Author name code: bellot-rubio ADS astronomy entries on 2022-09-14 author:"Bellot Rubio, Luis Ramon" ------------------------------------------------------------------------ Title: The on-ground data reduction and calibration pipeline for SO/PHI-HRT Authors: Sinjan, J.; Calchetti, D.; Hirzberger, J.; Orozco Suárez, D.; Albert, K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutierrez Marquez, P.; Kahil, F.; Kolleck, M.; Solanki, S. K.; del Toro Iniesta, J. C.; Volkmer, R.; Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Carmona, M.; Deutsch, W.; Fernandez-Rico, G.; Fernández-Medina, A.; García Parejo, P.; Gasent Blesa, J. L.; Gizon, L.; Grauf, B.; Heerlein, K.; Korpi-Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.; Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai, E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.; Torralbo, I.; Valori, G. Bibcode: 2022arXiv220814904S Altcode: The ESA/NASA Solar Orbiter space mission has been successfully launched in February 2020. Onboard is the Polarimetric and Helioseismic Imager (SO/PHI), which has two telescopes, a High Resolution Telescope (HRT) and the Full Disc Telescope (FDT). The instrument is designed to infer the photospheric magnetic field and line-of-sight velocity through differential imaging of the polarised light emitted by the Sun. It calculates the full Stokes vector at 6 wavelength positions at the Fe I 617.3 nm absorption line. Due to telemetry constraints, the instrument nominally processes these Stokes profiles onboard, however when telemetry is available, the raw images are downlinked and reduced on ground. Here the architecture of the on-ground pipeline for HRT is presented, which also offers additional corrections not currently available on board the instrument. The pipeline can reduce raw images to the full Stokes vector with a polarimetric sensitivity of $10^{-3}\cdot I_{c}$ or better. Title: Unipolar versus Bipolar Internetwork Flux Appearance Authors: Gosic, Milan; Katsukawa, Yukio; Bellot Rubio, L. R.; Del Toro Iniesta, Jose Carlos; Cheung, Mark; Orozco Suárez, David Bibcode: 2022cosp...44.2513G Altcode: Small-scale internetwork (IN) magnetic fields are considered to be the main building blocks of the quiet Sun magnetism. It is therefore of paramount importance to understand how these fields are generated on the solar surface. To shed new light on this open question, we studied the appearance modes and spatio-temporal evolution of individual IN magnetic elements inside one supergranular cell. For that purpose, we employed a high-resolution, high-sensitivity, long-duration Hinode/NFI magnetogram sequence. From identification of flux patches and magnetofrictional simulations, we show that there are two distinct populations of IN flux concentrations: unipolar and bipolar features. Bipolar features tend to be bigger, live longer and carry more flux than unipolar features. About $70$% of the total instantaneous IN flux detected inside the supergranule is in the form of bipoles. Both types of flux concentrations are uniformly distributed over the solar surface. However, bipolar features appear (randomly oriented) at a faster rate than unipolar features (68 as opposed to 55~Mx~cm$^{-2}$~day$^{-1}$). Our results lend support to the idea that bipolar features may be the signature of local dynamo action, while unipolar features seem to be formed by coalescence of background flux. Title: Emergence of internetwork magnetic fields into the chromosphere and transition region Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, L. R.; Sainz Dalda, A.; Esteban Pozuelo, Sara Bibcode: 2022cosp...44.2511G Altcode: Internetwork (IN) magnetic fields are highly dynamic, short-lived magnetic structures that populate the interior of supergranular cells. Since they are spread all over the Sun, they may hold a significant fraction of the total magnetic energy stored in the photosphere. Therefore, it is crucial to understand their role in the quiet Sun magnetism and impact on the energetics and dynamics of the solar atmosphere. To provide new insights into this topic, we studied three flux emergence events and followed them as they emerge into the photosphere and reach the chromosphere and transition region. We used coordinated, high-resolution, multiwavelength observations obtained with the Swedish 1-m Solar Telescope (SST) and the Interface Region Imaging Spectrograph (IRIS). SST Fe I 6173 and Mg I b$_2$ 5173 magnetograms show the footpoints of the IN bipoles emerging at the solar surface and rising toward the upper solar atmosphere. For the first time, our spectropolarimetric measurements in the Ca II 8542 \AA\/ line provide direct observational evidence that IN fields are capable of reaching the chromosphere. IRIS observations reveal another important piece of information - small-scale IN loops can even reach transition region heights, and locally heat the upper solar atmosphere. Title: Magnetic properties of short-lived penumbral microjets Authors: Tapia, Azaymi Siu; Bellot Rubio, L. R.; Gafeira, Ricardo; Orozco Suárez, David Bibcode: 2022cosp...44.2520T Altcode: Penumbral microjets (PMJs) are fast elongated brightenings above sunspots penumbrae. They are presumed to be related to photospheric magnetic reconnection processes and contribute to the heating of the plasma in the higher atmospheric layers. Studying the spectral and polarization properties of the shortest-living microjets requires the fastest temporal cadence possible and is currently a challenging task. In this work, we use fast spectropolarimetric measurements of the Ca II 8542 A line made with the CRISP instrument at the Swedish 1 m Solar Telescope, and exploit the diagnostic capabilities of this line to retrieve the magnetic field configuration and its evolution at different atmospheric heights during PMJs. Our findings show that short-lived PMJs are associated with a transient perturbation in the photospheric magnetic field and sometimes they show clear but weaker changes in the chromospheric field as well. We will describe the different types of evolution that were identified. These results support the idea that PMJs may be the result of magnetic reconnection at low altitudes in sunspot penumbra. Title: The magnetic canopy of pores and quiet Sun features as observed through the Mg I b2 line Authors: Tapia, Azaymi Siu; Bellot Rubio, L. R. Bibcode: 2022cosp...44.2512T Altcode: We study the expansion of the magnetic field above pores and quiet Sun magnetic elements from the photosphere to the low chromosphere, using high-spatial-resolution observations in the Fe I 6173 Å and Mg I 5173 Å lines made with CRISP at the SST. The longitudinal component of the magnetic field and its variation with height have been inferred by applying the weak-field approximation (WFA) in different spectral windows within the Mg line and a simple SIR inversion to the Fe line. We also present the first non-LTE inversions of these two lines performed over a large field of view. The results from such inversions validate the applicability of the WFA as a diagnostic tool that can be used to analyze the magnetic field intensity and orientation, as well as their gradients with height, in these lines. This work also provides observational evidence on the formation of low-lying canopies above bright quiet Sun magnetic structures, network elements, and pores, near the temperature minimum region. Title: The European Solar Telescope Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.; Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein, C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados, M.; the EST team Bibcode: 2022arXiv220710905Q Altcode: The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR, the French Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope (DOT). With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems. Title: The magnetic drivers of campfires seen by the Polarimetric and Helioseismic Imager (PHI) on Solar Orbiter Authors: Kahil, F.; Hirzberger, J.; Solanki, S. K.; Chitta, L. P.; Peter, H.; Auchère, F.; Sinjan, J.; Orozco Suárez, D.; Albert, K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutiérrez Márquez, P.; Kolleck, M.; del Toro Iniesta, J. C.; Volkmer, R.; Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Calchetti, D.; Carmona, M.; Deutsch, W.; Fernández-Rico, G.; Fernández-Medina, A.; García Parejo, P.; Gasent-Blesa, J. L.; Gizon, L.; Grauf, B.; Heerlein, K.; Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.; Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai, E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.; Torralbo, I.; Valori, G.; Aznar Cuadrado, R.; Teriaca, L.; Berghmans, D.; Verbeeck, C.; Kraaikamp, E.; Gissot, S. Bibcode: 2022A&A...660A.143K Altcode: 2022arXiv220213859K Context. The Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter (SO) spacecraft observed small extreme ultraviolet (EUV) bursts, termed campfires, that have been proposed to be brightenings near the apexes of low-lying loops in the quiet-Sun atmosphere. The underlying magnetic processes driving these campfires are not understood.
Aims: During the cruise phase of SO and at a distance of 0.523 AU from the Sun, the Polarimetric and Helioseismic Imager on Solar Orbiter (SO/PHI) observed a quiet-Sun region jointly with SO/EUI, offering the possibility to investigate the surface magnetic field dynamics underlying campfires at a spatial resolution of about 380 km.
Methods: We used co-spatial and co-temporal data of the quiet-Sun network at disc centre acquired with the High Resolution Imager of SO/EUI at 17.4 nm (HRIEUV, cadence 2 s) and the High Resolution Telescope of SO/PHI at 617.3 nm (HRT, cadence 2.5 min). Campfires that are within the SO/PHI−SO/EUI common field of view were isolated and categorised according to the underlying magnetic activity.
Results: In 71% of the 38 isolated events, campfires are confined between bipolar magnetic features, which seem to exhibit signatures of magnetic flux cancellation. The flux cancellation occurs either between the two main footpoints, or between one of the footpoints of the loop housing the campfire and a nearby opposite polarity patch. In one particularly clear-cut case, we detected the emergence of a small-scale magnetic loop in the internetwork followed soon afterwards by a campfire brightening adjacent to the location of the linear polarisation signal in the photosphere, that is to say near where the apex of the emerging loop lays. The rest of the events were observed over small scattered magnetic features, which could not be identified as magnetic footpoints of the campfire hosting loops.
Conclusions: The majority of campfires could be driven by magnetic reconnection triggered at the footpoints, similar to the physical processes occurring in the burst-like EUV events discussed in the literature. About a quarter of all analysed campfires, however, are not associated to such magnetic activity in the photosphere, which implies that other heating mechanisms are energising these small-scale EUV brightenings. Title: CASPER: A mission to study the time-dependent evolution of the magnetic solar chromosphere and transition regions Authors: Orozco Suárez, D.; del Toro Iniesta, J. C.; Bailén, F. J.; López Jiménez, A.; Balaguez Jiménez, M.; Bellot Rubio, L. R.; Ishikawa, R.; Katsukawa, Y.; Kano, R.; Shimizu, T.; Trujillo Bueno, J.; Asensio Ramos, A.; del Pino Alemán, T. Bibcode: 2022ExA...tmp...26O Altcode: Our knowledge about the solar chromosphere and transition region (TR) has increased in the last decade thanks to the huge scientific return of space-borne observatories like SDO, IRIS, and Hinode, and suborbital rocket experiments like CLASP1, CLASP2, and Hi-C. However, the magnetic nature of those solar regions remain barely explored. The chromosphere and TR of the Sun harbor weak fields and are in a low ionization stage both having critical effects on their thermodynamic behavior. Relatively cold gas structures, such as spicules and prominences, are located in these two regions and display a dynamic evolution in high-resolution observations that static and instantaneous 3D-magnetohydrodynamic (MHD) models are not able to reproduce. The role of the chromosphere and TR as the necessary path to a (largely unexplained) very hot corona calls for the generation of observationally based, time-dependent models of these two layers that include essential, up to now disregarded, ingredients in the modeling such as the vector magnetic field. We believe that the community is convinced that the origin of both the heat and kinetic energy observed in the upper layers of the solar atmosphere is of magnetic origin, but reliable magnetic field measurements are missing. The access to sensitive polarimetric measurements in the ultraviolet wavelengths has been elusive until recently due to limitations in the available technology. We propose a low-risk and high-Technology Readiness Level (TRL) mission to explore the magnetism and dynamics of the solar chromosphere and TR. The mission baseline is a low-Earth, Sun-synchronous orbit at an altitude between 600 and 800 km. The proposed scientific payload consists of a 30 cm aperture telescope with a spectropolarimeter covering the hydrogen Ly-alpha and the Mg II h&k ultraviolet lines. The instrument shall record high-cadence, full spectropolarimetric observations of the solar upper atmosphere. Besides the answers to a fundamental solar problem the mission has a broader scientific return. For example, the time-dependent modeling of the chromospheres of stars harboring exoplanets is fundamental for estimating the planetary radiation environment. The mission is based on technologies that are mature enough for space and will provide scientific measurements that are not available by other means. Title: The Solar Internetwork. III. Unipolar versus Bipolar Flux Appearance Authors: Gošić, M.; Bellot Rubio, L. R.; Cheung, M. C. M.; Orozco Suárez, D.; Katsukawa, Y.; del Toro Iniesta, J. C. Bibcode: 2022ApJ...925..188G Altcode: 2021arXiv211103208G Small-scale internetwork (IN) magnetic fields are considered to be the main building blocks of quiet Sun magnetism. For this reason, it is crucial to understand how they appear on the solar surface. Here, we employ a high-resolution, high-sensitivity, long-duration Hinode/NFI magnetogram sequence to analyze the appearance modes and spatiotemporal evolution of individual IN magnetic elements inside a supergranular cell at the disk center. From identification of flux patches and magnetofrictional simulations, we show that there are two distinct populations of IN flux concentrations: unipolar and bipolar features. Bipolar features tend to be bigger and stronger than unipolar features. They also live longer and carry more flux per feature. Both types of flux concentrations appear uniformly over the solar surface. However, we argue that bipolar features truly represent the emergence of new flux on the solar surface, while unipolar features seem to be formed by the coalescence of background flux. Magnetic bipoles appear at a faster rate than unipolar features (68 as opposed to 55 Mx cm-2 day-1), and provide about 70% of the total instantaneous IN flux detected in the interior of the supergranule. Title: A journey of exploration to the polar regions of a star: probing the solar poles and the heliosphere from high helio-latitude Authors: Harra, Louise; Andretta, Vincenzo; Appourchaux, Thierry; Baudin, Frédéric; Bellot-Rubio, Luis; Birch, Aaron C.; Boumier, Patrick; Cameron, Robert H.; Carlsson, Matts; Corbard, Thierry; Davies, Jackie; Fazakerley, Andrew; Fineschi, Silvano; Finsterle, Wolfgang; Gizon, Laurent; Harrison, Richard; Hassler, Donald M.; Leibacher, John; Liewer, Paulett; Macdonald, Malcolm; Maksimovic, Milan; Murphy, Neil; Naletto, Giampiero; Nigro, Giuseppina; Owen, Christopher; Martínez-Pillet, Valentín; Rochus, Pierre; Romoli, Marco; Sekii, Takashi; Spadaro, Daniele; Veronig, Astrid; Schmutz, W. Bibcode: 2021ExA...tmp...93H Altcode: 2021arXiv210410876H A mission to view the solar poles from high helio-latitudes (above 60°) will build on the experience of Solar Orbiter as well as a long heritage of successful solar missions and instrumentation (e.g. SOHO Domingo et al. (Solar Phys. 162(1-2), 1-37 1995), STEREO Howard et al. (Space Sci. Rev. 136(1-4), 67-115 2008), Hinode Kosugi et al. (Solar Phys. 243(1), 3-17 2007), Pesnell et al. Solar Phys. 275(1-2), 3-15 2012), but will focus for the first time on the solar poles, enabling scientific investigations that cannot be done by any other mission. One of the major mysteries of the Sun is the solar cycle. The activity cycle of the Sun drives the structure and behaviour of the heliosphere and of course, the driver of space weather. In addition, solar activity and variability provides fluctuating input into the Earth climate models, and these same physical processes are applicable to stellar systems hosting exoplanets. One of the main obstructions to understanding the solar cycle, and hence all solar activity, is our current lack of understanding of the polar regions. In this White Paper, submitted to the European Space Agency in response to the Voyage 2050 call, we describe a mission concept that aims to address this fundamental issue. In parallel, we recognise that viewing the Sun from above the polar regions enables further scientific advantages, beyond those related to the solar cycle, such as unique and powerful studies of coronal mass ejection processes, from a global perspective, and studies of coronal structure and activity in polar regions. Not only will these provide important scientific advances for fundamental stellar physics research, they will feed into our understanding of impacts on the Earth and other planets' space environment. Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST) Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST Instrument Scientists; DKIST Science Working Group; DKIST Critical Science Plan Community Bibcode: 2021SoPh..296...70R Altcode: 2020arXiv200808203R The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. Title: Emergence of Internetwork Magnetic Fields through the Solar Atmosphere Authors: Gošić, M.; De Pontieu, B.; Bellot Rubio, L. R.; Sainz Dalda, A.; Pozuelo, S. Esteban Bibcode: 2021ApJ...911...41G Altcode: 2021arXiv210302213G Internetwork (IN) magnetic fields are highly dynamic, short-lived magnetic structures that populate the interior of supergranular cells. Since they emerge all over the Sun, these small-scale fields bring a substantial amount of flux, and therefore energy, to the solar surface. Because of this, IN fields are crucial for understanding the quiet Sun (QS) magnetism. However, they are weak and produce very small polarization signals, which is the reason why their properties and impact on the energetics and dynamics of the solar atmosphere are poorly known. Here we use coordinated, high-resolution, multiwavelength observations obtained with the Swedish 1 m Solar Telescope and the Interface Region Imaging Spectrograph (IRIS) to follow the evolution of IN magnetic loops as they emerge into the photosphere and reach the chromosphere and transition region. We studied in this paper three flux emergence events having total unsigned magnetic fluxes of 1.9 × 1018, 2.5 × 1018, and 5.3 × 1018 Mx. The footpoints of the emerging IN bipoles are clearly seen to appear in the photosphere and to rise up through the solar atmosphere, as observed in Fe I 6173 Å and Mg I b2 5173 Å magnetograms, respectively. For the first time, our polarimetric measurements taken in the chromospheric Ca II 8542 Å line provide direct observational evidence that IN fields are capable of reaching the chromosphere. Moreover, using IRIS data, we study the effects of these weak fields on the heating of the chromosphere and transition region. Title: A Journey of Exploration to the Polar Regions of a Star: Probing the Solar Poles and the Heliosphere from High Helio-Latitude Authors: Finsterle, W.; Harra, L.; Andretta, V.; Appourchaux, T.; Baudin, F.; Bellot Rubio, L.; Birch, A.; Boumier, P.; Cameron, R. H.; Carlsson, M.; Corbard, T.; Davies, J. A.; Fazakerley, A. N.; Fineschi, S.; Gizon, L. C.; Harrison, R. A.; Hassler, D.; Leibacher, J. W.; Liewer, P. C.; Macdonald, M.; Maksimovic, M.; Murphy, N.; Naletto, G.; Nigro, G.; Owen, C. J.; Martinez-Pillet, V.; Rochus, P. L.; Romoli, M.; Sekii, T.; Spadaro, D.; Veronig, A. Bibcode: 2020AGUFMSH0110005F Altcode: A mission to view the solar poles from high helio-latitudes (above 60°) will build on the experience of Solar Orbiter as well as a long heritage of successful solar missions and instrumentation (e.g. SOHO, STEREO, Hinode, SDO), but will focus for the first time on the solar poles, enabling scientific investigations that cannot be done by any other mission. One of the major mysteries of the Sun is the solar cycle. The activity cycle of the Sun drives the structure and behaviour of the heliosphere and is, of course, the driver of space weather. In addition, solar activity and variability provides fluctuating input into the Earth climate models, and these same physical processes are applicable to stellar systems hosting exoplanets. One of the main obstructions to understanding the solar cycle, and hence all solar activity, is our current lack of understanding of the polar regions. We describe a mission concept that aims to address this fundamental issue. In parallel, we recognise that viewing the Sun from above the polar regions enables further scientific advantages, beyond those related to the solar cycle, such as unique and powerful studies of coronal mass ejection processes, from a global perspective, and studies of coronal structure and activity in polar regions. Not only will these provide important scientific advances for fundamental stellar physics research, they will feed into our understanding of impacts on the Earth and other planets' space environment. Title: Lagrangian chaotic saddles and objective vortices in solar plasmas Authors: Chian, Abraham C. -L.; Silva, Suzana S. A.; Rempel, Erico L.; Bellot Rubio, Luis R.; Gošić, Milan; Kusano, Kanya; Park, Sung-Hong Bibcode: 2020PhRvE.102f0201C Altcode: We report observational evidence of Lagrangian chaotic saddles in plasmas, given by the intersections of finite-time unstable and stable manifolds, using an ≈22 h sequence of spacecraft images of the horizontal velocity field of solar photosphere. A set of 29 persistent objective vortices with lifetimes varying from 28.5 to 298.3 min are detected by computing the Lagrangian averaged vorticity deviation. The unstable manifold of the Lagrangian chaotic saddles computed for ≈11 h exhibits twisted folding motions indicative of recurring vortices in a magnetic mixed-polarity region. We show that the persistent objective vortices are formed in the gap regions of Lagrangian chaotic saddles at supergranular junctions. Title: Chromospheric response to emergence of internetwork magnetic fields Authors: Gosic, M.; De Pontieu, B.; Bellot Rubio, L.; Sainz Dalda, A. Bibcode: 2020AGUFMSH0010006G Altcode: Internetwork (IN) magnetic fields are weak, short-lived, but highly dynamic magnetic structures that emerge all over the Sun. They bring an enormous amount of magnetic flux and energy to the solar surface. Therefore, IN fields are of paramount importance for maintenance of the QS magnetism. Since these fields are ubiquitous, they may have a substantial impact on the energetics and dynamics of the solar atmosphere. In this work, we use coordinated, high-resolution, multiwavelength observations obtained with the Interface Region Imaging Spectrograph (IRIS) and the Swedish 1 m Solar Telescope (SST) to follow the evolution of IN magnetic loops as they emerge into the photosphere. The footpoints of the emerging IN bipoles are clearly visible as they appear in the photosphere and rise up through the solar atmosphere, as seen in SST magnetograms taken in the Fe I 6173 Å and Mg I b2 5173 Å lines, respectively. Our polarimetric measurements, taken in the Ca II 8542 Å line, provide the first direct observational evidence that IN fields are capable of reaching the chromosphere. Moreover, using IRIS data, we describe in detail how individual IN bipoles affect the dynamics and energetics of the chromosphere and transition region. Title: The Solar Orbiter Science Activity Plan. Translating solar and heliospheric physics questions into action Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.; Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra, A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.; Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.; Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.; Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.; Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio, L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun, A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso, F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.; Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.; Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.; van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi, L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine, D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot, S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham, G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier, K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins, J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis, I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.; Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis, G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.; Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.; Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis, K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien, H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.; Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.; Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines, J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.; Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.; Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.; Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.; Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.; Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula, G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio, A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.; Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann, T.; Young, P. R.; Zhukov, A. N. Bibcode: 2020A&A...642A...3Z Altcode: 2020arXiv200910772Z Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate?; (2) How do solar transients drive heliospheric variability?; (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere?; (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission's science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit's science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans, resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime. This allows for all four mission goals to be addressed. In this paper, we introduce Solar Orbiter's SAP through a series of examples and the strategy being followed. Title: The Polarimetric and Helioseismic Imager on Solar Orbiter Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer, A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.; Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.; Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.; Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.; Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott, D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.; Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.; Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.; Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.; Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.; Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.; Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila, B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.; Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.; Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond, J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h, J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.; Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell, A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai, E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa, J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas, A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.; Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel, H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I. Bibcode: 2020A&A...642A..11S Altcode: 2019arXiv190311061S
Aims: This paper describes the Polarimetric and Helioseismic Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and helioseismology instrument to observe the Sun from outside the Sun-Earth line. It is the key instrument meant to address the top-level science question: How does the solar dynamo work and drive connections between the Sun and the heliosphere? SO/PHI will also play an important role in answering the other top-level science questions of Solar Orbiter, while hosting the potential of a rich return in further science.
Methods: SO/PHI measures the Zeeman effect and the Doppler shift in the Fe I 617.3 nm spectral line. To this end, the instrument carries out narrow-band imaging spectro-polarimetry using a tunable LiNbO3 Fabry-Perot etalon, while the polarisation modulation is done with liquid crystal variable retarders. The line and the nearby continuum are sampled at six wavelength points and the data are recorded by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data are reduced on board, including being inverted under the assumption of a Milne-Eddington atmosphere, although simpler reduction methods are also available on board. SO/PHI is composed of two telescopes; one, the Full Disc Telescope, covers the full solar disc at all phases of the orbit, while the other, the High Resolution Telescope, can resolve structures as small as 200 km on the Sun at closest perihelion. The high heat load generated through proximity to the Sun is greatly reduced by the multilayer-coated entrance windows to the two telescopes that allow less than 4% of the total sunlight to enter the instrument, most of it in a narrow wavelength band around the chosen spectral line.
Results: SO/PHI was designed and built by a consortium having partners in Germany, Spain, and France. The flight model was delivered to Airbus Defence and Space, Stevenage, and successfully integrated into the Solar Orbiter spacecraft. A number of innovations were introduced compared with earlier space-based spectropolarimeters, thus allowing SO/PHI to fit into the tight mass, volume, power and telemetry budgets provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal) challenges posed by the mission's highly elliptical orbit. Title: Models and data analysis tools for the Solar Orbiter mission Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.; Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.; Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.; Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi, N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla, T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.; Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.; Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.; Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.; Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot, V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.; Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.; Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp, E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud, B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.; Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.; Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti, S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.; Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez, L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca, L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.; Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov, A. N. Bibcode: 2020A&A...642A...2R Altcode: Context. The Solar Orbiter spacecraft will be equipped with a wide range of remote-sensing (RS) and in situ (IS) instruments to record novel and unprecedented measurements of the solar atmosphere and the inner heliosphere. To take full advantage of these new datasets, tools and techniques must be developed to ease multi-instrument and multi-spacecraft studies. In particular the currently inaccessible low solar corona below two solar radii can only be observed remotely. Furthermore techniques must be used to retrieve coronal plasma properties in time and in three dimensional (3D) space. Solar Orbiter will run complex observation campaigns that provide interesting opportunities to maximise the likelihood of linking IS data to their source region near the Sun. Several RS instruments can be directed to specific targets situated on the solar disk just days before data acquisition. To compare IS and RS, data we must improve our understanding of how heliospheric probes magnetically connect to the solar disk.
Aims: The aim of the present paper is to briefly review how the current modelling of the Sun and its atmosphere can support Solar Orbiter science. We describe the results of a community-led effort by European Space Agency's Modelling and Data Analysis Working Group (MADAWG) to develop different models, tools, and techniques deemed necessary to test different theories for the physical processes that may occur in the solar plasma. The focus here is on the large scales and little is described with regards to kinetic processes. To exploit future IS and RS data fully, many techniques have been adapted to model the evolving 3D solar magneto-plasma from the solar interior to the solar wind. A particular focus in the paper is placed on techniques that can estimate how Solar Orbiter will connect magnetically through the complex coronal magnetic fields to various photospheric and coronal features in support of spacecraft operations and future scientific studies.
Methods: Recent missions such as STEREO, provided great opportunities for RS, IS, and multi-spacecraft studies. We summarise the achievements and highlight the challenges faced during these investigations, many of which motivated the Solar Orbiter mission. We present the new tools and techniques developed by the MADAWG to support the science operations and the analysis of the data from the many instruments on Solar Orbiter.
Results: This article reviews current modelling and tool developments that ease the comparison of model results with RS and IS data made available by current and upcoming missions. It also describes the modelling strategy to support the science operations and subsequent exploitation of Solar Orbiter data in order to maximise the scientific output of the mission.
Conclusions: The on-going community effort presented in this paper has provided new models and tools necessary to support mission operations as well as the science exploitation of the Solar Orbiter data. The tools and techniques will no doubt evolve significantly as we refine our procedure and methodology during the first year of operations of this highly promising mission. Title: Temporal evolution of short-lived penumbral microjets Authors: Siu-Tapia, A. L.; Bellot Rubio, L. R.; Orozco Suárez, D.; Gafeira, R. Bibcode: 2020A&A...642A.128S Altcode: 2020arXiv200715926S Context. Penumbral microjets (PMJs) is the name given to elongated jet-like brightenings observed in the chromosphere above sunspot penumbrae. They are transient events that last from a few seconds to several minutes, and their origin is presumed to be related to magnetic reconnection processes. Previous studies have mainly focused on their morphological and spectral characteristics, and more recently on their spectropolarimetric signals during the maximum brightness stage. Studies addressing the temporal evolution of PMJs have also been carried out, but they are based on spatial and spectral time variations only.
Aims: Here we investigate, for the first time, the temporal evolution of the polarization signals produced by short-lived PMJs (lifetimes < 2 min) to infer how the magnetic field vector evolves in the upper photosphere and mid-chromosphere.
Methods: We use fast-cadence spectropolarimetric observations of the Ca II 854.2 nm line taken with the CRisp Imaging Spectropolarimeter at the Swedish 1 m Solar Telescope. The weak-field approximation (WFA) is used to estimate the strength and inclination of the magnetic field vector. By separating the Ca II 854.2 nm line into two different wavelength domains to account for the chromospheric origin of the line core and the photospheric contribution to the wings, we infer the height variation of the magnetic field vector.
Results: The WFA reveals larger magnetic field changes in the upper photosphere than in the chromosphere during the PMJ maximum brightness stage. In the photosphere, the magnetic field inclination and strength undergo a transient increase for most PMJs, but in 25% of the cases the field strength decreases during the brightening. In the chromosphere, the magnetic field tends to be slightly stronger during the PMJs.
