Magnetic field and turbulent velocities in the solar corona

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

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Faint Hα Emission in the Corona and Its Relation to the Prominences

International Astronomical Union Colloquium ◽

10.1017/s0252921100025550 ◽

1994 ◽

Vol 144 ◽

pp. 339-342

Author(s):

V. N. Dermendjiev ◽

Z. Mouradian ◽

J.- L. Leroy ◽

P. Duchlev

Keyword(s):

Magnetic Field ◽

Solar Corona ◽

Essential Role ◽

Hα Emission

AbstractThe relation between episodically observed in the solar corona faint Hαemission structures and the long lived prominences was studied. Particular consideration was given for cases in which the corresponding prominences had undergone DB process. An MHD interpretation of the phenomenon “emissions froides” (cool emission) is proposed in which an essential role plays the prominence supporting magnetic field.

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Radio Measurements of Coronal Magnetic Fields

International Astronomical Union Colloquium ◽

10.1017/s0252921100024933 ◽

1994 ◽

Vol 144 ◽

pp. 21-28 ◽

Cited By ~ 4

Author(s):

G. B. Gelfreikh

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Solar Corona ◽

Active Regions ◽

High Sensitivity ◽

Coronal Magnetic Field ◽

Transverse Magnetic ◽

Radio Sources ◽

Radio Waves ◽

Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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Propagation of an MHD Shock in the Vicinity of a Magnetic Neutral Sheet

Symposium - International Astronomical Union ◽

10.1017/s0074180900067802 ◽

1980 ◽

Vol 91 ◽

pp. 323-326

Author(s):

D. J. Mullan ◽

R. S. Steinolfson

Keyword(s):

Magnetic Field ◽

Cosmic Rays ◽

Solar Corona ◽

Large Scale ◽

Field Structure ◽

Neutral Sheet ◽

Solar Cosmic Rays ◽

Magnetic Field Structure ◽

Large Scale Magnetic Field ◽

Highly Correlated

The acceleration of solar cosmic rays in association with certain solar flares is known to be highly correlated with the propagation of an MHD shock through the solar corona (Svestka, 1976). The spatial structure of the sources of solar cosmic rays will be determined by those regions of the corona which are accessible to the flare-induced shock. The regions to which the flare shock is permitted to propagate are determined by the large scale magnetic field structure in the corona. McIntosh (1972, 1979) has demonstrated that quiescent filaments form a single continuous feature (a “baseball stitch”) around the surface of the sun. It is known that helmet streamers overlie quiescent filaments (Pneuman, 1975), and these helmet streamers contain large magnetic neutral sheets which are oriented essentially radially. Hence the magnetic field structure in the low solar corona is characterized by a large-scale radial neutral sheet which weaves around the entire sun following the “baseball stitch”. There is therefore a high probability that as a shock propagates away from a flare, it will eventually encounter this large neutral sheet.

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An MHD simulation model of time-dependent global solar corona with temporally varying solar-surface magnetic field maps

Journal of Geophysical Research Space Physics ◽

10.1002/2013ja018991 ◽

2013 ◽

Vol 118 (11) ◽

pp. 6889-6906 ◽

Cited By ~ 17

Author(s):

K. Hayashi

Keyword(s):

Magnetic Field ◽

Simulation Model ◽

Solar Corona ◽

Solar Surface ◽

Time Dependent ◽

Mhd Simulation ◽

Surface Magnetic Field

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EVOLUTION CHANGES OF MAGNETIC FIELD STRUCTURE OF SOLAR CORONA

Proceedings of the 22nd All-Russia Conference on Solar and Solar-Terrestrial Physics ◽

10.31725/0552-5829-2018-287-290 ◽

2018 ◽

Author(s):

V.L. Merzlyakov ◽

◽

L.I. Starkova ◽

Keyword(s):

Magnetic Field ◽

Solar Corona ◽

Field Structure ◽

Magnetic Field Structure

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The Evolution of a Sheared Potential Magnetic Field in the Solar Corona

Basic Plasma Processes on the Sun ◽

10.1007/978-94-009-0667-9_54 ◽

1990 ◽

pp. 309-312

Author(s):

J. T. Karpen ◽

S. K. Antiochos ◽

C. R. DeVore

Keyword(s):

Magnetic Field ◽

Solar Corona

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Magnetically Driven Motions in Solar Corona

Symposium - International Astronomical Union ◽

10.1017/s0074180900068005 ◽

1980 ◽

Vol 91 ◽

pp. 487-489 ◽

Cited By ~ 1

Author(s):

B. V. Somov ◽

S. I. Syrovatskii

Keyword(s):

Magnetic Field ◽

Solar Corona ◽

Magnetic Reconnection ◽

Current Sheet ◽

Magnetic Dipole ◽

Plasma Flow ◽

Strong Field ◽

Plasma Velocity ◽

Rapid Process

Solution of the nonlinear MHD problem of plasma flow in an increasing dipolar magnetic field is obtained in the approximation of a strong field. The distributions of plasma velocity, displacement, and density are calculated. The situation when the magnetic dipole is ‘increased’ by rapid process of magnetic reconnection or current sheet rupture is illustrated. Possible applications are discussed in connection with plasma ejections from chromosphere in corona.

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Magnetohydrodynamic calculation of the temperature and wind velocity profile of the solar transition region. Preliminary results.

MATEC Web of Conferences ◽

10.1051/matecconf/201814503009 ◽

2018 ◽

Vol 145 ◽

pp. 03009 ◽

Cited By ~ 2

Author(s):

Todor M. Mishonov ◽

Albert M. Varonov ◽

Nedeltcho I. Zahariev ◽

Rositsa V. Topchiyska ◽

Boian V. Lazov ◽

...

Keyword(s):

Magnetic Field ◽

Spectral Density ◽

Solar Corona ◽

Temperature Profile ◽

Transition Region ◽

Wind Velocity ◽

Spectral Lines ◽

Mhd Waves ◽

Dimensional Approximation ◽

Height Dependence

The sharp almost step like increase the temperature in the transition region (TR) between chromosphere and solar corona is well-known from decades; for first time we are giving a detailed magnetohydrodynamic (MHD) calculation of the height dependence of the temperature. The width of the transition region is evaluated by maximal value of the logarithmic derivative of the temperature. At fixed heating, only MHD can give such a narrow width and in such sense, even the qualitative agreement with the observational data, gives the final verdict what the heating mechanism of the solar corona is. Static profiles of the temperature and wind velocity are calculated for static frequency dependent spectral density of the incoming MHD waves; no time dependent computer simulations. At fixed spectral density of MHD waves, the MHD calculation predicts height dependence of the non-thermal broadening of spectral lines and its angular dependence. For illustration is used one dimensional approximation of completely ionized hydrogen plasma in weak magnetic field, but it is considered that the width of the TR is weakly dependent with respect of further elaboration. The analyzed MHD calculation is a numerical confirmation of the qualitative concept of self-induced opacity of the plasma with respect to MHD waves. The plasma viscosity strongly increases with the temperature. Heated by MHD waves, plasma increases the wave absorption and this positive feedback leads to further heating. The static temperature profile is a result of a self-consistent calculation of propagation of MHD wave through the static background of wind and temperature profile. The numerical method allows consideration of incoming MHD waves with an arbitrary spectral density. Further elaboration of the method are briefly discussed: influence of second viscosity in the chromospheric part of the TR, influence of the magnetic field on the coronal side of the TR and investigation of such type effects on the width of the TR.

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