Ian R. Mann
Timo Qvick
Kalevi Mursula
Jeffrey J. Love
2025
<p>From a survey of published accounts of visual sightings of aurorae, a compilation is presented of the lowest identified geomagnetic latitude at which discrete aurorae were seen at local zenith during magnetic storms having intensities with maximum −<strong><i>Dst</i></strong> > <strong>200</strong> nT. The compilation includes data for the superstorms of 2 September 1859, 4 February 1872, and 15 May 1921. A statistical model is developed representing the equatorward boundary of discrete aurorae versus storm intensity. The model indicates that a once-per-century storm would likely induce discrete aurorae at zenith down to a geomagnetic latitude of <strong>34</strong><span>°</span>. Insofar as aurorae can be taken as a proxy for electrojet currents, such a storm would expose many nighttime electric-power systems, in the contiguous United States or Europe, to high levels of geomagnetic disturbance. A Carrington-class storm would induce discrete aurorae down to 24<span>°</span>. These exposures are much greater than those indicated in recent numerical simulations of extreme magnetic storms. Using the model to infer storm intensity from reports of low-latitude aurorae, a storm on 28 August 1859, likely had maximum −<strong><i>Dst</i></strong> = <strong>673</strong> nT. That this storm occurred just a few days before the Carrington storm of 2 September (maximum −<strong><i>Dst</i></strong> = <strong>964</strong> nT) deserves attention. A storm that occurred on 17 September 1770 is estimated to have had maximum −<strong><i>Dst</i></strong> = <strong>928</strong> nT. The vision of Ezekiel could have been inspired by aurorae from a storm with maximum −<i><strong>Dst</strong></i> = <strong>550</strong> nT.</p>
application/pdf
10.1029/2024SW004286
en
American Geophysical Union
What is the lowest latitude of discrete aurorae during superstorms?
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