Thin current sheets of sub-ion scales observed in planetary magnetotails

2021 ◽  
Author(s):  
Elena Grigorenko ◽  
Makar Leonenko ◽  
Lev Zelenyi ◽  
Helmi Malova ◽  
Victor Popov
Keyword(s):  
Magnetic Field ◽  
Larmor Radius ◽  
High Time Resolution ◽  
Current Layer ◽  
Ion Composition ◽  
Kinetic Description ◽  
Small Component ◽  
Current Sheets ◽  
The Earth ◽  
Plasma Characteristics

<p>Current sheets (CSs) play a crucial role in the storage and conversion of magnetic energy in planetary magnetotails. Spacecraft observations in the terrestrial magnetotail reported that the CS thinning and intensification can result in formation of multiscale current structure in which a very thin and intense current layer at the center of the CS is embedded into a thicker sheet. To describe such CSs fully kinetic description taking into account all peculiarities of non-adiabatic particle dynamics is required. Kinetic description brings kinetic scales to the CS models. Ion scales are controlled by thermal ion Larmor radius, while scales of sub-ion embedded CS are controlled by the topology of magnetic field lines until the electron motion is magnetized by a small component of the magnetic field existing in a very center of the CS. MMS observations in the Earth magnetotail as well as MAVEN observations in the Martian magnetotail with high time resolution revealed the formation of similar multiscale structure of the cross-tail CS in spite of very different local plasma characteristics. We revealed that the typical half‐thickness of the embedded Super Thin Current Sheet (STCSs) observed at the center of the CS in the magnetotails of both planets is much less than the gyroradius of thermal protons. The formation of STCS does not depend on ion composition, density and temperature,  but it is controlled by the small value of the normal component of the magnetic field at the neutral plane. Our analysis showed that there is a good agreement between the spatial scaling of multiscale CSs observed in both magnetotails and the scaling predicted by the quasi-adiabatic model of thin anisotropic CS taking into account the coupling between ion and electron currents. Thus, in spite of the significant differences in the CS formation, ion composition, and plasma characteristics in the Earth’s and Martian magnetotails, similar kinetic features are observed in the CS structures in the magnetotails of both planets. This phenomenon can be explained by the universal principles of nature. The CS once has been formed, then it should be self-consistently supported by the internal coupling of the total current carried by particles in the CS and its magnetic configuration, and as soon as the system achieved the quasi-equilibrium state, it “forgets” the mechanisms of its formation, and its following existence is ruled by the general principles of plasma kinetic described by Vlasov–Maxwell equations.</p><p>This work is supported by the Russian Science Foundation grant № 20-42-04418</p>

scholarly journals Diffusion at the Earth magnetopause: enhancement by Kelvin-Helmholtz instability

2007 ◽  
Vol 25 (1) ◽  
pp. 271-282 ◽  
Author(s):  
R. Smets ◽  
G. Belmont ◽  
D. Delcourt ◽  
L. Rezeau
Keyword(s):  
Magnetic Field ◽  
Distribution Functions ◽  
Larmor Radius ◽  
Simple Analytical Model ◽  
Helmholtz Instability ◽  
Field Reversal ◽  
Finite Larmor Radius ◽  
The Earth ◽  
Specific Distribution ◽  
The Magnetic Field

Abstract. Using hybrid simulations, we examine how particles can diffuse across the Earth's magnetopause because of finite Larmor radius effects. We focus on tangential discontinuities and consider a reversal of the magnetic field that closely models the magnetopause under southward interplanetary magnetic field. When the Larmor radius is on the order of the field reversal thickness, we show that particles can cross the discontinuity. We also show that with a realistic initial shear flow, a Kelvin-Helmholtz instability develops that increases the efficiency of the crossing process. We investigate the distribution functions of the transmitted ions and demonstrate that they are structured according to a D-shape. It accordingly appears that magnetic reconnection at the magnetopause is not the only process that leads to such specific distribution functions. A simple analytical model that describes the built-up of these functions is proposed.

