scholarly journals Global View of Current Sheet Thinning: Plasma Pressure Gradients and Large‐Scale Currents

2019 ◽  
Vol 124 (1) ◽  
pp. 264-278 ◽  
Author(s):  
A. V. Artemyev ◽  
V. Angelopoulos ◽  
A. Runov ◽  
A. A. Petrukovich
Keyword(s):  
Current Sheet ◽  
Large Scale ◽  
Plasma Pressure ◽  
Pressure Gradients ◽  
Global View

Juno Observations of Ion-Inertial Scale Flux Ropes in the Jovian Magnetotail

2020 ◽  
Author(s):  
Yash Sarkango ◽  
James A. Slavin ◽  
Xianzhe Jia ◽  
Gina A. DiBraccio ◽  
Daniel J. Gershman ◽  
...  
Keyword(s):  
Current Sheet ◽  
Large Scale ◽  
Flux Rope ◽  
System Size ◽  
Travel Speed ◽  
Plasma Pressure ◽  
Small Scale ◽  
High Resolution Data ◽  
High Eigenvalue ◽  
Flux Ropes

<p>Magnetic flux ropes – helical magnetic structures which are produced due to simultaneous reconnection at multiple X-lines, have been observed at the magnetospheres of most magnetized planets. The size of these flux ropes, also called “plasmoids” if they contain significant plasma pressure, can vary from being a significant fraction of the system size (e.g. tens of Earth radii at the terrestrial magnetotail) to small flux ropes with diameters less than the local ion inertial length. The smallest flux ropes are expected because reconnection in the Earth’s cross-tail current sheet only occurs when it thins to or below the ion-inertial scale and tearing instabilities produce periodic X-lines with spacing of ~2 times the thickness of the current sheet. While much is still to be understood, it is hypothesized on the basis of Particle-in-Cell simulations that the smaller flux ropes soon come together and “coalesce”, via reconnection, into larger flux ropes. The coalescence process continues until the observed distribution of plasmoid diameters is produced.</p> <p>For the giant magnetospheres like Jupiter, which encompass multiple moons that lose mass to the rapidly rotating inner plasma disk, the momentum in the outer layers of the disk is believed to continuously shed mass by the release of plasmoids down the tail plasma sheet. This periodic ejection of plasmoids to balance the mass being added to the magnetosphere by Jupiter’s moons is termed the Vasyliunas-cycle. Rather than being formed by multiple x-line reconnection in a highly thinned current sheet, these Vasyliunas-cycle plasmoids are thought to form when a single X-line disconnects a highly stretched closed flux tube and allows its momentum to carry it down the tail. Due to the limited single-spacecraft measurements obtained by Galileo in the dusk-side magnetosphere, relatively little is known about these Vasyliunas-type plasmoids. Signatures of most Jovian plasmoids and flux ropes lasted ~6.8 minutes on average (Vogt et al., 2014), corresponding to diameters larger than 1 Jovian radii (R<sub>J</sub>); much larger than the ion inertial length expected in the outer magnetosphere. Potential flux ropes on the ion-inertial scale, which would typically last for less than a minute could not have been identified using the Galileo magnetometer owing to the low cadence of several seconds per vector measurement.</p> <p>As part of its 53-day orbits, Juno spent a considerable amount of time in the dawn-side magnetotail. Using the high-resolution data from the Juno magnetometer, we identified two potential ion-scale flux ropes in the Jovian magnetotail by searching for bipolar variations in the magnetic field component normal to the current sheet. The two events were 22 s and 62 s in duration and were located at radial distances of roughly 74 R<sub>J</sub> and 92 R<sub>J</sub> between 03 and 04 local time. Assuming that the travel speed of the flux rope is limited by the Alfven speed in the surrounding magnetotail lobes, which is calculated using the plasma density inferred by the cutoff for the continuum radiation detected by the Waves instrument (0.003 to 0.012 cm<sup>-3</sup>), we estimated the diameters of these flux ropes to be 0.14 and 0.19 R<sub>J</sub> respectively. The flux ropes’ diameters were comparable to the ion inertial length during these intervals, which was roughly between 0.11 to 0.23 R<sub>J</sub>, (assuming a mass of 16.6 amu for the average ion). The selected events were analyzed using the minimum variance analysis and both events were seen to possess a strong core field with relatively high eigenvalue ratios, indicating that the MVA coordinate system was well-defined. Using a force-free model which is fitted to the observations, it was found that the flux ropes are quasi-force-free.</p> <p>These are the first reported observations of ion-scale flux ropes in the Jovian magnetotail. Although the large-scale dynamics of the magnetosphere may be dominated by the Vasyliunas cycle, the observations show that small-scale flux ropes, which are likely generated due to the tearing instability in a thin current sheet, also exist in the Jovian magnetotail, similar to the magnetotails of Earth and Mercury.</p>

scholarly journals Fluid simulations of three-dimensional reconnection that capture the lower-hybrid drift instability

