scholarly journals Magnetohydrodynamic waves and coronal seismology: an overview of recent results

2012 ◽  
Vol 370 (1970) ◽  
pp. 3193-3216 ◽  
Author(s):  
Ineke De Moortel ◽  
Valery M. Nakariakov
Keyword(s):  
Solar Atmosphere ◽  
Solar Flares ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Coronal Loops ◽  
Magnetohydrodynamic Waves ◽  
Coronal Seismology ◽  
Wide Range ◽  
Current Controversy ◽  
Intense Debate

Recent observations have revealed that magnetohydrodynamic (MHD) waves and oscillations are ubiquitous in the solar atmosphere, with a wide range of periods. We give a brief review of some aspects of MHD waves and coronal seismology that have recently been the focus of intense debate or are newly emerging. In particular, we focus on four topics: (i) the current controversy surrounding propagating intensity perturbations along coronal loops, (ii) the interpretation of propagating transverse loop oscillations, (iii) the ongoing search for coronal (torsional) Alfvén waves, and (iv) the rapidly developing topic of quasi-periodic pulsations in solar flares.

Linear Visco-Resistive Computations of Magnetohydrodynamic Waves: II. Viscous Effects

1994 ◽  
Vol 144 ◽  
pp. 506-508
Author(s):  
R. Erdélyi ◽  
M. Goossens
Keyword(s):  
Stress Tensor ◽  
Resonant Absorption ◽  
Mhd Waves ◽  
Larmor Radius ◽  
Coronal Loops ◽  
Viscous Effects ◽  
Viscous Stress Tensor ◽  
Magnetohydrodynamic Waves ◽  
Finite Larmor Radius ◽  
Viscosity Coefficients

AbstractResonant absorption of MHD waves in coronal loops is studied in linear, viscous MHD. Viscosity is described by Braginskii’s viscosity stress tensor. The dependence of the process of resonant absorption on the viscosity coefficients is studied. The compressive viscosity and viscosity due to the finite Larmor radius do not produce absorption. Shear viscosity produces absorption and is a viable candidate for heating coronal loops. The width of the dissipation layer is found to be proportional to, whereη1is the shear viscous coefficient of the full viscous stress tensor.

Slow magnetohydrodynamic waves in the solar atmosphere

2005 ◽  
Vol 364 (1839) ◽  
pp. 447-460 ◽  
Author(s):  
B Roberts
Keyword(s):  
Solar Atmosphere ◽  
Gordon Equation ◽  
Observational Evidence ◽  
Stratified Medium ◽  
Coronal Loops ◽  
Slow Mode ◽  
Magnetohydrodynamic Equations ◽  
Magnetohydrodynamic Waves ◽  
Klein Gordon ◽  
Special Case

There is increasingly strong observational evidence that slow magnetoacoustic modes arise in the solar atmosphere, either as propagating or standing waves. Sunspots, coronal plumes and coronal loops all appear to support slow modes. Here we examine theoretically how the slow mode may be extracted from the magnetohydrodynamic equations, considering the special case of a vertical magnetic field in a stratified medium: the slow mode is described by the Klein–Gordon equation. We consider its application to recent observations of slow waves in coronal loops.

scholarly journals Contribution of observed multi frequency spectrum of Alfvén waves to coronal heating

2019 ◽  
Vol 623 ◽  
pp. A37 ◽  
Author(s):  
P. Pagano ◽  
I. De Moortel
Keyword(s):  
Active Region ◽  
Power Spectrum ◽  
Solar Corona ◽  
Coronal Loop ◽  
Alfven Waves ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Coronal Loops ◽  
Phase Mixing ◽  
Transverse Oscillations

Context. Whilst there are observational indications that transverse magnetohydrodynamic (MHD) waves carry enough energy to maintain the thermal structure of the solar corona, it is not clear whether such energy can be efficiently and effectively converted into heating. Phase-mixing of Alfvén waves is considered a candidate mechanism, as it can develop transverse gradient where magnetic energy can be converted into thermal energy. However, phase-mixing is a process that crucially depends on the amplitude and period of the transverse oscillations, and only recently have we obtained a complete measurement of the power spectrum for transverse oscillations in the corona. Aims. We aim to investigate the heating generated by phase-mixing of transverse oscillations triggered by buffeting of a coronal loop that follows from the observed coronal power spectrum as well as the impact of these persistent oscillations on the structure of coronal loops. Methods. We considered a 3D MHD model of an active region coronal loop and we perturbed its footpoints with a 2D horizontal driver that represents a random buffeting motion of the loop footpoints. Our driver was composed of 1000 pulses superimposed to generate the observed power spectrum. Results. We find that the heating supply from the observed power spectrum in the solar corona through phase-mixing is not sufficient to maintain the million-degree active region solar corona. We also find that the development of Kelvin–Helmholtz instabilities could be a common phenomenon in coronal loops that could affect their apparent life time. Conclusions. This study concludes that is unlikely that phase-mixing of Alfvén waves resulting from an observed power spectrum of transverse coronal loop oscillations can heat the active region solar corona. However, transverse waves could play an important role in the development of small scale structures.