Conclusions: The propagation of compressive perturbation fronts followed by a rarefaction phase in the aftershock region may explain the observed behavior of the magnetic field vector. The fact that such behavior varies among the analyzed PMJs could be a consequence of the limited temporal resolution of the observations and the fast-evolving nature of the PMJs. Title: Magnetic properties of short-lived penumbral microjets Authors: Siu-Tapia, A.; Bellot Rubio, L.; Orozco Suárez, D.; Gafeira, R. Bibcode: 2020sea..confE.208S Altcode: We investigate the temporal evolution of the polarization properties during penumbral microjets (PMJs). Studying the magnetic properties of these transients requires spectropolarimetric observations with the fastest temporal cadence possible and is currently a challenging task. In this work, we used fast temporal cadence spectropolarimetric measurements of the Ca II 8542 Å line from the CRISP instrument at the Swedish 1 m Solar Telescope, and exploited the diagnosis capabilities of this line to retrieve the magnetic field configuration and its evolution at different atmospheric heights during PMJs. Our findings show that the short-lived PMJs are associated to a transient perturbation in the photospheric magnetic field and sometimes they show clear but weaker changes in the chromospheric field as well. Here we describe the different types of evolution that were identified. Title: On the Magnetic Nature of an Exploding Granule as Revealed by Sunrise/IMaX Authors: Guglielmino, Salvo L.; Martínez Pillet, Valentín; Ruiz Cobo, Basilio; Bellot Rubio, Luis R.; del Toro Iniesta, José Carlos; Solanki, Sami K.; Riethmüller, Tino L.; Zuccarello, Francesca Bibcode: 2020ApJ...896...62G Altcode: 2020arXiv200503371G We study the photospheric evolution of an exploding granule observed in the quiet Sun at high spatial (∼0"3) and temporal (31.5 s) resolution by the imaging magnetograph Sunrise/IMaX in 2009 June. These observations show that the exploding granule is cospatial to a magnetic flux emergence event occurring at mesogranular scale (up to ∼12 Mm2 area). Using a modified version of the SIR code for inverting the IMaX spectropolarimetric measurements, we obtain information about the magnetic configuration of this photospheric feature. In particular, we find evidence of highly inclined emerging fields in the structure, carrying a magnetic flux content up to ∼4 × 1018 Mx. The balance between gas and magnetic pressure in the region of flux emergence, compared with a very quiet region of the Sun, indicates that the additional pressure carried by the emerging flux increases the total pressure by about 5% and appears to allow the granulation to be modified, as predicted by numerical simulations. The overall characteristics suggest that a multipolar structure emerges into the photosphere, resembling an almost horizontal flux sheet. This seems to be associated with exploding granules. Finally, we discuss the origin of such flux emergence events. Title: Solar physics in the 2020s: DKIST, parker solar probe, and solar orbiter as a multi-messenger constellation Authors: Martinez Pillet, V.; Tritschler, A.; Harra, L.; Andretta, V.; Vourlidas, A.; Raouafi, N.; Alterman, B. L.; Bellot Rubio, L.; Cauzzi, G.; Cranmer, S. R.; Gibson, S.; Habbal, S.; Ko, Y. K.; Lepri, S. T.; Linker, J.; Malaspina, D. M.; Matthews, S.; Parenti, S.; Petrie, G.; Spadaro, D.; Ugarte-Urra, I.; Warren, H.; Winslow, R. Bibcode: 2020arXiv200408632M Altcode: The National Science Foundation (NSF) Daniel K. Inouye Solar Telescope (DKIST) is about to start operations at the summit of Haleakala (Hawaii). DKIST will join the early science phases of the NASA and ESA Parker Solar Probe and Solar Orbiter encounter missions. By combining in-situ measurements of the near-sun plasma environment and detail remote observations of multiple layers of the Sun, the three observatories form an unprecedented multi-messenger constellation to study the magnetic connectivity inside the solar system. This white paper outlines the synergistic science that this multi-messenger suite enables. Title: Science Requirement Document (SRD) for the European Solar Telescope (EST) (2nd edition, December 2019) Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.; Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.; Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse, K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.; Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller, T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno, J.; Utz, D.; Zuccarello, F. Bibcode: 2019arXiv191208650S Altcode: The European Solar Telescope (EST) is a research infrastructure for solar physics. It is planned to be an on-axis solar telescope with an aperture of 4 m and equipped with an innovative suite of spectro-polarimetric and imaging post-focus instrumentation. The EST project was initiated and is driven by EAST, the European Association for Solar Telescopes. EAST was founded in 2006 as an association of 14 European countries. Today, as of December 2019, EAST consists of 26 European research institutes from 18 European countries. The Preliminary Design Phase of EST was accomplished between 2008 and 2011. During this phase, in 2010, the first version of the EST Science Requirement Document (SRD) was published. After EST became a project on the ESFRI roadmap 2016, the preparatory phase started. The goal of the preparatory phase is to accomplish a final design for the telescope and the legal governance structure of EST. A major milestone on this path is to revisit and update the Science Requirement Document (SRD). The EST Science Advisory Group (SAG) has been constituted by EAST and the Board of the PRE-EST EU project in November 2017 and has been charged with the task of providing with a final statement on the science requirements for EST. Based on the conceptual design, the SRD update takes into account recent technical and scientific developments, to ensure that EST provides significant advancement beyond the current state-of-the-art. The present update of the EST SRD has been developed and discussed during a series of EST SAG meetings. The SRD develops the top-level science objectives of EST into individual science cases. Identifying critical science requirements is one of its main goals. Those requirements will define the capabilities of EST and the post-focus instrument suite. The technical requirements for the final design of EST will be derived from the SRD. Title: Erratum: Supergranular turbulence in the quiet Sun: Lagrangian coherent structures Authors: Chian, Abraham C. -L.; Silva, Suzana S. A.; Rempel, Erico L.; Gošić; , Milan; Bellot Rubio, Luis R.; Kusano, Kanya; Miranda, Rodrigo A.; Requerey, Iker S. Bibcode: 2019MNRAS.489..707C Altcode: 2019MNRAS.tmp.2225C No abstract at ADS Title: Achievements of Hinode in the first eleven years Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick; Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks, David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio; Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra, Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.; Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao, Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota, Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu, Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin; Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young, Peter R. Bibcode: 2019PASJ...71R...1H Altcode: Hinode is Japan's third solar mission following Hinotori (1981-1982) and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in operation currently. Hinode carries three instruments: the Solar Optical Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These instruments were built under international collaboration with the National Aeronautics and Space Administration and the UK Science and Technology Facilities Council, and its operation has been contributed to by the European Space Agency and the Norwegian Space Center. After describing the satellite operations and giving a performance evaluation of the three instruments, reviews are presented on major scientific discoveries by Hinode in the first eleven years (one solar cycle long) of its operation. This review article concludes with future prospects for solar physics research based on the achievements of Hinode. Title: Supergranular turbulence in the quiet Sun: Lagrangian coherent structures Authors: Chian, Abraham C. -L.; Silva, Suzana S. A.; Rempel, Erico L.; Gošić; , Milan; Bellot Rubio, Luis R.; Kusano, Kanya; Miranda, Rodrigo A.; Requerey, Iker S. Bibcode: 2019MNRAS.488.3076C Altcode: 2019MNRAS.tmp.1841C; 2019arXiv190408472C The quiet Sun exhibits a wealth of magnetic activities that are fundamental for our understanding of solar magnetism. The magnetic fields in the quiet Sun are observed to evolve coherently, interacting with each other to form prominent structures as they are advected by photospheric flows. The aim of this paper is to study supergranular turbulence by detecting Lagrangian coherent structures (LCS) based on the horizontal velocity fields derived from Hinode intensity images at disc centre of the quiet Sun on 2010 November 2. LCS act as transport barriers and are responsible for attracting/repelling the fluid elements and swirling motions in a finite time. Repelling/attracting LCS are found by computing the forward/backward finite-time Lyapunov exponent (FTLE), and vortices are found by the Lagrangian-averaged vorticity deviation method. We show that the Lagrangian centres and boundaries of supergranular cells are given by the local maximum of the forward and backward FTLE, respectively. The attracting LCS expose the location of the sinks of photospheric flows at supergranular junctions, whereas the repelling LCS interconnect the Lagrangian centres of neighbouring supergranular cells. Lagrangian transport barriers are found within a supergranular cell and from one cell to other cells, which play a key role in the dynamics of internetwork and network magnetic elements. Such barriers favour the formation of vortices in supergranular junctions. In particular, we show that the magnetic field distribution in the quiet Sun is determined by the combined action of attracting/repelling LCS and vortices. Title: Evolution of bipolar internetwork magnetic fields Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, Luis Ramon Bibcode: 2019AAS...23431102G Altcode: Internetwork (IN) magnetic fields can be found inside supergranular cells all over the solar surface. Thanks to their abundance and appearance rate, IN fields are considered to be an essential contributor to the magnetic flux and energy budget of the solar photosphere, and may also play a major role in the energy budget of the chromosphere and transition region. Therefore, it is crucial to understand how IN magnetic fields appear, evolve, interact with the preexisting magnetic structures, and what impact they have on the upper solar atmosphere. Here, we analyze spatio-temporal evolution of IN magnetic bipolar structures, i.e, loops and clusters, employing multi-instrument (IRIS and SST), multi-wavelength observations of IN regions with the highest sensitivity and resolution possible. For the first time, our observations allow us to describe in detail how IN bipoles emerge in the photosphere and even reach the chromosphere. We estimate the field strengths of these IN magnetic structures both in the photosphere and the chromosphere, using full Stokes measurements in Fe I 6173 Å, Mg I b2 5173 Å, and Ca II 8542 Å. Employing the IRIS FUV and NUV spectra, we show that IN fields contribute to the chromospheric and transition region heating through interaction with the preexisting ambient fields. Title: On the Magnetic Nature of Solar Exploding Granules Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo, B.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Solanki, S. K.; Zuccarello, F. Bibcode: 2019ASPC..526..299G Altcode: We report on spectropolarimetric observations acquired by the imaging magnetograph SUNRISE/IMaX at high spatial 0.''3 and temporal (31.5 s) resolution during the first science flight of this balloon-borne solar observatory. We describe the photospheric evolution of an exploding granule observed in the quiet Sun. This granule is cospatial with a magnetic flux emergence event occurring at mesogranular scales (up to ∼12 Mm2 area). Using a modified version of the SIR code, we show that we can estimate the longitudinal field also in the presence of a residual cross-talk in these IMaX longitudinal measurements. We determine the magnetic flux content of the structure (∼3 ×1018 Mx), which appears to have a multipolar configuration, and discuss the origin of such flux emergence events. Title: Quiet Sun magnetic fields: an observational view Authors: Bellot Rubio, Luis; Orozco Suárez, David Bibcode: 2019LRSP...16....1B Altcode: The quiet Sun is the region of the solar surface outside of sunspots, pores, and plages. In continuum intensity it appears dominated by granular convection. However, in polarized light the quiet Sun exhibits impressive magnetic activity on a broad range of scales, from the 30,000 km of supergranular cells down to the smallest magnetic features of about 100 km resolvable with current instruments. Quiet Sun fields are observed to evolve in a coherent way, interacting with each other as they are advected by the horizontal photospheric flows. They appear and disappear over surprisingly short time scales, bringing large amounts of magnetic flux to the solar surface. For this reason they may be important contributors to the heating of the chromosphere. Peering into such fields is difficult because of the weak signals they produce, which are easily affected, and even completely hidden, by photon noise. Thus, their evolution and nature remain largely unknown. In recent years the situation has improved thanks to the advent of high-resolution, high-sensitivity spectropolarimetric measurements and the application of state-of-the-art Zeeman and Hanle effect diagnostics. Here we review this important aspect of solar magnetism, paying special attention to the techniques used to observe and characterize the fields, their evolution on the solar surface, and their physical properties as revealed by the most recent analyses. We identify the main open questions that need to be addressed in the future and offer some ideas on how to solve them. Title: Emergence of internetwork magnetic fields through the solar atmosphere Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, L. R. Bibcode: 2018cosp...42E1261G Altcode: Internetwork (IN) magnetic fields are highly dynamic, short-lived magnetic structures that populate the interior of supergranular cells. Since they emerge all over the Sun, these small-scale fields bring a substantial amount of flux, and therefore energy, to the solar surface. Because of this, IN fields are crucial for understanding the quiet Sun magnetism. However, they are weak and produce very small polarization signals, which is the reason why their properties and impact on the energetics and dynamics of the solar atmosphere are largely unknown. Here we use coordinated IRIS and SST observations of IN regions at high spatial and temporal resolution. They give us the opportunity to follow the evolution of IN magnetic loops as they emerge into the photosphere. For the first time, our polarimetric measurements provide a direct observational evidence of IN fields reaching the chromosphere. Moreover, we show that IN magnetic loops contribute to the chromospheric and transition region heating through interaction with preexisting ambient fields. Title: Transport of Internetwork Magnetic Flux Elements in the Solar Photosphere : Signatures of Large-Scale Flows and their Effect on Transport Statistics Authors: Agrawal, Piyush; Rast, Mark; Gosic, Milan; Rempel, Matthias; Bellot Rubio, Luis Bibcode: 2018tess.conf21704A Altcode: The motions of small-scale magnetic <span class="s1" flux elements in the solar photosphere can provide some measure of the Lagrangian properties of the convective <span class="s1" flow. Measurements of these motions have been critical in estimating the turbulent diffusion coef<span class="s1" ficient in <span class="s1" flux-transport dynamo models and in determining the Alfvén wave excitation spectrum for coronal heating models. We examine the motions of internetwork <span class="s1" flux elements in Hinode<span class="s1" /Narrowband Filter Imager magnetograms and study the scaling of their mean squared displacement and the shape of their displacement probability distribution as a function of time. We <span class="s1" find that the mean squared displacement scales super-diffusively with a slope of about 1.48. Super-diffusive scaling has been observed in other studies for temporal increments as small as 5 s, increments over which ballistic scaling would be expected. Using high-cadence MURaM simulations, we show that the observed super-diffusive scaling at short increments is a consequence of random changes in barycenter positions due to <span class="s1" flux evolution. We also <span class="s1" find that for long temporal increments, beyond granular lifetimes, the observed displacement distribution deviates from that expected for a diffusive process, evolving from Rayleigh to Gaussian. This change in distribution can be modeled analytically by accounting for supergranular advection along with granular motions. These results complicate the interpretation of magnetic element motions as strictly advective or diffusive on short and long timescales and suggest that measurements of magnetic element motions must be used with caution in turbulent diffusion or wave excitation models. We propose that passive tracer motions in measured photospheric <span class="s1" flows may yield more robust transport statistics. Title: Emergence of internetwork magnetic fields through the solar atmosphere Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, Luis Bibcode: 2018tess.conf21701G Altcode: Internetwork (IN) magnetic fields are highly dynamic, short-lived magnetic structures that populate the interior of supergranular cells. Since they emerge all over the Sun, these small-scale fields bring a substantial amount of flux, and therefore energy, to the solar surface. Because of this, IN fields are crucial for understanding the quiet Sun magnetism. However, they are weak and produce very small polarization signals, which is the reason why their properties and impact on the energetics and dynamics of the solar atmosphere are largely unknown. Here we use coordinated IRIS and SST observations of IN regions at high spatial and temporal resolution. They give us the opportunity to follow the evolution of IN magnetic loops as they emerge into the photosphere. For the first time, our polarimetric measurements provide a direct observational evidence of IN fields reaching the chromosphere. Moreover, we show that IN magnetic loops contribute to the chromospheric and transition region heating through interaction with preexisting ambient fields. Title: Chromospheric Heating due to Cancellation of Quiet Sun Internetwork Fields Authors: Gošić, M.; de la Cruz Rodríguez, J.; De Pontieu, B.; Bellot Rubio, L. R.; Carlsson, M.; Esteban Pozuelo, S.; Ortiz, A.; Polito, V. Bibcode: 2018ApJ...857...48G Altcode: 2018arXiv180207392G The heating of the solar chromosphere remains one of the most important questions in solar physics. Our current understanding is that small-scale internetwork (IN) magnetic fields play an important role as a heating agent. Indeed, cancellations of IN magnetic elements in the photosphere can produce transient brightenings in the chromosphere and transition region. These bright structures might be the signature of energy release and plasma heating, probably driven by the magnetic reconnection of IN field lines. Although single events are not expected to release large amounts of energy, their global contribution to the chromosphere may be significant due to their ubiquitous presence in quiet Sun regions. In this paper, we study cancellations of IN elements and analyze their impact on the energetics and dynamics of the quiet Sun atmosphere. We use high-resolution, multiwavelength, coordinated observations obtained with the Interface Region Imaging Spectrograph and the Swedish 1 m Solar Telescope (SST) to identify cancellations of IN magnetic flux patches and follow their evolution. We find that, on average, these events live for ∼3 minutes in the photosphere and ∼12 minutes in the chromosphere and/or transition region. Employing multi-line inversions of the Mg II h and k lines, we show that cancellations produce clear signatures of heating in the upper atmospheric layers. However, at the resolution and sensitivity accessible to the SST, their number density still seems to be one order of magnitude too low to explain the global chromospheric heating. Title: Persistent magnetic vortex flow at a supergranular vertex Authors: Requerey, Iker S.; Cobo, Basilio Ruiz; Gošić, Milan; Bellot Rubio, Luis R. Bibcode: 2018A&A...610A..84R Altcode: 2017arXiv171201510R Context. Photospheric vortex flows are thought to play a key role in the evolution of magnetic fields. Recent studies show that these swirling motions are ubiquitous in the solar surface convection and occur in a wide range of temporal and spatial scales. Their interplay with magnetic fields is poorly characterized, however.
