[OKDXA] The Great Geomagnetic Storm of 1921

[Kim Elmore]

This from a friend that, while not a ham, has a lot of interest in 
astrophysics.

73,

Kim N5OP

*THE GREAT GEOMAGNETIC STORM OF MAY 1921: *99 years ago this week, 
people around the world woke up to some unusual headlines.

"Telegraph Service Prostrated, Comet Not to Blame" — declared the Los 
Angeles Times on May 15, 1921. "Electrical Disturbance is 'Worst Ever 
Known'” — reported the Chicago Daily Tribune. "Sunspot credited with 
Rail Tie-up" — deadpanned the New York Times.

<https://spaceweather.com/images2020/11may20/newspapers2.jpg>

They didn’t know it at the time, but the newspapers were covering the 
biggest solar storm of the 20th Century. Nothing quite like it has 
happened since.

It began on May 12, 1921 when giant sunspot AR1842, crossing the sun 
during the declining phase of Solar Cycle 15, began to flare. One 
explosion after another hurled coronal mass ejections (CMEs) directly 
toward Earth. For the next 3 days, CMEs rocked Earth’s magnetic field. 
Scientists around the world were surprised when their magnetometers 
suddenly went offscale, pens in strip chart recorders pegged uselessly 
to the top of the paper.

Then the fires began. Around 02:00 GMT on May 15th, a telegraph exchange 
in Sweden burst into flames. About an hour later, the same thing 
happened across the Atlantic in the village of Brewster, New York. 
Flames engulfed the switch-board at the Brewster station of the Central 
New England Railroad and quickly spread to destroy the whole building. 
That fire, along with another one about the same time in a railroad 
control tower near New York City's Grand Central Station, is why the 
event is sometimes referred to as the "New York Railroad Superstorm."

What caused the fires? Electrical currents induced by geomagnetic 
activity surged through telephone and telegraph lines, heating them to 
the point of combustion. Strong currents disrupted telegraph systems in 
Australia, Brazil, Denmark, France, Japan, New Zealand, Norway, Sweden, 
the UK and USA. The Ottawa Journal reported that many long-distance 
telephone lines in New Brunswick were burned out by the storm. On some 
telegraph lines in the USA voltages spiked as high as 1000 V.

<https://spaceweather.com/images2020/11may20/sunspotar1842.jpg>
*Above:* Sunspot AR1842 on May 13, 1921. [more 
<https://www.ann-geophys.net/33/109/2015/angeo-33-109-2015.pdf>]

During the storm's peak on May 15th, southern cities like Los Angeles 
and Atlanta felt like Fairbanks, with Northern Lights dancing overhead 
while telegraph lines crackled with geomagnetic currents. Auroras were 
seen in the USA as far south as Texas while, in the Pacific, red auroras 
were sighted from Samoa and Tonga and ships at sea crossing the equator.

What would happen if such a storm occurred today?

Researchers have long grappled with that question–most recently in a 
pair of in-depth papers published in the journal /Space Weather/: "The 
Great Storm of May 1921: An Exemplar of a Dangerous Space Weather Event 
<https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019SW002195>" by 
Mike Hapgood (Rutherford Appleton Laboratory, UK) and "Intensity and 
Impact of the New York Railroad Superstorm of May 1921 
<https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019SW002250>" 
by Jeffrey Love (US Geological Survey) and colleagues.

The summary, above, is largely a result of Hapgood’s work. He 
painstakingly searched historical records including scientific journals, 
newspaper clippings, and other reports to create a moment-by-moment 
timeline of the storm. Such timelines are invaluable to emergency 
planners, who can use them to prepare for future storms.

<https://spaceweather.com/images2020/11may20/aurorasightings_big.png>
*Above: *Aurora sightings in May 1921. The leftmost red circle marks 
Apia, Samoa.

Jeffrey Love and colleagues also looked into the past and–jackpot!–they 
found some old magnetic chart recordings that did *not go offscale* when 
the May 1921 CMEs hit. Using the data, they calculated "/Dst/" 
(disturbance storm time index), a measure of geomagnetic activity 
favored by many space weather researchers.

"The storm attained an estimated maximum −/Dst/ on 15 May of 907 ± 132 
nT, an intensity comparable to that of the Carrington Event of 1859," 
they wrote in their paper.

This dry-sounding result upends conventional wisdom. Students of space 
weather have long been taught that the Carrington Event 
<https://www.swsc-journal.org/articles/swsc/pdf/2013/01/swsc130015.pdf> 
(-/Dst/ = 900 nT) was the strongest solar storm in recorded history. Now 
we know that the May 1921 storm was about equally intense.

If the May 1921 storm hit today, "I’d expect it to lead to most, if not 
all, of the impacts outlined in the 2013 Royal Academy of Engineering 
report 
<https://www.raeng.org.uk/publications/reports/space-weather-summary-report> 
led by Paul Cannon," says Hapgood. "This could include regional power 
outages, profound changes to satellite orbits, and loss of radio-based 
technologies such as GPS. The disruption of GPS could significantly 
impact logistics and emergency services."

It’s something to think about on the 99th anniversary of a 100-year storm….