Damping of magnetohydrodynamic waves by resonant absorption in the solar atmosphere

2005 ◽  
Vol 364 (1839) ◽  
pp. 433-446 ◽  
Author(s):  
M Goossens ◽  
J Andries ◽  
I Arregui
Keyword(s):  
Resonant Absorption ◽  
Mhd Waves ◽  
Coronal Loops ◽  
Two Dimensional ◽  
Heliospheric Observatory ◽  
Magnetohydrodynamic Waves ◽  
One Dimensional ◽  
Magnetic Structures ◽  
Different Types ◽  
Kink Waves

In the last decade we have been overwhelmed by an avalanche of discoveries of magnetohydrodynamic (MHD) waves by the Solar and Heliospheric Observatory and Transition Region and Coronal Explorer observatories. Both standing and propagating versions of fast magnetoacoustic and slow magnetoacoustic MHD waves have been detected. Information on the damping times and damping distances of these waves is less detailed and less accurate than that on periods and amplitudes. Nevertheless, observations show the damping times and damping lengths are often short. Also, different types of MHD waves in different types of magnetic structures likely require different damping mechanisms. The phenomenon of fast damping is well documented for the standing fast magnetosonic kink waves in coronal loops. This paper concentrates on standing fast magnetosonic waves. It reports on results on periods and damping times due to resonant absorption in one-dimensional and two-dimensional models of coronal loops. Special attention is given to multiple modes.

scholarly journals Phase Mixing of Propagating Alfvén Waves

1985 ◽  
Vol 107 ◽  
pp. 365-369
Author(s):  
L. Nocera ◽  
B. Leroy ◽  
E. R. Priest
Keyword(s):  
Solar Corona ◽  
Solar Atmosphere ◽  
Outer Part ◽  
Alfven Waves ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Phase Mixing ◽  
The Waves

Among MHD waves, Alfvén waves have been proved to be the best candidates to reach the solar corona and, eventually, to be responsible for the heating of this outer part of the solar atmosphere. The problem arises, however, about the mechanism able to transform the energy stored in the waves into heat.

Linear Visco-Resistive Computations of Magnetohydrodynamic Waves: I. The Code and Test Cases

1994 ◽  
Vol 144 ◽  
pp. 503-505
Author(s):  
R. Erdélyi ◽  
M. Goossens ◽  
S. Poedts
Keyword(s):  
Resonant Absorption ◽  
Numerical Code ◽  
Mhd Waves ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Element Discretization ◽  
Flux Tubes ◽  
Magnetohydrodynamic Waves ◽  
Viscosity Coefficients ◽  
Magnetic Flux Tubes

AbstractThe stationary state of resonant absorption of linear, MHD waves in cylindrical magnetic flux tubes is studied in viscous, compressible MHD with a numerical code using finite element discretization. The full viscosity tensor with the five viscosity coefficients as given by Braginskii is included in the analysis. Our computations reproduce the absorption rates obtained by Lou in scalar viscous MHD and Goossens and Poedts in resistive MHD, which guarantee the numerical accuracy of the tensorial viscous MHD code.

Estimation of the Energy Flux of Torsional Alfvén Waves in the Lower Solar Atmosphere Based on Measurements of the Doppler Velocities

2021 ◽  
Vol 61 (7) ◽  
pp. 1035-1037
Author(s):  
Yu. T. Tsap ◽  
A. V. Stepanov ◽  
Yu. G. Kopylova ◽  
O. V. Khaneychuk ◽  
T. B. Goldvarg
Keyword(s):  
Solar Atmosphere ◽  
Energy Flux ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Lower Solar Atmosphere

Thermal trigger for solar flares and coronal loops formation

Solar Physics ◽  
1982 ◽  
Vol 75 (1-2) ◽  
pp. 237-244 ◽  
Author(s):  
B. V. Somov ◽  
S. I. Syrovatskii
Keyword(s):  
Solar Flares ◽  
Coronal Loops

Plasma Diagnostics of Microflares observed by STIX and AIA

2021 ◽  
Author(s):  
Jonas Saqri ◽  
Astrid Veronig ◽  
Ewan Dickson ◽  
Säm Krucker ◽  
Andrea Francesco Battaglia ◽  
...  
Keyword(s):  
Solar Flares ◽  
Magnetic Energy ◽  
Emission Measure ◽  
Transport Processes ◽  
X Rays ◽  
Solar Dynamics Observatory ◽  
Energy Bands ◽  
Accurate Analysis ◽  
Great Opportunity ◽  
Wide Range

<p>Solar flares are generally thought to be the impulsive release of magnetic energy giving rise to a wide range of solar phenomena that influence the heliosphere and in some cases even conditions of earth. Part of this liberated energy is used for particle acceleration and to heat up the solar plasma. The Spectrometer/Telescope for Imaging X-rays (STIX) instrument onboard the Solar Orbiter mission launched on February 10th 2020 promises advances in the study of solar flares of various sizes. It is capable of measuring X-ray spectra from 4 to 150 keV with 1 keV resolution binned into 32 energy bins before downlinking. With this energy range and sensitivity, STIX is capable of sampling thermal plasma with temperatures of≳10 MK, and to diagnose the nonthermal bremsstrahlung emission of flare-accelerated electrons. During the spacecraft commissioning phase in the first half of the year 2020, STIX observed 68 microflares. Of this set, 26 events could clearly be identified in at least two energy channels, all of which originated in an active region that was also visible from earth. These events provided a great opportunity to combine the STIX observations with the multi-band EUV imagery from the Atmospheric Imaging Assembly (AIA) instrument on board the earth orbiting Solar Dynamics Observatory (SDO). For the microflares that could be identified in two STIX science energy bands, it was possible to derive the temperature and emission measure (EM) of the flaring plasma assuming an isothermal source. For larger events where more detailed spectra could be derived, a more accurate analysis was performed by fitting the spectra assuming various thermal and nonthermal sources. These results are compared to the diagnostics derived from AIA images. To this aim, the Differential EmissionMeasure (DEM) was reconstructed from AIA observations to infer plasma temperatures and EM in the flaring regions. Combined with the the relative timing between the emission seen by STIX and AIA, this allows us to get deeper insight into the flare energy release and transport processes.</p>

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