Found 10 talks width keyword solar chromosphere

Tuesday June 2, 2020
Prof. Manuela Temmer
Institute of Physics, University of Graz


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.

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Tuesday October 15, 2019
Dr. Sergio Javier Gonzalez Manrique
Astronomical Institute, Slovak Academy of Sciences


Emerging flux regions (EFRs) are seen as magnetic concentrations in the photosphere of the Sun. From a theoretical point of view, the EFRs are formed in the convection zone and then emerge because of magnetic buoyancy (Parker instability) to the solar surface. During the formation process of EFRs, merging and cancellation of different polarities occur, leading to various configurations of the magnetic field. Often, EFRs are visible in the chromosphere in form of magnetic loops loaded with plasma, which are often called “cool loops” when seen in the chromosphere along with dark fibrils and they can reach up to the corona. Nowadays, we refer to them as an arch filament system (AFS) which connects two different polarities.  The AFSs are commonly observed in several chromospheric spectral lines. A suitable spectral line to investigate chromospheric features and particularly AFSs is the He I 10830 Å triplet. The new generation of solar telescopes and instruments such EST and DKIST, will allow us to record very high spectral, spatial, and temporal resolution observations necessary to investigate the dynamics, magnetic field, and characteristics of AFSs. These observations will help us to answer many open questions related to flux emergence such: (1) What are the observational consequences of the emerging flux? (2) How do EFRs evolve with time in the different layers of the solar atmosphere and how are these layers linked? (3) Is it possible to measure the height difference between the photosphere and the chromosphere connected by the legs of the AFSs?

Thursday December 11, 2014
Prof. Mats Carlsson
Institute of Theoretical Physics, University of Oslo


Magnetic fields break through the solar surface in a hierarchy of magnetic elements ranging from Earth-sized sunspots down to tiny concentrations that are barely resolved in the highest-resolution photospheric images. In the chromosphere they combine in intricate, highly dynamic, and continuously evolving fibrilar patterns. Movements of the photospheric field-line footpoints drive, guide, and control the flows of energy and mass into the corona, and trigger energy-releasing magnetic reconnection through relentless topological rearrangement. The conversion from convectively driven footpoint motion to outer-atmosphere outflows and loading takes place in the dynamic, fine-structured chromosphere.

A number of important facilities for observing the solar chromosphere have recently come on line (e.g. the SDO and IRIS satellites and ground-based Fabry-Perot interferometers) or will become operational in the near future (e.g. DKIST). The overwhelming complexity of the chromosphere makes it necessary to have numerical simulations for the interpretation of the observations. Such realistic simulations, spanning the solar atmosphere from the convection zone to the corona, are now becoming feasible.

This presentation will introduce the fascinating aspects of chromospheric physics and review recent results from both observations and numerical simulations.

Tuesday October 28, 2014
Dr. Alfred G. de Wijn
High Altitude Observatory of the National Center for Atmospheric Research


The Chromosphere and Prominence Magnetometer (ChroMag) is a synoptic  instrument with the goal of quantifying the intertwined dynamics and  magnetism of the solar chromosphere and in prominences through imaging  spectro-polarimetry of the full solar disk in a synoptic fashion. The  picture of chromospheric magnetism and dynamics is rapidly developing,  and a pressing need exists for breakthrough observations of  chromospheric vector magnetic field measurements at the true lower  boundary of the heliospheric system. ChroMag will provide measurements  that will enable scientists to study and better understand the  energetics of the solar atmosphere, how prominences are formed, how  energy is stored in the magnetic field structure of the atmosphere and  how it is released during space weather events like flares and coronal  mass ejections. An essential part of the ChroMag program is a commitment  to develop and provide community access to the `inversion' tools  necessary to interpret the measurements and derive the  magneto-hydrodynamic parameters of the plasma. Measurements of an  instrument like ChroMag provide critical physical context for the Solar  Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph  (IRIS) as well as ground-based observatories such as the future Daniel  K. Inouye Solar Telescope (DKIST). A prototype is currently deployed in  Boulder, CO, USA. We will present an overview of instrument design and  capabilities, show some recent observations, and discuss the future of  the project.

Wednesday March 19, 2014
Prof. Rob Rutten


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.

Thursday October 24, 2013
Dr. Alberto Sainz-Dalda
Stanford-Lockheed Institute for Space Research


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.

