scholarly journals Critical decay index for eruptions of ‘short’ filaments

2021 ◽  
Vol 503 (3) ◽  
pp. 3926-3930
Author(s):  
B Filippov
Keyword(s):  
Magnetic Field ◽  
Sharp Increase ◽  
Flux Rope ◽  
Critical Index ◽  
Straight Line ◽  
Decay Index ◽  
Catastrophic Loss ◽  
Steep Decrease ◽  
Line Tying ◽  
Partial Current

ABSTRACT Model of a partial current-carrying torus loop anchored to the photosphere is analysed. Conditions of the catastrophic loss of equilibrium are considered and corresponding value of the critical decay index of external magnetic field is found. Taking into account line-tying conditions leads to non-monotonous dependence of the critical decay index on the height of the apex and length of the flux rope (its endpoints separation). For relatively short flux ropes, the critical decay index is significantly lower than unity, which is in contrast to widespread models with the typical critical decay index above unity. The steep decrease of the critical index with height at low heights is due to the sharp increase of the curvature of the flux-rope axis that transforms from a nearly straight line to a crescent.

scholarly journals Evolution of photospheric flows under an erupting filament in the quiet-Sun region

2020 ◽  
Vol 636 ◽  
pp. A102
Author(s):  
Jiří Wollmann ◽  
Michal Švanda ◽  
David Korda ◽  
Thierry Roudier
Keyword(s):  
Magnetic Field ◽  
Solar Atmosphere ◽  
Surface Velocity ◽  
Line Of Sight ◽  
Quiet Sun ◽  
Filament Eruption ◽  
Decay Index ◽  
Steep Decrease ◽  
Filament Activation ◽  
The Magnetic Field

Context. We studied the dynamics of the solar atmosphere in the region of a large quiet-Sun filament, which erupted on 21 October 2010. The filament eruption started at its northern end and disappeared from the Hα line-core filtergrams line within a few hours. The very fast motions of the northern leg were recorded in ultraviolet light by the Atmospheric Imaging Assembly (AIA) imager. Aims. We aim to study a wide range of available datasets describing the dynamics of the solar atmosphere for five days around the filament eruption. This interval covers three days of the filament evolution, one day before the filament growth and one day after the eruption. We search for possible triggers that lead to the eruption of the filament. Methods. The surface velocity field in the region of the filament were measured by means of time–distance helioseismology and coherent structure tracking. The apparent velocities in the higher atmosphere were estimated by tracking the features in the 30.4 nm AIA observations. To capture the evolution of the magnetic field, we extrapolated the photospheric line-of-sight magnetograms and also computed the decay index of the magnetic field. Results. We found that photospheric velocity fields showed some peculiarities. Before the filament activation, we observed a temporal increase of the converging flows towards the filament’s spine. In addition, the mean squared velocity increased temporarily before the activation and peaked just before it, followed by a steep decrease. We further see an increase in the average shear of the zonal flow component in the filament’s region, followed by a steep decrease. The photospheric line-of-sight magnetic field shows a persistent increase of induction eastward from the filament spine. The decay index of the magnetic field at heights around 10 Mm shows a value larger than critical one at the connecting point of the northern filament end. The value of the decay index increases monotonically there until the filament activation. Then, it decreased sharply.

Connecting a Star’s Convection Zone with its Corona

1995 ◽  
Vol 12 (2) ◽  
pp. 180-185 ◽  
Author(s):  
D. J. Galloway ◽  
C. A. Jones
Keyword(s):  
Magnetic Field ◽  
Convection Zone ◽  
Flux Rope ◽  
Field System ◽  
Stellar Convection ◽  
Coronal Activity ◽  
Flux Concentration ◽  
Global Understanding ◽  
The Magnetic Field

AbstractThis paper discusses problems which have as their uniting theme the need to understand the coupling between a stellar convection zone and a magnetically dominated corona above it. Interest is concentrated on how the convection drives the atmosphere above, loading it with the currents that give rise to flares and other forms of coronal activity. The role of boundary conditions appears to be crucial, suggesting that a global understanding of the magnetic field system is necessary to explain what is observed in the corona. Calculations are presented which suggest that currents flowing up a flux rope return not in the immediate vicinity of the rope but rather in an alternative flux concentration located some distance away.

scholarly journals A multispacecraft study of a small flux rope entrained by rolling back magnetic field lines

2017 ◽  
Vol 122 (7) ◽  
pp. 6927-6939 ◽  
Author(s):  
Jia Huang ◽  
Yong C.‐M. Liu ◽  
Jun Peng ◽  
Hui Li ◽  
Berndt Klecker ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Flux Rope ◽  
Field Lines

scholarly journals Photospheric magnetic field of an eroded-by-solar-wind coronal mass ejection

