A Great Space Weather Event in February 1730

TL;DR

This study analyzes a significant 1730 magnetic storm using historical auroral and sunspot records, revealing its intensity and extent comparable to modern major storms, and contextualizing it within solar activity of the time.

Contribution

It reconstructs the 1730 magnetic storm's auroral extent and solar activity, providing a detailed historical analysis and comparison with modern extreme events.

Findings

Auroras extended down to 25.8° MLAT in East Asia.

Auroral boundary reached 45.1° MLAT, possibly down to 31.5° MLAT.

The storm was as intense as the 1989 storm, less than the Carrington event.

Abstract

Aims. Historical records provide evidence of extreme magnetic storms with equatorward auroral extensions before the epoch of systematic magnetic observations. One significant magnetic storm occurred on February 15, 1730. We scale this magnetic storm with auroral extension and contextualise it based on contemporary solar activity. Methods. We examined historical records in East Asia and computed the magnetic latitude (MLAT) of observational sites to scale magnetic storms. We also compared them with auroral records in Southern Europe. We examined contemporary sunspot observations to reconstruct detailed solar activity between 1729 and 1731. Results. We show 29 auroral records in East Asian historical documents and 37 sunspot observations. Conclusions. These records show that the auroral displays were visible at least down to 25.8{\deg} MLAT throughout East Asia. In comparison with contemporary European records, we show that the boundary of the auroral display closest to the equator surpassed 45.1{\deg} MLAT and possibly came down to 31.5{\deg} MLAT in its maximum phase, with considerable brightness. Contemporary sunspot records show an active phase in the first half of 1730 during the declining phase of the solar cycle. This magnetic storm was at least as intense as the magnetic storm in 1989, but less intense than the Carrington event.