Thursday March 22, 2012
Dr. María Jesús Martínez González


Solar magnetism may look deceptively boring (a rather common star with relatively low activity). As it turns out, even the most quiet areas of the Sun (away from the sunspots) harbour a rich and interesting magnetic activity which is extremely complex and dynamic at spatial scales as small as ~100 km. And more importantly, this magnetism permeates most of the Sun, all the time. Therefore, it is not surprising that it might play an important role for solving some longstanding questions of stellar magnetism as: how is the million degree corona maintained when all sunspots have disappeared during the minimum of magnetic activity? And this is of interest not only for solar physics but for stellar astrophysics too, since it is expected that every star with a convective envelope harbours small-scale magnetic activity that we cannot hope to observe with the great detail we observe it in the Sun. From the first evidence of the presence of magnetic fields in the quiet areas of the Sun to the discovery of the smallest organised magnetic structures ever observed in a stellar surface just 30 years have passed. In this seminar, I will give an overview of our present knowledge about the small-scale quiet Sun magnetism. In particular, I will show how small loops of sizes of several hundreds of kilometers appear in the surface and travel across the solar atmosphere, reaching upper layers and having direct implications on chromospheric (coronal) magnetism. I will also show some of the properties of these newly discovered magnetic structures such as their spatial distribution, a key ingredient for understanding their origin.

Thursday November 11, 2010
Dr. Jaime de la Cruz Rodríguez
The Institute for Solar Physics of the Royal Swedish Academy of Science.


Fibrils are thin elongated features visible in the solar chromosphere in and around magnetized regions. Because of their visual appearance they have been traditionally considered a tracer of the magnetic field lines. In this work we challenge that notion for the first time by comparing their orientation to that of the magnetic field, obtained via high-resolution spectro-polarimetric observations of Ca II lines. The short answer to the question posed in the title is that mostly yes, but not always.

Thursday April 29, 2010
Prof. Jack Harvey
National Solar Observatory, USA


The Sun presents us with many unsolved mysteries. In this talk I discuss three of them that have intrigued me for the last 50 years. Solar flares are the most powerful explosions in space between here and the nearby stars. The only viable power source is stored magnetic energy. Yet definitive observations of changes in the magnetic field associated with flares have been lacking until recently. Measurements with the GONG network have helped to address this mystery and the results are surprising. Efforts to observe the weak magnetic fields in the solar photosphere date nearly to the discovery of magnetism on the Sun. Improvements in observational capabilities have made this area a 'hot' topic with many important contributions from people at the IAC. High resolution observations are clarifying many features. I will focus on the role played by lower resolution work in defining the uniformity of the still mysterious weak magnetic fields over large spatial and temporal scales. Physics changes from hydrodynamic to magnetic dominance as one moves upward from the photosphere to the chromosphere. This leads to significant and complicated changes in the magnetic field in both the active and quiet Sun. Observations of the chromospheric magnetic field show several unexpected and mysterious features. Solving these mysteries will be an exciting area as observational and spectral inversion capabilities develop.

Tuesday April 27, 2010
Dr. María Jesús Martínez González
Instituto de Astrofísica de Canarias, Spain


The quiet Sun (the 99%, or more, of the solar surface not covered by sunspots or active regions) is receiving increased attention in recent years; its role on the global magnetism and its complexity are being increasingly recognised. A picture of a rather stochastic quiet Sun magnetism is emerging. From these recent works, the quiet Sun magnetism is presented as a myriad of magnetic field vectors having an isotropical distribution with a cascade of scales down to the mean free path of the photon. But this chaotic representation also shows clear signs of intermittency: at a low frequency rate (0.022 events h-1 arcsec-2) the magnetic field appear in the quiet Sun forming well-organised loop structures at granular scales. More interesting, these loops rise to higher layers and their energy input into the chromosphere can be important for the heating of this layer. In the talk, I will present a pedagogic view of the quiet Sun magnetism. I will focus on the ascent of the smallest ever observed magnetic flux emergence through the solar atmosphere. More specifically, I will show how to infer from high resolution, spectro-polarimetric observations (taken with the SOT instrument onboard Hinode) the magnetic topology of the fields, how they rise through the photosphere to the chromosphere, and the implications of this phenomena for chromospheric (and coronal) heating.

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