The three-day May 1921 geomagnetic storm, also known as the New York Railroad Storm, was caused by the impact of an extraordinarily powerful

coronal mass ejection A coronal mass ejection (CME) is a significant ejection of plasma mass from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accepted theoretical understandin ...

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior Dynamo ...

. It occurred on 13–15 May as part of

solar cycle 15 Solar cycle 15 was the fifteenth solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 10.1 years, beginning in July 1913 and ending in August 1923. The maximum smoothed sunspot number observed dur ...

, and was the most intense geomagnetic storm of the 20th century. Since it occurred before the extensive interconnectivity of electrical systems and the general electrical dependence of infrastructure in the developed world, its effect was restricted; however, its ground currents were up to an order of magnitude greater than those of the

March 1989 geomagnetic storm The March 1989 geomagnetic storm occurred as part of severe to extreme solar storms during early to mid March 1989, the most notable being a geomagnetic storm that struck Earth on March 13. This geomagnetic storm caused a nine-hour outage of Hyd ...

which interrupted electrical service to large parts of northeastern North America.

Effects

The storm's electrical current sparked a number of fires worldwide, including one near

Grand Central Terminal Grand Central Terminal (GCT; also referred to as Grand Central Station or simply as Grand Central) is a commuter rail terminal station, terminal located at 42nd Street (Manhattan), 42nd Street and Park Avenue in Midtown Manhattan, New York Ci ...

which made it known as the "New York Railroad Storm". Contemporary scientists estimated the size of the

sunspot Sunspots are temporary spots on the Sun's surface that are darker than the surrounding area. They are one of the most recognizable Solar phenomena and despite the fact that they are mostly visible in the solar photosphere they usually aff ...

(AR1842) which began on May 10—and caused the storm—as . The storm was extensively reported in

New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...

, which was a center of telegraph activity as a railroad hub.

Aurora An aurora ( aurorae or auroras), also commonly known as the northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in Earth's sky, predominantly observed in high-latitude regions (around the Arc ...

s ("northern lights") appeared throughout the eastern

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, creating brightly lit night skies.

Telegraph Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...

service in the U.S. first slowed and then virtually stopped at about midnight on 14 May due to blown fuses and damaged equipment. Radio propagation was enhanced during the storm due to ionosphere involvement, however, enabling unusually good long-distance reception. Electric lights were not noticeably affected. Undersea telegraph cables were affected by the storm. Damage to telegraph systems was also reported in Europe and the Southern Hemisphere.

Comparison to other geomagnetic storms

In space weather, the

disturbance storm time index The disturbance storm time index, also known as the Dst index or Kyoto Dst index, is a measure of the strength of the Earth's ring current. The ring current around Earth produces a magnetic field that is directly opposite Earth's magnetic field; t ...

(Dst index) is a measure often used for determining the intensity of solar storms. A negative Dst index means that

Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from structure of Earth, Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from ...

is weakened—particularly the case during solar storms—with a more negative Dst index indicating a stronger solar storm. A paper in 2019 estimated that the May 1921 geomagnetic storm had a peak Dst of −907±132 nT. For comparison, the

Carrington Event The Carrington Event was the most intense geomagnetic storm in recorded history, peaking on 1–2 September 1859 during solar cycle 10. It created strong auroral displays that were reported globally and caused sparking and even fires in telegr ...

of 1859 had a peak Dst estimated to be between and . The

had a peak Dst index of −589 nT.

References

Footnotes

Bibliography

*The Aurora Borealis of May 14, 1921 * A bibliography of newspaper and journal articles. * * * * * * * * * * * * * {{Solar storms 1921 in science 1921 natural disasters Geomagnetic storms 1921 natural disasters in the United States May 1921

Effects

Comparison to other geomagnetic storms

See also

References

Footnotes

Bibliography