The effect of plasmaspheric material on magnetopause reconnection

2020 ◽  
Author(s):  
Stephen Fuselier ◽  
Stein Haaland ◽  
Paul Tenfjord ◽  
David Malaspina ◽  
James Burch ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Low Temperature ◽  
Magnetic Reconnection ◽  
Plasma Wave ◽  
Outer Part ◽  
Field Measurements ◽  
Ion Composition ◽  
The Earth ◽  
Magnetospheric Multiscale ◽  
Magnetic Field Measurements

<p>The Earth’s plasmasphere contains cold (~eV energy) dense (>100 cm<sup>-3</sup>) plasma of ionospheric origin. The primary ion constituents of the plasmasphere are H<sup>+ </sup>and He<sup>+</sup>, and a lower concentration of O<sup>+</sup>. The outer part of the plasmasphere, especially on the duskside of the Earth, drains away into the dayside outer magnetosphere when geomagnetic activity increases. Because of its high density and low temperature, this plasma has the potential to modify magnetic reconnection at the magnetopause. To investigate the effect of plasmaspheric material at the magnetopause, Magnetospheric Multiscale (MMS) data are surveyed to identify magnetopause crossings with the highest He<sup>+</sup>densities. Plasma wave, ion, and ion composition data are used to determine densities and mass densities of this plasmaspheric material and the magnetosheath plasma adjacent to the magnetopause. These measurements are combined with magnetic field measurements to determine how the highest density plasmaspheric material in the MMS era may affect reconnection at the magnetopause.</p>

scholarly journals Collisionless reconnection: mechanism of self-ignition in thin plane homogeneous current sheets

2010 ◽  
Vol 28 (10) ◽  
pp. 1935-1943 ◽  
Author(s):  
R. A. Treumann ◽  
R. Nakamura ◽  
W. Baumjohann
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Current Layer ◽  
Current Sheets ◽  
Thermal Anisotropy ◽  
Collisionless Reconnection ◽  
Magnetic Electron ◽  
Spontaneous Onset

Abstract. The spontaneous onset of magnetic reconnection in thin plane collisionless current sheets is shown to result from a thermal-anisotropy driven non-relativistic magnetic electron Weibel-mode, generating seed-magnetic field X-points in the centre of the current layer. The proposed mechanism is of larger generality. It also works in the presence of magnetic guide fields.

Current Sheets in the Earth Magnetotail: Plasma and Magnetic Field Structure with Cluster Project Observations

2015 ◽  
Vol 188 (1-4) ◽  
pp. 311-337 ◽  
Author(s):  
Anatoli Petrukovich ◽  
Anton Artemyev ◽  
Ivan Vasko ◽  
Rumi Nakamura ◽  
Lev Zelenyi
Keyword(s):  
Magnetic Field ◽  
Field Structure ◽  
Magnetic Field Structure ◽  
Current Sheets ◽  
The Earth

scholarly journals Cluster observes the Earth’s magnetopause: coordinated four-point magnetic field measurements

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1449-1460 ◽  
Author(s):  
M. W. Dunlop ◽  
A. Balogh ◽  
P. Cargill ◽  
R. C. Elphic ◽  
K.-H. Fornaçon ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Field Measurements ◽  
Interplanetary Shock ◽  
Minimum Variance ◽  
Magnetic Activity ◽  
High Time Resolution ◽  
Current Layer ◽  
Data Set ◽  
The Magnetic Field