2021 ◽  
Vol 87 (1) ◽  
Author(s):  
F. Allmann-Rahn ◽  
S. Lautenbach ◽  
R. Grauer ◽  
R. D. Sydora
Keyword(s):  
Current Sheet ◽  
Large Scale ◽  
Fluid Model ◽  
Initial Perturbation ◽  
Three Dimensional ◽  
Continuum Models ◽  
Lower Hybrid ◽  
Pressure Gradients ◽  
Kinetic Effects ◽  
Drift Instability

Fluid models that approximate kinetic effects have received attention recently in the modelling of large-scale plasmas such as planetary magnetospheres. In three-dimensional reconnection, both reconnection itself and current sheet instabilities need to be represented appropriately. We show that a heat flux closure based on pressure gradients enables a 10-moment fluid model to capture key properties of the lower-hybrid drift instability (LHDI) within a reconnection simulation. Characteristics of the instability are examined with kinetic and fluid continuum models, and its role in the three-dimensional reconnection simulation is analysed. The saturation level of the electromagnetic LHDI is higher than expected, which leads to strong kinking of the current sheet. Therefore, the magnitude of the initial perturbation has significant impact on the resulting turbulence.

scholarly journals Numerical study of the reconnection process between magnetic cloud and heliospheric current sheet

2018 ◽  
Vol 619 ◽  
pp. A82
Author(s):  
Man Zhang ◽  
Yu Fen Zhou ◽  
Xue Shang Feng ◽  
Bo Li ◽  
Ming Xiong
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Dynamic Process ◽  
Large Scale ◽  
Magnetic Cloud ◽  
Numerical Study ◽  
Three Dimensional ◽  
Heliospheric Current Sheet ◽  
Reconnection Process ◽  
Magnetic Filed

In this paper, we have used a three-dimensional numerical magnetohydrodynamics model to study the reconnection process between magnetic cloud and heliospheric current sheet. Within a steady-state heliospheric model that gives a reasonable large-scale structure of the solar wind near solar minimum, we injected a spherical plasmoid to mimic a magnetic cloud. When the magnetic cloud moves to the heliospheric current sheet, the dynamic process causes the current sheet to become gradually thinner and the magnetic reconnection begin. The numerical simulation can reproduce the basic characteristics of the magnetic reconnection, such as the correlated/anticorrelated signatures in V and B passing a reconnection exhaust. Depending on the initial magnetic helicity of the cloud, magnetic reconnection occurs at points along the boundary of the two systems where antiparallel field lines are forced together. We find the magnetic filed and velocity in the MC have a effect on the reconnection rate, and the magnitude of velocity can also effect the beginning time of reconnection. These results are helpful in understanding and identifying the dynamic process occurring between the magnetic cloud and the heliospheric current sheet.

scholarly journals Interrogation of kinase genetic interactions provides a global view of PAK1-mediated signal transduction pathways

2020 ◽  
Vol 295 (50) ◽  
pp. 16906-16919
Author(s):  
Jae-Hong Kim ◽  
Yeojin Seo ◽  
Myungjin Jo ◽  
Hyejin Jeon ◽  
Young-Seop Kim ◽  
...  
Keyword(s):  
Signal Transduction ◽  
Cell Migration ◽  
Intracellular Signaling ◽  
Mammalian Cells ◽  
Drug Targets ◽  
Large Scale ◽  
Genetic Interaction ◽  
Genetic Interactions ◽  
Signal Transduction Pathways ◽  
Global View