Aims: We study the relation between a persistent photospheric vortex flow and the evolution of a network magnetic element at a supergranular vertex.
Methods: We used long-duration sequences of continuum intensity images acquired with Hinode and the local correlation-tracking method to derive the horizontal photospheric flows. Supergranular cells are detected as large-scale divergence structures in the flow maps. At their vertices, and cospatial with network magnetic elements, the velocity flows converge on a central point.
Results: One of these converging flows is observed as a vortex during the whole 24 h time series. It consists of three consecutive vortices that appear nearly at the same location. At their core, a network magnetic element is also detected. Its evolution is strongly correlated to that of the vortices. The magnetic feature is concentrated and evacuated when it is caught by the vortices and is weakened and fragmented after the whirls disappear.
Conclusions: This evolutionary behavior supports the picture presented previously, where a small flux tube becomes stable when it is surrounded by a vortex flow.

A movie attached to Fig. 2 is available at https://www.aanda.org Title: Occurrence and persistence of magnetic elements in the quiet Sun Authors: Giannattasio, F.; Berrilli, F.; Consolini, G.; Del Moro, D.; Gošić, M.; Bellot Rubio, L. Bibcode: 2018A&A...611A..56G Altcode: 2018arXiv180103871G Context. Turbulent convection efficiently transports energy up to the solar photosphere, but its multi-scale nature and dynamic properties are still not fully understood. Several works in the literature have investigated the emergence of patterns of convective and magnetic nature in the quiet Sun at spatial and temporal scales from granular to global.
Aims: To shed light on the scales of organisation at which turbulent convection operates, and its relationship with the magnetic flux therein, we studied characteristic spatial and temporal scales of magnetic features in the quiet Sun.
Methods: Thanks to an unprecedented data set entirely enclosing a supergranule, occurrence and persistence analysis of magnetogram time series were used to detect spatial and long-lived temporal correlations in the quiet Sun and to investigate their nature.
Results: A relation between occurrence and persistence representative for the quiet Sun was found. In particular, highly recurrent and persistent patterns were detected especially in the boundary of the supergranular cell. These are due to moving magnetic elements undergoing motion that behaves like a random walk together with longer decorrelations ( 2 h) with respect to regions inside the supergranule. In the vertices of the supegranular cell the maximum observed occurrence is not associated with the maximum persistence, suggesting that there are different dynamic regimes affecting the magnetic elements. Title: Transport of Internetwork Magnetic Flux Elements in the Solar Photosphere Authors: Agrawal, Piyush; Rast, Mark P.; Gošić, Milan; Bellot Rubio, Luis R.; Rempel, Matthias Bibcode: 2018ApJ...854..118A Altcode: 2017arXiv171101290A The motions of small-scale magnetic flux elements in the solar photosphere can provide some measure of the Lagrangian properties of the convective flow. Measurements of these motions have been critical in estimating the turbulent diffusion coefficient in flux-transport dynamo models and in determining the Alfvén wave excitation spectrum for coronal heating models. We examine the motions of internetwork flux elements in Hinode/Narrowband Filter Imager magnetograms and study the scaling of their mean squared displacement and the shape of their displacement probability distribution as a function of time. We find that the mean squared displacement scales super-diffusively with a slope of about 1.48. Super-diffusive scaling has been observed in other studies for temporal increments as small as 5 s, increments over which ballistic scaling would be expected. Using high-cadence MURaM simulations, we show that the observed super-diffusive scaling at short increments is a consequence of random changes in barycenter positions due to flux evolution. We also find that for long temporal increments, beyond granular lifetimes, the observed displacement distribution deviates from that expected for a diffusive process, evolving from Rayleigh to Gaussian. This change in distribution can be modeled analytically by accounting for supergranular advection along with granular motions. These results complicate the interpretation of magnetic element motions as strictly advective or diffusive on short and long timescales and suggest that measurements of magnetic element motions must be used with caution in turbulent diffusion or wave excitation models. We propose that passive tracer motions in measured photospheric flows may yield more robust transport statistics. Title: Chromospheric Heating Driven by Cancellations of Internetwork Magnetic Flux Authors: Gosic, M.; de la Cruz Rodriguez, J.; De Pontieu, B.; Bellot Rubio, L.; Esteban Pozuelo, S.; Ortiz-Carbonell, A. N. Bibcode: 2017AGUFMSH41C..02G Altcode: The heating of the solar chromosphere remains to be one of the most important questions in solar physics. It is believed that this phenomenon may significantly be supported by small-scale internetwork (IN) magnetic fields. Indeed, cancellations of IN magnetic flux can generate transient brightenings in the chromosphere and transition region. These bright structures might be the signature of energy release and plasma heating, probably driven by magnetic reconnection of IN field lines. Using high resolution, multiwavelength, coordinated observations recorded with the Interface Region Imaging Spectrograph (IRIS) and the Swedish 1-m Solar Telescope (SST), we analyzed cancellations of IN flux and their impact on the energetics and dynamics of the quiet Sun atmosphere. From their temporal and spatial evolution, we determine that these events can heat locally the upper atmospheric layers. However, employing multi-line inversions of the Mg II h & k lines, we show that cancellations, although occurring ubiquitously over IN regions, are not capable of sustaining the total radiative losses of the quiet Sun chromosphere. Title: Chromospheric heating due to internetwork magnetic flux cancellations Authors: Gosic, Milan; de la Cruz Rodriguez, Jaime; De Pontieu, Bart; Bellot Rubio, Luis; Ortiz, Ada; Esteban Pozuelo, Sara Bibcode: 2017SPD....4810404G Altcode: The heating of the solar chromosphere is one of the most intriguing unanswered problems in solar physics. It is believed that this phenomenon may significantly be supported by small-scale internetwork (IN) magnetic fields. Indeed, cancellations of IN magnetic flux patches might be an efficient way to transport flux and energy from the photosphere to the chromosphere. Because of this, it is essential to determine where they occur, the rates at which they proceed, and understand their influence on the chromosphere. Here we study the spatial and temporal evolution of IN cancelling patches using high resolution, multiwavelength, coordinated observations obtained with the Interface Region Imaging Spectrograph (IRIS) and the Swedish 1-m Solar Telescope (SST). Employing multi-line inversions of the Mg II h&k lines we show that cancelling events, while occurring ubiquitously over IN regions, produce clear signatures of heating in the upper atmospheric layers. Using the RADYN code we determine the energy released due to cancellations of IN elements and discuss about their impact on the dynamics and energetics of the solar chromosphere. Title: Convectively Driven Sinks and Magnetic Fields in the Quiet-Sun Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.; Schmidt, Wolfgang Bibcode: 2017ApJS..229...14R Altcode: 2016arXiv161007622R We study the relation between mesogranular flows, convectively driven sinks and magnetic fields using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board Sunrise. We obtain the horizontal velocity flow fields of two quiet-Sun regions (31.2 × 31.2 Mm2) via local correlation tracking. Mesogranular lanes and the central position of sinks are identified using Lagrange tracers. We find 6.7× {10}-2 sinks per Mm2 in the two observed regions. The sinks are located at the mesogranular vertices and turn out to be associated with (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 components of the magnetic field stronger than 500 G are located in the close neighborhood of sinks. In contrast, the small-scale magnetic loops detected by Martínez González et al. in the same two observed areas do not show any preferential distribution at mesogranular scales. The study of individual examples reveals that sinks can play an important role in the evolution of quiet-Sun magnetic features. Title: Properties of Supersonic Evershed Downflows Authors: Pozuelo, S. Esteban; Bellot Rubio, L. R.; de la Cruz Rodríguez, J. Bibcode: 2016ApJ...832..170P Altcode: 2016ApJ...832..170E; 2016arXiv160901106E We study supersonic Evershed downflows in a sunspot penumbra by means of high spatial resolution spectropolarimetric data acquired in the Fe I 617.3 nm line with the CRISP instrument at the Swedish 1 m Solar Telescope. Physical observables, such as Dopplergrams calculated from line bisectors and Stokes V zero-crossing wavelengths, and Stokes V maps in the far red-wing, are used to find regions where supersonic Evershed downflows may exist. We retrieve the line-of-sight velocity and the magnetic field vector in these regions using two-component inversions of the observed Stokes profiles with the help of the SIR code. We follow these regions during their lifetime to study their temporal behavior. Finally, we carry out a statistical analysis of the detected supersonic downflows to characterize their physical properties. Supersonic downflows are contained in compact patches moving outward, which are located in the mid- and outer penumbra. They are observed as bright, roundish structures at the outer end of penumbral filaments that resemble penumbral grains. The patches may undergo fragmentations and mergings during their lifetime; some of them are recurrent. Supersonic downflows are associated with strong and rather vertical magnetic fields with a reversed polarity compared to that of the sunspot. Our results suggest that downflows returning back to the solar surface with supersonic velocities are abruptly stopped in dense deep layers and produce a shock. Consequently, this shock enhances the temperature and is detected as a bright grain in the continuum filtergrams, which could explain the existence of outward-moving grains in the mid- and outer penumbra. Title: A study on Ca II 854.2 nm emission in a sunspot umbra using a thin cloud model Authors: Hamedivafa, H.; Sobotka, M.; Bellot Rubio, L.; Esteban Pozuelo, S. Bibcode: 2016arXiv161206636H Altcode: In the present work, we introduce and explain a method of solution of the radiative transfer equation based on a thin cloud model. The efficiency of this method to retrieve dynamical chromospheric parameters from Stokes I profiles of Ca II 854.2 nm line showing spectral emission is investigated. The analyzed data were recorded with the Crisp Imaging Spectro-Polarimeter (CRISP) at Swedish 1-m Solar Telescope on La Palma on 2012 May 5 between 8:11 - 9:00 UT. The target was a large decaying sunspot (NOAA 11471) at heliocentric position W 15 deg S 19 deg. This sunspot has a large umbra divided into two umbral cores (UCs). One of these UCs shows steady spectral emission in both Ca II 854.2 nm and H-alpha lines, where downflows prevail. The other UC shows intermittent spectral emission only in Ca II 854.2 nm, when umbral flashes are propagating. The statistics of the obtained Doppler velocities in both UCs is discussed. Title: Emergence of Granular-sized Magnetic Bubbles Through the Solar Atmosphere. III. The Path to the Transition Region Authors: Ortiz, Ada; Hansteen, Viggo H.; Bellot Rubio, Luis Ramón; de la Cruz Rodríguez, Jaime; De Pontieu, Bart; Carlsson, Mats; Rouppe van der Voort, Luc Bibcode: 2016ApJ...825...93O Altcode: 2016arXiv160400302O We study, for the first time, the ascent of granular-sized magnetic bubbles from the solar photosphere through the chromosphere into the transition region and above. Such events occurred in a flux emerging region in NOAA 11850 on 2013 September 25. During that time, the first co-observing campaign between the Swedish 1-m Solar Telescope (SST) and the Interface Region Imaging Spectrograph (IRIS) spacecraft was carried out. Simultaneous observations of the chromospheric Hα 656.28 nm and Ca II 854.2 nm lines, plus the photospheric Fe I 630.25 nm line, were made with the CRISP spectropolarimeter at the Spitzer Space Telescope (SST) reaching a spatial resolution of 0.″14. At the same time, IRIS was performing a four-step dense raster of the emerging flux region, taking slit jaw images at 133 (C II, transition region), 140 (Si IV, transition region), 279.6 (Mg II k, core, upper chromosphere), and 283.2 nm (Mg II k, wing, photosphere). Spectroscopy of several lines was performed by the IRIS spectrograph in the far- and near-ultraviolet, of which we have used the Si IV 140.3 and the Mg II k 279.6 nm lines. Coronal images from the Atmospheric Imaging Assembly of the Solar Dynamics Observatory were used to investigate the possible coronal signatures of the flux emergence events. The photospheric and chromospheric properties of small-scale emerging magnetic bubbles have been described in detail in Ortiz et al. Here we are able to follow such structures up to the transition region. We describe the properties, including temporal delays, of the observed flux emergence in all layers. We believe this may be an important mechanism of transporting energy and magnetic flux from subsurface layers to the transition region and corona. Title: Turbulent transport of Small-scale magnetic flux elements on Solar Photosphere Authors: Agrawal, Piyush; Rempel, Matthias; Bellot Rubio, Luis; Rast, Mark Bibcode: 2016SPD....47.1201A Altcode: We study the transport of small-scale magnetic elements on the solar photosphere using both observations and simulations. Observational data was obtained from Hinode - Solar Optical Telescope (SOT/SP) instrument and simulations from MURaM code. The magnetic flux elements were tracked in both data sets and statistics were obtained. We compute the probability density of the Eulerian distances traveled by the flux elements along Lagrangian trajectories. For a two-dimensional random walk process this distribution should be Rayleigh. Preliminary results show that the measured probability distribution in both the observed and simulated data approximates a random walk, on time scale close to the lifetime of granules, but deviates from it for longer times. This implies that diffusion may not be an appropriate framework for transport in the solar photosphere. We explore the roles of flux cancelation and element trapping in producing this result. Work is ongoing. Title: Flux appearance and disappearance rates in the solar internetwork Authors: Gosic, Milan; Bellot Rubio, Luis; Del Toro Iniesta, Jose Carlos; Orozco Suarez, David; Katsukawa, Yukio Bibcode: 2016SPD....4740105G Altcode: The solar internetwork contains weak and highly dynamic magnetic fields that are essential to understanding the solar magnetism at small spatial and temporal scales. Therefore, it is important to determine how these fields are maintained on the solar surface. Using unique Hinode observations, we follow the evolution of individual magnetic elements in the interior of two supergranular cells at the disk center. From up to 38 hr of continuous measurements, we show that magnetic flux appears in internetwork regions at a rate of 120±3 Mx cm-2 day-1 (3.7±0.4 × 1024 Mx day-1 over the entire solar surface). Flux disappears from the internetwork at a rate of 125±6 Mx cm-2 day-1 (3.9±0.5 × 1024 Mx day-1) through fading of magnetic elements, cancellation between opposite-polarity features, and interactions with network patches, which converts internetwork elements into network features. The removal of flux from supergranules occurs mainly through fading and interactions with network, at nearly the same rate of about 50 Mx cm-2 day-1. Our results demonstrate that the sources and sinks of internetwork magnetic flux are well balanced, reflecting the steady-state nature of the quiet Sun. Using the instantaneous flux appearance and disappearance rates, we successfully reproduce, for the first time, the temporal evolution of the total unsigned flux in the interior of supergranular cells. Title: The Solar Internetwork. II. Flux Appearance and Disappearance Rates Authors: Gošić, M.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Orozco Suárez, D.; Katsukawa, Y. Bibcode: 2016ApJ...820...35G Altcode: 2016arXiv160205892G Small-scale internetwork magnetic fields are important ingredients of the quiet Sun. In this paper we analyze how they appear and disappear on the solar surface. Using high resolution Hinode magnetograms, we follow the evolution of individual magnetic elements in the interior of two supergranular cells at the disk center. From up to 38 hr of continuous measurements, we show that magnetic flux appears in internetwork regions at a rate of 120 ± 3 Mx cm-2 day-1 (3.7 ± 0.4 × 1024 Mx day-1 over the entire solar surface). Flux disappears from the internetwork at a rate of 125 ± 6 Mx cm-2 day-1 (3.9 ± 0.5 × 1024 Mx day-1) through fading of magnetic elements, cancelation between opposite-polarity features, and interactions with network patches, which converts internetwork elements into network features. Most of the flux is lost through fading and interactions with the network, at nearly the same rate of about 50 Mx cm-2 day-1. Our results demonstrate that the sources and sinks of internetwork magnetic flux are well balanced. Using the instantaneous flux appearance and disappearance rates, we successfully reproduce the time evolution of the total unsigned flux in the two supergranular cells. Title: Small-scale magnetic flux emergence in a sunspot light bridge Authors: Louis, Rohan E.; Bellot Rubio, Luis R.; de la Cruz Rodríguez, Jaime; Socas-Navarro, Héctor; Ortiz, Ada Bibcode: 2015A&A...584A...1L Altcode: 2015arXiv150900741L Context. Light bridges are convective intrusions in sunspots that often show enhanced chromospheric activity.
