scholarly journals Theoretical Models of Magnetic Flux Tubes: Structure and Dynamics

1994 ◽  
Vol 154 ◽  
pp. 407-421
Author(s):  
O Steiner
Keyword(s):  
Magnetic Flux ◽  
Line Emission ◽  
Theoretical Models ◽  
Small Scale ◽  
Solar Photosphere ◽  
Model Calculations ◽  
Flux Tubes ◽  
Wide Range ◽  
Magnetic Flux Tubes ◽  
Lower Chromosphere

Two types of model calculations for small scale magnetic flux tubes in the solar atmosphere are reviewed. In the first kind, one follows the temporal evolution governed by the complete set of the MHD and radiative transfer equations to a (quasi) stationary solution. From such a solution the continuum contrasts of a photospheric flux tube in the visible and in the infrared continuum at 1.6 μm have been computed and are briefly discussed. The second, more empirical type of method assumes the flux tubes to be in magnetohydrostatic equilibrium. It is computationally faster and more flexible and allows us to explore a wide range of parameters. Models and insights obtained from such parameter studies are discussed in some detail. These include an explanation for the peculiar variation of the area asymmetry of Stokes V profiles across the solar disk in terms of mass motions in the surroundings of magnetic flux tubes.Furthermore, a two-dimensional model of the lower chromosphere that has been developed is presented. Emphasis is laid on the effect of thermal bifurcation of the lower chromosphere on the structure of the chromospheric magnetic field. If the cool carbon monoxide clouds, observed in the infrared, occupy the non-magnetic regions, the flux tubes expand very strongly and form a magnetic canopy with an almost horizontal base. This has consequences for the spatial distribution of the Ca II K spectral line emission.Finally, some consideration is given to the formation and destruction of intense magnetic flux tubes in the solar photosphere. The formation is described as a consequence of the flux expulsion process that leads to a convective instability. A possible observational signature of this mechanism is proposed.

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 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.

scholarly journals Heating of Stellar Chromospheres and Transition Regions

2004 ◽  
Vol 219 ◽  
pp. 437-448
Author(s):  
Zdzislaw E. Musielak
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Acoustic Waves ◽  
Theoretical Models ◽  
Flux Tubes ◽  
Stellar Convection ◽  
Wave Heating ◽  
Active Stars ◽  
Magnetic Flux Tubes ◽  
Magnetic Waves

To explain the heating of stellar chromospheres and transition regions, two classes of heating mechanisms have been considered: dissipation of acoustic and magnetic waves generated in stellar convection zones; and dissipation of currents generated by photospheric motions of surface magnetic fields. The focus of this paper is on the wave heating mechanisms and on recent results which demonstrate that theoretical models of stellar chromospheres based on the wave heating can explain the “basal flux” and the observed Ca II emission in most stars but cannot account for the observed Mg II emission in active stars. The obtained results clearly show that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres and transition regions.

scholarly journals Magnetic structure of sunspot under the photosphere

2009 ◽  
Vol 5 (H15) ◽  
pp. 351-351
Author(s):  
Elena A. Kirichek ◽  
Alexandr A. Solov'ev
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Large Scale ◽  
Propagation Speed ◽  
Theoretical Models ◽  
Flux Tubes ◽  
Magnetoacoustic Waves ◽  
Deep Layers ◽  
Magnetic Flux Tubes ◽  
Wave Propagation Speed

In recent years, the local helioseismology has become a highly effective tool for investigating subphotospheric layers of the Sun, which can yield fairly detailed distributions of the subphotospheric temperatures and large-scale plasma flows based on the spectra of the oscillations observed at the photospheric layers and the observed peculiarities of propagation of magnetoacoustic waves in this medium (Zhao et al. (2001), Kosovichev (2006)). Unfortunately, the effects of temperature and the magnetic field on the wave propagation speed have not yet been separated Kosovichev (2006), so that the structure of the sunspot magnetic field in deep layers, beneath the photosphere, remains a subject of purely theoretical analysis. In his analysis of some theoretical models of the subphotospheric layers of sunspots based on recent helioseismological data, Kosovichev (2006) concluded that Parker's (“spaghetti”) cluster model Parker (1979) is most appropriate. In this model, the magnetic flux in the sunspot umbra is concentrated into separate, strongly compressed, vertical magnetic flux tubes that are interspaced with plasma that is almost free of magnetic field; the plasma can move between these tubes.

scholarly journals Multi-scale dynamics of magnetic flux tubes and inverse magnetic energy transfer

