scholarly journals Magnetic depression and electron transport in an ion-scale flux rope associated with Kelvin–Helmholtz waves

2018 ◽  
Vol 36 (3) ◽  
pp. 879-889 ◽  
Author(s):  
Binbin Tang ◽  
Wenya Li ◽  
Chi Wang ◽  
Lei Dai ◽  
Yuri Khotyaintsev ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Local Density ◽  
Flux Rope ◽  
Local Magnetic Field ◽  
Lower Hybrid ◽  
Magnetic Flux Rope ◽  
Magnetic Field Increase ◽  
Magnetospheric Multiscale ◽  
Current Flows ◽  
Current Filaments

Abstract. We report an ion-scale magnetic flux rope (the size of the flux rope is ∼ 8.5 ion inertial lengths) at the trailing edge of Kelvin–Helmholtz (KH) waves observed by the Magnetospheric Multiscale (MMS) mission on 27 September 2016, which is likely generated by multiple X-line reconnection. The currents of this flux rope are highly filamentary: in the central flux rope, the current flows are mainly parallel to the magnetic field, supporting a local magnetic field increase at about 7 nT, while at the edges the current filaments are predominantly along the antiparallel direction, which induce an opposing field that causes a significant magnetic depression along the axis direction (> 20 nT), meaning the overall magnetic field of this flux rope is depressed compared to the ambient magnetic field. Thus, this flux rope, accompanied by the plasma thermal pressure enhancement in the center, is referred to as a crater type. Intense lower hybrid drift waves (LHDWs) are found at the magnetospheric edge of the flux rope, and the wave potential is estimated to be ∼ 17 % of the electron temperature. Though LHDWs may be stabilized by the mechanism of electron resonance broadening, these waves could still effectively enable diffusive electron transports in the cross-field direction, corresponding to a local density dip. This indicates LHDWs could play important roles in the evolution of crater flux ropes. Keywords. Magnetospheric physics (magnetopause, cusp, and boundary layers; solar wind–magnetosphere interactions)

scholarly journals Small-scale Magnetic Flux Ropes with Field-aligned Flows via the PSP In-situ Observations

2021 ◽  
Author(s):  
Yu Chen ◽  
Qiang Hu ◽  
Lingling Zhao
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Rope ◽  
Local Magnetic Field ◽  
Small Scale ◽  
Magnetic Flux Rope ◽  
Magnetic Flux Ropes ◽  
Flux Ropes ◽  
Field Lines

<p>Magnetic flux rope, formed by the helical magnetic field lines, can sometimes remain its shape while carrying significant plasma flow that is aligned with the local magnetic field. We report the existence of such structures and static flux ropes by applying the Grad-Shafranov-based algorithm to the Parker Solar Probe (PSP) in-situ measurements in the first five encounters. These structures are detected at heliocentric distances, ranging from 0.13 to 0.66 au, in a total of 4-month time period. We find that flux ropes with field-aligned flows have certain properties similar to those of static flux ropes, such as the decaying relations of the magnetic fields within structures with respect to heliocentric distances. Moreover, these events are more likely with magnetic pressure dominating over the thermal pressure and occurring more frequently in the relatively fast-speed solar wind. Taking into account the high Alfvenicity, we also compare these events with switchbacks and present the cross-section maps via the new Grad-Shafranov type reconstruction. Finally, the possible evolution and relaxation of the magnetic flux rope structures are discussed.</p>

Estimation of the spatial structure of a detached magnetic flux rope at Mars based on simultaneous MAVEN plasma and magnetic field observations

2015 ◽  
Vol 42 (21) ◽  
pp. 8933-8941 ◽  
Author(s):  
Takuya Hara ◽  
David L. Mitchell ◽  
James P. McFadden ◽  
Kanako Seki ◽  
David A. Brain ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Spatial Structure ◽  
Flux Rope ◽  
Field Observations ◽  
Magnetic Flux Rope

scholarly journals Microwave indicator of potential geoeffectiveness and magnetic flux-rope structure of a solar active region

2021 ◽  
Vol 7 (1) ◽  
pp. 3-12
Author(s):  
Anastasiia Kudriavtseva ◽  
Ivan Myshyakov ◽  
Arkadiy Uralov ◽  
Victor Grechnev
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Flux ◽  
Neutral Line ◽  
Flux Rope ◽  
Coronal Magnetic Field ◽  
Horizontal Magnetic Field ◽  
Magnetic Flux Rope ◽  
Magnetic Flux Ropes ◽  
Class Flare

