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 on
Earth's
magnetosphere. It occurred on 13–15 May as part of
solar cycle 15, and was the most intense geomagnetic storm of the 20th century.[1]
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 which interrupted electrical service to large parts of northeastern North America.[2]
Effects
The storm's electrical current sparked a number of fires worldwide, including one near
Grand Central Terminal which made it known as the "New York Railroad Storm".[1] Contemporary scientists estimated the size of the
sunspot (AR1842)[1] which began on May 10—and caused the storm—as 151,000 by 34,000 km (94,000 by 21,000 miles).[3][4]
The storm was extensively reported in
New York City, which was a center of telegraph activity as a railroad hub.[5]Auroras ("northern lights") appeared throughout the eastern
United States, creating brightly lit night skies.
Telegraph service in the U.S. first slowed and then virtually stopped at about midnight on 14 May due to blown fuses and damaged equipment.[6] Radio propagation was enhanced during the storm due to ionosphere involvement, however, enabling unusually good long-distance reception. Electric lights were not noticeably affected.[7]
Undersea telegraph cables were affected by the storm. Damage to telegraph systems was also reported in Europe[8] and the
Southern Hemisphere.[9]
A paper in 2019 estimates intensity of Dst = −907±132 nT.[10]
"Dst" is the "
Disturbance Storm Time index"; for comparison, for the
Carrington Event superstorm of 1859 the estimated Dst was included between -850 nT (Siscoe et al., 2006) and -1050 nT (Gonzalez et al., 2011).
^"Sun Spots Vanishing"(PDF). The Los Angeles Times. May 16, 1921. pp. 1 & 2. Archived from
the original(PDF) on August 12, 2014. Retrieved December 19, 2012.
Henry K. Bunn (May 15, 1921).
"The Story The Week Has Told"(PDF). The Atlanta Constitution. p. 8. Archived from
the original(PDF) on March 4, 2016. Retrieved December 19, 2012.
"Aurora is Disturber"(PDF). The Los Angeles Times. May 15, 1921. pp. 1 & 2. Archived from
the original(PDF) on March 3, 2016. Retrieved December 19, 2012.
"The Aurora Borealis"(PDF). The Los Angeles Times. May 16, 1921. p. 14. Archived from
the original(PDF) on March 3, 2016. Retrieved December 19, 2012.