Abstract. The four-spacecraft Cluster mission has provided high-time resolution measurements of the magnetic field from closely maintained separation distances (200–600 km). Four-point coverage of the Earth’s magnetopause began on the 9 and 10 November 2000 when all spacecraft first exited the dusk-side magnetosphere at about 19:00 LT, providing extensive coverage of the near flank magnetosheath and magnetopause boundary layer on re-entry to the magnetosphere. The traversals on this occasion were caused by the arrival of an intense CME at the Earth, which produced a large compression of the magnetopause and high magnetic activity. The magnetopause traversals represent an unprecedented data set, allowing detailed analysis of the local magnetic structure (gradients) and dynamics of the magnetopause boundary. By performing minimum variance analysis (MVA) on the magnetic field data from all four spacecraft, we demonstrate that the magnetopause was planar on the scale of the spacecraft separation scales and that the transverse scale size of the magnetopause boundary layer was 1000–1100 km. We also show that the motion of the boundary (defined by the magnetic shear at the current layer), is changing over the sequence of spacecraft crossings so that acceleration of the magnetopause can be very high in this region of the magnetosphere. Indeed, the magnetopause speed reaches the order of 300 km/s in response to the arrival of the interplanetary shock. Using MVA coordinates, we have identified a number of magnetospheric and magnetosheath FTE signatures, which are sampled simultaneously by all spacecraft at different distances from and on either side of the magnetopause. The signatures show a variation of scale with distance from the boundary.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers) Space plasma physics (discontinuities; magnetic reconnection)

Analysis of electromagnetic instabilities parallel to the magnetic field

1971 ◽  
Vol 6 (1) ◽  
pp. 1-17 ◽  
Author(s):  
W. Pilipp ◽  
H. J. Völk
Keyword(s):  
Magnetic Field ◽  
Cyclotron Frequency ◽  
Larmor Radius ◽  
Collisionless Shocks ◽  
Transverse Waves ◽  
Homogeneous Plasma ◽  
Finite Larmor Radius ◽  
Long Wavelength ◽  
The Earth ◽  
The Magnetic Field

Transverse waves and instabilities propagating along the magnetic field in a homogeneous plasma are discussed analytically and numerically for frequencies of the order of the ion cyclotron frequency and below. The free energy driving the instabilities is assumed to be provided by thermal anisotropies, with the parallel temperature exceeding the perpendicular temperature, a situation appropriate to the solar wind near the earth and to the downstream conditions in collisionless shocks propagating approximately parallel to the magnetic field. It is shown that in the case where the ion β is of order one the long wavelength Firehose instability is not stabilized by finite Larmor radius effects, but that for smaller wavelengths it goes over smoothly into the resonant proton mode, discussed by Kennel & Scarf (1968).

scholarly journals The structure of strongly tilted current sheets in the Earth magnetotail

2014 ◽  
Vol 32 (2) ◽  
pp. 133-146 ◽  
Author(s):  
I. Y. Vasko ◽  
A. V. Artemyev ◽  
A. A. Petrukovich ◽  
R. Nakamura ◽  
L. M. Zelenyi
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Current Density ◽  
Neutral Plane ◽  
Current Sheets ◽  
Transverse Current ◽  
The Earth ◽  
Electron Current Density ◽  
Total Current Density ◽  
Using Data

Abstract. We investigate strongly tilted (in the y–z GSM plane) current sheets (CSs) in the Earth magnetotail using data from the Cluster mission. We analyze 29 CS crossings observed in 2001–2004. The characteristic current density, magnetic field at the CS boundary and the CS thickness of strongly tilted CSs are similar to those reported previously for horizontal (not tilted) CSs. We confirm that strongly tilted CSs are generally characterized by a rather large northward component of the magnetic field. The field-aligned current in strongly tilted CSs is on average two times larger than the transverse current. The proton adiabaticity parameter, κp, is larger than 0.5 in 85% of strongly tilted CSs due to the large northward magnetic field. Thus, the proton dynamics is stochastic for 18 current sheets with 0.5 < κp < 3 and protons are magnetized for 6 sheets with κp > 3, whereas electrons are magnetized for all observed current sheets. Strongly tilted CSs provide a unique opportunity to measure the electric field component perpendicular to the CS plane. We find that most of the electric field perpendicular to the CS plane is due to the decoupling of electron and ion motions (plasma polarization). For 27 CSs we determine profiles of the electrostatic potential, which is due to the plasma polarization. Drops in the potential between the neutral plane and the CS boundary are within the range of 200 V to 12 kV, while maximal values of the electric field are within the range of 0.2 mV m−1 to 8 mV m−1. For 16 CSs the observed potentials are in accordance with Ohm's law, if the electron current density is assumed to be comparable to the total current density. In 15 of these CSs the profile of the polarization potential is approximately symmetric with respect to the neutral plane and has minimum therein.

