Magnetic reconnection is important to the dynamics of many astrophysical and fusion plasmas but our understanding of it is incomplete. Petaflop-scale simulations of the evolution of turbulent magnetic reconnection in a three-dimensional plasma indicate that it proceeds in a way that is dramatically different from classical theory.

/pdf/role-of-electron-physics-in-the-development-of-turbulent-4dvxxy5olc.pdf

Role of electron physics in the development of turbulent magnetic reconnection in collisionless plasmas

This paper considers the concept of magnetic reconnection from a general point of view, with special consideration given to magnetic reconnection in nonvanishing magnetic fields, i.e., finite-B reconnection as distinct from zero-B reconnection. It is shown that the electric field component parallel to the magnetic field (E-parallel) plays a crucial physical role in finite-B reconnection. Two theorems involving E-parallel are proposed. The first defines a necessary and sufficient condition of E-parallel for global reconnection to occur. The second theorem is concerned with the change of magnetic helicity to E-parallel for cases where the electric field vanishes at large distances. The general magnetic reconnection concept is tested by applying it to the process of plasmoid formation process.

General magnetic reconnection, parallel electric fields, and helicity

What are flux transfer events

A model of flux transfer events (FTEs) at the dayside magnetopause is proposed, which is based on non-stationary reconnection along a single X line over a large longitudinal segment. An individual field line coming from the magnetospheric side constitutes after reconnection a loop-like structure in the magnetopause current layer and leaves into the magnetosheath. In the presence of a By component of the magnetic field in the transition region of the magnetopause each loop is twisted in the y direction. Whereas traditionally FTEs are considered to be localized flux tubes with a helical field inside, in the present model field lines come from the magnetospheric side over a large longitudinal segment, have a loop-like structure in the magnetopause resulting in the FTE signatures, and leave over the same segment in longitude into interplanetary space.

/pdf/magnetic-flux-transfer-at-the-magnetopause-based-on-single-x-40za68oeqk.pdf

Magnetic flux transfer at the magnetopause based on single X line bursty reconnection

The author examines the motion of an isolated flux tube connecting the interplanetary and terrestrial magnetic field that has been created by reconnection at the dayside magnetopause. Such tubes should create a distinct localized flow pattern at their feet in the ionosphere. Observational effects are discussed. It is argued that the delay time of the order of a minute or more corresponding to the time for propagation of information from the reconnection site to the ionosphere is important and could control the creation of flux transfer events. It is predicted that magnetic pulsations in the Pc 5 frequency band are likely to be set up on closed flux tubes immediately neighboring the newly connected tubes.

The ionospheric signature of flux transfer events

It is suggested that the flux transfer events (FTE's) observed by ISEE satellites can be the result of multiple X-line reconnection at the dayside magnetopause, which may be caused by the development of a tearing instability. In the presence of the y-component of the magnetic field (By) in the transition region of the magnetopause, the tearing instability leads to the interconnection of the geomagnetic field lines and the interplanetary field lines, and hence to the occurrence of FTE's. Twisted field lines and field-aligned currents are formed as a consequence of the tearing instability. The flow direction of the field-aligned currents depends on By and the results are found to be consistent with satellite observations.

A theory of magnetic flux transfer at the Earth's magnetopause

The multiple X-line reconnection process, which was proposed by Lee and Fu [1985] for the dayside magnetopause, is simulated based on a two-dimensional incompressible MHD model. It is found that when the system length is much larger than the thickness of the current layer, magnetic flux tubes are repeatedly formed and convected out of the system. Impulsive magnetic reconnections associated with the formation of magnetic flux tubes are observed. In the case of the dayside magnetopause, magnetic flux tubes with a cross-section of ∼ 1 RE² are found to be formed repeatedly every 5-10 minutes, consistent with satellite observations.

Z. F. Fu

Papers

A theory of magnetic flux transfer at the Earth's magnetopause

Simulation of multiple X‐line reconnection at the dayside magnetopause