The Plasma Sheet as Natural Symmetry Plane for Dipolarization Fronts in the Earth's Magnetotail

Abstract

In this work, observations of multispacecraft mission Time History of Events and Macroscale Interactions during Substorms are used for statistical investigation of dipolarization fronts in the near‐Earth plasma sheet of the magnetotail. Using very stringent criteria, 460 events are detected in almost 10 years of mission data. Minimum variance analysis is used to determine the normal directions of the phase fronts, providing evidence for the existence of a natural symmetry of these phenomena, given by the neutral sheet of the magnetotail. This finding enables the definition of a local coordinate system based on the Tsyganenko model, reflecting the intrinsic orientation of the neutral sheet and, therefore, the dipolarization fronts. In this way, the comparison of events with very different background conditions is improved. Through this study, the statistical results of Liu, Angelopoulos, Runov, et al. (2013) are both confirmed and extended. In a case study, the knowledge of this plane of symmetry helps to explain the concave curvature of dipolarization fronts in the XZ plane through phase propagation speeds of magnetoacoustic waves. A second case study is presented to determine the central current system of a passing dipolarization front through a constellation of three spacecraft. With this information, a statistical analysis of spacecraft observations above and below the neutral sheet is used to provide further evidence for the neutral sheet as the symmetry plane and the central current system. Furthermore, it is shown that the signatures of dipolarization fronts are under certain conditions closely related to that of flux ropes, indicating a possible relationship between these two transient phenomena.

Using Multiple Signatures to Improve Accuracy of Substorm Identification

“…While the plasmoid propagates tailward, the magnetic fields Earthward of the X‐line undergo a dipolarization. Previous studies have identified dipolarizations by searching for sharp increases in B z (e.g., Birn et al, ; Frühauff & Glassmeier, ; Lee & Lyons, ; Liu et al, ; Runov et al, , ) or elevation angle …”

Study of earth’s changing polarity using compound difference synchronization

“…This is done by either studying the rock magnetization i.e. laboratory study of rock samples or by spacecraft missions revolving around the earth and airborne and marine mission (Parkhomenko et al 2019;Fruhauff and Glassmeier 2017;Lui 2014).Major drawbacks in these directions are that where rock samples give idea only of the visible magnetic field strength the contribution from the hidden part is generally ignored; the satellite study is unable to consider the direction and the strength of the magnetization from magnetic field measurements (Vervelidou and Lesur 2018;Ferre et al 2014). Therefore studying the problem by numerically modeling the earth's magnetic field would bring new dimension in the understanding of the changing strength and polarity.…”

Using multiple signatures to improve accuracy of substorm identification

“…While the plasmoid propagates tailward, the magnetic fields Earthward of the X-line undergo a dipolarization. Previous studies have identified dipolarizations by searching for sharp increases in B z (e.g., Birn et al, 2011;Frühauff & Glassmeier, 2017;Lee & Lyons, 2004;Liu et al, 2013;Runov et al, 2009Runov et al, , 2012 or elevation angle…”