Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.

Physics of Solar Prominences: II—Magnetic Structure and Dynamics

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) Alfven waves, and (iv) the rapidly developing topic of quasi-periodic pulsations in solar flares.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2011.0640

Magnetohydrodynamic waves and coronal seismology: an overview of recent results

The interaction of waves with obstacles is an everyday phenomenon in science and engineering, arising for example in acoustics, electromagnetism, seismology and hydrodynamics. The mathematical theory and technology needed to understand the phenomenon is known as multiple scattering, and this book is the first devoted to the subject. The author covers a variety of techniques, describing first the single-obstacle methods and then extending them to the multiple-obstacle case. A key ingredient in many of these extensions is an appropriate addition theorem: a coherent, thorough exposition of these theorems is given, and computational and numerical issues around them are explored. The application of these methods to different types of problems is also explained; in particular, sound waves, electromagnetic radiation, waves in solids and water waves. A comprehensive bibliography of some 1400 items rounds off the book, which will be an essential reference on the topic for applied mathematicians, physicists and engineers.

Multiple Scattering: Interaction of Time-Harmonic Waves with N Obstacles

Recent observations have revealed that 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 which 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,

MHD Waves and Coronal Seismology: an overview of recent results

Hydrodynamic and hydromagnetic stability

Quasi-biennial oscillations (QBOs) are frequently observed in solar activity indices. However, no clear physical mechanism for the observed variations has been suggested so far. Here, we study the stability of magnetic Rossby waves in the solar tachocline using the shallow water magnetohydrodynamic approximation. Our analysis shows that the combination of typical differential rotation and a toroidal magnetic field with a strength of ?105?G triggers the instability of the m = 1 magnetic Rossby wave harmonic with a period of ~2?years. This harmonic is antisymmetric with respect to the equator and its period (and growth rate) depends on the differential rotation parameters and magnetic field strength. The oscillations may cause a periodic magnetic flux emergence at the solar surface and consequently may lead to the observed QBO in solar activity features. The period of QBOs may change throughout a cycle, and from cycle to cycle, due to variations of the mean magnetic field and differential rotation in the tachocline.

https://iopscience.iop.org/article/10.1088/2041-8205/724/1/L95/pdf

Quasi-biennial Oscillations in the Solar Tachocline Caused by Magnetic Rossby Wave Instabilities

Recent observations with the Hinode Solar Optical Telescope display an active region prominence whose fine threads oscillate in the vertical direction as they move along a path parallel to the photosphere. A seismological analysis of this event is carried out by taking advantage of the small radius of these structures compared to the total length of magnetic field lines, i.e., by using the thin-tube approximation. This analysis reveals that the oscillatory period is only slightly modified by the existence of the flow and that the difference between the period of a flowing thread and a static one is below the error bars of these observations. Moreover, although it is not possible to obtain values of the physical parameters, a lower bound for the Alfven speed (ranging between 120 and 350 km s−1) is obtained for each of the threads. Such Alfven speeds agree with the intense magnetic fields and large densities usually found in active region prominences.

Transverse Oscillations of Flowing Prominence Threads Observed with Hinode

Aims. The influence of a toroidal magnetic field on the dynamics of Rossby waves in a thin layer of ideal conductive fluid on a rotating sphere is studied in the “shallow water” magnetohydrodynamic approximation for the first time. Methods. Dispersion relations for magnetic Rossby waves are derived analytically in Cartesian and spherical coordinates. Results. It is shown that the magnetic field causes the splitting of low order (long wavelength) Rossby waves into two different modes, here denoted fast and slow magnetic Rossby waves. The high frequency mode (the fast magnetic Rossby mode) corresponds to an ordinary hydrodynamic Rossby wave slightly modified by the magnetic field, while the low frequency mode (the slow magnetic Rossby mode) has new and interesting properties since its frequency is significantly smaller than that of the same harmonics of pure Rossby and Alfven waves.

/pdf/rossby-waves-in-shallow-water-magnetohydrodynamics-1kgwm4z40z.pdf

Rossby waves in "shallow water" magnetohydrodynamics

High-resolution observations suggest that quiescent solar prominences are made of small-scale brils stacked one after another in both the vertical and horizontal directions. These brils are interpreted as the cool, highermost part of much larger coronal loops which are rooted in the solar photosphere. On the other hand, there is some evidence showing that small amplitude oscillations in prominences can aect individual or groups of brils, which vibrate with their own periods. Using a simple magnetostatic model to represent the bril structure of quiescent solar prominences, Joarder et al. (1997) investigated some oscillatory properties of the Alfv en and fast magnetohydrodynamic modes. In this paper, with a proper treatment of boundary conditions, we reexamine their conguration and explore more deeply the basic features (mainly frequency and spatial structure) of the fast mode. The main conclusion is that, for reasonable values of the bril's width, perturbations extend far away from its axis and, therefore, a single oscillating bril can excite oscillations in neighbouring ones.

/pdf/fast-mhd-oscillations-in-prominence-fine-structures-55fn9fe6lw.pdf

Fast MHD oscillations in prominence fine structures

In this paper we present a numerical study of the time evolution of solar prominences embedded in sheared magnetic arcades. The prominence is represented by a density enhancement in a background-stratified atmosphere and is connected to the photosphere through the magnetic field. By solving the ideal magnetohydrodynamic equations in three dimensions, we study the dynamics for a range of parameters representative of real prominences. Depending on the parameters considered, we find prominences that are suspended above the photosphere, i.e., detached prominences, but also configurations resembling curtain or hedgerow prominences whose material continuously connects to the photosphere. The plasma-β is an important parameter that determines the shape of the structure. In many cases magnetic Rayleigh-Taylor instabilities and oscillatory phenomena develop. Fingers and plumes are generated, affecting the whole prominence body and producing vertical structures in an essentially horizontal magnetic field. However, magnetic shear is able to reduce or even to suppress this instability.

http://iopscience.iop.org/article/10.1088/0004-637X/799/1/94/pdf

R. Oliver

Papers

Quasi-biennial Oscillations in the Solar Tachocline Caused by Magnetic Rossby Wave Instabilities

Transverse Oscillations of Flowing Prominence Threads Observed with Hinode

Rossby waves in "shallow water" magnetohydrodynamics

Fast MHD oscillations in prominence fine structures

Morphology and dynamics of solar prominences from 3d mhd simulations