Found 11 talks width keyword solar corona

A solar flare involves the conversion of magnetic energy stored in the coronal magnetic field into the kinetic energy of thermal and non-thermal particles, mass motion, and radiation. How this happens remains a central question in solar physics. A particular long-standing puzzle is how such a high fraction of the stored magnetic energy - up to a half - arrives in the kinetic energy of accelerated non-thermal particles. In this talk I will present an observational overview of solar flares with an emphasis on accelerated particles, discuss some ideas and constraints on particle acceleration, and present some new observations of the possible role of plasma turbulence in the acceleration process.

The Sun is an active star that influences the Earth as well as the entire solar system. Most dynamic phenomena on the Sun are observed as coronal mass ejections (CMEs) and flares. CMEs present massive clouds of magnetized plasma having speeds up to a few thousand km/s, that may propagate over Sun-Earth distance within less than a day and may cause strong geomagnetic disturbances at Earth (Space Weather). As CMEs are optically thin, using remote sensing data measurements of intrinsic properties such as speed, width, propagation direction, density etc. are severely affected by projection effects. By combining image data with in-situ measurements, valuable information is provided enabling CME 3D analyzes, and with that facilitate a better quantification of the uncertainties in the observational measurements that are used to feed CME propagation models. With that, a much better understanding of CMEs as they propagate in interplanetary space could be gained.

The talk will cover the physisc about CME-flare phenomena, the interplanetary propagation behavior of CMEs related to the background solar wind, and Space Weather forecasting.

Zoom link: https://rediris.zoom.us/j/92170419398

The Sun is a magnetic star, not as magnetic as some stars, or as it was when it
was younger, but nonetheless magnetic fields dominate and even construct its
atmosphere. There would be no corona without magnetic fields. The surface is
also dappled with small scale magnetic field associated with surface convection
cells, granules and supergranules. But sometimes we also see much larger and
more powerful Active Regions containing sunspots. These are wounds in the
surface of the Sun that allow waves and oscillations in the solar interior and
atmosphere to be coupled much more directly than they usually are. In
particular, they allow the Sun's internal seismology (the p-modes) to drive a
variety of waves through the Active Region atmosphere, and conversely, the
atmospheres to pollute the internal seismology. This makes active region
helioseismology a very challenging field.

Progress in our understanding of the Solar corona and its underlying heating and acceleration processes, depends critically on our ability to measure fundamental plasma parameters, such as magnetic field, density, temperature and composition. In this talk, I will introduce my main research topics which concern measurement of fundamental plasma parameters in the Solar corona and the development of new plasma diagnostic tools, in order to provide constraints for the various proposed physical mechanisms.

Coronal observations are always integrated along a line of sight (LOS). Because there may be multiple emitting sources, this considerably complicates the interpretation of the observations. To avoid this ambiguity there are several tools, including the widely used Differential Emission Measure (DEM) analysis and the tomography reconstruction technique. However, both the derivation and the interpretation of the DEM from observations are difficult mainly due to the inverse nature of the problem. I will present a new strategy to evaluate the robustness of the DEM inversion problem. An application of the DEM formalism will be presented, allowing us to measure the relative abundances in both interplumes and plumes using Hinode/Extreme Ultraviolet Imaging Spectrometer (EIS) data. Finally, I will present the inversion code I developed, able to perform the coupling of the DEM formalism and the tomography, providing a three dimensional diagnostic in temperature and density of the solar corona.

Recent observations of the solar atmosphere have provided new insights concerning medium-sized jet phenomena taking place in the solar corona. These jets are magnetically controlled and typically take place in regions where the mean magnetic field has an open structure. Observations indicate that at least two different types of jets exist. A simple jet that generally has a near steady state evolution phase with a well behaved and collimated outflow stream. The second type typically combines the characteristics of the first type with an explosive behaviour that significantly changes the topological structure of the jet outflow. Models have attempted to provide physical explanations to the observations, and are in general able to capture a number of the observational characteristics. This talk will discuss both the observations and the models, emphasizing where we succeed and where new progress is need

The chromosphere is the interface between the photospheric solar surface and the outer corona and wind.  In this complex domain the
solar gas becomes transparent throughout the ultraviolet and in the strongest spectral lines while magnetic pressure becomes dominant over gas pressure even in weak-field regions.  Fine-scale magnetically caused or guided dynamic processes in the chromosphere constitute the roots of mass and energy loading of the corona and solar wind. Notwithstanding this pivotal role the chromosphere remained ill-understood after its basic NLTE radiation physics was formulated in the 1960s and 70s.  Presently, both chromospheric observation and
chromospheric simulation mature towards the required sophistication.  The open-field features seem of greater interest than the easier-to-see closed-field features. For the latter, the grail of coronal topology and eruption prediction comes in sight.

I will start with an introductory overview, show movies to present the state of art in observation and simulation, and treat some
recent success stories in more detail.

Flares are among the most energetic magnetic solar phenomena. They are often accompanied by ejections of charged particles, which have a direct influence on the Earth in terms of Aurora or radio and satellite outages. The sudden nature of flares - some of them only last minutes - makes them an elusive feature when observed from ground-based telescopes. These measurements are especially challenging when we focus on magnetic fields and velocities in the different solar layers where flares develop and occur. I will present flare observations taken with different instruments, each targeting different observables, and I will show what we can learn from ground-based polarization measurements.

The strongest He II emission in the visible spectral range, at 4686 A, is for the first time observed at a spectral resolution sufficiently high for a line profile analysis in quiescent solar prominences. It is found that the He II line width exceeds by far that of emissions from neutral helium which, in turn, show significant differences between the triplet and singlet emissions. The width hierarchy from singlet over triplet to He II suggests an origin in increasingly hot plasma of the transition to hot coronal surroundings. The ratio of integrated line emission is found to be independent on the prominence size suggesting that each fine-structure has its own transition to hot coronal gas in between the treads.

This talk will give an overview of our understanding of the Sun in the 1960's, the major discoveries since then, and the main questions that need to be answered in future. It will focus on the role of the magnetic field in the solar interior, the photosphere, prominences, coronal heating and eruptive flares.

The coronal heating problem has been with us for almost 70 years now. Among the different proposed explanations, wave-based heating mechanisms are recurrently invoked. In the last decade, a wealth of high resolution observations have shown that wave-like dynamics is present at almost all layers of the solar atmosphere. As a consequence, a renewed interest has grown on their role in plasma heating mechanisms. We will discuss a series of aspects related to the current status of MHD wave heating of the solar corona. The talk will focus on the following ones: a) recent observational discoveries of waves and their relevance to the heating problem; b) our theoretical understanding on their nature and properties; c) our current level of comprehension of the sequence of physical processes that link oscillations with dissipation and heat conversion; and d) the merits and faults of current theories, including suggestions for the way forward in both theory and observations.