2016 ◽  
Vol 12 (S327) ◽  
pp. 67-70
Author(s):  
J. Palacios ◽  
C. Cid ◽  
E. Saiz ◽  
A. Guerrero
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Mass Ejection ◽  
Coronal Hole ◽  
Interplanetary Medium ◽  
Flux Rope ◽  
Magnetic Characteristics ◽  
Interplanetary Coronal Mass Ejection ◽  
Fast Wind ◽  
Mass Ejection

AbstractWe have investigated the case of a coronal mass ejection that was eroded by the fast wind of a coronal hole in the interplanetary medium. When a solar ejection takes place close to a coronal hole, the flux rope magnetic topology of the coronal mass ejection (CME) may become misshapen at 1 AU as a result of the interaction. Detailed analysis of this event reveals erosion of the interplanetary coronal mass ejection (ICME) magnetic field. In this communication, we study the photospheric magnetic roots of the coronal hole and the coronal mass ejection area with HMI/SDO magnetograms to define their magnetic characteristics.

scholarly journals Non-damping oscillations at flaring loops

2018 ◽  
Vol 617 ◽  
pp. A86 ◽  
Author(s):  
D. Li ◽  
D. Yuan ◽  
Y. N. Su ◽  
Q. M. Zhang ◽  
W. Su ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Line Width ◽  
Line Emission ◽  
Flux Rope ◽  
Doppler Velocity ◽  
Narrow Slit ◽  
Plasma Properties ◽  
Spectral Window ◽  
Peak Intensity ◽  
The Magnetic Field

Context. Quasi-periodic oscillations are usually detected as spatial displacements of coronal loops in imaging observations or as periodic shifts of line properties (i.e., Doppler velocity, line width and intensity) in spectroscopic observations. They are often applied for remote diagnostics of magnetic fields and plasma properties on the Sun. Aims. We combine the imaging and spectroscopic measurements of available space missions, and investigate the properties of non-damping oscillations at flaring loops. Methods. We used the Interface Region Imaging Spectrograph (IRIS) to measure the spectrum over a narrow slit. The double-component Gaussian fitting method was used to extract the line profile of Fe XXI 1354.08 Å at the “O I” spectral window. The quasi-periodicity of loop oscillations were identified in the Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected in the line properties of Fe XXI 1354.08 Å, hard X-ray emissions in GOES 1−8 Å derivative, and Fermi 26−50 keV. The Doppler velocity and line width oscillate in phase, while a phase shift of about π/2 is detected between the Doppler velocity and peak intensity. The amplitudes of Doppler velocity and line width oscillation are about 2.2 km s−1 and 1.9 km s−1, respectively, while peak intensity oscillates with amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period of about 155 s is identified in the Doppler velocity and peak intensity of the Fe XXI 1354.08 Å line emission, and AIA 131 Å intensity. Conclusions. The oscillations at about 40 s are not damped significantly during the observation; this might be linked to the global kink modes of flaring loops. The periodicity at about 155 s is most likely a signature of recurring downflows after chromospheric evaporation along flaring loops. The magnetic field strengths of the flaring loops are estimated to be about 120−170 G using the magnetohydrodynamic seismology diagnostics, which are consistent with the magnetic field modeling results using the flux rope insertion method.

scholarly journals Use of Magnetic Field for Mitigating Gyroscope Errors for Indoor Pedestrian Positioning

Sensors ◽  
2018 ◽  
Vol 18 (8) ◽  
pp. 2592 ◽  
Author(s):  
Ming Ma ◽  
Qian Song ◽  
Yang Gu ◽  
Zhimin Zhou
Keyword(s):  
Magnetic Field ◽  
Static Magnetic Field ◽  
Inertial Navigation System ◽  
Three Dimensional ◽  
Calibration Method ◽  
Rate Of Change ◽  
Superior Performance ◽  
Novel Approach ◽  
Straight Line ◽  
Magnetometer Calibration

In the field of indoor pedestrian positioning, the improved Quasi-Static magnetic Field (iQSF) method has been proposed to estimate gyroscope biases in magnetically perturbed environments. However, this method is only effective when a person walks along straight-line paths. For other curved or more complex path patterns, the iQSF method would fail to detect the quasi-static magnetic field. To address this issue, a novel approach is developed for quasi-static magnetic field detection in foot-mounted Inertial Navigation System. The proposed method detects the quasi-static magnetic field using the rate of change in differences between the magnetically derived heading and the heading derived from gyroscope. In addition, to eliminate the distortions caused by system platforms and shoes, a magnetometer calibration method is developed and the calibration is transformed from three-dimensional to two-dimensional coordinate according to the motion model of a pedestrian. The experimental results demonstrate that the proposed method can provide superior performance in suppressing the heading errors with the comparison to iQSF method.

