High-Energy Aspects of Solar Flares: Overview of the Volume

In this introductory chapter, we provide a brief summary of the successes and remaining challenges in understanding the solar flare phenomenon and its attendant implications for particle acceleration mechanisms in astrophysical plasmas. We also provide a brief overview of the contents of the other chapters in this volume, with particular reference to the well-observed flare of 2002 July 23Comment: This is the introductory article for a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011

Turbulent kinetic energy in the energy balance of a solar flare

The energy released in solar flares derives from a reconfiguration of magnetic fields to a lower energy state, and is manifested in several forms, including bulk kinetic energy of the coronal mass ejection, acceleration of electrons and ions, and enhanced thermal energy that is ultimately radiated away across the electromagnetic spectrum from optical to X-rays. Using an unprecedented set of coordinated observations, from a suite of instruments, we here report on a hitherto largely overlooked energy component -- the kinetic energy associated with small-scale turbulent mass motions. We show that the spatial location of, and timing of the peak in, turbulent kinetic energy together provide persuasive evidence that turbulent energy may play a key role in the transfer of energy in solar flares. Although the kinetic energy of turbulent motions accounts, at any given time, for only \sim (0.5-1)\% of the energy released, its relatively rapid (\sim1-10~s) energization and dissipation causes the associated throughput of energy (i.e., power) to rival that of major components of the released energy in solar flares, and thus presumably in other astrophysical acceleration sites

Transient Magnetic and Doppler Features Related to the White-light Flares in NOAA 10486

Rapidly moving transient features have been detected in magnetic and Doppler images of super-active region NOAA 10486 during the X17/4B flare of 28 October 2003 and the X10/2B flare of 29 October 2003. Both these flares were extremely energetic white-light events. The transient features appeared during impulsive phases of the flares and moved with speeds ranging from 30 to 50 km s$^{-1}$. These features were located near the previously reported compact acoustic \cite{Donea05} and seismic sources \cite{Zharkova07}. We examine the origin of these features and their relationship with various aspects of the flares, {\it viz.}, hard X-ray emission sources and flare kernels observed at different layers - (i) photosphere (white-light continuum), (ii) chromosphere (H$\alpha$ 6563\AA), (iii) temperature minimum region (UV 1600\AA), and (iv) transition region (UV 284\AA).Comment: 26 pages, 13 figures, 2 tables, accepted for publication in Solar Physic

Recent Advances in Understanding Particle Acceleration Processes in Solar Flares

We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional magnetic field configurations (e.g., current sheets, collapsing traps, separatrix regions) and stochastic acceleration in a turbulent environment. Fluid, test-particle, and particle-in-cell approaches are used and results compared. While these studies show considerable promise in accounting for the various observational manifestations of solar flares, they are limited by a number of factors, mostly relating to available computational power. Not the least of these issues is the need to explicitly incorporate the electrodynamic feedback of the accelerated particles themselves on the environment in which they are accelerated. A brief prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011

Plan de actividades recreativas utilizando como medio el juego de balonmano adaptado, para los adolescentes entre 12 y 16 años del sexo masculino, de la circunscripción 117 El Batey de Sánchez, del Consejo Popular Las Ovas del municipio Pinar del Río

Este trabajo fue realizado en la circunscripción 117 “El Batey de Sánchez”, del Consejo Popular Las Ovas municipio Pinar del Río, el mismo surge debido a la carencia de actividades-físico recreativas destinadas a los adolescentes con edades comprendidas entre 12 y 16 años. Para su realización nos trazamos como problema científico el siguiente: ¿Cómo mejorar la recreación física en los adolescentes entre 12 y 16 años de edad del sexo masculino de la circunscripción 117 “El Batey de Sánchez”, del consejo popular las Ovas? el mismo surge por la problemática que presentan los adolescentes de esta circunscripción, dentro de los cuales podemos mencionar las peleas de gallos, perros, tomeguines, lo cual se pudo comprobar con la aplicación de los diferentes métodos utilizados en nuestro trabajo. Debido a la importancia del mismo nos propusimos el siguiente Objetivo: Aplicar un plan de actividades recreativas utilizando como medio el juego de balonmano adaptado para los adolescentes entre 12 y 16 años de edad del sexo masculino de la circunscripción 117 “El Batey de Sánchez”, del consejo popular Las Ovas municipio Pinar del Rió. Al final del mismo se presentan conclusiones y recomendaciones, las cuales dan respuestas a las interrogantes planteadas al comienz