2020 ◽  
Vol 86 (4) ◽  
Author(s):  
Muni Zhou ◽  
Nuno F. Loureiro ◽  
Dmitri A. Uzdensky
Keyword(s):  
Magnetic Flux ◽  
Time Evolution ◽  
Magnetic Energy ◽  
Numerical Study ◽  
Three Dimensional ◽  
Early Time ◽  
Small Scale ◽  
Flux Tubes ◽  
Seed Field ◽  
Magnetic Flux Tubes

We report on an analytical and numerical study of the dynamics of a three-dimensional array of identical magnetic flux tubes in the reduced-magnetohydrodynamic description of the plasma. We propose that the long-time evolution of this system is dictated by flux-tube mergers, and that such mergers are dynamically constrained by the conservation of the pertinent (ideal) invariants, viz. the magnetic potential and axial fluxes of each tube. We also propose that in the direction perpendicular to the merging plane, flux tubes evolve in a critically balanced fashion. These notions allow us to construct an analytical model for how quantities such as the magnetic energy and the energy-containing scale evolve as functions of time. Of particular importance is the conclusion that, like its two-dimensional counterpart, this system exhibits an inverse transfer of magnetic energy that terminates only at the system scale. We perform direct numerical simulations that confirm these predictions and reveal other interesting aspects of the evolution of the system. We find, for example, that the early time evolution is characterized by a sharp decay of the initial magnetic energy, which we attribute to the ubiquitous formation of current sheets. We also show that a quantitatively similar inverse transfer of magnetic energy is observed when the initial condition is a random, small-scale magnetic seed field.

Emergence of undulatory magnetic flux tubes by small scale reconnections

2006 ◽  
Vol 38 (5) ◽  
pp. 902-905 ◽  
Author(s):  
E. Pariat ◽  
G. Aulanier ◽  
B. Schmieder ◽  
M.K. Georgoulis ◽  
D.M. Rust ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Small Scale ◽  
Flux Tubes ◽  
Magnetic Flux Tubes

scholarly journals Mass and energy supply of a cool coronal loop near its apex

2018 ◽  
Vol 611 ◽  
pp. A49 ◽  
Author(s):  
Limei Yan ◽  
Hardi Peter ◽  
Jiansen He ◽  
Lidong Xia ◽  
Linghua Wang
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Magnetic Reconnection ◽  
Transition Region ◽  
Doppler Velocity ◽  
Small Scale ◽  
Solar Dynamics Observatory ◽  
Plasma Properties ◽  
Flux Tubes ◽  
Magnetic Flux Tubes

Context. Different models for the heating of solar corona assume or predict different locations of the energy input: concentrated at the footpoints, at the apex, or uniformly distributed. The brightening of a loop could be due to the increase in electron density ne, the temperature T, or a mixture of both.Aim. We investigate possible reasons for the brightening of a cool loop at transition region temperatures through imaging and spectral observation.Methods. We observed a loop with the Interface Region Imaging Spectrograph (IRIS) and used the slit-jaw images together with spectra taken at a fixed slit position to study the evolution of plasma properties in and below the loop. We used spectra of Si iv, which forms at around 80 000 K in equilibrium, to identify plasma motions and derive electron densities from the ratio of inter-combination lines of O IV. Additional observations from the Solar Dynamics Observatory (SDO) were employed to study the response at coronal temperatures (Atmospheric Imaging Assembly, AIA) and to investigate the surface magnetic field below the loop (Helioseismic and Magnetic Imager, HMI).Results. The loop first appears at transition region temperatures and later also at coronal temperatures, indicating a heating of the plasma in the loop. The appearance of hot plasma in the loop coincides with a possible accelerating upflow seen in Si IV, with the Doppler velocity shifting continuously from ~−70 km s−1 to ~−265 km s−1. The 3D magnetic field lines extrapolated from the HMI magnetogram indicate possible magnetic reconnection between small-scale magnetic flux tubes below or near the loop apex. At the same time, an additional intensity enhancement near the loop apex is visible in the IRIS slit-jaw images at 1400 Å. These observations suggest that the loop is probably heated by the interaction between the loop and the upflows, which are accelerated by the magnetic reconnection between small-scale magnetic flux tubes at lower altitudes. Before and after the possible heating phase, the intensity changes in the optically thin (Si IV) and optical thick line (C II) are mainly contributed by the density variation without significant heating.Conclusions. We therefore provide evidence for the heating of an envelope loop that is affected by accelerating upflows, which are probably launched by magnetic reconnection between small-scale magnetic flux tubes underneath the envelope loop. This study emphasizes that in the complex upper atmosphere of the Sun, the dynamics of the 3D coupled magnetic field and flow field plays a key role in thermalizing 1D structures such as coronal loops.

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