scholarly journals Empirical Models of Photospheric Flux Tubes

1990 ◽  
Vol 138 ◽  
pp. 103-120
Author(s):  
S.K. Solanki
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Empirical Models ◽  
Size Spectrum ◽  
Flux Tubes ◽  
Magnetic Elements ◽  
Derived Properties ◽  
Quantitative Results ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

The empirically derived properties of magnetic flux tubes at both ends of the size spectrum, i.e. magnetic elements and sunspots, are reviewed. Emphasis is placed on quantitative results. The following parameters are discussed in greater detail: The strength and structure of the magnetic field, the temperature stratification and the structure of the velocity field.

scholarly journals Solar and stellar magnetic flux tubes

1996 ◽  
Vol 176 ◽  
pp. 201-216
Author(s):  
Sami K. Solanki
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Magnetic Flux ◽  
Large Range ◽  
The Sun ◽  
Flux Tubes ◽  
Magnetic Elements ◽  
Turbulent Pressure ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

The magnetic field of the Sun is mainly concentrated into intense magnetic flux tubes having field strengths of the order of 1 kG. In this paper an overview is given of the thermal and magnetic properties of these flux tubes, which are known to exhibit a large range in size, from the smallest magnetic elements to sunspots. Differences and similarities between the largest and smallest features are stressed. Some thoughts are also presented on how the properties of magnetic flux tubes are expected to scale from the solar case to that of solar-like stars. For example, it is pointed out that on giants and supergiants turbulent pressure may dominate over gas pressure as the main confining agent of the magnetic field. Arguments are also presented in favour of a highly complex magnetic geometry on very active stars. Thus the very large starspots seen in Doppler images probably are conglomerates of smaller (but possibly still sizable) spots.

scholarly journals What are the Radio Filaments Near the Galactic Center?

1996 ◽  
Vol 169 ◽  
pp. 247-261 ◽  
Author(s):  
Mark Morris
Keyword(s):  
Magnetic Field ◽  
Galactic Center ◽  
Galactic Plane ◽  
Local Source ◽  
Flux Tubes ◽  
Flux Lines ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field ◽  
Relativistic Particles ◽  
Projected Distance

A population of nonthermally-emitting radio filaments tens of parsecs in length has been observed within a projected distance of ∼130 pc of the Galactic center. More or less perpendicular to the Galactic plane, they appear to define the flux lines of a milligauss magnetic field. The characteristics of the known filaments are summarized. Three fundamental questions raised by these structures are discussed: 1) Do they represent magnetic flux tubes embedded within an ubiquitous, dipole magnetic field permeating the inner Galaxy, but which have been illuminated by some local source of relativistic particles, or are they instead isolated, self-sustaining current paths with an approximately force-free magnetic configuration in pressure equilibrium with the interstellar medium? 2) What is the source of either the magnetic field or the current? and 3) What is the source of the relativistic particles which provide the illuminating synchrotron radiation? We are nearer an answer to the the last of these questions than to the others, although several interesting models have been proposed.

scholarly journals Twist and writhe of δ-island active regions

2010 ◽  
Vol 6 (S273) ◽  
pp. 153-156
Author(s):  
M. C. López Fuentes ◽  
C. H. Mandrini ◽  
P. Démoulin
Keyword(s):  
Magnetic Field ◽  
Flux Tube ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Coronal Structure ◽  
Flux Tubes ◽  
Single Mechanism ◽  
Magnetic Flux Tubes ◽  
Kink Instability ◽  
The Magnetic Field

AbstractWe study the magnetic helicity properties of a set of peculiar active regions (ARs) including δ-islands and other high-tilt bipolar configurations. These ARs are usually identified as the most active in terms of flare and CME production. Due to their observed structure, they have been associated with the emergence of magnetic flux tubes that develop a kink instability. Our main goal is to determine the chirality of the twist and writhe components of the AR magnetic helicity in order to set constrains on the possible mechanisms producing the flux tube deformations. We determine the magnetic twist comparing observations of the AR coronal structure with force-free models of the magnetic field. We infer the flux-tube writhe from the rotation of the main magnetic bipole during the observed evolution. From the relation between the obtained twist and writhe signs we conclude that the development of the kink instability cannot be the single mechanism producing deformed flux-tubes.

scholarly journals Generation and propagation of Alfvén waves in solar atmosphere

2008 ◽  
Vol 4 (S257) ◽  
pp. 555-561 ◽  
Author(s):  
Yuri T. Tsap ◽  
Alexander V. Stepanov ◽  
Yulia. G. Kopylova
Keyword(s):  
Magnetic Field ◽  
Cutoff Frequency ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Flux Tubes ◽  
Convective Motions ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field ◽  
Lower Chromosphere

AbstractThe propagation of Alfvén waves from the photosphere into the corona with regard to the fine structure of the magnetic field is considered. The energy flux of Alfvén–type waves generated in the photosphere by convective motions does not depend on the ionization ratio. The reflection coefficient continuously decreases with a decrease of wave period. Influence of the external magnetic field on the Spruit cutoff frequency for transverse (kink) modes excited in the thin magnetic flux tubes is analyzed. Torsional modes can penetrate into the upper atmosphere most effectively since their amplitudes does not increase with height in the photosphere while kink ones can be transformed into shock waves in the lower chromosphere because of a significant increase of amplitudes. In spite of stratification the linearity of Alfvén–type modes in the chromosphere is conserved due to violation of the WKB approximation. The important role of the magnetic canopy is discussed. Alfvén waves generated by convective motions in the photosphere can contribute significantly to the heating of the coronal plasma in quite regions of the Sun.

