Variation of the Interplanetary Shocks in the Inner Heliosphere

• Published in: The Astrophysical journal 2021-08, Vol.917 (2), p.91
• Main Author: Hajra, Rajkumar
• Format: Article
• Language: English
• Subjects: Astrophysics; Coronal mass ejection; Corotating Interaction Regions (CIR); Corotating streams; Heliosphere; Interplanetary magnetic field; Interplanetary magnetic fields; Interplanetary shocks; Mach number; Magnetic fields; Solar coronal mass ejections; Solar magnetic field; Solar wind; Spacecraft
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac0897

Observations of the solar wind plasma and interplanetary magnetic field in the ecliptic plane by the Voyager 1 and 2 spacecraft are utilized to study the variation of the interplanetary shocks (with magnetosonic Mach number >1) encountered in the inner heliosphere, between ∼1 and ∼15 au from the Sun. The overwhelming majority (∼76%) of the shocks are fast forward (FF) moving at an average shock speed ( V sh ) of ∼458 km s −1 away from the Sun, and only ∼24% are fast reverse (FR) shocks with an average V sh of ∼323 km s −1 toward the Sun. About ∼89% of the shocks are quasi-perpendicular with an average shock angle ( θ Bn ) of ∼72° relative to the ambient magnetic field, and only ∼11% are quasi-parallel with an average θ Bn of ∼32°. While the interplanetary coronal mass ejections are the major (∼89%) driver of the FF shocks, a significant part (∼41%) of the FR shocks are associated with the corotating interaction regions. The shock occurrence rate, with a peak at the heliocentric distance ( R h ) of ∼5 au, exhibits a clear decrease with the increasing R h . While the shock strength and propagation angle do not exhibit any systematic change with R h , V sh increases with the increasing R h at a rate of ∼11 km s −1 au −1 .