Mesoscale Structures in Earth's Magnetotail Observed Using Energetic Neutral Atom Imaging

Abstract

Mesoscale structures in Earth's magnetotail are a primary feature of particle transport to the inner magnetosphere during storms and substorms. We demonstrate that such structures can be observed in energetic neutral atom (ENA) data which can provide remote, global images of the magnetosphere. In particular, we present localized regions of increased ion temperatures that appear in equatorial ion temperature maps calculated from Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) ENA data. These regions are associated with a dipolarization front with bursty ion flows measured by Magnetospheric MultiScale (MMS) and are concurrent with substorm features observed in field aligned currents (FAC) from Active Magnetosphere and Planetary Electrodynamics Response Experiment measurements. We conduct a magnetohydrodynamics simulation of the same event and show simulated ion temperatures, ion flows, and FACs that agree with the measurements. However, the observed plasma heating is less intense in the simulated results than in the TWINS and MMS data, indicating that some heating processes may be missing from the model.

The Role of Mesoscale Plasma Sheet Dynamics in Ring Current Formation

“…Important questions remain regarding: the relative role of large-scale versus mesoscale convection; the statistical distribution of bubble lengthscales and the physical mechanisms that govern the size of bubbles; and the mechanisms of ion energization. Sparse spacecraft coverage of the transition region makes it difficult to spatially localize injections, although there has been progress using multi-mission conjunctions (Turner et al, 2017) and remote imaging (Keesee et al, 2021). Modeling multiscale transport in the transition requires: energydependent drifts, not included in global magnetohydrodynamic (MHD) models which approximate the bulk flow with the E × B drift; fast flows outside the quasi-static slow-flow approximation of typical ring current models (see e.g., Toffoletto, 2020, and references therein); global models that produce mesoscale magnetotail structures (Wiltberger et al, 2015;Cramer et al, 2017;Merkin et al, 2019), requiring high spatial resolution and low dissipation algorithms; a representation of wave-particle interactions that contribute to ion heating (e.g., Chaston et al, 2014;Cheng et al, 2020); and finite gyroradius effects, as H+ in the transition region is known to be quasi-adiabatic (Runov et al, 2017), while heavier ion species like O+, likely exhibit highly nonadiabatic behavior (e.g., Moebius et al, 1987;Delcourt et al, 1997;Nosé et al, 2000;Keika et al, 2013;Bingham et al, 2020).…”

RAS Specialist Discussion Meeting report

“…Amy Keesee (University of New Hampshire) described how energetic neutral atom imaging can provide a global view of the magnetosphere, providing information about the connection from the magnetotail to the inner magnetosphere. In a study of a storm-time substorm interval, the observed plasma heating is less intense in the simulated results than in the TWINS and MMS data, indicating that some heating processes may be missing from the model (Keesee et al, 2021). An automated detection algorithm currently being validated will help with identifying more interesting events for case studies as well as conducting statistical analyses of the regions of enhanced ion temperatures.…”

Explicit IMF By‐Dependence of Energetic Protons and the Ring Current

“…The total number of grid points is ∼8 × 10 6 . It is acknowledged that magnetic field reconnection in ideal MHD model is defined by numerical resistivity, however multiple studies of substorms with different MHD codes (Birn & Hesse, 2013;Fedder et al, 1995;Gordeev et al, 2017;Keesee et al, 2021;Merkin et al, 2019;Raeder et al, 2010) confirm that this approach works reasonably well for the Earth's magnetosphere (although with some caveats). Global MHD model provides a reasonable solution for 3D structure of currents, magnetic field and plasma parameters (bulk velocity, pressure and density).…”