Abstract
Abstract Using multipoint Magnetospheric Multiscale (MMS) observations in an unusual string-of-pearls configuration, we examine in detail observations of the reformation of a fast magnetosonic shock observed on the upstream edge of a foreshock transient structure upstream of Earth's bow shock. The four MMS spacecraft were separated by several hundred kilometers, comparable to suprathermal ion gyroradius scales or several ion inertial lengths. At least half of the shock reformation cycle was observed, with a new shock ramp rising up out of the “foot” region of the original shock ramp. Using the multipoint observations, we convert the observed time-series data into distance along the shock normal in the shock's rest frame. That conversion allows for a unique study of the relative spatial scales of the shock's various features, including the shock's growth rate, and how they evolve during the reformation cycle. Analysis indicates that the growth rate increases during reformation, electron-scale physics play an important role in the shock reformation, and energy conversion processes also undergo the same cyclical periodicity as reformation. Strong, thin electron-kinetic-scale current sheets and large-amplitude electrostatic and electromagnetic waves are reported. Results highlight the critical cross-scale coupling between electron-kinetic- and ion-kinetic-scale processes and details of the nature of nonstationarity, shock-front reformation at collisionless, fast magnetosonic shocks.
Highlights
Collisionless, fast magnetosonic shocks are ubiquitous features of space plasma throughout the universe (e.g., Kozarev et al 2011; Ghavamian et al 2013; Masters et al 2013; Cohen et al 2018)
During a ∼1 month period in 2019, the spacecraft were realigned into a “string-of-pearls” configuration, in which they were separated by up to several hundreds of kilometers along a common orbit to study turbulence in the solar wind at ion-kinetic scales. While in both the tetrahedron and string-of-pearls configurations, Magnetospheric Multiscale (MMS) are ideal for disambiguating spatiotemporal features in dynamic space plasmas. With this uncommon MMS configuration, we examined in detail a foreshock transient event reported in Turner et al (2020), which showcased an intriguing evolution of a fast magnetosonic shock
At 04:39 UT on 2019 January 30, MMS was fortuitously positioned to capture what was likely at least half of the reformation cycle of a fast magnetosonic shock on the upstream edge of a transient structure in the quasi-parallel foreshock upstream of Earths bow shock
Summary
Collisionless, fast magnetosonic shocks are ubiquitous features of space plasma throughout the universe (e.g., Kozarev et al 2011; Ghavamian et al 2013; Masters et al 2013; Cohen et al 2018). Are clearly significant considering the formation of ion-scale structures, such as the magnetic “foot” and “overshoot” on either side of the ramp of supercritical shocks (e.g., Gosling & Robson 1985), and ion-kinetic- and electron-kinetic-scale wave modes present around the shock ramp and in both the upstream and downstream regimes (e.g., Wilson et al 2007, 2012; Breuillard et al 2018; Chen et al 2018; Goodrich et al 2019) By their nature, collisionless shocks convert the energy necessary to slow and divert super-fast magnetosonic flows across a transition region that is much shorter than the collisional mean-free path of particles in the plasma. We examined fortuitous multipoint observations during a single cycle of shock reformation on the upstream edge of a foreshock transient using NASAs Magnetospheric Multiscale (MMS) mission upstream of Earths bow shock
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