Found 17 talks width keyword solar magnetic fields

Thursday April 7, 2016
Dr. Iker S. Requerey


Solar surface convection displays highly localized sinks where cold plasma returns to the solar interior. On its way to being engulfed by a downdraft the plasma can also advect and intensify magnetic fields up to kG field strengths. Such theoretical predictions strengthen the idea that localized downdrafts are places where the concentration of magnetic fields is favored. The observational discovery of convectively driven sinks is rather recent, however, and its role in the formation and evolution of quiet-Sun magnetic features is still poorly characterized. In our work, we provide both quantitative and qualitative bases for the association between sinks and magnetic fields using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board Sunrise. We find 3.1 x 10-3 sinks Mm-2 minute-1 located at mesogranular vertices. These sinks are associated to (1) horizontal velocity flows converging to a central point and (2) long-lived downdrafts.  The spatial distribution of magnetic fields in the quiet Sun is also examined. The strongest magnetic fields are preferentially located at sinks. We find that 40% of the pixels with longitudinal component of the magnetic field higher than 500 G are located in the close neighborhood of sinks.  The study of individual examples reveal that sinks can play an important role in the evolution of quiet-Sun magnetic features.

Thursday February 5, 2015
Dr. Nataliia Shchukina
Main Astronomical Observatory, National Academy of Sciences, Kyiv


The solar abundance of chemical elements play an important role in addressing such important issues as the formation, structure, and evolution of the Sun and the solar system, the origin of the chemical elements, the evolution of stars and galaxies. Despite the large number of papers published on this issue, debates about the solar composition of the Sun continue. In this talk we start summarizing the current understanding of the solar abundances of iron and CNO elements, which play a crucial role on the determination of the solar metallicity. We then pay especial attention to the impact of the quiet Sun magnetism on the determination of the abundances of these elements. The solar photosphere is significantly magnetized, due to the ubiquitous presence of a small-scale magnetic field whose mean strength is thought to be of the order of 100 gauss. Here we address the problem of the determination of the abundances of chemical elements taking into account the significant magnetization of the quiet Sun photosphere. To this end, we use 3D models of the quiet solar photosphere resulting from a state-of-the-art magneto-convection simulation with small-scale dynamo action where the net magnetic flux is zero. We conclude that if the magnetism of the quiet solar photosphere is mainly produced by a small-scale dynamo,then its impact on the determination of the solar abundance of iron and CNO elements is negligible.

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.

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 January 10, 2013
Prof. Eric Priest
St Andrews University


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.

Tuesday December 11, 2012
Mrs. Illa Rivero


The formation of active regions and its most visible outcome-sunspots-are still a matter of research. Magnetic flux tubes theory tends to explain the formation of sunspots, but it still faces some unresolved questions: How are they generated? Why can they survive all along the convective zone? How do they rise? I will review this theory and introduce a new way to understand sunspot formation: the negative effective magnetic pressure instability (NEMPI). NEMPI was predicted long ago (Kleeorin et al., 1989, 1990; Kleeorin \& Rogackevskii, 1994; Kleeorin et al., 1996) but has only been seen recently (Branderburg et. al., 2011). It arised as a effect of strong stratication and the presence of turbulence with a weak mean magnetic field. Under suitable conditions, a large-scale instability resulting in the formation of non-uniform magnetic structures, can be excited over the scale of many turbulent eddies or convection cells. This instability is caused by a negative contribution of turbulence to the effective (mean-field) magnetic pressure and has previously been discussed in connection with the formation of active regions and perhaps sunspots. Now, we want to understand the effects of rotation on this instability in both two and three dimensions. We use mean-field magnetohydrodynamics in a parameter regime in which the properties of the negative effective magnetic pressure instability have previously been found to be in agreement with those of direct numerical simulations. We find that the instability is suppressed already for relatively slow rotation with Coriolis numbers (i.e. inverse Rossby numbers) around 0.2. The suppression is strongest at the equator. In the nonlinear regime, we find traveling wave solutions with propagation in the prograde direction at the equator with additional poleward migration away from the equator. The prograde rotation of the magnetic pattern near the equator is argued to be a possible explanation for the faster rotation speed of magnetic tracers found on the Sun. In the bulk of the domain, kinetic and current helicities are negative in the northern hemisphere and positive in the southern.

Thursday May 3, 2012
Dr. Valentín Martínez Pillet


Solar Orbiter is the first mission of the ESA Cosmic Vision program and that has recently been approved at implementation level. It is an M class mission with a predicted launch in 2017. Solar Orbiter will approach the Sun to a distance of 0.28 AU and perform coordinated in-situ and remote sensing observations of the Heliosphere and the Sun. It's main scientific goal is to understand the link between physical processes at the solar surface and their impact in the inner Heliosphere. A series of gravity assist manoeuvres with Venus will kick the mission out of the ecliptic plane until it reaches an angle of 35 degrees. From this vantage point, we will observe for the first time the Solar Poles without suffering from strong projection effects. These observations can help us understand key physical ingredients of the solar dynamos such as the meridional flow and the polar field reversal. Solar Orbiter includes ESA and NASA participation and it is the first time a space mission has two instruments where Spain participates at PI level. In particular IAC/INTA is co-PI of the Polarimetric and Helioseismic Imager, a magnetograph to image the solar surface magnetic field.

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 December 16, 2010
Dr. Damian Fabbian, Dr. Héctor Socas-Navarro
Instituto de Astrofísica de Canarias, Spain


(1) In a recently published differential analysis (see Fabbian et al) we have derived abundance corrections for iron lines, using synthetic spectra from solar magneto-convection simulations that were performed via running the Copenhagen stagger-code on massively-parallel clusters. The series of 3D snapshots used for the spectral synthesis covers 2.5 solar hours in the statistically stationary regime of the convection. Crucially, we show that the effect of magnetic fields on solar abundance determinations cannot be neglected. This is equally valid for all three different Fe abundance indicators which we have studied, though the sign of the abundance correction changes depending on the interplay of the magnetic-sensitivity of the spectral line under consideration and of temperature structure variations.
Interestingly, for two of the abundance indicators (respectively, at 608.27nm and 624.07 nm) that were used in Asplund et al's analysis and that we also included in our investigation, the presence of a magnetic field has a predominantly indirect (i.e., due to temperature changes between MHD and HD models) effect, leading to positive abundance corrections (since the final equivalent width of those Fe I lines is found to decrease with increasing magnetic flux). The direct magnetic effect due to Zeeman broadening dominates instead for the 1564.85 nm absorption line, causing for it increasingly negative abundance corrections when making the initially implanted magnetic flux larger.

(2) A new three-dimensional model of the solar photosphere is presented in this paper and made publicly available to the community. This model has the peculiarity that it has been obtained by inverting spectro-polarimetric observations, rather than from numerical radiation hydrodynamical simulations. The data used here are from the spectro-polarimeter on-board the Hinode satellite, which routinely delivers Stokes I, Q, U and V profiles in the 6302 Å spectral region with excellent quality, stability and spatial resolution (approximately 0.3''). With such spatial resolution, the major granular components are well resolved, which implies that the derived model needs no micro- or macro-turbulence to properly fit the widths of the observed spectral lines. Not only this model fits the observed data used for its construction, but it can also fit previous solar atlas observations satisfactorily.

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.

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