Low-latitude Aurorae during the Extreme Space Weather Events in 1859

Abstract The Carrington storm (1859 September 1/2) is one of the largest magnetic storms ever observed, and it caused global auroral displays in low-latitude areas, together with a series of multiple magnetic storms from 1859 August 28 to September 4. In this study, we revisit contemporary auroral observation records to extract information on their elevation angle, color, and direction to investigate this stormy interval in detail. We first examine the equatorward boundary of the “auroral emission with multiple colors” based on descriptions of elevation angle and color. We find that their locations were 36.°5 ILAT on August 28/29 and 32.°7 ILAT on September 1/2, suggesting that trapped electrons moved to, at least, L ∼ 1.55 and L ∼ 1.41, respectively. The equatorward boundary of “purely red emission” was likely located at 30.°8 ILAT on September 1/2. If the “purely red emission” was a stable auroral red arc, it would suggest that trapped protons moved to, at least, L ∼ 1.36. This reconstruction with observed auroral emission regions provides conservative estimations of magnetic storm intensities. We compare the auroral records with magnetic observations. We confirm that multiple magnetic storms occurred during this stormy interval, and that the equatorward expansion of the auroral oval is consistent with the timing of magnetic disturbances. It is possible that the August 28/29 interplanetary coronal mass ejections (ICMEs) cleared out the interplanetary medium, making the ICME for the Carrington storm on September 1/2 more geoeffective.