scholarly journals Investigation of Spatially Unresolved Magnetic Field Outside Sunspots Using Hinode/SOT Observations

2016 ◽  
Vol 12 (S325) ◽  
pp. 59-62
Author(s):  
Olga Botygina ◽  
Mykola Gordovskyy ◽  
Vsevolod Lozitsky
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Zeeman Effect ◽  
Active Regions ◽  
Line Ratio ◽  
Optical Telescope ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

AbstractThe structure of photospheric magnetic fields outside sunspots is investigated in three active regions using Hinode/Solar Optical Telescope(SOT) observations. We analyze Zeeman effect in FeI 6301.5 and FeI 6302.5 lines and determine the observed magnetic field value Beff for each of them. We find that the line ratio Beff(6301)/Beff(6302) is close to 1.3 in the range Beff < 0.2 kG, and close to 1.0 for 0.8 kG < Beff < 1.2 kG. We find that the observed magnetic field is formed by flux tubes with the magnetic field strengths 1.3 − 2.3 kG even in places with weak observed magnetic field fluxes. We also estimate the diameters of smallest magnetic flux tubes to be 15 − 20 km.

scholarly journals Guided flows in coronal magnetic flux tubes

2017 ◽  
Vol 609 ◽  
pp. A18 ◽  
Author(s):  
A. Petralia ◽  
F. Reale ◽  
P. Testa
Keyword(s):  
Magnetic Field ◽  
Cylindrical Symmetry ◽  
Flow Speed ◽  
Back Reaction ◽  
Solar Dynamics Observatory ◽  
Initial Alignment ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
Solar Dynamics ◽  
The Magnetic Field

Context. There is evidence that coronal plasma flows break down into fragments and become laminar. Aims. We investigate this effect by modelling flows confined along magnetic channels. Methods. We consider a full magnetohydrodynamic (MHD) model of a solar atmosphere box with a dipole magnetic field. We compare the propagation of a cylindrical flow perfectly aligned with the field to that of another flow with a slight misalignment. We assume a flow speed of 200 km s-1 and an ambient magnetic field of 30 G. Results. We find that although the aligned flow maintains its cylindrical symmetry while it travels along the magnetic tube, the misaligned one is rapidly squashed on one side, becoming laminar and eventually fragmented because of the interaction and back-reaction of the magnetic field. This model could explain an observation made by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory of erupted fragments that fall back onto the solar surface as thin and elongated strands and end up in a hedge-like configuration. Conclusions. The initial alignment of plasma flow plays an important role in determining the possible laminar structure and fragmentation of flows while they travel along magnetic channels.

scholarly journals Energy Storage and Instability in Magnetic Flux Tubes

1980 ◽  
Vol 91 ◽  
pp. 291-294
Author(s):  
Takashi Sakurai
Keyword(s):  
Magnetic Field ◽  
Energy Storage ◽  
Magnetic Flux ◽  
Solar Corona ◽  
Free Field ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
Image Position ◽  
The Magnetic Field ◽  
Force Free Field

Now it is known that the solar corona consists of many loops which are believed to represent the structure of the magnetic field. Since the plasma is very tenuous in the corona, the equilibrium of the magnetic field is approximated by the force-free field:

scholarly journals Magnetic Flux Concentration by Siphon Flows in Isolated Magnetic Flux Tubes

1990 ◽  
Vol 138 ◽  
pp. 263-266
Author(s):  
John H. Thomas ◽  
Benjamin Montesinos
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Magnetic Polarity ◽  
Small Scale ◽  
Solar Photosphere ◽  
Flux Tubes ◽  
Magnetic Structures ◽  
Flux Concentration ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

Siphon flows along arched, isolated magnetic flux tubes, connecting photospheric footpoints of opposite magnetic polarity, cause a significant increase in the magnetic field strength of the flux tube due to the decreased internal gas pressure associated with the flow (the Bernoulli effect). These siphon flows offer a possible mechanism for producing intense, inclined, small-scale magnetic structures in the solar photosphere.

scholarly journals Study of helicity properties of peculiar active regions

2009 ◽  
Vol 5 (S264) ◽  
pp. 102-104 ◽  
Author(s):  
M. C. López Fuentes ◽  
C. H. Mandrini ◽  
P. Démoulin
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Active Regions ◽  
Solar Interior ◽  
Magnetic Helicity ◽  
Flux Tubes ◽  
Origin And Evolution ◽  
Magnetic Structures ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

AbstractPeculiar solar active regions (ARs), such as δ-islands and other high tilt bipoles, are commonly associated with the emergence of severely deformed magnetic flux tubes. Therefore, the study of these ARs provides valuable information on the origin and evolution of magnetic structures in the solar interior. Here, we infer the magnetic helicity properties of the flux tubes associated to a set of peculiar ARs by studying the evolution of photospheric magnetograms (SOHO/MDI) and coronal observations (SOHO/EIT and TRACE) in combination with force-free models of the magnetic field. We discuss how our results relate to different models of the evolution of emerging magnetic flux tubes.

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