The Great Storm of May 1921: An Exemplar of a Dangerous Space Weather Event

Abstract

We reconstruct the timeline of the extreme space weather event of May 1921, reviewing a wealth of reports from scientific literature, databases, newspaper reports, and reports by historians and astronomers. A series of coronal mass ejections (CMEs) bombarded Earth between 13 and 16 May, as shown by a series of sudden commencements observed across the global network of magnetometers. These CMEs produced three major periods of geomagnetic activity. The first period followed the arrival of two CMEs on 13 May. These may have cleared much density from the inner heliosphere, enabling a subsequent CME to travel quickly to Earth and cause intense activity. Continuing moderate magnetic activity following the first period may also have preconditioned the magnetosphere so it responded strongly to that later CME. This arrived late on 14 May, driving a short period of very intense activity early on 15 May, including technological impacts indicative of strong geoelectric fields. Another CME arrived early on 16 May, driving intense activity similar to that on 13 May. We show how these impacts fit with scientific observations to give a timeline that can be used in worst‐case studies/benchmarks. We also show that some impacts were probably coincidental with the storm, but due to more prosaic faults. This sequence of preconditioning, intense geoelectric fields, and their impacts, plus coincidental faults, makes the 1921 event an excellent basis for building space weather scenarios. Such scenarios are vital scientific input to the development and implementation of policies for mitigation of severe space weather.

A 21st Century View of the March 1989 Magnetic Storm

“…The extremely fast travel time in the 1859 Carrington event was probably also the result of the passage of a previous ICME that caused telegraph disruptions 4 days earlier (Boteler, ). This effect of multiple ICMEs also likely contributed to the magnetic storms and effects seen in 1921 (Hapgood, ) and 1972 (Knipp et al, ). This preconditioning of the upstream solar wind by an earlier ICME allowing for a faster transit of a following ICME was identified by Liu et al () in the observations of the July 2012 eruptions detected by the Solar Terrestrial Relations Observatory.…”

Temporal and Spatial Evolutions of a Large Sunspot Group and Great Auroral Storms Around the Carrington Event in 1859

“…Regarding the extreme magnetic storm on 14/15 May 1921 (Hapgood, ; Silverman & Cliver, ), the aurora was reported down to Apia with a significant magnetic disturbance (Angenheister & Westland, , p. 202). The Dst value is computed to be ≈−907 ± 132 nT, on the basis of magnetograms at Apia, Vassouras, San Fernando, and Watheroo (Love et al, ).…”

Intensity and Impact of the New York Railroad Superstorm of May 1921

“…At 07:04 local time (11:04 GMT), on 15 May, during storm recovery, the New York Central Railroad was abruptly brought to a halt below 125th Street (New York City) when the signal and switching system was put out of operation; this was followed by a fire in the control tower at 57th Street and Park Avenue (New York Times, 16 May 1921, p. 2). In a recent review of the effects of the May 1921 storm, Hapgood () has questioned whether or not this particular event (disruption of the New York Central Railroad) was actually related to the storm, especially since it was reported to have occurred after storm maximum when local geomagnetic intensity was probably more subdued than during storm main phase; Hapgood raises good points, but we remain impressed with reports of “ground currents” in and around New York City exceeding 1000 volts—these would, more certainly, have caused “mischief” to signaling systems of the New York Central Railroad (New York Times, 17 May 1921, pp. 1 and 4).…”