Dissipation in magnetic reconnection with a guide magnetic field

2006 ◽  
Vol 13 (12) ◽  
pp. 122107 ◽  
Author(s):  
Michael Hesse
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Guide Magnetic Field

scholarly journals The Location of Magnetic Reconnection at Earth’s Magnetopause

2021 ◽  
Vol 217 (3) ◽  
Author(s):  
K. J. Trattner ◽  
S. M. Petrinec ◽  
S. A. Fuselier
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Ion Beams ◽  
Review Article ◽  
Observational Evidence ◽  
Magnetic Shear ◽  
General Direction ◽  
Shear Model ◽  
Wide Range

AbstractOne of the major questions about magnetic reconnection is how specific solar wind and interplanetary magnetic field conditions influence where reconnection occurs at the Earth’s magnetopause. There are two reconnection scenarios discussed in the literature: a) anti-parallel reconnection and b) component reconnection. Early spacecraft observations were limited to the detection of accelerated ion beams in the magnetopause boundary layer to determine the general direction of the reconnection X-line location with respect to the spacecraft. An improved view of the reconnection location at the magnetopause evolved from ionospheric emissions observed by polar-orbiting imagers. These observations and the observations of accelerated ion beams revealed that both scenarios occur at the magnetopause. Improved methodology using the time-of-flight effect of precipitating ions in the cusp regions and the cutoff velocity of the precipitating and mirroring ion populations was used to pinpoint magnetopause reconnection locations for a wide range of solar wind conditions. The results from these methodologies have been used to construct an empirical reconnection X-line model known as the Maximum Magnetic Shear model. Since this model’s inception, several tests have confirmed its validity and have resulted in modifications to the model for certain solar wind conditions. This review article summarizes the observational evidence for the location of magnetic reconnection at the Earth’s magnetopause, emphasizing the properties and efficacy of the Maximum Magnetic Shear Model.

scholarly journals Ion Dynamics in the Meso-scale 3-D Kelvin–Helmholtz Instability: Perspectives From Test Particle Simulations

2021 ◽  
Vol 8 ◽  
Author(s):  
Xuanye Ma ◽  
Peter Delamere ◽  
Katariina Nykyri ◽  
Brandon Burkholder ◽  
Stefan Eriksson ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Test Particle ◽  
Acoustic Waves ◽  
Particle Simulation ◽  
Three Dimensions ◽  
Small Scale ◽  
Physical Processes ◽  
Length Scales ◽  
Ion Species

Over three decades of in-situ observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath and magnetospheric plasma often occurs on the magnetopause of Earth and other planets under various interplanetary magnetic field (IMF) conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solar-wind-magnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kinetic-scale) physical processes, such as magnetic reconnection, kinetic Alfvén waves, ion-acoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability on the cross-scale process requires a numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, different simulation methods are required to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. Test particle simulation provides such a bridge to connect the MHD scale to the kinetic scale. This study applies different test particle approaches and cross validates the different results against one another to investigate the behavior of different ion species (i.e., H+ and O+), which include particle distributions, mixing and heating. It shows that the ion transport rate is about 1025 particles/s, and mixing diffusion coefficient is about 1010 m2 s−1 regardless of the ion species. Magnetic field lines change their topology via the magnetic reconnection process driven by the three-dimensional KH instability, connecting two flux tubes with different temperature, which eventually causes anisotropic temperature in the newly reconnected flux.

Formation of non-thermal electron velocity distribution functions in kinetic magnetic reconnection

2021 ◽  
Author(s):  
Xin Yao ◽  
Patricio A. Muñoz ◽  
Jörg Büchner
Keyword(s):  
Magnetic Field ◽  
Free Energy ◽  
Field Strength ◽  
Magnetic Reconnection ◽  
Electron Beams ◽  
Distribution Functions ◽  
Electron Velocity ◽  
Diffusion Region ◽  
Electron Velocity Distribution ◽  
Velocity Distribution Functions

