Abstract

Glancing blows of three interplanetary shocks caused an unexpectedly large magnetic storm on November 4-6, 2023, which was popular for citizen scientists because of the surprising appearance of the crimson-red auroras world-wide in middle latitudes. Based on the analysis of the in-situ interplanetary magnetic field data at DSCOVR and STEREO-A, we show that the multi-step main phase of the magnetic storm is explained by the shock pileup, i.e. slow interplanetary shock was caught up from behind by the fast one, and the multi-step prolonged recovery phase by the remnant structure associated with the shock pileup.