Revisiting the Superstorm on 6–7 April 2000 Caused by an Extraordinary Corotating Interaction Region (With an Embedded Coronal Jet?)

The 6–7 April 2000 superstorm of SYM-H intensity = −319 nT discussed in Meng et al. (2019; https://doi.org/10.1029/2018JA026425) was misidentified as being due to an interplanetary coronal mass ejection associated with a solar flare. The interplanetary cause was a highly unusual corotating interaction region (CIR) bounded by a strong fast forward shock (FS) with magnetosonic Mach number M_ms = 4.6 and a fast reverse shock (RS) with M_ms = 1.9. The exceptionally strong FS caused a ∼3-factor interplanetary magnetic field (IMF) magnitude amplification in the leading half of the CIR with peak southward IMF B_z = −27 nT causing the superstorm. A plasma region between a tangential discontinuity and the stream interface had a scale size of ∼0.096 AU. We hypothesize that this is the first detection of a coronal jet at 1 AU. The jet/Gold magnetic tongue (1959; https://doi.org/10.1029/JZ064i011p01665) was embedded within the CIR, contained the southward B_z and caused the magnetic storm. We hypothesize that a shrinking coronal hole and magnetic reconnection caused the formation and release of the jet.