Revisiting the structure of low‐Mach number, low‐beta, quasi‐perpendicular shocks

Abstract

A study of the structure of 145 low‐Mach number (M≤3), low‐beta (β≤1), quasi‐perpendicular interplanetary collisionless shock waves observed by the Wind spacecraft has provided strong evidence that these shocks have large‐amplitude whistler precursors. The common occurrence and large amplitudes of the precursors raise doubts about the standard assumption that such shocks can be classified as laminar structures. This directly contradicts standard models. In 113 of the 145 shocks (∼78%), we observe clear evidence of magnetosonic‐whistler precursor fluctuations with frequencies ∼0.1–7 Hz. We find no dependence on the upstream plasma beta, or any other shock parameter, for the presence or absence of precursors. The majority (∼66%) of the precursors propagate at ≤45° with respect to the upstream average magnetic field and most (∼87%) propagate ≥30° from the shock normal vector. Further, most (∼79%) of the waves propagate at least 20° from the coplanarity plane. The peak‐to‐peak wave amplitudes (δBpk‐pk) are large with a range of maximum values for the 113 precursors of ∼0.4–13 nT with an average of ∼2 nT. When we normalize the wave amplitudes to the upstream averaged magnetic field and the shock ramp amplitude, we find average values of ∼40% and ∼220%, respectively.

Kinetic Properties of an Interplanetary Shock Propagating inside a Coronal Mass Ejection

“…The values of θ kB , θ kn and θ kV of the waves examined here exhibit broad ranges, consistent with the theory of (Wu et al 1983) and prior observations (e.g., Wilson et al 2009Wilson et al , 2012Wilson et al , 2017Sundkvist et al 2012). The specific ranges of the angles are : 5.6 • < θ kB < 71.8 • , 31.7 • < θ kn < 74.0 • and 31.1 • < θ kV < 81.5 • .…”

“…The specific ranges of the angles are : 5.6 • < θ kB < 71.8 • , 31.7 • < θ kn < 74.0 • and 31.1 • < θ kV < 81.5 • . Compared with the observations of Wilson et al (2009Wilson et al ( , 2017, the whistler waves in this case are similar to the shocklet whistlers. Both of them have a broad range of θ kB and tend to be more oblique than the precursor whistler waves.…”

Statistical Study of the Properties of Magnetosheath Lion Roars

“…The individual LR intervals were then analyzed using a minimum variance analysis (MVA) with adaptive interval selection (e.g., see Wilson III et al, , for discussion). The software splits the original interval into smaller subintervals which maximize the intermediate to minimum ( λ int / λ min ) eigenvalue ratio and minimize the maximum to intermediate ( λ max / λ int ) ratio.…”

Rankine‐Hugoniot Relations in Multispecies Plasma With Gyrotropic Anisotropic Downstream Ion Distributions

“…The region to the right of x 3 is referred to as the downstream region. The profile is simplified since whistler waves can be present in the upstream region and superimposed on the ramp (Wilson et al, 2012;Wilson III et al, 2017). For ions the effect of the macroscopic profile strongly dominates (Gedalin, 2017;Ofman et al, 2009;Oka et al, 2005).…”