MHD oscillations in solar and stellar coronae: Current results and perspectives (original) (raw)
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Solar Physics
Established in the late 1990s, solar MHD seismology has rapidly grown into a unique tool for diagnostics of the solar atmospheric plasma. This Topical Collection presents the current state-of-the-art in the field, addressing both observational and theoretical aspects: from oscillations in coronal loops and filaments to quasi-periodic pulsations in flares, MHD wave dynamics in non-adiabatic coronal conditions, waves in the lower atmosphere, and novel techniques and approaches to theoretical modelling and data analysis.
Magnetohydrodynamic waves and coronal seismology: an overview of recent results
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2012
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.
Astronomy & Astrophysics, 2006
Aims. We study the possible role of magnetohydrodynamic (MHD) waves in the heating of solar corona and magnetic coronal loops. Methods. Taking into account viscosity and thermal conductivity, we obtained a general fifth order dispersion relation for MHD waves propagating in a homogeneous, magnetically structured, compressible low-β plasma. The general fifth order dispersion relation has been solved numerically, and we discuss its application to magnetic coronal loops with the help of data provided by the NIXT mission. Results. The dispersion relation results in three modes, namely slow, fast, and thermal. The damping of both slow-and fast-mode waves depends upon the plasma density, the temperature, the magnetic field strength, and the angle of propagation relative to the background magnetic field. Slow-mode waves contribute to the heating of the solar corona, if one considers that they are generated in the corona by turbulent motions at magnetic reconnection sites. Calculations of wave damping rates determined from the dispersion relation indicate that slow-mode waves with periods of less than 60 s damp sufficiently rapidly and dissipate enough energy to balance the radiative losses, whereas the fast-mode waves with periods of less than 3 s may damp at rates great enough to balance the radiative losses in active regions. In the case of magnetic coronal loops, it is observed that slow-mode waves with frequencies greater than 0.003 Hz and fast mode waves with frequencies greater than 0.28 Hz (high frequency) are needed for coronal heating and to balance the radiative losses in active regions.
MESSENGER Observations of Magnetohydrodynamic Waves in the Solar Corona from Faraday Rotation
Solar Physics, 2012
During the declining phase of the longest solar minimum in a century, the arrival of the MESSENGER spacecraft at superior conjunction allowed the measurement of magnetohydrodynamic (MHD) waves in the solar corona with its 8 GHz radio frequency signal. MHD waves crossing the line of sight were measured via Faraday rotation fluctuations (FRFs) in the plane of polarization (PP) of MESSENGER's signal. FRFs in previous observations of the solar corona (at greater offset distances) consisted of a turbulent spectrum that decreased in power with increasing frequency and distance from the Sun. Occasionally a spectral line, a distinct peak in the power spectral density spectrum around 4 to 8 mHz,
Magnetohydrodynamic waves in coronal polar plumes
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2006
Polar plumes are cool, dense, linear, magnetically open structures that arise from predominantly unipolar magnetic footpoints in the solar polar coronal holes. As the Alfvén speed is decreased in plumes in comparison with the surrounding medium, these structures are natural waveguides for fast and slow magnetoacoustic waves. The simplicity of the geometry of polar plumes makes them an ideal test ground for the study of magnetohydrodynamic (MHD) wave interaction with solar coronal structures. The review covers recent observational findings of compressible and incompressible waves in polar plumes with imaging and spectral instruments, and interpretation of the waves in terms of MHD theory.
The Temporal Evolution of Linear Fast and Alfven MHD Waves in Solar Coronal Arcades
Highlights of Spanish Astrophysics V, 2010
The excitation and temporal evolution of fast and Alfvén magnetohydrodynamic oscillations in a two-dimensional coronal arcade are investigated. The approach is to consider an equilibrium magnetic and plasma structure and then to introduce a perturbation trying to mimic a nearby disturbance, such as a flare or filament eruption. By numerically solving the time-dependent linearised MHD wave equations the properties of the solutions have been studied. First, the properties of uncoupled fast and Alfvén waves are described. Then, longitudinal propagation of perturbations is included, and the properties of coupled waves are determined.
Magnetohydrodynamic Waves and Coronal Heating: Unifying Empirical and MHD Turbulence Models
The Astrophysical Journal, 2013
We present a new global model of the solar corona, including the low corona, the transition region and the top of chromosphere. The realistic 3D magnetic field is simulated using the data from the photospheric magnetic field measurements. The distinctive feature of the new model is incorporating the MHD Alfven wave turbulence. We assume this turbulence and its non-linear dissipation to be the only momentum and energy source for heating the coronal plasma and driving the solar wind. The difference between the turbulence dissipation efficiency in coronal holes and that in closed field regions is because the non-linear cascade rate degrades in strongly anisotropic (imbalanced) turbulence in coronal holes (no inward propagating wave), thus resulting in colder coronal holes with the bi-modal solar wind originating from them. The detailed presentation of the theoretical model is illustrated with the synthetic images for multi-wavelength EUV emission compared with the observations from SDO AIA and Stereo EUVI instruments for the Carrington rotation 2107.
MHD-Oscillations of Coronal Loops and Diagnostics of Flare Plasma
Effects of ballooning and radial oscillations of coronal magnetic loops on the modulations of microwave and X-ray emission from flare loops are considered. The damping mechanisms of loop MHD modes are analyzed. The method for diagnostics of flare plasma parameters using peculiarities of the microwave and X-ray pulsations is proposed. The diagnostic method was applied for two solar flares: on May 8, 1998 and August 28, 1999 observed with the Nobeyama Radioheliograph.
MHD waves in the solar north polar coronal hole
Astronomische Nachrichten, 2010
The effects, hitherto not treated, of the temperature and the number density gradients, both in the parallel and the perpendicular direction to the magnetic field, of O VI ions, on the MHD wave propagation characteristics in the solar North Polar Coronal Hole are investigated. We investigate the magnetosonic wave propagation in a resistive MHD regime where only the thermal conduction is taken into account. Heat conduction across the magnetic field is treated in a non-classical approach wherein the heat is assumed to be conducted by the plasma waves emitted by ions and absorbed at a distance from the source by other ions. Anisotropic temperature and the number density distributions of O VI ions revealed the chaotic nature of MHD standing wave, especially near the plume/interplume lane borders. Attenuation length scales of the fast mode is shown not to be smoothly varying function of the radial distance from the Sun.