Theory of MHD Waves in the Solar Corona

2003 ◽  
pp. 167-191 ◽  
Author(s):  
B. Roberts ◽  
V. M. Nakariakov
Keyword(s):  
Solar Corona ◽  
Mhd Waves

scholarly journals Prominence Seismology

2013 ◽  
Vol 8 (S300) ◽  
pp. 30-39 ◽  
Author(s):  
J. L. Ballester
Keyword(s):  
Solar Corona ◽  
Small Amplitude ◽  
Dense Plasma ◽  
Mhd Waves ◽  
Physical Parameters ◽  
Solar Prominences ◽  
Dynamic Structures

AbstractQuiescent solar prominences are cool and dense plasma clouds located inside the hot and less dense solar corona. They are highly dynamic structures displaying flows, instabilities, oscillatory motions, etc. The oscillations have been mostly interpreted in terms of magnetohydrodynamic (MHD) waves, which has allowed to perform prominence seismology as a tool to determine prominence physical parameters difficult to measure. Here, several prominence seismology applications to large and small amplitude oscillations are reviewed.

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

2018 ◽  
Vol 145 ◽  
pp. 03009 ◽  
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.

scholarly journals MHD simulations of the in situ generation of kink and sausage waves in the solar corona by collision of dense plasma clumps

2019 ◽  
Vol 626 ◽  
pp. A53 ◽  
Author(s):  
P. Pagano ◽  
H. J. Van Damme ◽  
P. Antolin ◽  
I. De Moortel
Keyword(s):  
Solar Corona ◽  
Theoretical Study ◽  
Simple Technique ◽  
Mhd Waves ◽  
Mhd Simulations ◽  
Wave Guides ◽  
2D And 3D ◽  
The Waves ◽  
Space Description

Context. Magnetohydrodynamic (MHD) waves are ubiquitous in the solar corona where the highly structured magnetic fields provide efficient wave guides for their propagation. While MHD waves have been observed originating from lower layers of the solar atmosphere, recent studies have shown that some can be generated in situ by the collision of dense counter-propagating flows. Aims. In this theoretical study, we analyse the mechanism that triggers the propagation of kink and sausage modes in the solar corona following the collision of counter-propagating flows, and how the properties of the flows affect the properties of the generated waves. Methods. To study in detail this mechanism we ran a series of ideal 2D and 3D MHD simulations where we varied the properties of the counter-propagating flows; by means of a simple technique to estimate the amplitudes of the kink and sausage modes, we investigated their role in the generation and propagation of the MHD waves. Results. We find that the amplitude of the waves is largely dependent on the kinetic energy of the flows, and that the onset of kink or sausage modes depends on the asymmetries between the colliding blobs. Moreover, the initial wavelength of the MHD waves is associated with the magnetic configuration resulting from the collision of the flows. We also find that genuine 3D systems respond with smaller wave amplitudes. Conclusions. In this study, we present a parameter space description of the mechanism that leads to the generation of MHD waves from the collision of flows in the corona. Future observations of these waves can be used to understand the properties of the plasma and magnetic field of the solar corona.

scholarly journals MHD Seismology of the Solar Corona with SOHO and TRACE

2001 ◽  
Vol 203 ◽  
pp. 353-355 ◽  
Author(s):  
V. M. Nakariakov
Keyword(s):  
Magnetic Field ◽  
Solar Corona ◽  
Decay Time ◽  
Transport Coefficients ◽  
Mhd Waves ◽  
The Mean ◽  
Temporal And Spatial ◽  
Wave Phenomena ◽  
The Magnetic Field ◽  
Imaging Telescopes

Recent discoveries of MHD wave motions in the solar corona done with EUV imaging telescopes onboard SOHO and TRACE provide an observational basis for the MHD seismology of the corona. Measuring the properties of MHD waves and oscillations (periods, wavelengths, amplitudes, temporal and spatial signatures), combined with theoretical modeling of the wave phenomena, allow us to determine values of the mean parameters of the corona (the magnetic field strength, transport coefficients, etc.). As an example, we consider post-flare decaying oscillations of loops, observed with TRACE (14th July 1998 at 12:55 UT). An analysis of the oscillations shows that they are quasi-harmonic, with a period of about 265 s, and quickly decaying with the decay time of about 14.5 min. The period of oscillations allows us to determine the Alfvén speed in the oscillating loop about 770 km/s. This value can be used for deduction of the value of the magnetic field in the loop (giving 10-30 G). The decay time, in the assumption that the decay is caused by viscous (or resistive) dissipation, gives us the Reynolds number of 105.3-6.1 (or the Lundquist number of 105.0-5.8).

scholarly journals Mode Coupling in the Solar Corona. V. Reduction of the Coupled Equations

1977 ◽  
Vol 30 (6) ◽  
pp. 661 ◽  
Author(s):  
DB Melrose
Keyword(s):  
Solar Corona ◽  
Mode Coupling ◽  
Mhd Waves ◽  
Fast Mode ◽  
Coupling Theory ◽  
Mode Coupling Theory ◽  
Coupled Equations

A simplified version of the mode-coupling theory of Clemmow and Heading is developed by reducing the set of coupled equations to two for the magnetoionic theory and three for the MHD theory. The simplified theory reproduces known results for coupling in the neighbourhood of coupling points. It is used to treat coupling between the MHD waves, and it is found that coupling between the fast mode and the Alfven mode for VA ;?; C, is stronger than the coupling between any other pair of modes. The strongest coupling of all is between the Alfven and slow (magnetoacoustic) modes for VA ~ C,.

