Ion-acoustic instability caused by large-scale electric field in solar active regions

Solar Physics ◽  
1996 ◽  
Vol 165 (1) ◽  
pp. 139-153 ◽  
Author(s):  
A. N. Kryshtal ◽  
V. P. Kucherenko
Keyword(s):  
Electric Field ◽  
Large Scale ◽  
Active Regions ◽  
Acoustic Instability ◽  
Ion Acoustic ◽  
Solar Active Regions

scholarly journals The ion-acoustic instability in the pre-flare plasma near the loop footpoints at solar active regions

2013 ◽  
Vol 31 (12) ◽  
pp. 2193-2200 ◽  
Author(s):  
A. Kryshtal ◽  
S. Gerasimenko ◽  
A. Voitsekhovska ◽  
V. Fedun
Keyword(s):  
Large Scale ◽  
Active Regions ◽  
Threshold Value ◽  
Small Scale ◽  
Loop Current ◽  
Flare Loop ◽  
Acoustic Instability ◽  
Physical Conditions ◽  
Ion Acoustic ◽  
Flare Plasma

Abstract. The necessary physical conditions for development of the ion-acoustic instability in the chromospheric part of a flaring loop current circuit are investigated. Two possible scenarios have been studied. First, we consider that pre-flare loop plasma with the large-scale sub-Dreicer electric field has a classical Coulomb conductivity and, second, when anomalous resistance appears due to saturation of Bernstein turbulence. The Fontenla-Avrett-Loeser (FAL) model of the solar atmosphere was used to describe the pre-flare plasma. We have shown that investigated instability can grow and develop either in the presence of the Coulomb conductivity or saturated Bernstein turbulence. We demonstrate that in the case of small-scale instability, the threshold value for the degree of nonisothermality is high and, therefore, cannot be reached by inclusion of the ordinary Joule heating. The ion-acoustic instability can develop at the pre-flare loop footpoints provided the electrons are more than 10 times hotter than the ions there.

scholarly journals Solar photosphere magnetization

2020 ◽  
Vol 634 ◽  
pp. A40 ◽  
Author(s):  
Véronique Bommier
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Field Gradient ◽  
Magnetic Field Gradient ◽  
Active Regions ◽  
Spectral Lines ◽  
Solar Interior ◽  
Solar Photosphere ◽  
Total Charge ◽  
Solar Active Regions

Context. A recent review shows that observations performed with different telescopes, spectral lines, and interpretation methods all agree about a vertical magnetic field gradient in solar active regions on the order of 3 G km−1, when a horizontal magnetic field gradient of only 0.3 G km−1 is found. This represents an inexplicable discrepancy with respect to the divB = 0 law. Aims. The objective of this paper is to explain these observations through the law B = μ0(H + M) in magnetized media. Methods. Magnetization is due to plasma diamagnetism, which results from the spiral motion of free electrons or charges about the magnetic field. Their usual photospheric densities lead to very weak magnetization M, four orders of magnitude lower than H. It is then assumed that electrons escape from the solar interior, where their thermal velocity is much higher than the escape velocity, in spite of the effect of protons. They escape from lower layers in a quasi-static spreading, and accumulate in the photosphere. By evaluating the magnetic energy of an elementary atom embedded in the magnetized medium obeying the macroscopic law B = μ0(H + M), it is shown that the Zeeman Hamiltonian is due to the effect of H. Thus, what is measured is H. Results. The decrease in density with height is responsible for non-zero divergence of M, which is compensated for by the divergence of H, in order to ensure div B = 0. The behavior of the observed quantities is recovered. Conclusions. The problem of the divergence of the observed magnetic field in solar active regions finally reveals evidence of electron accumulation in the solar photosphere. This is not the case of the heavier protons, which remain in lower layers. An electric field would thus be present in the solar interior, but as the total charge remains negligible, no electric field or effect would result outside the star.

scholarly journals Joint Discussion 3 Solar active regions and 3D magnetic structure

2006 ◽  
Vol 2 (14) ◽  
pp. 139-168
Author(s):  
Debi Prasad Choudhary ◽  
Michal Sobotka
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Large Scale ◽  
Focal Point ◽  
Active Regions ◽  
Theoretical Modelling ◽  
Solar Chromosphere ◽  
Origin And Evolution ◽  
Solar Active Regions ◽  
The Magnetic Field

AbstractKeeping in view of the modern powerful observing tools, among othersHinode(formerlySOLAR-B),STEREOand Frequency-Agile Solar Radiotelescope, and sophisticated modelling techniques, Joint Discussion 3 during the IAU General Assembly 2006 focused on the properties of magnetic field of solar active regions starting in deep interior of the Sun, from where they buoyantly rise to the coronal heights where the site of most explosive events are located. Intimately related with the active regions, the origin and evolution of the magnetic field of quiet Sun, the large scale chromospheric structures were also the focal point of the Joint Discussion. The theoretical modelling of the generation and dynamics of magnetic field in solar convective zone show that the interaction of the magnetic field with the Coriolis force and helical turbulent convection results in the tilts and twists in the emerging flux. In the photosphere, some of these fluxes appear in sunspots with field strengths up to about 6100 G. Spectro-polarimetric measurements reveal that the line of sight velocities and magnetic field of these locations are found to be uncombed and depend on depth in the atmosphere and exhibit gradients or discontinuities. The inclined magnetic fields beyond penumbra appear as moving magnetic features that do not rise above upper photospheric heights. As the flux rises, the solar chromosphere is the most immediate and intermediary layer where competitive magnetic forces begin to dominate their thermodynamic counterparts. The magnetic field at these heights is now measured using several diagnostic lines such as CaII854.2 nm, HI656.3 nm, and HeI1083.0 nm. The radio observations show that the coronal magnetic field of post flare loops are of the order of 30 G, which might represent the force-free magnetic state of active region in the corona. The temperatures at these coronal heights, derived from the line widths, are in the range from 2.4 to 3.7 million degree. The same line profile measurements indicate the existence of asymmetric flows in the corona. The theoretical extrapolation of photospheric field into coronal heights and their comparison with the observations show that there exists a complex topology with separatrices associated to coronal null points. The interaction of these structures often lead to flares and coronal mass ejections. The current MHD modelling of active region field shows that for coronal mass ejection both local active region magnetic field and global magnetic field due to the surrounding magnetic flux are important. Here, we present an extended summary of the papers presented in Joint Discussion 03 and open questions related to the solar magnetic field that are likely to be the prime issue with the modern observing facilities such asHinodeandSTEREOmissions.

Large-scale patterns formed by solar active regions during the ascending phase of cycle 21

1983 ◽  
Vol 265 ◽  
pp. 1056 ◽  
Author(s):  
V. Gaizauskas ◽  
K. L. Harvey ◽  
J. W. Harvey ◽  
C. Zwaan
Keyword(s):  
Large Scale ◽  
Active Regions ◽  
Solar Active Regions

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
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.

On the nature of microwave pulsations from solar active regions

2003 ◽  
Vol 8 (5-6) ◽  
pp. 136-139
Author(s):  
G.B. Gelfreikh ◽  
◽  
Y.T. Tsap ◽  
Y.G. Kopylova ◽  
L.I. Tsvetkov ◽  
...  
Keyword(s):  
Active Regions ◽  
Solar Active Regions
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