Aims: We seek to determine the nature of flux emergence in a light bridge and the processes related to its evolution in the solar atmosphere.
Methods: We analyse a sequence of high-resolution spectropolarimetric observations of a sunspot taken at the Swedish 1-m Solar Telescope. The data consist of spectral scans of the photospheric Fe i line pair at 630 nm and the chromospheric Ca ii 854.2 nm line. Bisectors were used to construct Dopplergrams from the Fe i 630.15 nm measurements. We employed LTE and non-LTE inversions to derive maps of physical parameters in the photosphere and chromosphere, respectively.
Results: We observe the onset of blueshifts of about 2 km s-1 near the entrance of a granular light bridge on the limbward side of the spot. The blueshifts lie immediately next to a strongly redshifted patch that appeared six minutes earlier. Both patches can be seen for 25 min until the end of the sequence. The blueshifts coincide with an elongated emerging granule, while the redshifts appear at the end of the granule. In the photosphere, the development of the blueshifts is accompanied by a simultaneous increase in field strength of about 400 G. The field inclination increases by some 25°, becoming nearly horizontal. At the position of the redshifts, the magnetic field is equally horizontal but of opposite polarity. An intense brightening is seen in the Ca ii filtergrams over the blueshifts and redshifts, about 17 min after their detection in the photosphere. The brightening is due to emission in the blue wing of the Ca ii 854.2 nm line, close to its knee. Non-LTE inversions reveal that this kind of asymmetric emission is caused by a temperature enhancement of ~700 K between -5.0 ≤ log τ ≤ -3.0 and a blueshift of 3 km s-1 at log τ = -2.3 that decreases to zero at log τ = -6.0
Conclusions: The photospheric blueshifts and redshifts observed in a granular light bridge seem to be caused by the emergence of a small-scale, flat Ω-loop with highly inclined footpoints of opposite polarity that brings new magnetic field to the surface. The gas motions detected in the two footpoints are reminiscent of a siphon flow. The rising loop is probably confined to the lower atmosphere by the overlying sunspot magnetic field and the interaction between the two flux systems may be responsible for temperature enhancements in the upper photosphere/lower chromosphere. This is the first time that magnetic flux is observed to emerge in the strongly magnetised environment of sunspots, pushed upwards by the convective flows of a granular light bridge.

The movie associated to Fig. 2 is available in electronic form at http://www.aanda.org Title: ADAHELI: exploring the fast, dynamic Sun in the x-ray, optical, and near-infrared Authors: Berrilli, Francesco; Soffitta, Paolo; Velli, Marco; Sabatini, Paolo; Bigazzi, Alberto; Bellazzini, Ronaldo; Bellot Rubio, Luis Ramon; Brez, Alessandro; Carbone, Vincenzo; Cauzzi, Gianna; Cavallini, Fabio; Consolini, Giuseppe; Curti, Fabio; Del Moro, Dario; Di Giorgio, Anna Maria; Ermolli, Ilaria; Fabiani, Sergio; Faurobert, Marianne; Feller, Alex; Galsgaard, Klaus; Gburek, Szymon; Giannattasio, Fabio; Giovannelli, Luca; Hirzberger, Johann; Jefferies, Stuart M.; Madjarska, Maria S.; Manni, Fabio; Mazzoni, Alessandro; Muleri, Fabio; Penza, Valentina; Peres, Giovanni; Piazzesi, Roberto; Pieralli, Francesca; Pietropaolo, Ermanno; Martinez Pillet, Valentin; Pinchera, Michele; Reale, Fabio; Romano, Paolo; Romoli, Andrea; Romoli, Marco; Rubini, Alda; Rudawy, Pawel; Sandri, Paolo; Scardigli, Stefano; Spandre, Gloria; Solanki, Sami K.; Stangalini, Marco; Vecchio, Antonio; Zuccarello, Francesca Bibcode: 2015JATIS...1d4006B Altcode: Advanced Astronomy for Heliophysics Plus (ADAHELI) is a project concept for a small solar and space weather mission with a budget compatible with an European Space Agency (ESA) S-class mission, including launch, and a fast development cycle. ADAHELI was submitted to the European Space Agency by a European-wide consortium of solar physics research institutes in response to the "Call for a small mission opportunity for a launch in 2017," of March 9, 2012. The ADAHELI project builds on the heritage of the former ADAHELI mission, which had successfully completed its phase-A study under the Italian Space Agency 2007 Small Mission Programme, thus proving the soundness and feasibility of its innovative low-budget design. ADAHELI is a solar space mission with two main instruments: ISODY: an imager, based on Fabry-Pérot interferometers, whose design is optimized to the acquisition of highest cadence, long-duration, multiline spectropolarimetric images in the visible/near-infrared region of the solar spectrum. XSPO: an x-ray polarimeter for solar flares in x-rays with energies in the 15 to 35 keV range. ADAHELI is capable of performing observations that cannot be addressed by other currently planned solar space missions, due to their limited telemetry, or by ground-based facilities, due to the problematic effect of the terrestrial atmosphere. Title: Parallelization of the SIR code for the investigation of small-scale features in the solar photosphere Authors: Thonhofer, Stefan; Bellot Rubio, Luis R.; Utz, Dominik; Hanslmeier, Arnold; Jurçák, Jan Bibcode: 2015IAUS..305..251T Altcode: 2015arXiv150303710T Magnetic fields are one of the most important drivers of the highly dynamic processes that occur in the lower solar atmosphere. They span a broad range of sizes, from large- and intermediate-scale structures such as sunspots, pores and magnetic knots, down to the smallest magnetic elements observable with current telescopes. On small scales, magnetic flux tubes are often visible as Magnetic Bright Points (MBPs). Apart from simple V/I magnetograms, the most common method to deduce their magnetic properties is the inversion of spectropolarimetric data. Here we employ the SIR code for that purpose. SIR is a well-established tool that can derive not only the magnetic field vector and other atmospheric parameters (e.g., temperature, line-of-sight velocity), but also their stratifications with height, effectively producing 3-dimensional models of the lower solar atmosphere. In order to enhance the runtime performance and the usability of SIR we parallelized the existing code and standardized the input and output formats. This and other improvements make it feasible to invert extensive high-resolution data sets within a reasonable amount of computing time. An evaluation of the speedup of the parallel SIR code shows a substantial improvement in runtime. Title: Dynamics of Multi-cored Magnetic Structures in the Quiet Sun Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.; Schmidt, Wolfgang Bibcode: 2015ApJ...810...79R Altcode: 2015arXiv150806998R We report on the dynamical interaction of quiet-Sun magnetic fields and granular convection in the solar photosphere as seen by Sunrise. We use high spatial resolution (0.″15-0.″18) and temporal cadence (33 s) spectropolarimetric Imaging Magnetograph eXperiment data, together with simultaneous CN and Ca ii H filtergrams from Sunrise Filter Imager. We apply the SIR inversion code to the polarimetric data in order to infer the line of sight velocity and vector magnetic field in the photosphere. The analysis reveals bundles of individual flux tubes evolving as a single entity during the entire 23 minute data set. The group shares a common canopy in the upper photospheric layers, while the individual tubes continually intensify, fragment and merge in the same way that chains of bright points in photometric observations have been reported to do. The evolution of the tube cores are driven by the local granular convection flows. They intensify when they are “compressed” by surrounding granules and split when they are “squeezed” between two moving granules. The resulting fragments are usually later regrouped in intergranular lanes by the granular flows. The continual intensification, fragmentation and coalescence of flux results in magnetic field oscillations of the global entity. From the observations we conclude that the magnetic field oscillations first reported by Martínez González et al. correspond to the forcing by granular motions and not to characteristic oscillatory modes of thin flux tubes. Title: Emergence of Granular-sized Magnetic Bubbles through the Solar Atmosphere. II. Non-LTE Chromospheric Diagnostics and Inversions Authors: de la Cruz Rodríguez, Jaime; Hansteen, Viggo; Bellot-Rubio, Luis; Ortiz, Ada Bibcode: 2015ApJ...810..145D Altcode: 2015arXiv150303846D Magnetic flux emergence into the outer layers of the Sun is a fundamental mechanism for releasing energy into the chromosphere and the corona. In this paper, we study the emergence of granular-sized flux concentrations and the structuring of the corresponding physical parameters and atmospheric diagnostics in the upper photosphere and in the chromosphere. We make use of a realistic 3D MHD simulation of the outer layers of the Sun to study the formation of the Ca ii 8542 line. We also derive semi-empirical 3D models from non-LTE inversions of our observations. These models contain information on the line-of-sight stratifications of temperature, velocity, and the magnetic field. Our analysis explains the peculiar Ca ii 8542 Å profiles observed in the flux emerging region. Additionally, we derive detailed temperature and velocity maps describing the ascent of a magnetic bubble from the photosphere to the chromosphere. The inversions suggest that, in active regions, granular-sized bubbles emerge up to the lower chromosphere where the existing large-scale field hinders their ascent. We report hints of heating when the field reaches the chromosphere. Title: Magnetic bright point dynamics and evolutions observed by Sunrise/IMaX and other instruments Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L.; Thonhofer, S.; Jurčák, J. Bibcode: 2015hsa8.conf..689U Altcode: In this proceeding we will have a closer look on recent observations and results regarding the dynamics and evolution of so-called magnetic bright points (MBPs). MBPs are manifestations of kG magnetic field strong flux concentrations seen in the solar photosphere. They belong to the class of small-scale solar magnetic features with diameters starting from low values around the current observational resolution limit - about 100 km - up to a few hundred km. They might play an important role in several key research questions like the total solar irradiance variation (TSI variation) as well as the solar atmospheric heating problem. Especially their dynamic behaviour is of interest for the heating problem as they might trigger all kinds of MHD waves which travel up to the higher solar atmospheric layers, where they can get damped leading to a heating of the plasma. Furthermore they might engage in magnetic field reconnection processes leading consequently also to a heating. Due to these reasons, and also for the sake of a better understanding of the physical processes involved on small-scales, detailed investigations on the dynamical behaviour and evolution of such magnetic field proxies like MBPs is in order. In this conference proceeding we wish to give in a first part an overview about the obtained knowledge so far. In a second part we highlight recent results regarding the dynamical evolution of plasma parameters of MBPs such as magnetic field strength, temperature, and line of sight velocity. This proceeding is completed by an outlook on what can and should be done in the near future with available data from recent telescopes. Title: Lateral Downflows in Sunspot Penumbral Filaments and their Temporal Evolution Authors: Esteban Pozuelo, S.; Bellot Rubio, L. R.; de la Cruz Rodríguez, J. Bibcode: 2015ApJ...803...93E Altcode: 2015arXiv150202981E We study the temporal evolution of downflows observed at the lateral edges of penumbral filaments in a sunspot located very close to the disk center. Our analysis is based on a sequence of nearly diffraction-limited scans of the Fe i 617.3 nm line taken with the CRisp Imaging Spectro-Polarimeter instrument at the Swedish 1 m Solar Telescope. We compute Dopplergrams from the observed intensity profiles using line bisectors and filter the resulting velocity maps for subsonic oscillations. Lateral downflows appear everywhere in the center-side penumbra as small, weak patches of redshifts next to or along the edges of blueshifted flow channels. These patches have an intermittent life and undergo mergings and fragmentations quite frequently. The lateral downflows move together with the hosting filaments and react to their shape variations, very much resembling the evolution of granular convection in the quiet Sun. There is a good relation between brightness and velocity in the center-side penumbra, with downflows being darker than upflows on average, which is again reminiscent of quiet Sun convection. These results point to the existence of overturning convection in sunspot penumbrae, with elongated cells forming filaments where the flow is upward but very inclined, and weak lateral downward flows. In general, the circular polarization profiles emerging from the lateral downflows do not show sign reversals, although sometimes we detect three-lobed profiles that are suggestive of opposite magnetic polarities in the pixel. Title: Long time variations of Magnetic Bright Points observed by Hinode/SOT Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot-Rubio, L.; Bodnárová, M.; Muller, R.; Bárta, M.; Thonhofer, S.; Hanslmeier, A. Bibcode: 2015CEAB...39...91U Altcode: Magnetic bright points (MBPs) are manifestations of small-scale solar magnetic flux concentrations, best observable due to their high contrast in molecular bands like the G-band. Moreover, they are among the most interesting magnetic features to be studied in high spatial and temporal resolution in the solar photosphere. Their relevance for solar physics is not only given by their contribution to fundamental solar plasma physics on small