An analysis of the Trouvelot’s Auroral Drawing on 1/2 March 1872: Plausible Evidence for Recurrent Geomagnetic Storms
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Author/Creator ORCID
Date
2020-06-22
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Citation of Original Publication
Ankush Bhaskar et al., An analysis of the Trouvelot’s Auroral Drawing on 1/2 March 1872: Plausible Evidence for Recurrent Geomagnetic Storms, Journal of Geophysical Research: Space Physics (2020), https://doi.org/10.1029/2020JA028227
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©2020 American Geophysical Union. All rights reserved
Access to this item will begin on 12/22/2020
©2020 American Geophysical Union. All rights reserved
Access to this item will begin on 12/22/2020
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Abstract
This work examines Trouvelot’s observations and drawing of an auroral display during the night of 1 March 1872. It is known that the auroral oval moves equatorward to mid‐ and even low‐latitudes during large geomagnetic storms. Trouvelot’s graphical record of the great aurora on 1 March 1872 has been often cited as a remarkable example of a mid‐latitude aurora, although it is puzzling that this occurred on a geomagnetically quiet day. Kataoka et al . (2019, JSWSC , 9 , A16) even regarded this as a dating error. Here, we investigate Trouvelot’s descriptions and available geomagnetic measurements in detail. Our analysis shows that the original date of Trouvelot’s auroral drawing is most probably accurate. Moreover, Trouvelot’s descriptions and the observational site show that the auroral visibility fell at the beginning of 2 March 1872 in Greenwich Mean Time (GMT). Consulting simultaneous variations of magnetograms at Helsinki and Greenwich, we found that the nightside aurora specifically coincides with the initial phase of the storm (substorm) and suggests a close association with a substorm triggered by sudden magnetospheric compression. This case study shows that even short geomagnetic storms can be overlooked in a daily Aa index and they can also cause mid‐latitude aurorae. Moreover, we found ≈ 27‐day intervals between this storm, the extreme storms on 4‐6 February 1872, and another “bright aurora” that was reported on 6 January 1872. Based on their interval, these mid‐latitude aurorae have probably resulted from recurrent solar activity.