Home Weather The greatest geomagnetic storm of the 20th Century…May 13-15, 1921…a century ago, New York City/New York State were especially hard hit

The greatest geomagnetic storm of the 20th Century…May 13-15, 1921…a century ago, New York City/New York State were especially hard hit

The greatest geomagnetic storm of the 20th Century…May 13-15, 1921…a century ago, New York City/New York State were especially hard hit

Paul Dorian

A powerful solar storm in May 1921 had major impacts on Earth ranging from fires at telegraph stations and railroad facilities to the disruption of telephone lines and radio broadcasts to the knocking out of telegraph lines across the United States and Europe. Because many problems took place near New York’s Grand Central Terminal, the storm is sometimes referred to as the “New York Railroad Storm”. (Credit: background image- NASA/SDO, headlines- StarDate).

*The greatest geomagnetic storm of the 20th Century…May 13-15, 1921…a century ago, New York City/New York State were especially hard hit*


The most intense geomagnetic storm of the 20th Century took place during solar cycle 15 in a 3-day period from May 13-15 in 1921.  The storm occurred before the widespread electrical dependence of infrastructure that we have in today’s world, but the impact from an extraordinarily powerful coronal mass ejection was still quite extensive.  The storm’s electrical current sparked a number of fires around the world including one near the Grand Central Terminal in New York City. In addition, auroras appeared throughout the eastern US creating brightly lit nighttime skies and telegraph service virtually stopped in its tracks due to blown fuses and damaged equipment. Research in recent years has suggested that this super solar storm of May 1921 was equally as intense as the granddaddy of all super storms in recorded history – the “Carrington Event of 1859”.

Sunspot region now referred to as “AR1842” as it was recorded on May 13, 1921. Courtesy spaceweather.com

Gigantic sunspot

The biggest solar storm of the 20th Century actually took place during the declining phase of solar cycle #15 with the culprit being a gigantic sunspot that was referred to then as “Greenwich region 933404”.   This sunspot was first seen on the sun’s east limb on May 8th, 1921 and it rotated to the west limb over the next ten days or so. This sunspot likely produced as many as six coronal mass ejections (CMEs) directly toward Earth during this time period as registered in ground-based magnetometer measurements (Newton, 1948, p. 178).  Scientists around the world were surprised and likely quite amazed when their magnetometers went “off the scales” in the peak part of the storm during the May 13-15 time period. Little did they know that this would turn out to be the biggest solar storm of the century – and there has been nothing quite like it ever since according to Dr. Tony Phillips of spaceweather.com. 

Impact was especially intense in New York City/New York State

The impact of the super solar storm of May 1921 was especially acute in New York City and across New York State and this is why this event is sometimes referred to as the “New York Railroad Superstorm” (Love, et al, 2019). Electrical currents induced by geomagnetic activity surged through telephone and telegraph lines, heating them to the point of combustion. The railroad control tower near New York City’s Grand Central Station broke out in flames.  Flames also engulfed the switch-board just north of New York City at the Brewster station of the Central New England railroad and spread enough to destroy the entire building.  A telegraph operator there was driven from his keys by “electric fluid” that suddenly “flared out” (The Bridgeport Telegram, 17 May 1921, p. 11).  On May 14th, excessive electric currents on telephone lines caused the Union Railroad Station in Albany, NY to catch fire and the station burned to the ground. The New York Times reported that storm-related effects were particularly pronounced throughout the eastern US where fluctuating electric currents grew to a level where “hardly a wire was working anywhere” and stray voltages on some wires exceeded 1000 V. Auroras over New York City were apparently so bright that even the “intense lights of the electric signs along Broadway could not dim the brilliance of the flaring skies” (The New York Times, 15 May 1921, p. 1; 17 May 1921, p. 1).

Headlines from the great solar storm of May 1921 (courtesy spaceweather.com)

The impact of the super solar storm spread around the world with fires erupting in numerous places including, for example, a telegraph exchange in Sweden that burst into flames on May 15th.  There were disruptions to telegraph systems in Australia, Brazil, Denmark, France, Japan, New Zealand, Norway, Sweden, and the UK.  At the peak of the storm, “northern lights” were seen as far south as Texas in the US, by ships at sea crossing the equator, and even in the southern hemisphere in places like Samoa and Tonga.