scales but in addition due to their involvement in processes like the solar atmospheric heating problem (chromosphere and corona), their influence on granulation and hence the convective energy transport, as well as their contribution to the variations in total solar irradiance caused by their higher relative intensity. In this ongoing study we focus on the long-time evolution of statistical parameters of MBPs over the solar cycle. Are parameters like the mean intensity, average size/diameter, and number of MBPs per unit surface element variable with time? If so, how do these parameters vary and is there a relationship to the solar cycle? In the actual contribution we will discuss preliminary results regarding the variation of the number of MBPs with time. We saw a decrease in the number of MBPs for the first years of observation (2006 until 2011) with two distinct local minima in the years 2009 and 2011. After 2011 the number of MBPs is increasing again along with an increase in general solar activity (as seen by the number of sunspots, flares, and CMEs). Title: The Formation and Disintegration of Magnetic Bright Points Observed by Sunrise/IMaX Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.; Jurčák, J.; Martínez Pillet, V.; Solanki, S. K.; Schmidt, W. Bibcode: 2014ApJ...796...79U Altcode: 2014arXiv1411.3240U The evolution of the physical parameters of magnetic bright points (MBPs) located in the quiet Sun (mainly in the interwork) during their lifetime is studied. First, we concentrate on the detailed description of the magnetic field evolution of three MBPs. This reveals that individual features follow different, generally complex, and rather dynamic scenarios of evolution. Next, we apply statistical methods on roughly 200 observed MBP evolutionary tracks. MBPs are found to be formed by the strengthening of an equipartition field patch, which initially exhibits a moderate downflow. During the evolution, strong downdrafts with an average velocity of 2.4 km s-1 set in. These flows, taken together with the concurrent strengthening of the field, suggest that we are witnessing the occurrence of convective collapses in these features, although only 30% of them reach kG field strengths. This fraction might turn out to be larger when the new 4 m class solar telescopes are operational as observations of MBPs with current state of the art instrumentation could still be suffering from resolution limitations. Finally, when the bright point disappears (although the magnetic field often continues to exist) the magnetic field strength has dropped to the equipartition level and is generally somewhat weaker than at the beginning of the MBP's evolution. Also, only relatively weak downflows are found on average at this stage of the evolution. Only 16% of the features display upflows at the time that the field weakens, or the MBP disappears. This speaks either for a very fast evolving dynamic process at the end of the lifetime, which could not be temporally resolved, or against strong upflows as the cause of the weakening of the field of these magnetic elements, as has been proposed based on simulation results. It is noteworthy that in about 10% of the cases, we observe in the vicinity of the downflows small-scale strong (exceeding 2 km s-1) intergranular upflows related spatially and temporally to these downflows. The paper is complemented by a detailed discussion of aspects regarding the applied methods, the complementary literature, and in depth analysis of parameters like magnetic field strength and velocity distributions. An important difference to magnetic elements and associated bright structures in active region plage is that most of the quiet Sun bright points display significant downflows over a large fraction of their lifetime (i.e., in more than 46% of time instances/measurements they show downflows exceeding 1 km s-1). Title: The Solar Internetwork. I. Contribution to the Network Magnetic Flux Authors: Gošić, M.; Bellot Rubio, L. R.; Orozco Suárez, D.; Katsukawa, Y.; del Toro Iniesta, J. C. Bibcode: 2014ApJ...797...49G Altcode: 2014arXiv1408.2369G The magnetic network (NE) observed on the solar surface harbors a sizable fraction of the total quiet Sun flux. However, its origin and maintenance are not well known. Here we investigate the contribution of internetwork (IN) magnetic fields to the NE flux. IN fields permeate the interior of supergranular cells and show large emergence rates. We use long-duration sequences of magnetograms acquired by Hinode and an automatic feature tracking algorithm to follow the evolution of NE and IN flux elements. We find that 14% of the quiet Sun (QS) flux is in the form of IN fields with little temporal variations. IN elements interact with NE patches and modify the flux budget of the NE either by adding flux (through merging processes) or by removing it (through cancellation events). Mergings appear to be dominant, so the net flux contribution of the IN is positive. The observed rate of flux transfer to the NE is 1.5 × 1024 Mx day-1 over the entire solar surface. Thus, the IN supplies as much flux as is present in the NE in only 9-13 hr. Taking into account that not all the transferred flux is incorporated into the NE, we find that the IN would be able to replace the entire NE flux in approximately 18-24 hr. This renders the IN the most important contributor to the NE, challenging the view that ephemeral regions are the main source of flux in the QS. About 40% of the total IN flux eventually ends up in the NE. Title: Pair separation of magnetic elements in the quiet Sun Authors: Giannattasio, F.; Berrilli, F.; Biferale, L.; Del Moro, D.; Sbragaglia, M.; Bellot Rubio, L.; Gošić, M.; Orozco Suárez, D. Bibcode: 2014A&A...569A.121G Altcode: 2014arXiv1409.1010G The dynamic properties of the quiet Sun photosphere can be investigated by analyzing the pair dispersion of small-scale magnetic fields (i.e., magnetic elements). By using 25 h-long Hinode magnetograms at high spatial resolution (0.3 arcsec), we tracked 68 490 magnetic element pairs within a supergranular cell near the disk center. The computed pair separation spectrum, calculated on the whole set of particle pairs independently of their initial separation, points out what is known as a super-diffusive regime with spectral index γ = 1.55 ± 0.05, in agreement with the most recent literature, but extended to unprecedented spatial and temporal scales (from granular to supergranular). Furthermore, for the first time, we investigated here the spectrum of the mean square displacement of pairs of magnetic elements, depending on their initial separation r0. We found that there is a typical initial distance above (below) which the pair separation is faster (slower) than the average. A possible physical interpretation of such a typical spatial scale is also provided. Title: Inclinations of small quiet-Sun magnetic features based on a new geometric approach Authors: Jafarzadeh, S.; Solanki, S. K.; Lagg, A.; Bellot Rubio, L. R.; van Noort, M.; Feller, A.; Danilovic, S. Bibcode: 2014A&A...569A.105J Altcode: 2014arXiv1408.2443J Context. High levels of horizontal magnetic flux have been reported in the quiet-Sun internetwork, often based on Stokes profile inversions.
Aims: Here we introduce a new method for deducing the inclination of magnetic elements and use it to test magnetic field inclinations from inversions.
Methods: We determine accurate positions of a set of small, bright magnetic elements in high spatial resolution images sampling different photospheric heights obtained by the Sunrise balloon-borne solar observatory. Together with estimates of the formation heights of the employed spectral bands, these provide us with the inclinations of the magnetic features. We also compute the magnetic inclination angle of the same magnetic features from the inversion of simultaneously recorded Stokes parameters.
Results: Our new, geometric method returns nearly vertical fields (average inclination of around 14° with a relatively narrow distribution having a standard deviation of 6°). In strong contrast to this, the traditionally used inversions give almost horizontal fields (average inclination of 75 ± 8°) for the same small magnetic features, whose linearly polarised Stokes profiles are adversely affected by noise. We show that for such magnetic features inversions overestimate the flux in horizontal magnetic fields by an order of magnitude.
Conclusions: The almost vertical field of bright magnetic features from our geometric method is clearly incompatible with the nearly horizontal magnetic fields obtained from the inversions. This indicates that the amount of magnetic flux in horizontal fields deduced from inversions is overestimated in the presence of weak Stokes signals, in particular if Stokes Q and U are close to or under the noise level. Inversions should be used with great caution when applied to data with no clear Stokes Q and no U signal. By combining the proposed method with inversions we are not just improving the inclination, but also the field strength. This technique allows us to analyse features that are not reliably treated by inversions, thus greatly extending our capability to study the complete magnetic field of the quiet Sun. Title: The History of a Quiet-Sun Magnetic Element Revealed by IMaX/SUNRISE Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot Rubio, Luis R.; Bonet, José A.; Martínez Pillet, Valentín; Solanki, Sami K.; Schmidt, Wolfgang Bibcode: 2014ApJ...789....6R Altcode: 2014arXiv1405.2837R Isolated flux tubes are considered to be fundamental magnetic building blocks of the solar photosphere. Their formation is usually attributed to the concentration of magnetic field to kG strengths by the convective collapse mechanism. However, the small size of the magnetic elements in quiet-Sun areas has prevented this scenario from being studied in fully resolved structures. Here, we report on the formation and subsequent evolution of one such photospheric magnetic flux tube, observed in the quiet Sun with unprecedented spatial resolution (0.''15-0.''18) and high temporal cadence (33 s). The observations were acquired by the Imaging Magnetograph eXperiment on board the SUNRISE balloon-borne solar observatory. The equipartition field strength magnetic element is the result of the merging of several same polarity magnetic flux patches, including a footpoint of a previously emerged loop. The magnetic structure is then further intensified to kG field strengths by convective collapse. The fine structure found within the flux concentration reveals that the scenario is more complex than can be described by a thin flux tube model with bright points and downflow plumes being established near the edges of the kG magnetic feature. We also observe a daisy-like alignment of surrounding granules and a long-lived inflow toward the magnetic feature. After a subsequent weakening process, the field is again intensified to kG strengths. The area of the magnetic feature is seen to change in anti-phase with the field strength, while the brightness of the bright points and the speed of the downflows varies in phase. We also find a relation between the brightness of the bright point and the presence of upflows within it. Title: Diffusion of Magnetic Elements in a Supergranular Cell Authors: Giannattasio, F.; Stangalini, M.; Berrilli, F.; Del Moro, D.; Bellot Rubio, L. Bibcode: 2014ApJ...788..137G Altcode: 2014arXiv1405.0677G Small scale magnetic fields (magnetic elements) are ubiquitous in the solar photosphere. Their interaction can provide energy to the upper atmospheric layers, and contribute to heat the solar corona. In this work, the dynamic properties of magnetic elements in the quiet Sun are investigated. The high number of magnetic elements detected in a supergranular cell allowed us to compute their displacement spectrum lang(Δr)2rangvpropτγ (with γ > 0, and τ the time since the first detection), separating the contribution of the network (NW) and the internetwork (IN) regions. In particular, we found γ = 1.27 ± 0.05 and γ = 1.08 ± 0.11 in NW (at smaller and larger scales, respectively), and γ = 1.44 ± 0.08 in IN. These results are discussed in light of the literature on the topic, as well as the implications for the build-up of the magnetic network. Title: Orphan penumbrae: Submerging horizontal fields Authors: Jurčák, J.; Bellot Rubio, L. R.; Sobotka, M. Bibcode: 2014A&A...564A..91J Altcode: 2014arXiv1402.6558J
Aims: We investigate the properties of orphan penumbrae, which are photospheric filamentary structures observed in active regions near polarity inversion lines that resemble the penumbra of regular sunspots but are not connected to any umbra.
Methods: We use Hinode data from the Solar Optical Telescope to determine the properties of orphan penumbrae. Spectropolarimetric data are employed to obtain the vector magnetic field and line-of-sight velocities in the photosphere. Magnetograms are used to study the overall evolution of these structures, and G-band and Ca ii H filtergrams are to investigate their brightness and apparent horizontal motions.
Results: Orphan penumbrae form between regions of opposite polarity in places with horizontal magnetic fields. Their magnetic configuration is that of Ω-shaped flux ropes. In the two cases studied here, the opposite-polarity regions approach each other with time and the whole structure submerges as the penumbral filaments disappear. Orphan penumbrae are very similar to regular penumbrae, including the existence of strong gas flows. Therefore, they could have a similar origin. The main difference between them is the absence of a "background" magnetic field in orphan penumbrae. This could explain most of the observed differences.
Conclusions: The fast flows we detect in orphan penumbrae may be caused by the siphon flow mechanism. Based on the similarities between orphan and regular penumbrae, we propose that the Evershed flow is also a manifestation of siphon flows.