We analyze the presence of a microwave neutral-line-associated source (NLS) in a super-active region NOAA 12673, which produced a number of geo-effective events in September 2017. To estimate the NLS position, we use data from the Siberian Radioheliograph in a range 4–8 GHz and from the Nobeyama Radioheliograph at 17 GHz. Calculation of the coronal magnetic field in a non-linear force-free approximation has revealed an extended structure consisting of interconnected magnetic flux ropes, located practically along the entire length of the main polarity separation line of the photospheric magnetic field. NLS is projected into the region of the strongest horizontal magnetic field, where the main energy of this structure is concentrated. During each X-class flare, the active region lost magnetic helicity and became a CME source.

scholarly journals Polar spacecraft observations of the turbulent outer cusp/magnetopause boundary layer of Earth

1999 ◽  
Vol 6 (3/4) ◽  
pp. 195-204 ◽  
Author(s):  
J. S. Pickett ◽  
J. D. Menietti ◽  
J. H. Dowell ◽  
D. A. Gurnett ◽  
J. D. Scudder
Keyword(s):  
Magnetic Field ◽  
Index Of Refraction ◽  
Local Magnetic Field ◽  
Lower Hybrid ◽  
Frequency Wave ◽  
Turbulent Region ◽  
Wave Data ◽  
Field Environment ◽  
Whistler Mode Waves ◽  
The Waves

Abstract. The orbit of the Polar spacecraft has been ideally suited for studying the turbulent region of the cusp that is located near or just outside the magnetopause current sheet at 7-9 RE. The wave data obtained in this region show that electromagnetic turbulence is dominant in the frequency range 1-10 Hz. The waves responsible for this turbulence usually propagate perpendicular to the local magnetic field and have an index of refraction that generally falls between the estimated cold plasma theoretical values of the electromagnetic lower hybrid and whistler modes and may be composed of both modes in concert with kinetic Alfvén waves and/or fast magnetosonic waves. Fourier spectra of the higher frequency wave data also show the electromagnetic turbulence at frequencies up to and near the electron cyclotron frequency. This higher frequency electromagnetic turbulence is most likely associated with whistler mode waves. The lower hybrid drift and current gradient instabilities are suggested as possible mechanisms for producing the turbulence. The plasma and field environment of this turbulent region is examined and found to be extremely complex. Some of the wave activity is associated with processes occurring locally, such as changes in the DC magnetic field, while others are associated with solar wind and interplanetary magnetic field changes.

scholarly journals Pressure enhancement associated with meridional flow in high-speed solar wind: possible evidence for an interplanetary magnetic flux rope

1997 ◽  
Vol 15 (2) ◽  
pp. 137-142 ◽  
Author(s):  
C.-Y. Tu ◽  
E. Marsch ◽  
K. Ivory ◽  
R. Schwenn
Keyword(s):  
Magnetic Field ◽  
Angular Distribution ◽  
Magnetic Flux ◽  
High Speed ◽  
Electron Distribution Function ◽  
Flux Rope ◽  
Pressure Rise ◽  
High Energy ◽  
Magnetic Flux Rope ◽  
Background Magnetic Field

Abstract. A sizable total-pressure (magnetic pressure plus kinetic pressure) enhancement was found within the high-speed wind stream observed by Helios 2 in 1976 near 0.3 AU. The proton density and temperature and the magnetic magnitude simultaneously increased for about 6 h. This pressure rise was associated with a comparatively large southward flow velocity component (with Vz ≈ –100 km · s–1) and magnetic-field rotation. The pressure enhancement was associated with unusual features in the electron distribution function. It shows a wide angular distribution of electron counting rates in the low-energy (57.8 eV) channel, while previous to the enhancement it exhibits a wide angular distribution of electron count rate in the high-energy (112, 221 and 309 eV) channels, perhaps indicating the mirroring of electrons in the converging field lines of the background magnetic field. These fluid and kinetic phenomena may be explained as resulting from an interplanetary magnetic flux rope which is not fully convected by the flow but moves against the background wind towards the Sun.

scholarly journals The expected imprint of flux rope geometry on suprathermal electrons in magnetic clouds

