Influence of the rippling on the collisionless ion and electron motion in the shock front: A model study

Abstract

Abstract. Recent two-dimensional hybrid simulations show that the shock is inhomogeneous along the shock front (tippled). Observations also provide some evidence of spatial inhomogeneity, not necessarily related to nonstationary features (waves). Recent analysis of an observed high Mach number shock has shown that its observed features are inconsistent with the assumption that it is one-dimensional and stationary, although direct comparison of the two spacecraft measurements indicates good stationarity of its profile. We study the effects of the shock rippling alone on the collisionless motion of ions and electrons in a shock front on a simple model shock profile. We show that rippling may substantially affect ion motion, especially when the shock is tippled in the direction perpendicular to the main magnetic field. As a result, the downstream ion distribution becomes much more smooth and diffuse, which reduces the variations of the downstream ion pressure and may improve the shock stability. The smoothing is prompt and occurs at spatial scales substantially smaller than those required for the wave-particle interaction to be significant. The required rippling scale is between the ion inertial length and upstream ion convective gyroradius, thus being significantly larger than the ramp width or spatial scale of the small-scale structure. Electrons are much more sensitive to the rippling in the direction of the main magnetic field, which may help to partially fill the gap in the electron distribution which forms collisionlessly in the ramp.

Rippled quasi‐perpendicular collisionless shocks: Local and global normals

“…It is worth noting that the deviations are in both directions: parts of the shock surface have locally perpendicular geometry, θ n B ≈90°, while other parts are more oblique, θ n B ≈50°, than would be in a planar shock. Such coexistence of substantially oblique and nearly perpendicular pieces of the shock front may have significant implications for ion and electron motion [ Gedalin , ; Yang et al , ].…”

“…than would be in a planar shock. Such coexistence of substantially oblique and nearly perpendicular pieces of the shock front may have significant implications for ion and electron motion [Gedalin, 2001;Yang et al, 2012].…”

Magnetic holes in the vicinity of dipolarization fronts: Mirror or tearing structures?

“…These authors developed a Quasi‐Hydrodynamic (QH) model that combined both the illustrative advantage of hydrodynamics and was also able to account for many kinetic effects Southwood and Kivelson [1993]. was followed by a series of theoretical papers that treated the mirror instability in frame of QH, leading to significant advances and allowing the linear theory of mirror waves to account for finite electron temperature [ Pokhotelov et al , 2000], non‐maxwellian plasma [ Pokhotelov et al , 2002; Gedalin , 2001], multicomponent plasma [ Gedalin et al , 2002], and other effects [ Pokhotelov et al , 2001]. However, only long‐wavelength mirror waves can be treated using the QH approach.…”

First Observations of Irregular Surface of Interplanetary Shocks at Ion Scales by Cluster

“…Shock ripples and their importance for particle acceleration and for formation of downstream phenomena have been the subject of several works [i.e., Gedalin, 2001, Hao et al, 2016, Hietala et al, 2009, Yang et al, 2011, 2018. Rippling was observed at the Earth's bow-shock by several authors by using multi-spacecraft data from Cluster [Horbury et al, 2002, 2001, Lobzin et al, 2008, Moullard et al, 2006 and Magnetospheric Multiscale (MMS) mission [Gingell et al, 2017, Johlander et al, 2016.…”