Searching for Carrington-like events and their signatures and triggers

TL;DR

This study systematically searches for Carrington-like geomagnetic events, analyzes their interplanetary triggers, and highlights the importance of field-aligned currents and abrupt IMF reversals as key factors.

Contribution

It introduces a deep search methodology for Carrington-like events, identifies their triggers, and challenges previous assumptions about the main current involved.

Findings

Two Carrington-like events reinforce the risk of missing hazardous space weather.

Field-aligned currents are likely the main current involved in these events.

Abrupt southward IMF reversals and high solar wind pressure act as triggers.

Abstract

The Carrington storm in 1859 is considered to be the major geomagnetic disturbance related to solar activity. In a recent paper, Cid et al. (2015) discovered a geomagnetic disturbance case with a profile extraordinarily similar to the disturbance of the Carrington event at Colaba, but at a mid-latitude observatory, leading to a re- interpretation of the 1859 event. Based on those results, this paper performs a deep search for other 'Carrington-like' events and analyses interplanetary observations leading to the ground disturbances which emerged from the systematic analysis. The results of this study based on two Carrington-like events (1) reinforce the awareness about the possibility of missing hazardous space weather events as the large H-spike recorded at Colaba by using global geomagnetic indices, (2) argue against the role of the ring current as the major current involved in Carrington-like events, leaving field- aligned currents (FACs) as the main current involved, and (3) propose abrupt southward reversals of IMF along with high solar wind pressure as the interplanetary trigger of a Carrington-like event.