<div> <div>Magnetic reconnection can convert magnetic energy into non-thermal particle energy in the form of electron beams. Those accelerated electrons can, in turn, cause radio emission in environments such as solar flares. The actual properties of those electron velocity distribution functions (EVDFs) generated by reconnection are still not well understood. In particular the properties that are relevant for the micro-instabilities responsible for radio emission. We aim thus at characterizing the electron distributions functions generated by 3D magnetic reconnection by means of fully kinetic particle-in-cell (PIC) code simulations. Our goal is to characterize the possible sources of free energy of the generated EVDFs in dependence on an external (guide) magnetic field strength. We find that: (1) electron beams with positive gradients in their parallel (to the local magnetic field direction) distribution functions are observed in both diffusion region (parallel crescent-shaped EVDFs) and separatrices (bump-on-tail EVDFs). These non-thermal EVDFs cause counterstreaming and bump-on-tail instabilities. These electrons are adiabatic and preferentially accelerated by a parallel electric field in regions where the magnetic moment is conserved. (2) electron beams with positive gradients in their perpendicular distribution functions are observed in regions with weak magnetic field strength near the current sheet midplane. The characteristic crescent-shaped EVDFs (in perpendicular velocity space) are observed in the diffusion region. These non-thermal EVDFs can cause electron cyclotron maser instabilities. These non-thermal electrons in perpendicular velocity space are mainly non-adiabatic. Their EVDFs are attributed to electrons experiencing an E×B drift and meandering motion. (3) As the guide field strength increases, the number of locations in the current sheet with distributions functions featuring a perpendicular source of free energy significantly decreases.</div> </div>

Hybrid-Vlasov modelling of three-dimensional dayside magnetopause reconnection

2021 ◽  
Author(s):  
Yann Pfau-Kempf ◽  
Minna Palmroth ◽  
Andreas Johlander ◽  
Lucile Turc ◽  
Markku Alho ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Three Dimensional ◽  
Meridional Plane ◽  
Kinetic Behavior ◽  
Dayside Magnetopause ◽  
Field Junction ◽  
First Time ◽  
Kinetic Instabilities ◽  
Magnetopause Reconnection

<p>Dayside magnetic reconnection at the magnetopause, which is a major driver of space weather, is studied for the first time in a three-dimensional (3D) realistic setup using the Vlasiator hybrid-Vlasov kinetic model. A noon–midnight meridional plane simulation is extended in the dawn–dusk direction to cover 7 Earth radii. The southward interplanetary magnetic field causes magnetic reconnection to occur at the subsolar magnetopause. Perturbations arising from kinetic instabilities in the magnetosheath appear to modulate the reconnection. Its characteristics are consistent with multiple, bursty, and patchy magnetopause reconnection. It is shown that the kinetic behavior of the plasma, as simulated by the model, has consequences on the applicability of methods such as the four-field junction to identify and analyse magnetic reconnection in 3D kinetic simulations.</p>

Micro-scale tearing mode turbulence in the diffusion region during macro-scale evolution of turbulent reconnection

2021 ◽  
Author(s):  
Takuma Nakamura ◽  
Hiroshi Hasegawa ◽  
Tai Phan ◽  
Kevin Genestreti ◽  
Richard Denton ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energy Conversion ◽  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Efficient Energy ◽  
Micro Scale ◽  
Island Evolution ◽  
Macro Scale ◽  
Scale Evolution

<p>Magnetic reconnection is a key fundamental process in collisionless plasmas that explosively converts magnetic energy to plasma kinetic and thermal energies through a change of magnetic field topology in an electron-scale central region called the electron diffusion region. Past simulations and observations demonstrated that this process causes efficient energy conversion through the formation of multiple macro-scale or micro-scale magnetic islands/flux ropes. However, how these different spatiotemporal scale phenomena are coupled is still poorly understood. In this study, to investigate the turbulent evolution of magnetic reconnection, we perform a new large-scale fully kinetic simulation of a thin current sheet considering a power-law spectrum of initial fluctuations in the magnetic field as frequently observed in the Earth’s magnetotail. The simulation demonstrates that during a macro-scale evolution of turbulent reconnection, the merging of macro-scale islands results in reduction of the rate of reconnection as well as the aspect ratio of the electron diffusion region. This allows the repeated, quick formation of new electron-scale islands within the electron diffusion region, leading to an efficient energy cascade between macro- and micro-scales. The simulation also demonstrates that a strong electron acceleration/heating occurs during the micro-scale island evolution within the EDR. These new findings indicate the importance of non-steady features of the EDR to comprehensively understand the energy conversion and cascade processes in collisionless reconnection.</p>

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