A Carrington-like geomagnetic storm observed in the 21st century

TL;DR

This study analyzes a 2003 geomagnetic storm with a profile similar to the 1859 Carrington event, revealing that such extreme events may be more frequent and challenging to detect with traditional indices.

Contribution

It provides a new interpretation of the Carrington event, highlighting the role of field-aligned currents and local signatures in extreme geomagnetic disturbances.

Findings

Large geomagnetic disturbances can be missed by global indices.

Field-aligned currents, not just ring currents, cause major H-field drops.

Carrington-like events may occur more frequently than previously thought.

Abstract

In September 1859 the Colaba observatory measured the most extreme geomagnetic disturbance ever recorded at low latitudes related to solar activity: the Carrington storm. This paper describes a geomagnetic disturbance case with a profile extraordinarily similar to the disturbance of the Carrington event at Colaba: the event on 29 October 2003 at Tihany magnetic observatory in Hungary. The analysis of the H-field at different locations during the "Carrington-like" event leads to a re-interpretation of the 1859 event. The major conclusions of the paper are the following: (a) the global Dst or SYM-H, as indices based on averaging, missed the largest geomagnetic disturbance in the 29 October 2003 event and might have missed the 1859 disturbance, since the large spike in the horizontal component (H) of terrestrial magnetic field depends strongly on magnetic local time (MLT); (b) the main cause of the large drop in H recorded at Colaba during the Carrington storm was not the ring current but field-aligned currents (FACs), and (c) the very local signatures of the H-spike imply that a Carrington-like event can occur more often than expected.