A Revisit of the Masuda Flare

We revisit the flare on 1992 January 13, which is now universally termed the "Masuda flare". The revisit is motivated not only by its uniqueness despite accumulating observations of \hxr coronal emission, but also by the improvement of Yohkoh hard X-ray imaging, which was achieved after the intensive investigations on this celebrated event. Through an uncertainty analysis, we show that the hard X-ray coronal source is located much closer to the soft X-ray loop in the re-calibrated HXT images than in the original ones. Specifically, the centroid of the M1-band (23--33 keV) coronal source is above the brightest pixel of the SXT loop by ~5000+/-1000 km (~9600 km in the original data); and above the apex of the 30% brightness contour of the SXT loop by ~2000+/-1000 km (~7000 km in the original data). We suggest that this change may naturally account for the fact that the spectrum of the coronal emission was reported to be extremely hard below ~20 keV in the pre-calibration investigations, whereas it has been considerably softer in the literature since Sato's re-calibration circa 1999. Still, the coronal spectrum is flatter at lower energies than at higher energies, owing to the lack of a similar source in the L-band (14--23 keV), which remains a puzzle

A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source

We present a quantitative model of the magnetic energy stored and then released through magnetic reconnection for a flare on 26 Feb 2004. This flare, well observed by RHESSI and TRACE, shows evidence of non-thermal electrons only for a brief, early phase. Throughout the main period of energy release there is a super-hot (T>30 MK) plasma emitting thermal bremsstrahlung atop the flare loops. Our model describes the heating and compression of such a source by localized, transient magnetic reconnection. It is a three-dimensional generalization of the Petschek model whereby Alfven-speed retraction following reconnection drives supersonic inflows parallel to the field lines, which form shocks heating, compressing, and confining a loop-top plasma plug. The confining inflows provide longer life than a freely-expanding or conductively-cooling plasma of similar size and temperature. Superposition of successive transient episodes of localized reconnection across a current sheet produces an apparently persistent, localized source of high-temperature emission. The temperature of the source decreases smoothly on a time scale consistent with observations, far longer than the cooling time of a single plug. Built from a disordered collection of small plugs, the source need not have the coherent jet-like structure predicted by steady-state reconnection models. This new model predicts temperatures and emission measure consistent with the observations of 26 Feb 2004. Furthermore, the total energy released by the flare is found to be roughly consistent with that predicted by the model. Only a small fraction of the energy released appears in the super-hot source at any one time, but roughly a quarter of the flare energy is thermalized by the reconnection shocks over the course of the flare. All energy is presumed to ultimately appear in the lower-temperature T<20 MK, post-flare loops

RHESSI Results -- Time For a Rethink?

Hard X-rays and gamma-rays are the most direct signatures of energetic electrons and ions in the sun's atmosphere which is optically thin at these energies and their radiation involves no coherent processes. Being collisional they are complementary to gyro-radiation in probing atmospheric density as opposed to magnetic field and the electrons are primarily 10--100 keV in energy, complementing the (>100 keV) electrons likely responsible for microwave bursts. The pioneering results of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) are raising the first new major questions concerning solar energetic particles in many years. Some highlights of these results are discussed -- primarily around RHESSI topics on which the authors have had direct research involvement -- particularly when they are raising the need for re-thinking of entrenched ideas. Results and issues are broadly divided into discoveries in the spatial, temporal and spectral domains, with the main emphasis on flare hard X-rays/fast electrons but touching also on gamma-rays/ions, non-flare emissions, and the relationship to radio bursts.Comment: Proceedings CESRA Workshop 2004: "The High Energy Solar Corona: Waves, Eruptions, Particles", Lecture Notes in Physics, 2006 (accepted

Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares

The extreme ultraviolet portion of the solar spectrum contains a wealth of diagnostic tools for probing the lower solar atmosphere in response to an injection of energy, particularly during the impulsive phase of solar flares. These include temperature and density sensitive line ratios, Doppler shifted emission lines and nonthermal broadening, abundance measurements, differential emission measure profiles, and continuum temperatures and energetics, among others. In this paper I shall review some of the advances made in recent years using these techniques, focusing primarily on studies that have utilized data from Hinode/EIS and SDO/EVE, while also providing some historical background and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the Topical Issue on Solar and Stellar Flare

Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"

``EIT waves" are large-scale coronal bright fronts (CBFs) that were first observed in 195 \AA\ images obtained using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the \emph{Solar and Heliospheric Observatory (SOHO)}. Commonly called ``EIT waves", CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk at velocities of 100--700 km s$^{-1}$ with front widths of 50-100 Mm. As their speed is greater than the quiet coronal sound speed ($c_s\leq$200 km s$^{-1}$) and comparable to the local Alfv\'{e}n speed ($v_A\leq$1000 km s$^{-1}$), they were initially interpreted as fast-mode magnetoacoustic waves ($v_{f}=(c_s^2 + v_A^2)^{1/2}$). Their propagation is now known to be modified by regions where the magnetosonic sound speed varies, such as active regions and coronal holes, but there is also evidence for stationary CBFs at coronal hole boundaries. The latter has led to the suggestion that they may be a manifestation of a processes such as Joule heating or magnetic reconnection, rather than a wave-related phenomena. While the general morphological and kinematic properties of CBFs and their association with coronal mass ejections have now been well described, there are many questions regarding their excitation and propagation. In particular, the theoretical interpretation of these enigmatic events as magnetohydrodynamic waves or due to changes in magnetic topology remains the topic of much debate.Comment: 34 pages, 19 figure