The location of Component Reconnection at the Earth’s Magnetopause During Dominant IMF By and Large Dipole Tilt Conditions

2020 ◽  
Author(s):  
Karlheinz Trattner ◽  
Stephen Fuselier ◽  
Steven Petrinec ◽  
James Burch ◽  
Paul Cassak ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Magnetic Energy ◽  
Magnetic Shear ◽  
The Earth ◽  
Laboratory Plasmas ◽  
Reconnection Region ◽  
Dayside Magnetopause ◽  
Field Lines ◽  
Dipole Tilt

<p>The interplanetary magnetic field (IMF) convected with the solar wind drapes around the region of space dominated by Earth’s geomagnetic field and undergoes a process called magnetic reconnection at the magnetopause; the boundary layer that separates these two distinct regimes. Magnetic reconnection changes the topology of magnetic field lines and is known to convert magnetic energy into kinetic energy and heat. This fundamental process occurs in many environments, spanning from laboratory plasmas to the heliosphere, the solar atmosphere, and to astrophysical phenomena. Magnetic reconnection at the Earth’s magnetopause has been observed at various times and places as either anti-parallel and/or component reconnection. A model known as the Maximum Magnetic Shear Model combines these two scenarios, creating long reconnection lines crossing the dayside magnetopause along a ridge of maximum magnetic shear. <br>The connection points between the anti-parallel and the component reconnection segments of the reconnection line are known as ‘Knee’ regions. Using observations from the MMS satellites, it was shown that the location of the Knee region depends strongly on the local draping conditions of the IMF across the magnetopause, with certain draping conditions causing a deflection of the location along the anti-parallel reconnection region. This study discusses an event that shows that the entire component reconnection X-line crossing the dayside magnetopause can be affected by this deflection. This result emphasizes the importance of anti-parallel reconnection that seems to control where component reconnection is occurring. </p>

scholarly journals Separatrices: The crux of reconnection

2014 ◽  
Vol 81 (1) ◽  
Author(s):  
Giovanni Lapenta ◽  
Stefano Markidis ◽  
Andrey Divin ◽  
David Newman ◽  
Martin Goldman
Keyword(s):  
Magnetic Field ◽  
Kinetic Energy ◽  
Magnetic Reconnection ◽  
Electromagnetic Fields ◽  
Plasma Flow ◽  
Magnetic Energy ◽  
Laboratory Plasmas ◽  
Field Lines ◽  
Kinetic Physics ◽  
Over Time

Magnetic reconnection is one of the key processes in astrophysical and laboratory plasmas: it is the opposite of a dynamo. Looking at energy, a dynamo transforms kinetic energy in magnetic energy while reconnection takes magnetic energy and returns it to its kinetic form. Most plasma processes at their core involve first storing magnetic energy accumulated over time and then releasing it suddenly. We focus here on this release. A key concept in analysing reconnection is that of the separatrix, a surface (line in 2D) that separates the fresh unperturbed plasma embedded in magnetic field lines not yet reconnected with the hotter exhaust embedded in reconnected field lines. In kinetic physics, the separatrices become a layer where many key processes develop. We present here new results relative to the processes at the separatrices that regulate the plasma flow, the energization of the species, the electromagnetic fields and the instabilities developing at the separatrices.

scholarly journals A case study of dayside reconnection under extremely low solar wind density conditions

2008 ◽  
Vol 26 (11) ◽  
pp. 3571-3583
Author(s):  
R. Maggiolo ◽  
J. A. Sauvaud ◽  
I. Dandouras ◽  
E. Luceck ◽  
H. Rème
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
High Speed ◽  
Radial Distance ◽  
Plasma Jets ◽  
Solar Wind Density ◽  
Ion Distribution ◽  
Dayside Magnetopause ◽  
Field Lines

Abstract. From 15 February 2004, 20:00 UT to 18 February 2004, 01:00 UT, the solar wind density dropped to extremely low values (about 0.35 cm−3). On 17 February, between 17:45 UT and 18:10 UT, the CLUSTER spacecraft cross the dayside magnetopause several times at a large radial distance of about 16 RE. During each of these crossings, the spacecraft detect high speed plasma jets in the dayside magnetopause and boundary layer. These observations are made during a period of southward and dawnward Interplanetary Magnetic Field (IMF). The magnetic shear across the local magnetopause is ~90° and the magnetosheath beta is very low (~0.15). We evidence the presence of a magnetic field of a few nT along the magnetopause normal. We also show that the plasma jets, accelerated up to 600 km/s, satisfy the tangential stress balance. These findings strongly suggest that the accelerated jets are due to magnetic reconnection between interplanetary and terrestrial magnetic field lines northward of the satellites. This is confirmed by the analysis of the ion distribution function that exhibits the presence of D shaped distributions and of a reflected ion population as predicted by theory. A quantitative analysis of the reflected ion population reveals that the reconnection process lasts about 30 min in a reconnection site located at a very large distance of several tens RE from the Cluster spacecraft. We also estimate the magnetopause motion and thickness during this event. This paper gives the first experimental study of magnetic reconnection during such rare periods of very low solar wind density. The results are discussed in the frame of magnetospheric response to extremely low solar wind density conditions.