Daily observations of the number of sunspots since 1 January 1900 according to Solar Influences Data Analysis Center (SIDC). The thin blue line indicates the daily sunspot number, while the dark blue line indicates the running annual average. The arrow indicates the time period of the May 1921 super storm which occurred during the declining phase of solar cycle #15. (Plot courtesy climate4you.com)

Interesting impact on radio propagation

One of the interesting features of this solar storm according to a recent publication (Hapgood, 2019) was its variable impact on the propagation of long distance radio signals. There were reports showing both disruption and enhancement of radio propagation, with reports of enhancement gaining much attention because they were in stark contrast to the disruption of other telecommunications systems. One example of enhancement was a report in the New York Times (NYT, 1921a) that radio signals reaching New York from Berlin (some 6,400 km distant) and Bordeaux (5,800 km) were much stronger than usual between 02:30 and 04:00 GMT on 15 May. This report has particular credibility because the New York Times was one of a number of U.S. newspapers that then operated their own radio stations to receive news from Europe (Hudson et al., 2000). The good performance of radio links in the United States and at Bordeaux was also confirmed in statements by the Radio Corporation of America (Telegraph and Telephone Age, 1921b). Another example of enhancement came from the Pacific region, where Angenheister and Westland (1921a) and Gibbs (1921) reported unusually good conditions around 06:15 on radio links between radio stations at Apia in Samoa and Awanui in the north of New Zealand (a distance of 2,700 km).

To understand the enhancement of radio signals during the storm, it is essential to appreciate that the radio systems in use in 1921 operated in low‐frequency radio bands below 300 kHz. For example, the radio link between New Zealand and Samoa operated at 150 kHz (Gibbs, 1921). At this frequency, radio signals couple to the conductive surface of the Earth, both land and sea, and propagate along that surface, following the curvature of the Earth in a so‐called “ground wave.” The signals are gradually attenuated by the finite conductivity of the surface with less attenuation where conductivity is higher, mostly obviously over the salt water that forms the oceans (International Telecommunications Union, 2007). However, the signals can also propagate into the upper atmosphere and be reflected from the ionosphere giving a “sky wave” that can interfere with the ground wave signal, causing problems with signal reception. Sky wave interference can also arise from distant sources of natural radio signals such as lightning and other electrical activity in the atmosphere. Thus, good conditions for signal propagation at 150 kHz will arise when sky waves are heavily attenuated by absorption due to significant plasma density in the lower ionosphere below 90 km (credit Hapgood, 2019).

Potential impact on today’s world

Some recent research (e.g., Love, et al, 2019) now suggests that this great solar storm of May 1921 was about as equally intense as the “Carrington Event of 1859” which has been dubbed the strongest solar storm in recorded history. The super solar storm of 1859 took place during solar cycle #10 and was named for the British astronomer, Richard Carrington, as he observed from his own private observatory the solar flare which caused a major coronal mass ejection (CME) to travel directly toward Earth. Perhaps the most intense storm since the May 1921 super storm was the magnetic storm of March 1989 which caused an electricity blackout in Quebec, Canada.  

In today’s world, electronic technologies have become embedded into everyday life and are, of course, quite vulnerable to solar activity. Power lines, long-distance telephone cables, radar, cell phones, GPS, and satellites – all of which could be significantly affected by an event like the one of 1859 or the storm of 1921.  In other words, the world’s high-tech infrastructure could grind to a halt disrupting daily activities from purchasing a gallon gas to using the Internet.

Of particular concern is the fear about what this kind of solar storm could do to the electrical grid since power surges caused by solar particles can blow out giant transformers.  If numerous transformers happened to be destroyed at once, it would likely take a painfully long time to replace them.  The eastern US is especially vulnerable since the power infrastructure is highly interconnected so that failures in one location could cause failures in other regions. One long-term solution to this vulnerability would be to rebuild the aging power grid to be less susceptible to solar disruptions.

On the positive side, there is comfort in the fact that observations of the sun in today’s world are a constant with a fleet of spacecraft in position to monitor the sun and gather data on solar flares. Also, there is better forecasting today and solar scientists could give some sort of warning as to when solar flares might appear and whether a given storm is pointed at Earth.  Improved forecasting can allow for mitigating actions to be taken since the most damaging emissions travel slowly enough to be detected by satellites well before the particles strike the Earth.  For example, power companies could protect valuable transformers by taking them offline before a solar storm strikes.

One thing is certain, we should be prepared for another massive solar storm of the magnitude of the “Carrington Event of 1859” or the great geomagnetic storm of May 1921 – the most powerful solar storm of the 20th century.

Meteorologist Paul Dorian



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