A movie attached to Fig. 11 is available in electronic form at http://www.aanda.org Title: Emergence of Granular-sized Magnetic Bubbles through the Solar Atmosphere. I. Spectropolarimetric Observations and Simulations Authors: Ortiz, Ada; Bellot Rubio, Luis R.; Hansteen, Viggo H.; de la Cruz Rodríguez, Jaime; Rouppe van der Voort, Luc Bibcode: 2014ApJ...781..126O Altcode: 2013arXiv1312.5735O We study a granular-sized magnetic flux emergence event that occurred in NOAA 11024 in 2009 July. The observations were made with the CRISP spectropolarimeter at the Swedish 1 m Solar Telescope achieving a spatial resolution of 0.''14. Simultaneous full Stokes observations of the two photospheric Fe I lines at 630.2 nm and the chromospheric Ca II 854.2 nm line allow us to describe in detail the emergence process across the solar atmosphere. We report here on three-dimensional (3D) semi-spherical bubble events, where instead of simple magnetic footpoints, we observe complex semi-circular feet straddling a few granules. Several phenomena occur simultaneously, namely, abnormal granulation, separation of opposite-polarity legs, and brightenings at chromospheric heights. However, the most characteristic signature in these events is the observation of a dark bubble in filtergrams taken in the wings of the Ca II 854.2 nm line. There is a clear coincidence between the emergence of horizontal magnetic field patches and the formation of the dark bubble. We can infer how the bubble rises through the solar atmosphere as we see it progressing from the wings to the core of Ca II 854.2 nm. In the photosphere, the magnetic bubble shows mean upward Doppler velocities of 2 km s-1 and expands at a horizontal speed of 4 km s-1. In about 3.5 minutes it travels some 1100 km to reach the mid chromosphere, implying an average ascent speed of 5.2 km s-1. The maximum separation attained by the magnetic legs is 6.''6. From an inversion of the observed Stokes spectra with the SIR code, we find maximum photospheric field strengths of 480 G and inclinations of nearly 90° in the magnetic bubble interior, along with temperature deficits of up to 250 K at log τ = -2 and above. To aid the interpretation of the observations, we carry out 3D numerical simulations of the evolution of a horizontal, untwisted magnetic flux sheet injected in the convection zone, using the Bifrost code. The computational domain spans from the upper convection zone to the lower corona. In the modeled chromosphere, the rising flux sheet produces a large, cool, magnetized bubble. We compare this bubble with the observed ones and find excellent agreement, including similar field strengths and velocity signals in the photosphere and chromosphere, temperature deficits, ascent speeds, expansion velocities, and lifetimes. Title: Time evolution of a single, quiet-Sun magnetic structure Authors: Requerey, Iker S.; Bonet, José Antonio; Solanki, Sami K.; Bellot Rubio, L. R.; Del Toro Iniesta, Jose Carlos Bibcode: 2014cosp...40E2828R Altcode: Isolated flux tubes are considered to be fundamental magnetic building blocks of the solar photosphere. Their formation is usually attributed to the concentration of magnetic field to kG strengths by the convective instability mechanism. However, the small size of the magnetic elements in quiet-Sun areas has prevented this scenario from being studied in fully resolved structures. Here we report on the formation and subsequent evolution of a photospheric magnetic flux tube, observed in the quiet Sun with unprecedented spatial resolution (0. ('') 15 - 0. ('') 18) and high temporal cadence (33 s). The observations were acquired by the Imaging Magnetograph Experiment (IMaX) aboard the textsc{Sunrise} balloon-borne solar observatory. The equipartition field strength magnetic element is reached from the merging of several magnetic flux patches in a mesogranule-sized sink. The magnetic structure is then further intensified to kG field strengths by convective collapse and granular compression. The fine structure found within the flux concentration reveal that the scenario is more complex than a canonical flux tube model. After a subsequent weakening process, the field is further intensified to kG strengths. Seen as a whole, the evolution of the magnetic structure is compatible with oscillations in all basic physical quantities. A discussion on whether this evolution fits to the current theoretical descriptions is also presented. Title: Flux emergence in the solar internetwork and its contribution to the network Authors: Gosic, Milan; Katsukawa, Yukio; Orozco Suarez, David; Bellot Rubio, L. R. Bibcode: 2014cosp...40E1055G Altcode: Network and internetwork magnetic fields are believed to play a crucial role in the energy budget of the solar atmosphere. Therefore, it is essential to understand how they are maintained on the solar surface. Using high resolution Hinode/NFI magnetograms at disk center, we automatically follow quiet Sun magnetic elements from their appearance to disappearance. From up to 40 hours of continuous measurements, we derive the flux emergence rate in the solar internetwork to be around 40 Mx cm(-2) day(-1) . We show that internetwork fields appearing in the interior of individual supergranular cells contribute flux to the surrounding network at a rate of 2×10(19) Mx h(-1) . In only 10-20 hours, internetwork elements can transfer as much flux as resides in network features, establishing them as the most important source of flux for the network and the quiet Sun flux budget. Title: New insights into the evolution of magnetic bright point plasma parameters Authors: Utz, Dominik; Hanslmeier, Arnold; Bellot Rubio, L. R.; Del Toro Iniesta, Jose Carlos; Jurcak, Jan Bibcode: 2014cosp...40E3448U Altcode: The dynamics within the solar atmosphere are governed by the Suńs magnetic fields. In the recent years the resolution limits were steadily driven up by better and better instruments and telescopes (like Hinode, Sunrise, NST, Gregor, ..) leading to higher resolved data. Therefore the interest in ever smaller magnetic field structures within the solar atmosphere rises. Among the smallest yet identified structures are so-called magnetic bright points (MBPs). These features are thought to be made up of single flux tubes and they have been studied exhaustively in the Fraunhofer G-band since the 70´s of the last century. They are important features not only due to their small scale (about 200 km in diameter) and hence used as proxies for the smallest solar magnetic field physics and processes, but also because they are involved in topics like the chromospheric/coronal heating problem or the total solar irradiance variation. In the current contribution we want to study the evolution of important plasma parameters of MBPs, such as temperature, magnetic field strength and line of sight velocity, to get a deeper understanding of the involved physics and occuring processes. Among the used data will be G-band filtergam data from Hinode/SOT and spectro-polarimetric data from the IMaX instrument onboard the Sunrise mission. Title: New insights into the temporal evolution of MBPs Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.; Jurčak, J.; Thonhofer, S.; Bodnárová, M.; Hanslmeier, A.; Lemmerer, B.; Piantschitsch, I.; Guttenbrunner, S. Bibcode: 2014CEAB...38...73U Altcode: Magnetic bright points (MBPs) are among the most fascinating and interesting manifestations of small-scale solar magnetic fields. In the present work the temporal evolution of MBPs is followed in data sets taken by the Hinode satellite. The analysed data and obtained results confirm a recently presented study done with Sunrise/IMaX data, namely that MBPs are features undergoing fast evolution with magnetic fields starting around the equipartition field strength, then showing strong downflows (between 2 to 4 km/s) causing the magnetic field to amplify into the kG range (700 to 1500 G) before dissolving again. Furthermore the initial field inclinations depend on the initial magnetic field strengths and show an evolution with more vertical angles at some point during the evolution. Title: Effects of flux emergence in the outer solar atmosphere. Observational advances Authors: Ortiz Carbonell, Ada; De Pontieu, Bart; Bellot Rubio, L. R.; Hansteen, Viggo; Rouppe van der Voort, Luc; Carlsson, Mats Bibcode: 2014cosp...40E2387O Altcode: We study granular sized magnetic flux emergence events that occur in a flux emergence region in NOAA 11850 on September 25, 2013. During that time, the first co-observing campaign between the Swedish 1 m Solar Telescope and the IRIS spacecraft was carried out. Simultaneous observations of the Halpha 656.28 nm and Ca II 854.2 nm chromospheric lines, and the Fe I 630.25 nm photospheric line, were made with the CRISP/SST spectropolarimeter reaching a spatial resolution of 0."14. At the same time, IRIS was performing a four-step dense raster of the said emerging flux region, taking slit-jaw images at 133 (C II transiti on region), 140 (Si IV, transition region), 279.6 (Mg II k, core, upper chromosphere), and 283.2 nm (Mg II k, wing, photosphere), obtaining thus the highest resolution images ever taken of the upper chromosphere and transition region. The photospheric and chromospheric properties of the emerging magnetic flux bubbles have been described in detail in Ortiz et al. (2014). However, in the current work we are able to follow such lower atmosphere observations of flux emergence up to the transition region with unprecedented spatial and temporal resolution. We describe the properties (size, time delays, lifetime, velocities, temperature) of the observed signatures of flux emergence in the transition region. We believe this may be an important mechanism of transporting energy and magnetic flux to the upper layers of the solar atmosphere, namely the transition region and corona, at least in cases when active regions are formed by flux emerging through the photosphere. * Ortiz et al. (2014) ApJ 781, 126 Title: Parallelization of the SIR code Authors: Thonhofer, S.; Bellot Rubio, L. R.; Utz, D.; Jurčak, J.; Hanslmeier, A.; Piantschitsch, I.; Pauritsch, J.; Lemmerer, B.; Guttenbrunner, S. Bibcode: 2014CEAB...38...31T Altcode: A high-resolution 3-dimensional model of the photospheric magnetic field is essential for the investigation of small-scale solar magnetic phenomena. The SIR code is an advanced Stokes-inversion code that deduces physical quantities, e.g. magnetic field vector, temperature, and LOS velocity, from spectropolarimetric data. We extended this code by the capability of directly using large data sets and inverting the pixels in parallel. Due to this parallelization it is now feasible to apply the code directly on extensive data sets. Besides, we included the possibility to use different initial model atmospheres for the inversion, which enhances the quality of the results. Title: Diffusion of Solar Magnetic Elements up to Supergranular Spatial and Temporal Scales Authors: Giannattasio, F.; Del Moro, D.; Berrilli, F.; Bellot Rubio, L.; Gošić, M.; Orozco Suárez, D. Bibcode: 2013ApJ...770L..36G Altcode: 2013arXiv1305.4006G The study of spatial and temporal scales on which small magnetic structures (magnetic elements) are organized in the quiet Sun may be approached by determining how they are transported on the solar photosphere by convective motions. The process involved is diffusion. Taking advantage of Hinode high spatial resolution magnetograms of a quiet-Sun region at the disk center, we tracked 20,145 magnetic elements. The large field of view (~50 Mm) and the long duration of the observations (over 25 hr without interruption at a cadence of 90 s) allowed us to investigate the turbulent flows at unprecedented large spatial and temporal scales. In the field of view an entire supergranule is clearly recognizable. The magnetic element displacement spectrum shows a double-regime behavior: superdiffusive (γ = 1.34 ± 0.02) up to granular spatial scales (~1500 km) and slightly superdiffusive (γ = 1.20 ± 0.05) up to supergranular scales. Title: Temporal variations in solar magnetic bright points intensity and plasma parameters Authors: Jurčák, J.; Utz, D.; Bellot Rubio, L. R. Bibcode: 2013JPhCS.440a2032J Altcode: Magnetic bright points are one of the finest magnetic structures observed in the solar atmosphere. They possibly represent single flux tubes in quiet Sun regions. Their formation is described by the convective collapse model, while the decay phase of these structures is not well characterized yet. We attempt to follow the evolution of a few selected examples of MBPs and to study their changes in brightness and also the variations of plasma parameters during their lifetime. We use data from the Hinode satellite and the Sunrise mission. The G-band observations taken with a cadence of 30 seconds by the Hinode Solar Optical Telescope (SOT) show very fast changes of the maximum intensity of these structures. The complementary spectropolarimetric data, which are used to estimate the plasma parameters, were taken with a cadence of approximately two minutes. The variations of plasma parameters cannot be matched one to one to the changes in intensity due to the different temporal resolution. However, the slow changes of intensity with large amplitude are matched with variations of magnetic field strength and line-of-sight (LOS) velocity. The Sunrise/IMaX data have a temporal resolution of 32 seconds and show fast variations in the line wing intensity. These variations are associated with changes in the magnetic field strength and LOS velocity. Title: Is Magnetic Reconnection the Cause of Supersonic Upflows in Granular Cells? Authors: Borrero, J. M.; Martínez Pillet, V.; Schmidt, W.; Quintero Noda, C.; Bonet, J. A.; del Toro Iniesta, J. C.; Bellot Rubio, L. R. Bibcode: 2013ApJ...768...69B Altcode: 2013arXiv1303.2557B In a previous work, we reported on the discovery of supersonic magnetic upflows on granular cells in data from the SUNRISE/IMaX instrument. In the present work, we investigate the physical origin of these events employing data from the same instrument but with higher spectral sampling. By means of the inversion of Stokes profiles we are able to recover the physical parameters (temperature, magnetic field, line-of-sight velocity, etc.) present in the solar photosphere at the time of these events. The inversion is performed in a Monte-Carlo-like fashion, that is, repeating it many times with different initializations and retaining only the best result. We find that many of the events are characterized by a reversal in the polarity of the magnetic field along the vertical direction in the photosphere, accompanied by an enhancement in the temperature and by supersonic line-of-sight velocities. In about half of the studied events, large blueshifted and redshifted line-of-sight velocities coexist above/below each other. These features can be explained in terms of magnetic reconnection, where the energy stored in the magnetic field is released in the form of kinetic and thermal energy when magnetic field lines of opposite polarities coalesce. However, the agreement with magnetic reconnection is not perfect and, therefore, other possible physical mechanisms might also play a role. Title: A Magnetic Bright Point Case Study Authors: Utz, D.; Jurčák, J.; Bellot-Rubio, L.; del Toro Iniesta, J. C.; Thonhofer, S.; Hanslmeier, A.; Veronig, A.; Muller, R.; Lemmerer, B. Bibcode: 2013CEAB...37..459U Altcode: Due to its magnetic fields our host star - the Sun - becomes the interesting object for research as we know it. The magnetic fields themselves cover different spatial, lifetime and strength scales and reach down from enormous flux concentrations like active sunspot groups to single isolated magnetic flux tubes and even weaker, predominantly inclined intranetwork structures. Flux tubes can be seen in filtergram observations as magnetic bright points (MBPs). They are of interest for research not only due to their sheer existence but due to their important role in atmospheric heating (wave heating as well as reconnection processes), to their role in the understanding of creation and annihilation of magnetic fields as well as to their influence on the total solar irradiance variation. In this study we present a close look onto an evolutionary track of an MBP from its formation to its disintegration. Physical quantities of MBPs like their magnetic field strength and inclination, their line-of-sight velocity, and their temperature at different heights are inferred from the inversion of spectropolarimetric data. Original data are taken from the Sunrise/IMaX instrument and constitute a time series of some 60 min. The presented case resembles the convective collapse model and is in agreement with previous studies. Title: Inversions of L12-2 IMaX data of an emerging flux mantle Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo, B.