Found 21 talks width keyword solar magnetic fields

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.

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.

(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.

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.

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.

The magnetic landscape of the polar region (Tsuneta et al, 2008) is characterized by vertical kilogauss patches with super-equipartition field strength, a coherence in polarity, lifetimes of 5-15 hr, and ubiquitous weaker transient horizontal fields (Lites et al 2008, Ishikawa & Tsuneta, 2008, 2009). Polar region in 2007 have abundant vertical fields much stronger than the quiet Sun. Unipolar appearance and disappearance of the kG vertical patches must be closely related to properties of the horizontal flow field in the polar region. Difference and similarity between the quiet sun and the polar region are summarized, and its implication for solar dynamo will be discussed. All the open field lines forming the polar coronal hole essentially originate from such magnetic patches, and the fast solar wind would emanate from these vertical flux tubes seen in the photosphere. We conjecture that vertical flux tubes with large expansion around the photospheric-coronal boundary serve as efficient chimneys for Alfven waves that accelerate the solar wind. Indeed, we discovered propagating Alfven waves (kink mode) with magneto-acoustic waves (sausage mode) in the solar photosphere with period of 4-13 minutes with Hinode spectro-polarimeter (Fujimura and Tsuneta, 2009). We found that these fluctuations are superposition of ascending and descending Alfven waves with almost equal intensities from the analysis of the phase relationship between transverse magnetic and velocity fluctuations. Aflven waves along flux tubes in the quiet sun appear to be efficiently reflected back probably at photosphere-corona boundary. It would be very interesting to measure possible change in the reflectivity of Alfven waves depending on the magnetic environment.