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 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 A Storage Process of the Magnetic Energy in the Space Active Regions and Stellar Atmosphere

1990 ◽  
Vol 140 ◽  
pp. 17-19
Author(s):  
Li Zhongyuan
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Free Field ◽  
Stellar Atmosphere ◽  
Mhd Equations ◽  
Static Force ◽  
Specific Expression ◽  
Image Position ◽  
The Magnetic Field ◽  
Force Free Field

A few authors (Barnes and Sturrock, 1972; Ma, 1977; Svestka, 1977) have calculated the quantitative relationship between the static force-free field connecting the magnetic field and the twisting processes. They pointed out that the potential magnetic field without the current may be twisted into the force-free field with the enhanced current produced by the plasma rotation. Li et al. (1982) and Li and Hu (1984) have stated that the processes should be unsteady, and especially that they should not be static. The magnetic Reynold number is usually much larger than 100 in stellar atmosphere (Li et al., 1982). We adopt the following MHD equations: where the force - free factor α (t, r) depends on both, t and r. According to t h e kinematical momentum conservation, the following constraint is easily obtained: where V = (u, v, w) is the velocity field in the cylindrical coordinates. When studying the evolution of the kinematical force - free field, the in fluence of a reasonable flow on the variations of the magnetic field should be taken into account. After some reasonable simplification we deduce the specific expression of the variation law of the toroidal magnetic energy where J1 is the Bessel function of the first order. In the active region, magnetic energy including the term of a twisted effect f(t) is larger than that of the static force - free field.

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 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.

scholarly journals Nonlinear force-free modeling of magnetic fields in flare-productive active regions

2015 ◽  
Vol 11 (S320) ◽  
pp. 167-174
Author(s):  
M. S. Wheatland ◽  
S. A. Gilchrist
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Boundary Data ◽  
Numerical Solutions ◽  
Free Field ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Nonlinear Force ◽  
The Magnetic Field ◽  
Force Free Field

AbstractWe review nonlinear force-free field (NLFFF) modeling of magnetic fields in active regions. The NLFFF model (in which the electric current density is parallel to the magnetic field) is often adopted to describe the coronal magnetic field, and numerical solutions to the model are constructed based on photospheric vector magnetogram boundary data. Comparative tests of NLFFF codes on sets of boundary data have revealed significant problems, in particular associated with the inconsistency of the model and the data. Nevertheless NLFFF modeling is often applied, in particular to flare-productive active regions. We examine the results, and discuss their reliability.

scholarly journals Ion velocity distributions within the LLBL and their possible implication to multiple reconnections

2004 ◽  
Vol 22 (1) ◽  
pp. 213-236 ◽  
Author(s):  
O. L. Vaisberg ◽  
L. A. Avanov ◽  
T. E. Moore ◽  
V. N. Smirnov
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Tube ◽  
Magnetic Flux Tube ◽  
Flux Tubes ◽  
Different Types ◽  
Subsolar Point ◽  
Magnetic Flux Tubes ◽  
Ion Velocity ◽  
Field Lines

Abstract. We analyze two LLBL crossings made by the Interball-Tail satellite under a southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within the LLBL are observed: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counter-streaming components of magnetosheath-type, and (c) distributions with three components, one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a) type fits to the single magnetic flux tube formed by reconnection between the magnetospheric and magnetosheath magnetic fields. We argue that two counter-streaming magnetosheath-like ion components observed by Interball within the LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within the magnetosphere. Types (b) and (c) ion velocity distributions would form within spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in the LLBL indicate that a significant part of the LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection Χ-lines between magnetosheath and magnetospheric flux tubes. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind-magnetosphere interactions)

scholarly journals The Small-Scale Photospheric Magnetic Field as an Indicator of the Dynamo

1993 ◽  
Vol 141 ◽  
pp. 143-146
Author(s):  
K. Petrovay ◽  
G. Szakály
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Observational Data ◽  
Convective Zone ◽  
Small Scale ◽  
Dynamo Theory ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
Surface Fields

AbstractThe presently widely accepted view that the solar dynamo operates near the base of the convective zone makes it difficult to relate the magnetic fields observed in the solar atmosphere to the fields in the dynamo layer. The large amount of observational data concerning photospheric magnetic fields could in principle be used to impose constraints on dynamo theory, but in order to infer these constraints the above mentioned “missing link” between the dynamo and surface fields should be found. This paper proposes such a link by modeling the passive vertical transport of thin magnetic flux tubes through the convective zone.

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