Kinases are critical components of intracellular signaling pathways and have been extensively investigated with regard to their roles in cancer. p21-activated kinase-1 (PAK1) is a serine/threonine kinase that has been previously implicated in numerous biological processes, such as cell migration, cell cycle progression, cell motility, invasion, and angiogenesis, in glioma and other cancers. However, the signaling network linked to PAK1 is not fully defined. We previously reported a large-scale yeast genetic interaction screen using toxicity as a readout to identify candidate PAK1 genetic interactions. En masse transformation of the PAK1 gene into 4,653 homozygous diploid Saccharomyces cerevisiae yeast deletion mutants identified ∼400 candidates that suppressed yeast toxicity. Here we selected 19 candidate PAK1 genetic interactions that had human orthologs and were expressed in glioma for further examination in mammalian cells, brain slice cultures, and orthotopic glioma models. RNAi and pharmacological inhibition of potential PAK1 interactors confirmed that DPP4, KIF11, mTOR, PKM2, SGPP1, TTK, and YWHAE regulate PAK1-induced cell migration and revealed the importance of genes related to the mitotic spindle, proteolysis, autophagy, and metabolism in PAK1-mediated glioma cell migration, drug resistance, and proliferation. AKT1 was further identified as a downstream mediator of the PAK1-TTK genetic interaction. Taken together, these data provide a global view of PAK1-mediated signal transduction pathways and point to potential new drug targets for glioma therapy.

The Large-Scale Density Structure of the Solar Corona and the Heliospheric Current Sheet

1996 ◽  
Vol 458 ◽  
pp. 817 ◽  
Author(s):  
Madhulika Guhathakurta ◽  
Thomas E. Holzer ◽  
R. M. MacQueen
Keyword(s):  
Solar Corona ◽  
Current Sheet ◽  
Large Scale ◽  
Heliospheric Current Sheet ◽  
Density Structure

scholarly journals Nonlinear equilibrium structure of thin currents sheets: influence of electron pressure anisotropy

2004 ◽  
Vol 11 (5/6) ◽  
pp. 579-587 ◽  
Author(s):  
L. M. Zelenyi ◽  
H. V. Malova ◽  
V. Yu. Popov ◽  
D. Delcourt ◽  
A. S. Sharma
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Magnetic Energy ◽  
Plasma Pressure ◽  
Quasi Equilibrium ◽  
Electrostatic Effects ◽  
Current Sheets ◽  
Thin Current Sheet ◽  
Field Lines ◽  
The Magnetic Field

Abstract. Thin current sheets represent important and puzzling sites of magnetic energy storage and subsequent fast release. Such structures are observed in planetary magnetospheres, solar atmosphere and are expected to be widespread in nature. The thin current sheet structure resembles a collapsing MHD solution with a plane singularity. Being potential sites of effective energy accumulation, these structures have received a good deal of attention during the last decade, especially after the launch of the multiprobe CLUSTER mission which is capable of resolving their 3D features. Many theoretical models of thin current sheet dynamics, including the well-known current sheet bifurcation, have been developed recently. A self-consistent 1D analytical model of thin current sheets in which the tension of the magnetic field lines is balanced by the ion inertia rather than by the plasma pressure gradients was developed earlier. The influence of the anisotropic electron population and of the corresponding electrostatic field that acts to restore quasi-neutrality of the plasma is taken into account. It is assumed that the electron motion is fluid-like in the direction perpendicular to the magnetic field and fast enough to support quasi-equilibrium Boltzmann distribution along the field lines. Electrostatic effects lead to an interesting feature of the current density profile inside the current sheet, i.e. a narrow sharp peak of electron current in the very center of the sheet due to fast curvature drift of the particles in this region. The corresponding magnetic field profile becomes much steeper near the neutral plane although the total cross-tail current is in all cases dominated by the ion contribution. The dependence of electrostatic effects on the ion to electron temperature ratio, the curvature of the magnetic field lines, and the average electron magnetic moment is also analyzed. The implications of these effects on the fine structure of thin current sheets and their potential impact on substorm dynamics are presented.

scholarly journals Collapse of the neutral current sheet and reconnection at micro-scales

2008 ◽  
Vol 74 (2) ◽  
pp. 215-232 ◽  
Author(s):  
I. F. SHAIKHISLAMOV
Keyword(s):  
Current Sheet ◽  
Large Scale ◽  
Numerical Solutions ◽  
Neutral Current ◽  
Static Solution ◽  
New Process ◽  
Maximum Current ◽  
Nonlinear Static ◽  
Field Lines ◽  
Two Fluid

AbstractReconnection physics at micro-scales is investigated in an electron magnetohydrodynamics frame. A new process of collapse of the neutral current sheet is demonstrated by means of analytical and numerical solutions. It shows how at scales smaller than ion inertia length a compression of the sheet triggers an explosive evolution of current perturbation. Collapse results in the formation of a intense sub-sheet and then an X-point structure embedded into the equilibrium sheet. Hall currents associated with this structure support high reconnection rates. Nonlinear static solution at scales of the electron skin reveals that electron inertia and small viscosity provide an efficient mechanism of field lines breaking. The reconnection rate does not depend on the actual value of viscosity, while the maximum current is found to be restricted even for space plasmas with extremely rare collisions. The results obtained are verified by a two-fluid large-scale numerical simulation.