Energy Dissipation at Filamentary Structures Downstream of the Earth’s Parallel Bow Shock

2021 ◽  
Author(s):  
Harald Kucharek ◽  
Imogen Gingell ◽  
Steven Schwartz ◽  
Charles Farrugia ◽  
Karlheinz Trattner
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Energy Dissipation ◽  
Plasma Heating ◽  
Bow Shock ◽  
Small Scale ◽  
Ion Acceleration ◽  
Current Sheets ◽  
The Earth ◽  
Field Enhancements

&lt;p&gt;While the Earth&amp;#8217;s bow shock marks the location at which the solar wind is thermalized, recent publications provided evidence that filamentary structures such as reconnecting current sheets at the shock ramp region may participate in the thermalization process. &amp;#160;Small scale filamentary structures are distinct features that are abundant at the shock and inside the magnetosheath. These structures are not limited to current sheets but include electric and magnetic field enhancements. They may consist of a single or multiple filaments.&amp;#160; They originate&amp;#160;from energy dissipation at and downstream of the bow shock, in particular the parallel bow shock.&amp;#160;&lt;/p&gt;&lt;p&gt;We have studied several crossings of the magnetosheath made by the MMS spacecraft, characterising and quantifying the occurrence and consequences of current sheets and field enhancements in terms of local plasma heating and ion acceleration far downstream of the shock. These observations suggest that a combination of current sheet formation, and electric field and magnetic field gradients can contribute to local downstream ion acceleration, and heating. The associated turbulence is likely a consequence of solar wind input parameters. These observations provide evidence that under certain plasma conditions these filamentary structures can play a significant role in thermalizing of the magnetosheath plasma as it propagates further downstream toward the magnetopause, thus augmenting the effect due to the bow shock itself.&lt;/p&gt;

The fine structure of the subsolar MPB current layer from MAVEN observations: Implications for the Lorentz force

2020 ◽  
Author(s):  
Gabriela Boscoboinik ◽  
Cesar Bertucci ◽  
Daniel Gomez ◽  
Laura Morales ◽  
Christian Mazelle ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Fine Structure ◽  
Lorentz Force ◽  
Current Density ◽  
Current System ◽  
Minimum Variance ◽  
Current Layer ◽  
The Earth ◽  
Steady Current

&lt;p&gt;We report on the local structure of the Martian subsolar Magnetic Pileup Boundary (MPB) from minimum variance analysis of the magnetic field measured by the MAVEN spacecraft for six orbits. In particular, we detect a well defined current layer within the MPB&amp;#8217;s fine structure and&lt;br&gt;provide a local estimate of its current density and compare these results with the current density obtained by multi-fluid simulations.&lt;br&gt;This current is of the order of hundreds of nAm&lt;sup&gt;-2&lt;/sup&gt; which results in a sunward Lorentz force of the order of 10&lt;sup&gt;-14&lt;/sup&gt;&amp;#160;Nm&lt;sup&gt;-3&lt;/sup&gt;. We compare these results with multifluid numerical simulations.&lt;br&gt;This force is associated with the gradient of the magnetic pressure, it accounts for the&amp;#160;deflection of the solar wind ions near the MPB and for the acceleration of solar wind electrons which carry the interplanetary magnetic field through the MPB into the MPR. We also find that the&lt;br&gt;thickness of the MPB current layer is of the order of both the upstream (magnetosheath) solar wind proton inertial length and convective gyroradius. The former is consistent&amp;#160;with the demagnetization of the ions due to the Hall electric field, an effect observed&amp;#160;recently at the Earth magnetopause, while the latter would imply kinetic processes are&amp;#160;important at the MPB.&lt;br&gt;This study supports recent results that report the presence of a steady current system around Mars in a similar way to the Earth.&lt;/p&gt;

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