Photospheric Shear Flows along the Magnetic Neutral Line of Active Region 10486 prior to an X10 Flare

2004 ◽  
Vol 617 (2) ◽  
pp. L151-L154 ◽  
Author(s):  
Guo Yang ◽  
Yan Xu ◽  
Wenda Cao ◽  
Haimin Wang ◽  
Carsten Denker ◽  
...  
Keyword(s):  
Active Region ◽  
Shear Flows ◽  
Neutral Line ◽  
Magnetic Neutral Line

scholarly journals Siphon Flow Across the Magnetic Neutral-Line of an Active Region

1993 ◽  
Vol 141 ◽  
pp. 534-537 ◽  
Author(s):  
S.K. Solanki ◽  
I. Rüedi ◽  
D. Rabin
Keyword(s):  
Active Region ◽  
Field Strength ◽  
Flow Velocity ◽  
Neutral Line ◽  
Longitudinal Velocity ◽  
Theoretical Models ◽  
Magnetic Polarity ◽  
The Sun ◽  
Magnetic Neutral Line ◽  
Reliable Detection

AbstractWe present accurate measurements, based on the g = 3 line at 1.5648/µm, of the field strength and longitudinal velocity in the vicinity of the magnetic neutral-line of a solar active region. We find that very close to the neutral line the field strength and the flow velocity are correlated in the sense that the magnetic polarity with the larger field strength is associated with a downflow, while the polarity with the weaker field shows an upflow. This is exactly the signal predicted by theoretical models of siphon flows, and constitutes the first reliable detection of a siphon flow on the sun.

scholarly journals Vector Magnetic Fields at the Base of Filaments and the Filament Environment

1998 ◽  
Vol 167 ◽  
pp. 98-101 ◽  
Author(s):  
Jingxiu Wang ◽  
Wei Li
Keyword(s):  
Magnetic Fields ◽  
Magnetic Structure ◽  
Field Gradient ◽  
Neutral Line ◽  
Transverse Field ◽  
Line Of Sight ◽  
Horizontal Gradient ◽  
Major Fraction ◽  
Flux System ◽  
Magnetic Neutral Line

AbstractBased on an analysis of three active filaments in AR 6891, we find that vector magnetic fields at the base of filaments and the filament environment is characterized by the following: (1) The transverse field is parallel along the magnetic neutral line for most of the filaments. The average transverse field beneath the filaments is more than 400 G. (2) The horizontal gradient of the line-of-sight field crossing the neutral line is, more or less, constant along the major fraction of a filament, but very steep at the two ends. The average gradient is 0.06 G/km. (3) For each of the filaments there is a squeezing magnetic structure which represents an intrusion of a satellite bipole into the main flux system. The neutral line for a squeezing magnetic structure has a large curvature, a strong sheared transverse field of more than 1 KG, and a steep field gradient of approximate 0.3 G/km. (4) The transverse field and field gradient are clearly enhanced before the filament eruption.

scholarly journals Properties of Magnetic Neutral Line Gradients and Formation of Filaments

Solar Physics ◽  
2013 ◽  
Vol 289 (3) ◽  
pp. 821-830 ◽  
Author(s):  
Nina V. Karachik ◽  
Alexei A. Pevtsov
Keyword(s):  
Neutral Line ◽  
Magnetic Neutral Line

scholarly journals Non-normal origin of modal instabilities in rotating plane shear flows

2020 ◽  
Vol 476 (2233) ◽  
pp. 20190550
Author(s):  
Sharath Jose ◽  
Rama Govindarajan
Keyword(s):  
Reynolds Number ◽  
Shear Flows ◽  
Critical Reynolds Number ◽  
Flow System ◽  
Neutral Line ◽  
Plane Couette Flow ◽  
Plane Shear ◽  
Perturbation Amplitude ◽  
Fundamental Reason ◽  
The Stability