Mapping the global magnetic field in the solar corona through magnetoseismology

2021 ◽  
Author(s):  
Zihao Yang ◽  
Christian Bethge ◽  
Hui Tian ◽  
Steven Tomczyk ◽  
Richard Morton ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Solar Corona ◽  
Phase Speed ◽  
Magnetic Coupling ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Spectral Lines ◽  
Mhd Waves ◽  
Global Magnetic Field

<p>Magnetoseismology, a technique of magnetic field diagnostics based on observations of magnetohydrodynamic (MHD) waves, has been widely used to estimate the field strengths of oscillating structures in the solar corona. However, previously magnetoseismology was mostly applied to occasionally occurring oscillation events, providing an estimate of only the average field strength or one-dimensional distribution of field strength along an oscillating structure. This restriction could be eliminated if we apply magnetoseismology to the pervasive propagating transverse MHD waves discovered with the Coronal Multi-channel Polarimeter (CoMP). Using several CoMP observations of the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of the plasma density and wave phase speed in the corona, which allow us to map both the strength and direction of the coronal magnetic field in the plane of sky. We also examined distributions of the electron density and magnetic field strength, and compared their variations with height in the quiet Sun and active regions. Such measurements could provide critical information to advance our understanding of the Sun's magnetism and the magnetic coupling of the whole solar atmosphere.</p>

scholarly journals Mode Coupling in the Solar Corona. IV. Magnetohydrodynamic Waves

1977 ◽  
Vol 30 (6) ◽  
pp. 647 ◽  
Author(s):  
DB Melrose ◽  
MA Simpson
Keyword(s):  
General Theory ◽  
Solar Corona ◽  
Mode Coupling ◽  
Stratified Medium ◽  
Mhd Waves ◽  
Fast Mode ◽  
Slow Mode ◽  
Magnetohydrodynamic Waves ◽  
Quartic Equation ◽  
Obliquely Incident

A general theory for coupling between MHD waves obliquely incident on a stratified medium is developed. Coupling between the Alfvtln mode and the magnetoacoustic mode (the fast mode for VA > cs and the slow mode for VA < cs) is affected little by the finiteness of Cs/VA for VA >> Cs and the coupling becomes weaker as Cs/VA is increased towards unity. Coupling between the fast and slow modes for VA ≈ C. is discussed qualitatively using solutions of the MHD counterpart of the Booker quartic equation.

scholarly journals How Does Transverse MHD Wave-driven Turbulence Influence the Density Filling Factor in the Solar Corona?

2021 ◽  
Vol 923 (2) ◽  
pp. 178
Author(s):  
Samrat Sen ◽  
Vaibhav Pant
Keyword(s):  
Solar Corona ◽  
Filling Factor ◽  
Coronal Holes ◽  
Mhd Waves ◽  
Coronal Loops ◽  
Entire Volume ◽  
Mhd Simulations ◽  
Simulation Domain ◽  
Sensitive Line ◽  
Overdense Plasma

Abstract It is well established that transverse MHD waves are ubiquitous in the solar corona. One of the possible mechanisms for heating both open (e.g., coronal holes) and closed (e.g., coronal loops) magnetic field regions of the solar corona is MHD wave-driven turbulence. In this work, we study the variation of the filling factor of overdense structures in the solar corona due to the generation of transverse MHD wave-driven turbulence. Using 3D MHD simulations, we estimate the density filling factor of an open magnetic structure by calculating the fraction of the volume occupied by the overdense plasma structures relative to the entire volume of the simulation domain. Next, we perform forward modeling and generate synthetic spectra of Fe xiii 10749 Å and 10800 Å density-sensitive line pairs using FoMo. Using the synthetic images, we again estimate the filling factors. The estimated filling factors obtained from both methods are in reasonable agreement. Also, our results match fairly well with the observations of filling factors in coronal holes and loops. Our results show that the generation of turbulence increases the filling factor of the solar corona.

Wave-Based Heating Mechanisms for the Solar Corona

1994 ◽  
Vol 144 ◽  
pp. 443-451 ◽  
Author(s):  
F. Malara ◽  
M. Velli
Keyword(s):  
Solar Corona ◽  
Nonlinear Effects ◽  
Resonant Absorption ◽  
Mhd Waves ◽  
Small Scale ◽  
Phase Mixing ◽  
Low Dissipation ◽  
Wave Heating ◽  
Lower Solar Atmosphere ◽  
Small Scale Structures

AbstractDissipation of MHD waves generated in the lower solar atmosphere has long been proposed as a means to heat the solar corona. Because of the extremely low dissipation coefficients of the coronal plasma large gradients are necessary to efficiently dissipate such waves. Interactions with the inhomogeneities of the background medium may represent a way to create small scale structures, phase-mixing and resonant absorption being important examples. The generalization of such ideas to propagation in complex geometries (e.g., containing X type neutral points) and the extension to nonlinear effects are paramount to the development of wave-heating theories.

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