scholarly journals Why fast magnetic reconnection is so prevalent

2018 ◽  
Vol 84 (1) ◽  
Author(s):  
Allen H. Boozer
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Reconnection ◽  
Large Scale ◽  
Magnetic Energy ◽  
Recognition Theory ◽  
Coordinate Model ◽  
Field Lines ◽  
Large Scale Flow ◽  
Analogous Effect

Evolving magnetic fields are shown to generically reach a state of fast magnetic reconnection in which magnetic field line connections change and magnetic energy is released at an Alfvénic rate. This occurs even in plasmas with zero resistivity; only the finiteness of the mass of the lightest charged particle, an electron, is required. The speed and prevalence of Alfvénic or fast magnetic reconnection imply that its cause must be contained within the ideal evolution equation for magnetic fields, $\unicode[STIX]{x2202}\boldsymbol{B}/\unicode[STIX]{x2202}t=\unicode[STIX]{x1D735}\times (\boldsymbol{u}\times \boldsymbol{B})$, where $\boldsymbol{u}(\boldsymbol{x},t)$ is the velocity of the magnetic field lines. For a generic $\boldsymbol{u}(\boldsymbol{x},t)$, neighbouring magnetic field lines develop a separation that increases exponentially, as $e^{\unicode[STIX]{x1D70E}(\ell ,t)}$ with $\ell$ the distance along a line. This exponentially enhances the sensitivity of the evolution to non-ideal effects. An analogous effect, the importance of stirring to produce a large-scale flow and enhance mixing, has been recognized by cooks through many millennia, but the importance of the large-scale flow $\boldsymbol{u}$ to reconnection is customarily ignored. In part this is due to the sixty-year focus of recognition theory on two-coordinate models, which eliminate the exponential enhancement that is generic with three coordinates. A simple three-coordinate model is developed, which could be used to address many unanswered questions.

Magnetohydrodynamic Reconnection

2020 ◽  
Author(s):  
D. I. Pontin
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Extreme Values ◽  
Magnetic Energy ◽  
Liquid Metals ◽  
Domain Boundary ◽  
Continuum Approximation ◽  
Magnetic Topology ◽  
Field Lines ◽  
The Universe

Magnetic reconnection is a fundamental process that is important for the dynamical evolution of highly conducting plasmas throughout the Universe. In such highly conducting plasmas the magnetic topology is preserved as the plasma evolves, an idea encapsulated by Alfvén’s frozen flux theorem. In this context, “magnetic topology” is defined by the connectivity and linkage of magnetic field lines (streamlines of the magnetic induction) within the domain of interest, together with the connectivity of field lines between points on the domain boundary. The conservation of magnetic topology therefore implies that magnetic field lines cannot break or merge, but evolve only according to smooth deformations. In any real plasma the conductivity is finite, so that the magnetic topology is not preserved everywhere: magnetic reconnection is the process by which the field lines break and recombine, permitting a reconfiguration of the magnetic field. Due to the high conductivity, reconnection may occur only in small dissipation regions where the electric current density reaches extreme values. In many applications of interest, the change of magnetic topology facilitates a rapid conversion of stored magnetic energy into plasma thermal energy, bulk-kinetic energy, and energy of non-thermally accelerated particles. This energy conversion is associated with dynamic phenomena in plasmas throughout the Universe. Examples include flares and other energetic phenomena in the atmosphere of stars including the Sun, substorms in planetary magnetospheres, and disruptions that limit the magnetic confinement time of plasma in nuclear fusion devices. One of the major challenges in understanding reconnection is the extreme separation between the global system scale and the scale of the dissipation region within which the reconnection process itself takes place. Current understanding of reconnection has developed through mathematical and computational modeling as well as dedicated experiments in both the laboratory and space. Magnetohydrodynamic (MHD) reconnection is studied in the framework of magnetohydrodynamics, which is used to study plasmas (and liquid metals) in the continuum approximation.

