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.

The reconnection front (RF), one of the most efficient accelerators of particles in the terrestrial magnetosphere, is a sharp plasma boundary resulting from transient magnetic reconnection. It has been both theoretically predicted and observationally confirmed that electron-scale substructures can develop at the RFs. How such electron-scale structures modulate the electron energization and transport has not been fully explored. Based on high-resolution data from MMS spacecraft and particle tracing simulations, we investigate and compare the electron acceleration across two typical RFs with or without rippled electron-scale structures. Both observations and simulations reveal that high-energy electron flux behind the RF increases more dramatically if the electrons encounter a rippled RF surface, as compared to a smooth RF surface. The main acceleration mechanism is electron surfing acceleration, in which electrons are trapped by the ripples, due to the large local magnetic field gradient, and therefore undergo surfing motion along the motional electric field.

Dipolarization front (DF), a transient structure that is associated with the earthward plasma flow, is widely considered as a result of magnetic reconnection. It is often characterized with a sharp increase in the northward magnetic field Bz preceded by a minor decrease of it. However, the small magnetic dip ahead of the DF is not always present, the reason of which is not well known. By analyzing in site Magnetospheric MultiScale spacecraft measurements at the magnetotail, we present two events of DF with and without a dip ahead of it. It is found that the magnetic dip ahead of DF is accompanied by a guide field By. To investigate the physical mechanism that determines the appearance of the dip, we perform kinetic simulations of symmetric single X line magnetic reconnection under various guide fields. The simulation results show that the dip is generated due to the separation of the gyro‐motion between ions and electrons under the influence of the guide field. Ions are reflected at the DF and further deviated by the guide field away from the neutral sheet, while more electrons remain in the neutral sheet due to their small gyroradius. In the absence of a compensating ion current, a dawnward current thus is formed, carried by the electrons, and generates the dip. Our results bring in a new perspective on the formation of the dip in single X line reconnection.