2009 ◽  
Vol 27 (10) ◽  
pp. 4057-4067 ◽  
Author(s):  
M. J. Owens ◽  
N. U. Crooker ◽  
T. S. Horbury
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Pitch Angle ◽  
Flux Rope ◽  
Magnetic Clouds ◽  
Magnetic Field Direction ◽  
Magnetic Flux Rope ◽  
Suprathermal Electron ◽  
Angle Scattering ◽  
The Magnetic Field

Abstract. Magnetic clouds are a subset of interplanetary coronal mass ejections characterized by a smooth rotation in the magnetic field direction, which is interpreted as a signature of a magnetic flux rope. Suprathermal electron observations indicate that one or both ends of a magnetic cloud typically remain connected to the Sun as it moves out through the heliosphere. With distance from the axis of the flux rope, out toward its edge, the magnetic field winds more tightly about the axis and electrons must traverse longer magnetic field lines to reach the same heliocentric distance. This increased time of flight allows greater pitch-angle scattering to occur, meaning suprathermal electron pitch-angle distributions should be systematically broader at the edges of the flux rope than at the axis. We model this effect with an analytical magnetic flux rope model and a numerical scheme for suprathermal electron pitch-angle scattering and find that the signature of a magnetic flux rope should be observable with the typical pitch-angle resolution of suprathermal electron data provided ACE's SWEPAM instrument. Evidence of this signature in the observations, however, is weak, possibly because reconnection of magnetic fields within the flux rope acts to intermix flux tubes.

scholarly journals The physical and the geometrical properties of simulated cold HI structures

2020 ◽  
Author(s):  
Adriana Gazol ◽  
Marco A Villagran
Keyword(s):  
Magnetic Field ◽  
Mach Number ◽  
Local Density ◽  
Main Direction ◽  
Morphological Properties ◽  
Local Magnetic Field ◽  
Pressure Balance ◽  
Geometrical Properties ◽  
Aspect Ratios ◽  
And Shifts

Abstract The objective of this paper is to help shedding some light on the nature and the properties of the cold structures formed via thermal instability in the magnetized atomic interstellar medium. To this end, we searched for clumps formed in forced (magneto)hydrodynamic simulations with an initial magnetic field ranging from 0 to 8.3 μG. We statistically analyzed, through the use of Kernel Density Estimations, the physical and the morphological properties of a sample containing ∼1500 clumps, as well as the relative alignments between the main direction of clumps and the internal velocity and magnetic field. The density (n ∼ 50 − 200 cm−3), the thermal pressure (Pth/k ∼ 4.9 × 103 − 104 K cm−3), the mean magnetic field (∼3 − 11 μG ), and the sonic Mach number of the selected clumps have values comparable to those reported in observations. We find, however, that the cloud sample can not be described by a single regime concerning their pressure balance and their Alfénic Mach number. We measured the morphological properties of clumps mainly through the asphericity and the prolatness, which appear to be more sensitive than the aspect ratios. From this analysis we find that the presence of magnetic field, even if it is weak, does qualitatively affect the morphology of the clumps by increasing the probability of having highly aspherical and highly plolate clumps by a factor of two, that is by producing more filamentary clumps. Finally, we find that the angle between the main direction of the clumps and the local magnetic field lies between ∼π/4 − π/2 and shifts to more perpendicular alignments as the intensity of this field increases, while the relative direction between the local density structure and the local magnetic field transits from parallel to perpendicular.

scholarly journals The spatial relation between EUV cavities and linear polarization signatures

2013 ◽  
Vol 8 (S300) ◽  
pp. 395-396 ◽  
Author(s):  
Urszula Bak-Stȩślicka ◽  
Sarah E. Gibson ◽  
Yuhong Fan ◽  
Christian Bethge ◽  
Blake Forland ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Cross Section ◽  
Linear Polarization ◽  
Flux Rope ◽  
Spatial Relation ◽  
Coronal Magnetic Field ◽  
Systematic Analysis ◽  
Elliptical Cross ◽  
Magnetic Flux Rope

AbstractSolar coronal cavities are regions of rarefied density and elliptical cross-section. The Coronal Multi-channel Polarimeter (CoMP) obtains daily full-Sun coronal observations in linear polarization, allowing a systematic analysis of the coronal magnetic field in polar-crown prominence cavities. These cavities commonly possess a characteristic “lagomorphic” signature in linear polarization that may be explained by a magnetic flux-rope model. We analyze the spatial relation between the EUV cavity and the CoMP linear polarization signature.

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