Energetic Electron Acceleration in Unconfined Reconnection Jets

2020 ◽  
Author(s):  
Guo Chen ◽  
Huishan Fu ◽  
Ying Zhang ◽  
Xiaocan Li ◽  
Yasong Ge ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Corona ◽  
Magnetic Reconnection ◽  
Energetic Electron ◽  
Electron Acceleration ◽  
The Earth ◽  
Field Lines

<p>Magnetic reconnection in astronomical objects such as solar corona and the Earth’s magnetotail theoretically produces a fast jet toward the object (known as a confined jet as it connects to the object through magnetic field lines) and a fast jet departing the object (known as an unconfined jet as it propagates freely in space). So far, energetic electron acceleration has been observed in the confined jet but never in the unconfined jet, arousing a controversy about whether or not reconnection jets can intrinsically accelerate electrons. Our study is focused on the electron acceleration in unconfined reconnection jet based on Cluster observations and VPIC simulations.</p>

Magnetic reconnection induced by the Kelvin-Helmholtz vortex at the Earth’s magnetopause during southward IMF

2020 ◽  
Author(s):  
Takuma Nakamura ◽  
Ferdinand Plaschke ◽  
Hiroshi Hasegawa ◽  
Yi-Hsin Liu ◽  
Kyoung-Joo Hwang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Shear Flow ◽  
Magnetic Reconnection ◽  
Linear Growth ◽  
Low Latitude ◽  
The Earth ◽  
Non Linear ◽  
The Difference ◽  
Field Lines ◽  
The Magnetic Field

<p>When the magnetic field is oriented nearly perpendicular to the direction of the plasma shear flow, the flow easily satisfies the super-Alfvénic unstable condition for the Kelvin-Helmholtz (KH) instability. This configuration is realized at the Earth’s low-latitude magnetopause when the interplanetary magnetic field (IMF) is strongly northward or southward. Indeed, clear signatures of the KH waves have been frequently observed during periods of the northward IMF. However, these signatures have been much less frequently observed during the southward IMF. In this work, we performed the first 3-D fully kinetic simulation of the KH instability at the magnetopause under the southward IMF condition. The simulation demonstrates that magnetic reconnection, with a typical fast rate on the order of 0.1, is induced at multiple locations along the vortex edge in an early non-linear growth phase of the KH instability. The reconnection outflow jet, which grows in the direction nearly perpendicular to the initial shear flow, significantly disrupt the flow of the non-linear KH vortex. On the other hand, the shear and vortex flow strongly bends and twists the reconnected field lines towards the direction out of the reconnection plane. The resulting coupling of the complex field and flow patterns within the magnetopause boundary layer leads to a quick decay of the vortex structure. These simulation results suggest that clear signatures of the KH waves are expected to be observed only for a limited phase during periods of the southward IMF, which may explain the difference in the observation probability of KH waves between northward and southward IMFs.</p>

Disturbance of the front region of magnetic reconnection outflow jets due to the lower-hybrid drift instability

2020 ◽  
Author(s):  
Takuma Nakamura ◽  
Takayuki Umeda ◽  
Rumi Nakamura ◽  
Huishan Fu ◽  
Mitsuo Oka
Keyword(s):  
Energy Dissipation ◽  
Magnetic Reconnection ◽  
Solar Flares ◽  
Magnetic Energy ◽  
Substantial Effect ◽  
Lower Hybrid ◽  
Dipolarization Front ◽  
The Earth ◽  
Reconnection Region ◽  
Drift Instability

<p>Magnetic reconnection is a key process in collisionless plasmas that converts magnetic energy to plasma kinetic energies through changes in the magnetic field topology. The energy conversion in this process is believed to cause various explosive phenomena in space such as auroral substorms in the Earth’s magnetosphere and solar flares. Here, a 3D fully kinetic simulation shows that the lower-hybrid drift instability (LHDI) disturbs the front of magnetic reconnection outflow jets and additionally causes the energy dissipation. The peak energy dissipation at the jet fronts is comparable to the values seen near the center of the reconnection region where the topology change during reconnection occurs, indicating that the LHDI turbulence has a substantial effect on the energetics of reconnection. The result is well consistent with a disturbance observed at the dipolarization front (DF) in the Earth’s magnetotail by the Magnetospheric Multiscale (MMS) mission. A fully kinetic dispersion relation solver, validated by the MMS observations, further predicts that the disturbance of the reconnection jet front could occur over different parameter regimes in space plasmas including the Earth’s DF and solar flares.</p>

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.

MAGNETIC FIELD AMPLIFICATION BY RELATIVISTIC SHOCKS IN AN INHOMOGENEOUS MEDIUM

2012 ◽  
Vol 08 ◽  
pp. 364-367
Author(s):  
YOSUKE MIZUNO ◽  
MARTIN POHL ◽  
JACEK NIEMIEC ◽  
BING ZHANG ◽  
KEN-ICHI NISHIKAWA ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Inhomogeneous Medium ◽  
Magnetic Energy ◽  
Small Scale ◽  
Two Dimensional ◽  
Filamentary Structure ◽  
Field Amplification ◽  
Relativistic Shocks ◽  
Field Lines ◽  
Magnetohydrodynamic Simulations

We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that the so-called small-scale dynamo is occurring in the postshock region. We also find that the amplitude of magnetic-field amplification depends on the direction of the mean preshock magnetic field.

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