Dayside Magnetopause Reconnection and Flux Transfer Events: BepiColombo Earth-Flyby

2021 ◽  
Author(s):  
Wei-Jie Sun ◽  
James Slavin ◽  
Rumi Nakamura ◽  
Daniel Heyner ◽  
Johannes Mieth
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
European Space Agency ◽  
Flux Rope ◽  
Transfer Event ◽  
Flux Transfer Events ◽  
Space Agency ◽  
Flux Ropes ◽  
Flux Transfer ◽  
Magnetospheric Multiscale Mission

<p>BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury. The BepiColombo mission consists of two spacecraft, which are the Mercury Planetary Orbiter (MPO) and Mercury Magnetospheric Orbiter (Mio). The mission made its first planetary flyby, which is the only Earth flyby, on 10 April 2020, during which several instruments collected measurements. In this study, we analyze MPO magnetometer (MAG) observations of Flux Transfer Events (FTEs) in the magnetosheath and the structure of the subsolar magnetopause near the  flow stagnation point. The magnetosheath plasma beta was high with a value of ~ 8 and the interplanetary magnetic field (IMF) was southward with a clock angle that decreased from ~ 100 degrees to ~ 150 degrees.  As the draped IMF became increasingly southward several of the flux transfer event (FTE)-type flux ropes were observed. These FTEs traveled southward indicating that the magnetopause X-line was located northward of the spacecraft, which is consistent with a dawnward tilt of the IMF. Most of the FTE-type flux ropes were in ion-scale, <10 s duration, suggesting that they were newly formed. Only one large-scale FTE-type flux rope, ~ 20 s, was observed. It was made up of two successive bipolar signatures in the normal magnetic field component, which is evidence of coalescence at a secondary reconnection site. Further analysis demonstrated that the dimensionless reconnection rate of the re-reconnection associated with the coalescence site was ~ 0.14. While this investigation was limited to the MPO MAG observations, it strongly supports a key feature of dayside reconnection discovered in the Magnetospheric Multiscale mission, the growth of FTE-type flux ropes through coalescence at secondary reconnection sites.</p>

Force-free magnetic field in a cylindrical flux rope without a constant alpha

2005 ◽  
Vol 36 (12) ◽  
pp. 2268-2272 ◽  
Author(s):  
E. Romashets ◽  
M. Vandas
Keyword(s):  
Magnetic Field ◽  
Flux Rope

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 Flux rope, hyperbolic flux tube, and late extreme ultraviolet phases in a non-eruptive circular-ribbon flare

2017 ◽  
Vol 604 ◽  
pp. A76 ◽  
Author(s):  
Sophie Masson ◽  
Étienne Pariat ◽  
Gherardo Valori ◽  
Na Deng ◽  
Chang Liu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Flux Tube ◽  
Extreme Ultraviolet ◽  
Topological Analysis ◽  
Perfect Match ◽  
Free Field ◽  
Flux Rope ◽  
Null Point ◽  
Second Phase ◽  
Flare Loops

Context. The dynamics of ultraviolet (UV) emissions during solar flares provides constraints on the physical mechanisms involved in the trigger and the evolution of flares. In particular it provides some information on the location of the reconnection sites and the associated magnetic fluxes. In this respect, confined flares are far less understood than eruptive flares generating coronal mass ejections. Aims. We present a detailed study of a confined circular flare dynamics associated with three UV late phases in order to understand more precisely which topological elements are present and how they constrain the dynamics of the flare. Methods. We perform a non-linear force-free field extrapolation of the confined flare observed with the Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) instruments on board Solar Dynamics Observatory (SDO). From the 3D magnetic field we compute the squashing factor and we analyse its distribution. Conjointly, we analyse the AIA extreme ultraviolet (EUV) light curves and images in order to identify the post-flare loops, and their temporal and thermal evolution. By combining the two analyses we are able to propose a detailed scenario that explains the dynamics of the flare. Results. Our topological analysis shows that in addition to a null-point topology with the fan separatrix, the spine lines and its surrounding quasi-separatix layer (QSL) halo (typical for a circular flare), a flux rope and its hyperbolic flux tube (HFT) are enclosed below the null. By comparing the magnetic field topology and the EUV post-flare loops we obtain an almost perfect match between the footpoints of the separatrices and the EUV 1600 Å ribbons and between the HFT field line footpoints and bright spots observed inside the circular ribbons. We show, for the first time in a confined flare, that magnetic reconnection occurred initially at the HFT below the flux rope. Reconnection at the null point between the flux rope and the overlying field is only initiated in a second phase. In addition, we showed that the EUV late phase observed after the main flare episode is caused by the cooling loops of different length which have all reconnected at the null point during the impulsive phase. Conclusions. Our analysis shows in one example that flux ropes are present in null-point topology not only for eruptive and jet events, but also for confined flares. This allows us to conjecture on the analogies between conditions that govern the generation of jets, confined flares or eruptive flares.

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