the need for the added SOT inputs).

Not long after writing the first four chapters of my thesis, they appeared in distilled form, in two lengthy papers published in Solar Physics, e.g.

http://adsabs.harvard.edu/full/1983SoPh...88..137A

And a somewhat shorter paper that followed, e.g

http://adsabs.harvard.edu/full/1984SoPh...92..259A

Given all the material in the papers was basically from my thesis, the only elements not prepared by me (in the 2 co-authored papers) were the assorted final (publication ready) graphs and line diagrams. These were prepared by my thesis advisor (Dr. A. Achong) since he had the special technical implements to do the quality figures required. (This was for Solar Physics. ) The JRAS - for my original paper given above - didn't have these technical drawbacks and could convert ordinary black ink line drawings-figures to page compatible ones, hence I drew all those myself).

At times it was amusing leading up to the papers' submission, because I had to bring Achong up to speed on the statistical basis for the papers (e.g. Poisson distributions in the 2nd) and the physical basis for the interpretation in the first, i.e. using vector magnetograms  to support a mutual polarity intrusion leading to enhanced magnetic field gradient and higher probability of solar flare. However, Achong insisted his name go first because he was my advisor and "How would it look otherwise?"

Never mind, the ability to conceive and forge a project of my own - an extended, original work with numerous data sets and parameters - showed me I irrevocably qualified as a solar physicist. This project also sealed my identity along with my contribution to perhaps the most monumental space and solar physics project ever undertaken, The Solar -Terrestrial Predictions Workshop e.g.


The massive effort saw the input from over two  hundred solar and space physicists covering every aspect of the problem of solar-terrestrial interactions, including: long, medium and short term solar  forecasting, associated  geomagnetic activity and auroral (substorm) forecasts, as well as ionospheric predictions.

 My paper on the statistical limits to solar flare prognostication appeared on pp. 276-284 of the Proceedings and received much attention from the other contributors - since of course it impacted in multiple ways on their work as well.  The paper followed from the last  two chapters of my thesis and was based on the concept of a Poisson-based “delay time” for build up of magnetic free energy,  first postulated by me in early 1984,  for application to “SID” (sudden ionospheric disturbance-generating) flares, with the release attendant on a change in initial free magnetic energy (E _m = B²/2m ) given by[i]:

¶ / ¶  t  {ò _v  B²/2m  dV} = 1/m  ò _v div[(v  X B) X B] dV 

 -   ò _v  {h_an | J_ms |² }dV       

where the first term on the right side embodies footpoint motion, and the second, joule dissipation, but with J_ms the current density at marginal stability – since the marginal stability hypothesis is required for a driven process, and h _an  is the anomalous resistivity. In the same paper, it was shown how the flare distribution corresponds to a Poisson process of the form P(t) =    =   exp (- l)   l^t  / t!, where theoretically the Poisson mean rate of occurrence is: l_m =   l Dt, , with Dt  = t,  assuming the time interval Dt  = 1d. In reality, measuring constraints (say achieving uniformly equal time intervals between successive Mt. Wilson magnetograms), will usually ensure  Dt ¹ 1d, so  Dt  ¹  t  thereby introducing a selection effect variability, complicating computation of P(t).

 It was also suggested, but not proven, that variability in l arises from  variability in vertical magnetic gradients (B_z) and critical changes in the associated current density at marginal stability (Jz_ms) such that:  d(Ñ(+ B_z) ) Þ d Jz_msÞ dJ_z  ( dt)/ dt where J_z  is the vertical current density associated with putative footpoints magnetic induction (+ B_z ) and rate of change in |B_z| modulated by significant evolutionary changes (dt) in the lifetime of the magnetic field, especially critical if   dt < Dt.

Since magnetic gradients and associated scale lengths (ℓ_B) also will change in time, there would be scope for accepting a Poisson process of form P(t) =  =   exp (- l)   l^t  / t!  which would embody an energy modulation with some inbuilt variance, with the latter having to be known to determine how much energy might be released and when. In other words, the differing scale factors inevitably introduced variabilities that were difficult to account for. The Poisson statistics therefore had to be able to take these differing modalities into account.

Below: Photo taken after being awarded the M.Phil. in Physics:

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[i] Stahl, P.A. and  Achong, A.: 1984a, Proceedings of the Second Caribbean Physics Conference, Ed. L.L. Moseley, pp. 1-11.