Interplanetary circumstances of quasi-perpendicular interplanetary shocks in 1996-2005

• Published in: Journal of Geophysical Research. A. Space Physics 2010-07, Vol.115 (A7), p.n/a
• Main Authors: Richardson, I. G., Cane, H. V.
• Format: Article
• Language: English
• Subjects: Astrophysics; Configurations; Coronal mass ejection; Corotating Interaction Regions (CIR); Earth sciences; Earth, ocean, space; Exact sciences and technology; High speed; interplanetary magnetic fields; Interplanetary shocks; Magnetic fields; Magnetic properties; Particle acceleration; Planetology; Sheaths; shock-accelerated particles; Solar corona; Solar wind; Space; Streams; Upstream
• ISSN: 0148-0227; 2169-9380; 2156-2202; 2169-9402
• DOI: 10.1029/2009JA015039

The angle (θBn) between the normal to an interplanetary shock front and the upstream magnetic field direction, though often thought of as a property “of the shock,” is also determined by the configuration of the magnetic field immediately upstream of the shock. We investigate the interplanetary circumstances of 105 near‐Earth quasi‐perpendicular shocks during 1996–2005 identified by θBn ≥ 80° and/or by evidence of shock drift particle acceleration. Around 87% of these shocks were driven by interplanetary coronal mass ejections (ICMEs); the remainder were probably the forward shocks of corotating interaction regions. For around half of the shocks, the upstream field was approximately perpendicular to the radial direction, either east‐west or west‐east or highly inclined to the ecliptic. Such field directions will give quasi‐perpendicular configurations for radially propagating shocks. Around 30% of the shocks were propagating through, or closely followed, ICMEs at the time of observation. Another quarter were propagating through the heliospheric plasma sheet (HPS), and a further quarter occurred in slow solar wind that did not have characteristics of the HPS. Around 11% were observed in high‐speed streams, and 7% in the sheaths following other shocks. The fraction of shocks found in high‐speed streams is around a third of that expected based on the fraction of the time when such streams were observed at Earth. Quasi‐perpendicular shocks are found traveling through ICMEs around 2–3 times more frequently than expected. In addition, shocks propagating through ICMEs are more likely to have larger values of θBn than shocks outside ICMEs.