Comments on “New Insights From the 2003 Halloween Storm Into the Colaba 1600 nT Magnetic Depression During the 1859 Carrington Storm” by S. Ohtani (2022)

Abstract

AbstractThe Colaba, India ∼−1,600 nT magnetic spike caused by an interplanetary sheath magnetic field inducing a “dayside R1‐field aligned current wedge” during the Carrington magnetic storm proposed by Ohtani (2022), https://doi.org/10.1029/2022JA030596 seems highly improbable. Normal interplanetary magnetic field intensities of ∼5 nT have previously been shown to be sufficient to explain the ∼+120 nT sudden impulse (SI+) observed at Colaba during the storm (Tsurutani et al., 2018, https://doi.org/10.1002/2017JA024779). Magnetohydrodynamic theory (Kennel et al., 1985, https://doi.org/10.1029/GM034p0001) predicts a maximum of 4× magnetic field compression by a fast shock, giving an interplanetary sheath field of ∼20 nT, a value too low to support the Ohtani (2022), https://doi.org/10.1029/2022JA030596 hypothesis. The Ohtani (2022), https://doi.org/10.1029/2022JA030596 (and G. Siscoe et al., 2006, https://doi.org/10.1016/j.asr.2005.02.102) claim of a further 10× amplification of the interplanetary sheath fields has not been verified in near‐Earth interplanetary sheaths. The original (Tsurutani et al., 2003, https://doi.org/10.1029/2002JA009504) hypothesis that an interplanetary coronal mass ejection magnetic cloud (MC) having southward magnetic fields of ∼90 nT caused the Carrington magnetic storm main phase of peak SYM‐H/Dst = −1,760 nT seems more likely. The short time between the SI+ and the storm main phase onset implies a foreshortened interplanetary sheath. The extremely rapid recovery of the magnetic storm was hypothesized by Tsurutani et al. (2018), https://doi.org/10.1002/2017JA024779 as being due to nonlinear ring current losses. We point out that the Hydro‐Quebec 1989 storm was caused by multiple shock‐sheaths and MCs (Lakhina & Tsurutani, 2016, https://doi.org/10.1186/s40562‐016‐0037‐4) unlike the interplanetary causes of the Carrington storm. The Hydro‐Quebec event was a “stealth” magnetic storm.