South American auroral reports during the Carrington storm

TL;DR

This study analyzes South American auroral reports from the 1859 Carrington storm, reconstructing the auroral oval's extent and revealing a notable north-south asymmetry linked to magnetic field variations.

Contribution

It provides the first detailed reconstruction of the auroral oval during the Carrington storm from South American data, highlighting hemispheric differences and their magnetic causes.

Findings

Auroral oval extended to 25.1° invariant latitude.

Brighter auroras observed in South America than in the North.

Asymmetry linked to magnetic longitude and weaker magnetic field over South America.

Abstract

The importance of the investigation of magnetic superstorms is not limited to academic interest, because these superstorms can cause catastrophic impact on the modern civilisation due to our increasing dependency on technological infrastructure. In this context, the Carrington storm in September 1859 is considered as a benchmark of observational history owing to its magnetic disturbance and equatorial extent of the auroral oval. So far, several recent auroral reports at that time have been published but those reports are mainly derived from the Northern Hemisphere. In this study, we analyse datable auroral reports from South America and its vicinity, assess the auroral extent using philological and astrometric approaches, identify the auroral visibility at - 17.3{\deg} magnetic latitude and further poleward and reconstruct the equatorial boundary of the auroral oval to be 25.1{\deg} +/- 0.5{\deg} in invariant latitude. Interestingly, brighter and more colourful auroral displays were reported in the South American sector than in the Northern Hemisphere. This north-south asymmetry is presumably associated with variations of their magnetic longitude and the weaker magnetic field over South America compared to the magnetic conjugate point and the increased amount of magnetospheric electron precipitation into the upper atmosphere. These results attest that the magnitude of the Carrington storm indicates that its extent falls within the range of other superstorms, such as those that occurred in May 1921 and February 1872, in terms of the equatorial boundary of the auroral oval.