scholarly journals Experimental study of the formation of inverted-V structures and their stratification using AUREOL-3 observations

2000 ◽  
Vol 18 (11) ◽  
pp. 1399-1411 ◽  
Author(s):  
O. Luízar ◽  
M. V. Stepanova ◽  
J. M. Bosqued ◽  
E. E. Antonova ◽  
R. A. Kovrazhkin
Keyword(s):  
Current Density ◽  
Plasma Sheet ◽  
Large Scale ◽  
Initial Pressure ◽  
Auroral Zone ◽  
Total Width ◽  
Pressure Gradients ◽  
Ion Temperature ◽  
Field Aligned Current ◽  
Statistical Trends

Abstract. Multiple inverted-V structures are commonly observed on the same auroral zone crossing by a low-altitude orbiting satellite. Such structures appear grouped and apparently result from an ionospheric and/or magnetospheric mechanism of stratification. More than two years of AUREOL-3 satellite observations were analyzed to study their properties and their formation in the framework of the ionosphere-magnetosphere coupling model proposed by Tverskoy. This model predicts some natural periodicity in the electrostatic potential profile (and subsequently in the field-aligned current profiles) that could account for oscillations experimentally observed in the auroral zone, such as successive inverted-Vs. Experimental results obtained during quiet or moderately active periods demonstrate that the number of structures observed within a given event is well described by a 'scaling' parameter provided by the hot plasma stratification theory and expressed in terms of the field-aligned current density, the total width of the current band, the plasma sheet ion temperature, and the height-integrated Pedersen conductivity of the ionosphere. The latitudinal width, in the order of 100–200 km at ionospheric altitudes, is relatively independent of the current density, and is determined not only by the existence of a potential difference above the inverted-Vs, but also by basic oscillations of the ionosphere-magnetosphere coupling system predicted by Tverskoy. The large number of cases studied by the AUREOL-3 satellite provides reliable statistical trends which permits the validation of the model and the inference that the multiple structures currently observed can be related directly to oscillations of the magnetospheric potential (or the pressure gradients) on a scale of ~1000-2000 km in the near-Earth plasma sheet. These oscillations arise in the Tverskoy model and may naturally result when the initial pressure gradients needed to generate a large-scale field-aligned current have a sufficiently wide equatorial scale, of about 1 RE or more.Key words: Magnetospheric physics (current systems; energetic particles, precipitating; magnetosphere-ionosphere interactions)

scholarly journals Dynamics of Variable Dusk-Dawn Flow Associated with Magnetotail Current Sheet Flapping

2021 ◽  
Author(s):  
James Henry Lane ◽  
Adrian Grocott ◽  
Nathan Anthony Case ◽  
Maria-Theresia Walach
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Field Data ◽  
Large Scale ◽  
Magnetic Field Data ◽  
Analysis Technique ◽  
Upstream Solar Wind ◽  
Magnetotail Dynamics ◽  
Magnetotail Current Sheet

Abstract. Previous observations have provided a clear indication that the dusk-dawn (v⊥y) sense of both slow (< 200 km s−1) and fast (> 200 km s−1) convective magnetotail flows is strongly governed by the Interplanetary Magnetic Field (IMF) By conditions. The related “untwisting hypothesis” of magnetotail dynamics is commonly invoked to explain this dependence, in terms of a large-scale magnetospheric asymmetry. In the current study, we present Cluster spacecraft observations from 12 October 2006 of earthward convective magnetotail plasma flows whose dusk-dawn sense disagrees with the untwisting hypothesis of IMF By control of the magnetotail flows. During this interval, observations of the upstream solar wind conditions from OMNI, and ionospheric convection data using SuperDARN, indicate a large-scale magnetospheric morphology consistent with positive IMF By penetration into the magnetotail. Inspection of the in-situ Cluster magnetic field data reveals a flapping of the magnetotail current sheet; a phenomenon known to influence dusk-dawn flow. Results from the curlometer analysis technique suggest that the dusk-dawn flow perturbations may have been driven by the J x B force associated with a dawnward-propagating flapping of the magnetotail current sheet, locally overriding the expected IMF By control of the flows. We conclude that invocation of the untwisting hypothesis may be inappropriate when interpreting intervals of dynamic magnetotail behaviour such as during current sheet flapping.

Sign in / Sign up

Export Citation Format

Share Document