Structures of Hall Fields in Asymmetric Magnetic Reconnection

Abstract

Unlike a quadrupolar Hall magnetic field in symmetric magnetic reconnection, a bipolar or quadrupolar Hall magnetic field occurs in asymmetric reconnection as indicated by recent observations from the Magnetospheric Multiscale (MMS) mission. Here we present analytic calculations of the structures of Hall magnetic fields in asymmetric reconnection. The Hall magnetic fields are analyzed in terms of kinetic Alfvén wave eigenmodes of the reconnection layer. The bipolar and quadrupolar patterns of Hall magnetic fields correspond to a dominance of the n = 0 and n = 1 kinetic Alfvén wave eigenmode, respectively. The asymmetry of Hall fields is linked to the asymmetry of the Alfvé speed profile. The Hall magnetic fields are shifted toward and enhanced on the low Alfvén speed side of the reconnection layer. The asymmetry in the magnetic field strength of the reconnection layer has a major effect on the structures of Hall magnetic fields.

Whistler Waves Driven by Field‐Aligned Streaming Electrons in the Near‐Earth Magnetotail Reconnection

“…In general, the spatial scale of the Hall fields is about the current layer thickness (the ion scale) in the normal direction. The spatial scale and the ratio E Hall ∕B hall of the Hall fields is consistent with a Kinetic Alfven wave nature as shown in theoretical results (Dai, 2018(Dai, , 2009; Properties of whistler waves in events 1 and 2. The left panels, (a)-(g), show for event 1, (a) the filtered three magnetic field components in the FAC system; (b) the filtered three electric field components; (c) the wave Poynting flux from the filtered electric field and magnetic field components; (d) the wave normal angle at selected frequencies, (e) the degree of polarization of the wave, (f) the spectra of the wave normal angle with respect to B; and (g) the ellipticity of the waves.…”

“…In general, the spatial scale of the Hall fields is about the current layer thickness (the ion scale) in the normal direction. The spatial scale and the ratio E Hall / B hall of the Hall fields is consistent with a Kinetic Alfven wave nature as shown in theoretical results (Dai, , ; Dai et al, ), particle‐in‐cell simulations (Huang et al, ), and in situ observations (Duan et al, , ; Zhang et al, ). Around 21:57 UT, the ion flow (200–300 km/s) is much less than the Alfven speed (740 km/s).…”

Sub‐ion‐scale Dynamics of the Ion Diffusion Region in the Magnetotail: MMS Observations

“…Since 2015, magnetospheric multiscale (MMS) has provided high-resolution measurements of the IDR at the dayside magnetopause (e.g., Graham et al, 2016;Phan et al, 2016;Wang et al, 2016;Zhou et al, 2016). These IDRs were associated with asymmetric reconnection, in which the Hall electromagnetic fields are asymmetric with respect to the reconnecting magnetopause current sheet (Tanaka et al, 2008;Mozer et al, 2008;Dai, 2018). Zhou et al (2016) studied high-frequency plasma waves and inferred the wave-particle interactions based on the high-resolution electron velocity distributions.…”

Collisionless Magnetic Reconnection and Waves: Progress Review

“…KAWs are known to be important in forming of the diffusion region (Rogers et al, 2001;Dai, 2009Dai, , 2018, in transporting energy away from the reconnection site (Shay et al, 2011;Liang et al, 2016), setting up field aligned currents and eventually also interacting with the ionosphere (Duan et al, 2016). There is no well defined way to identify KAWs in data.…”