Small variations introduced in shear flows are known to affect stability dramatically. Rotation of the flow system is one example, where the critical Reynolds number for exponential instabilities falls steeply with a small increase in rotation rate. We ask whether there is a fundamental reason for this sensitivity to rotation. We answer in the affirmative, showing that it is the non-normality of the stability operator in the absence of rotation which triggers this sensitivity. We treat the flow in the presence of rotation as a perturbation on the non-rotating case, and show that the rotating case is a special element of the pseudospectrum of the non-rotating case. Thus, while the non-rotating flow is always modally stable to streamwise-independent perturbations, rotating flows with the smallest rotation are unstable at zero streamwise wavenumber, with the spanwise wavenumbers close to that of disturbances with the highest transient growth in the non-rotating case. The instability critical rotation number scales inversely as the square of the Reynolds number, which we demonstrate is the same as the scaling obeyed by the minimum perturbation amplitude in non-rotating shear flow needed for the pseudospectrum to cross the neutral line. Plane Poiseuille flow and plane Couette flow are shown to behave similarly in this context.

scholarly journals Magnetic Neutral Line Rotations in Flare-Productive Regions

2005 ◽  
Vol 13 ◽  
pp. 138-138
Author(s):  
Takako T. Ishii ◽  
Ayumi Asai ◽  
Hiroki Kurokawa ◽  
Tsutomu T. Takeuchi
Keyword(s):  
Neutral Line ◽  
Active Regions ◽  
Magnetic Configuration ◽  
Magnetic Neutral Line ◽  
Rotational Motions

AbstractWe examined the evolution of active regions and found that rotational motions of the neutral line in the δ-type magnetic configuration are common in the flare-productive active regions.

scholarly journals Hall MHD and Electron Inertia Effects in Current Sheet Formation at a Magnetic Neutral Line

2015 ◽  
Vol 5 (2) ◽  
pp. 109-125 ◽  
Author(s):  
Yuri E. Litvinenko ◽  
Liam C. McMahon
Keyword(s):  
Current Sheet ◽  
Finite Time ◽  
Numerical Solutions ◽  
Neutral Line ◽  
Singularity Formation ◽  
Time Singularity ◽  
Similarity Reduction ◽  
Electron Inertia ◽  
Magnetic Neutral Line ◽  
Finite Time Singularity

AbstractAn exact self-similar solution is used to investigate current sheet formation at a magnetic neutral line in incompressible Hall magnetohydrodynamics. The collapse to a current sheet is modelled as a finite-time singularity in the solution for electric current density at the neutral line. We establish that a finite-time collapse to the current sheet can occur in Hall magnetohydrodynamics, and we find a criterion for the finite-time singularity in terms of the initial conditions. We derive an asymptotic solution for the singularity formation and a formula for the singularity formation time. The analytical results are illustrated by numerical solutions, and we also investigate an alternative similarity reduction. Finally, we generalise our solution to incorporate resistive, viscous and electron inertia terms.

scholarly journals Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B ≠ 0 reconnection

2002 ◽  
Vol 9 (2) ◽  
pp. 139-147 ◽  
Author(s):  
T. Wiegelmann ◽  
J. Büchner
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Hall Current ◽  
Neutral Line ◽  
Magnetic Helicity ◽  
Perpendicular Magnetic Field ◽  
Guide Field ◽  
Magnetic Neutral Line ◽  
Field Lines ◽  
The Magnetic Field

Abstract. We investigate the evolution of magnetic helicity under kinetic magnetic reconnection in thin current sheets. We use Harris sheet equilibria and superimpose an external magnetic guide field. Consequently, the classical 2D magnetic neutral line becomes a field line here, causing a B ≠ 0 reconnection. While without a guide field, the Hall effect leads to a quadrupolar structure in the perpendicular magnetic field and the helicity density, this effect vanishes in the B ≠ 0 reconnection. The reason is that electrons are magnetized in the guide field and the Hall current does not occur. While a B = 0 reconnection leads just to a bending of the field lines in the reconnection area, thus conserving the helicity, the initial helicity is reduced for a B ≠ 0 reconnection. The helicity reduction is, however, slower than the magnetic field dissipation. The simulations have been carried out by the numerical integration of the Vlasov-equation.

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.

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