Comment on “Non-interacting coronal mass ejections and solar energetic particles near the quadrature configuration of solar terrestrial relations observatory”: CME shocks are fast magnetosonic shocks and not intermediate Alfvén shocks

¹ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
e-mail: bruce.tsurutani@gmail.com
² Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, PR China
³ Indian Institute of Geomagnetism, Navi Mumbai, India
⁴ Institut de Recherche en Astrophysique et Planétologie, University Paul Sabatier, CNRS, CNES, Toulouse, France

Received: 9 April 2021
Accepted: 24 September 2021

Abstract

Aims. The expression for the shock Mach number used by Ravishankar and Michalek (2020, A&A, 638, A42) is incorrect. We wish to provide a correct expression so they can redo their analyses.

Methods. Coronal mass ejection (CME) shocks are fast magnetosonic shocks and not intermediate Alfvén shocks. We give the steps for calculating the shock normal, shock velocity, and, thus, the shock Mach number. We also mention that the shock properties, such as being quasi-perpendicular or quasi-parallel, are another important parameter for the shock acceleration of energetic particles.

Results. We have corrected the errors existing in the Astronomy and Astrophysics literature concerning the mathematical expression for the Mach number for a CME shock. Hopefully, future authors will use the now-correct expression for the Mach number.

Conclusions. The correct shock Mach number expression has been given to Ravishankar and Michalek. It is hoped that they will redo their calculations (including using other shock properties) to see if their 2020 conclusions still hold true or not.