Kinetic Alfvén Waves Excited in Two‐Dimensional Magnetic Reconnection

Abstract

Kinetic Alfvén waves (KAWs) are believed to be capable of efficiently transporting energy and play an important role in facilitating magnetic reconnection. KAW eigenmode theory suggests that Hall fields can be considered as the components of KAW, providing a mechanism for the generation and dissipation of KAW in magnetic reconnection. Using particle‐in‐cell simulations, we examined Hall fields in the magnetic reconnection region and found that (1) Hall electric filed is balanced by the ion pressure gradient and (2) the ratio of Hall electric field to Hall magnetic field is on the order of Alfvén speed. These results are consistent with KAW physics. Simulation results also indicate that KAWs are excited in the reconnection site and then transmitted along the separatrices. The wave Poynting flux propagates parallel to the magnetic field lines, carrying substantial energy. It is further found that a thinner current sheet provides a favorable condition for the excitation of KAW and results in a higher ratio of the Hall 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, , ; 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).…”

“…In the same format of (a)-(g), panels (h)-(n) show the wave properties in event 2. Dai et al, 2017), particle-in-cell simulations (Huang et al, 2018), and in situ observations (Duan et al, 2016(Duan et al, , 2017Zhang et al, 2017). Around 21:57 UT, the ion flow (200-300 km/s) is much less than the Alfven speed (740 km/s).…”

Structures of Hall Fields in Asymmetric Magnetic Reconnection

“…Many predictions of the KAW solution have been confirmed in observations, including the quadrupolar structure of Hall fields in symmetric reconnection, the balance of the Hall electric field with the ion pressure gradient (Burch, Torbert, et al, ; Dai et al, ; Zhang et al, ), the ratio of Hall electric fields to Hall magnetic fields on the order of Alfvén speed (e.g, Dai et al, ), and the formation of the field‐aligned current in the Hall current system (Duan et al, , ; Nakamura et al, ). In particle‐in‐cell (PIC) simulations, the KAW properties of the Hall fields in reconnection has been quantitatively verified (Huang et al, ). The Hall fields can propagate out as KAW from the reconnection site (Duan et al, ; Liang et al, ; Shay et al, ).…”

Collisionless Magnetic Reconnection and Waves: Progress Review

“…There are several mechanisms proposed for the generation of KAWs. One is the diffusion region itself where the setup of the Hall structure of the diffusion region directly corresponds to KAWs propagating away from the diffusion region along the separatrix regions (Shay et al, 2011;Zhang et al, 2017;Huang et al, 2018). Other mechanisms that have been suggested are the firehose instability leading to the generation of KAWs (Jiansen et al, 2018;Wang et al, 2018), KAW generation due to intermittent reconnection (Cao et al, 2013), KAWs being part of the turbulence generated in reconnection outflows (Huang et al, 2012).…”

“…FIGURE 11 | Kinetic Alfvén wave observations in the separatrix region using 2D PIC simulations (Huang et al, 2018). (Left) Hall electric field corresponding to KAW generated in reconnection diffusion region.…”