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.; Solanki, S. K.; Sunrise/IMaX Team Bibcode: 2013MmSAI..84..355G Altcode: We present the analysis of a flux emergence event observed with the IMaX magnetograph flown aboard the SUNRISE balloon. IMaX took a 15' sequence with cadence of 31 s along the Fe I line at 525.0 nm, acquiring only Stokes I and V at 12 line positions (L12-2 mode). This sequence shows the emergence of a flux mantle at mesogranular scale, cospatial with a large exploding granule. An undesired cross-talk between Stokes U and V was found in such L12-2 data. We show that the use of a modified version of the SIR inversion code is able to remove such effect in inferring the physical quantities of interest. Title: Requirements for the Analysis of Quiet-Sun Internetwork Magnetic Elements with EST and ATST Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Katsukawa, Y. Bibcode: 2012ASPC..463...57O Altcode: 2012arXiv1203.2185O The quiet-Sun internetwork is permeated by weak and highly inclined magnetic fields whose physical properties, dynamics, and magnetic interactions are not fully understood. High spatial resolution magnetograms show them as discrete magnetic elements that appear/emerge and disappear/cancel continuously over the quiet Sun surface. The 4-m European Solar Telescope (EST) and the Advanced Technology Solar Telescope (ATST) will obtain two-dimensional, high cadence, high precision polarimetric measurements at the diffraction limit (30 km). Here, we compile the basic requirements for the observation of internetwork fields with EST and ATST (field of view, cadence, instrument configuration, etc.). More specifically, we concentrate on the field-of-view requirements. To set them we analyze the proper motion of internetwork magnetic elements across the solar surface. We use 13 hours of magnetograms taken with the Hinode satellite to identify and track thousands of internetwork magnetic element in an isolated supergranular cell. We calculate the velocity components of each element and the mean distance they travel. The results show that, on average, magnetic elements in the interior of supergranular cells move toward the network. The radial velocity is observed to depend on the distance to the center of the supergranule. Internetwork magnetic elements travel 4″ on average. These results suggest that ATST and EST should cover, at least, one supergranular cell to obtain a complete picture of the quiet Sun internetwork. Title: Comparing Simultaneous Measurements of two High-Resolution Imaging Spectropolarimeters: The `Göttingen' FPI@VTT and CRISP@SST Authors: Bello González, N.; Bellot Rubio, L. R.; Ortiz, A.; Rezaei, R.; Rouppe van der Voort, L.; Schlichenmaier, R. Bibcode: 2012ASPC..463..251B Altcode: 2012arXiv1204.1023B In July 2009, the leading spot of the active region NOAA11024 was observed simultaneously and independently with the ‘Göttingen’ FPI at VTT and CRISP at SST, i.e., at two different sites, telescopes, instruments and using different spectral lines. The data processing and data analysis have been carried out independently with different techniques. Maps of physical parameters retrieved from 2D spectro-polarimetric data observed with ‘Göttingen’ FPI and CRISP show an impressive agreement. In addition, the ‘Göttingen’ FPI maps also exhibit a notable resemblance with simultaneous TIP (spectrographic) observations. The consistency in the results demonstrates the excellent capabilities of these observing facilities. Besides, it confirms the solar origin of the detected signals and the reliability of FPI-based spectro-polarimeters. Title: Turbulent diffusion on the solar photosphere through 24-hour continuous observations of magnetic elements Authors: Giannattasio, F.; Berrilli, F.; Del Moro, D.; Bellot Rubio, L.; Orozco Suarez, D.; Gosic, M. Bibcode: 2012AGUFMSH13A2242G Altcode: Solar atmosphere is a unique laboratory for the study of turbulent flows under extreme conditions (e.g. very high Reynolds numbers). The turbulent nature of the flow may be approached by determining how magnetic flux elements are transported on the solar surface, and measuring the spatio-temporal scales on which these small magnetic structures are organized. The process involved is diffusion. Several works explored this topic, both by simulations and observations, and the results are often contradictory, ranging from fully-developed turbulent scenarios to normal-diffusive motions. We analyze 24-hour continuous Hinode SOT observations of a supergranular region (for the first time these long scales are explored), studying the evolution of the mutual distance between magnetic element pairs and its scaling laws, in order to investigate the diffusion process. We find a super-diffusive behavior, with a gamma index depending on the spatial scale selected. Title: The Connection between Internetwork Magnetic Elements and Supergranular Flows Authors: Orozco Suárez, D.; Katsukawa, Y.; Bellot Rubio, L. R. Bibcode: 2012ApJ...758L..38O Altcode: The advection of internetwork magnetic elements by supergranular convective flows is investigated using high spatial resolution, high cadence, and high signal-to-noise ratio Na I D1 magnetograms obtained with the Hinode satellite. The observations show that magnetic elements appear everywhere across the quiet Sun surface. We calculate the proper motion of these magnetic elements with the aid of a feature tracking algorithm. The results indicate that magnetic elements appearing in the interior of supergranules tend to drift toward the supergranular boundaries with a non-constant velocity. The azimuthally averaged radial velocities of the magnetic elements and of the supergranular flow, calculated from a local correlation tracking technique applied to Dopplergrams, are very similar. This suggests that, in the long term, surface magnetic elements are advected by supergranular flows, although on short timescales their very chaotic motions are driven mostly by granular flows and other processes. Title: Resolving the Internal Magnetic Structure of the Solar Network Authors: Martínez González, M. J.; Bellot Rubio, L. R.; Solanki, S. K.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; Barthol, P.; Schmidt, W. Bibcode: 2012ApJ...758L..40M Altcode: 2012arXiv1209.2584M We analyze the spectral asymmetry of Stokes V (circularly polarized) profiles of an individual network patch in the quiet Sun observed by Sunrise/IMaX. At a spatial resolution of 0farcs15-0farcs18, the network elements contain substructure which is revealed by the spatial distribution of Stokes V asymmetries. The area asymmetry between the red and blue lobes of Stokes V increases from nearly zero at the core of the structure to values close to unity at its edges (single-lobed profiles). Such a distribution of the area asymmetry is consistent with magnetic fields expanding with height, i.e., an expanding magnetic canopy (which is required to fulfill pressure balance and flux conservation in the solar atmosphere). Inversion of the Stokes I and V profiles of the patch confirms this picture, revealing a decreasing field strength and increasing height of the canopy base from the core to the periphery of the network patch. However, the non-roundish shape of the structure and the presence of negative area and amplitude asymmetries reveal that the scenario is more complex than a canonical flux tube expanding with height surrounded by downflows. Title: Temporal Evolution of Velocity and Magnetic Field in and around Umbral Dots Authors: Watanabe, Hiroko; Bellot Rubio, Luis R.; de la Cruz Rodríguez, Jaime; Rouppe van der Voort, Luc Bibcode: 2012ApJ...757...49W Altcode: 2012arXiv1207.6006W We study the temporal evolution of umbral dots (UDs) using measurements from the CRISP imaging spectropolarimeter at the Swedish 1 m Solar Telescope. Scans of the magnetically sensitive 630 nm iron lines were performed under stable atmospheric conditions for 71 minutes with a cadence of 63 s. These observations allow us to investigate the magnetic field and velocity in and around UDs at a resolution approaching 0farcs13. From the analysis of 339 UDs, we draw the following conclusions: (1) UDs show clear hints of upflows, as predicted by magnetohydrodynamic simulations. By contrast, we could not find systematic downflow signals. Only in very deep layers, we detect localized downflows around UDs, but they do not persist in time. (2) We confirm that UDs exhibit weaker and more inclined fields than their surroundings, as reported previously. However, UDs that have strong fields above 2000 G or are in the decay phase show enhanced and more vertical fields. (3) There are enhanced fields at the migration front of UDs detached from penumbral grains, as if their motion were impeded by the ambient field. (4) Long-lived UDs travel longer distances with slower proper motions. Our results appear to confirm some aspects of recent numerical simulations of magnetoconvection in the umbra (e.g., the existence of upflows in UDs), but not others (e.g., the systematic weakening of the magnetic field at the position of UDs). Title: Pervasive Linear Polarization Signals in the Quiet Sun Authors: Bellot Rubio, L. R.; Orozco Suárez, D. Bibcode: 2012ApJ...757...19B Altcode: 2012arXiv1207.0692B This paper investigates the distribution of linear polarization signals in the quiet-Sun internetwork using ultra-deep spectropolarimetric data. We reduce the noise of the observations as much as is feasible by adding single-slit measurements of the Zeeman-sensitive Fe I 630 nm lines taken by the Hinode spectropolarimeter. The integrated Stokes spectra are employed to determine the fraction of the field of view covered by linear polarization signals. We find that up to 69% of the quiet solar surface at disk center shows Stokes Q or U profiles with amplitudes larger than 0.032% (4.5 times the noise level of 7 × 10-5 reached by the longer integrations). The mere presence of linear polarization in most of the quiet Sun implies that the weak internetwork fields must be highly inclined, but we quantify this by inverting those pixels with Stokes Q or U signals well above the noise. This allows for a precise determination of the field inclination, field strength, and field azimuth because the information carried by all four Stokes spectra is used simultaneously. The inversion is performed for 53% of the observed field of view at a noise level of 1.3 × 10-4 I c. The derived magnetic distributions are thus representative of more than half of the quiet-Sun internetwork. Our results confirm the conclusions drawn from previous analyses using mainly Stokes I and V: internetwork fields are very inclined, but except in azimuth they do not seem to be isotropically distributed. Title: Analysis of a Fragmenting Sunspot Using Hinode Observations Authors: Louis, Rohan E.; Ravindra, B.; Mathew, Shibu K.; Bellot Rubio, Luis R.; Raja Bayanna, A.; Venkatakrishnan, P. Bibcode: 2012ApJ...755...16L Altcode: 2012arXiv1205.6669L We employ high-resolution filtergrams and polarimetric measurements from Hinode to follow the evolution of a sunspot for eight days starting on 2007 June 28. The imaging data were corrected for intensity gradients, projection effects, and instrumental stray light prior to the analysis. The observations show the formation of a light bridge at one corner of the sunspot by a slow intrusion of neighboring penumbral filaments. This divided the umbra into two individual umbral cores. During the light bridge formation, there was a steep increase in its intensity from 0.28 to 0.7 I QS in nearly 4 hr, followed by a gradual increase to quiet-Sun (QS) values in 13 hr. This increase in intensity was accompanied by a large reduction in the field strength from 1800 G to 300 G. The smaller umbral core gradually broke away from the parent sunspot nearly two days after the formation of the light bridge, rendering the parent spot without a penumbra at the location of fragmentation. The penumbra in the fragment disappeared first within 34 hr, followed by the fragment whose area decayed exponentially with a time constant of 22 hr. In comparison, the parent sunspot area followed a linear decay rate of 0.94 Mm2 hr-1. The depleted penumbra in the parent sunspot regenerated when the inclination of the magnetic field at the penumbra-QS boundary became within 40° from being completely horizontal and this occurred near the end of the fragment's lifetime. After the disappearance of the fragment, another light bridge formed in the parent which had similar properties as the fragmenting one, but did not divide the sunspot. The significant weakening in field strength in the light bridge along with the presence of granulation is suggestive of strong convection in the sunspot, which might have triggered the expulsion and fragmentation of the smaller spot. Although the presence of QS photospheric conditions in sunspot umbrae could be a necessary condition for fragmentation, it is not a sufficient one. Title: Bipolar Magnetic Structures in Sunspot Penumbrae Authors: Sainz Dalda, A.; Bellot Rubio, L. R. Bibcode: 2012ASPC..454..221S Altcode: We present a study of bipolar, sea-serpent-like structures in the penumbra of sunspots. Our analysis is based on longitudinal magnetograms and full Stokes spectra of AR 10923 taken with the NFI and SP instruments of Hinode. The circular polarization maps reveal the presence of many elongated structures in the mid penumbra and beyond. They consist of two opposite-polarity patches that move together as a single entity toward the outer penumbral boundary, where they become moving magnetic features. Their Stokes profiles suggest a complex magnetic topology. The existence of opposite polarities in the penumbra is well known from previous analyses, but this is the first time that their bipolar nature is unveiled. Our observations also demonstrate that they are intimately connected with the Evershed flow. These structures provide new constraints to theoretical and numerical models of sunspots. Title: Supersonic flows in the solar photosphere Authors: Bellot Rubio, Luis Bibcode: 2012cosp...39..133B Altcode: 2012cosp.meet..133B Except for sunspot penumbrae, very few instances of supersonic mass flows in the photosphere were known a few years ago. The situation has changed dramatically thanks to the extremely high spatial resolution provided by Hinode, SUNRISE, and the Swedish 1-m Solar Telescope. Using spectropolarimetric measurements from these instruments, supersonic flows have been discovered both in the quiet Sun and in active regions, in places where they were completely unexpected. Most of them are directed downward, but there are also cases of upward and horizontal motions. Quiescent, relatively stable structures that harbor supersonic flows include granular cells, small-scale flux tubes undergoing convective collapse, pores, light bridges, and sunspot penumbrae (at all radial distances). An overview of these flows will be given, emphasizing their properties and effects on higher atmospheric layers. Title: Evolution of internetwork magnetic fields inside supergranular cells Authors: Gosic, Milan; Katsukawa, Yukio; Bellot Rubio, Luis; Orozco Suarez, David Bibcode: 2012cosp...39..657G Altcode: 2012cosp.meet..657G To understand the formation of small-scale magnetic fields in the quiet Sun and their contribution to the solar activity, it is essential to investigate the properties of internetwork magnetic fields. Using Hinode/NFI magnetograms of very high sensitivity (7 Mx/cm^{2}), spatial resolution (0.16 arcsec/pixel), and cadence (90 s), we follow the evolution of magnetic fields inside of a supergranular cell located at disk center. In 5 hours of continuous measurements covering an area of 20.8 × 23.2 arcsec^{2}, we manually track 2415 magnetic elements from appearance to disappearance and derive their physical properties. The average values of the magnetic flux, effective diameter, lifetime, and horizontal velocity are 3 × 10^{17} Mx, 0.5 Mm, 17 min, and 2 km/s, respectively. We also investigate how the physical parameters of the individual elements vary as a function of time, flux, and spatial position. Using this unique data set, we determine with unprecedented accuracy the flux emergence and disappearance rate in the solar internetwork. Title: Properties of Umbral Dots from Stray Light Corrected Hinode Filtergrams Authors: Louis, Rohan E.; Mathew, Shibu K.; Bellot Rubio, Luis R.; Ichimoto, Kiyoshi; Ravindra, B.; Raja Bayanna, A. Bibcode: 2012ApJ...752..109L Altcode: 2012arXiv1204.4088L High-resolution blue continuum filtergrams from Hinode are employed to study the umbral fine structure of a regular unipolar sunspot. The removal of scattered light from the images increases the rms contrast by a factor of 1.45 on average. Improvement in image contrast renders identification of short filamentary structures resembling penumbrae that are well separated from the umbra-penumbra boundary and comprise bright filaments/grains flanking dark filaments. Such fine structures were recently detected from ground-based telescopes and have now been observed with Hinode. A multi-level tracking algorithm was used to identify umbral dots (UDs) in both the uncorrected and corrected images and to track them in time. The distribution of the values describing the photometric and geometric properties of UDs is more easily affected by the presence of stray light while it is less severe in the case of kinematic properties. Statistically, UDs exhibit a peak intensity, effective diameter, lifetime, horizontal speed, and a trajectory length of 0.29I QS, 272 km, 8.4 minutes, 0.45 km s-1, and 221 km, respectively. The 2 hr 20 minute time sequence depicts several locations where UDs tend to appear and disappear repeatedly with various time intervals. The correction for scattered light in the Hinode filtergrams facilitates photometry of umbral fine structure, which can be related to results obtained from larger telescopes and numerical simulations. Title: 4th Hinode Science Meeting: Unsolved Problems and Recent Insights Authors: Bellot Rubio, L.; Reale, F.; Carlsson, M. Bibcode: 2012ASPC..455.....B Altcode: 2012ASPC..455.....R No abstract at ADS Title: Observations of Supersonic Downflows near the Umbra-Penumbra Boundary of Sunspots as Revealed by Hinode Authors: Louis, R. E.; Bellot Rubio, L. R.; Mathew, S. K.; Venkatakrishnan, P. Bibcode: 2012ASPC..455...75L Altcode: 2011arXiv1101.0751L High resolution spectropolarimetric observations by Hinode have revealed the existence of supersonic downflows at the umbra-penumbra boundary of 3 sunspots (Louis et al. 2011). These downflows are observed to be co-spatial with bright penumbral filaments and occupy an area greater than 1.6 arcsec2. They are located at the center-side penumbra and have the same polarity as the sunspot which suggests that they are not associated with the Evershed flow. In this paper we describe the supersonic velocities observed in NOAA AR 10923 and discuss the photospheric as well as chromospheric brightenings that lie close to the downflowing areas. Our observations suggest that this phenomenon is driven by dynamic and energetic physical processes in the inner penumbra which affect the chromosphere, providing new constraints to numerical models of sunspots. Title: Analysis of Quiet-Sun Internetwork Magnetic Fields Based on Linear Polarization Signals Authors: Orozco Suárez, D.; Bellot Rubio, L. R. Bibcode: 2012ApJ...751....2O Altcode: 2012arXiv1203.1440O We present results from the analysis of Fe I 630 nm measurements of the quiet Sun taken with the spectropolarimeter of the Hinode satellite. Two data sets with noise levels of 1.2 × 10-3 and 3 × 10-4 are employed. We determine the distribution of field strengths and inclinations by inverting the two observations with a Milne-Eddington model atmosphere. The inversions show a predominance of weak, highly inclined fields. By means of several tests we conclude that these properties cannot be attributed to photon noise effects. To obtain the most accurate results, we focus on the 27.4% of the pixels in the second data set that have linear polarization amplitudes larger than 4.5 times the noise level. The vector magnetic field derived for these pixels is very precise because both circular and linear polarization signals are used simultaneously. The inferred field strength, inclination, and filling factor distributions agree with previous results, supporting the idea that internetwork (IN) fields are weak and very inclined, at least in about one quarter of the area occupied by the IN. These properties differ from those of network fields. The average magnetic flux density and the mean field strength derived from the 27.4% of the field of view with clear linear polarization signals are 16.3 Mx cm-2 and 220 G, respectively. The ratio between the average horizontal and vertical components of the field is approximately 3.1. The IN fields do not follow an isotropic distribution of orientations. Title: Granular-Scale Elementary Flux Emergence Episodes in a Solar Active Region Authors: Vargas Domínguez, S.; van Driel-Gesztelyi, L.; Bellot Rubio, L. R. Bibcode: 2012SoPh..278...99V Altcode: 2012SoPh..tmp..259F; 2012arXiv1203.6428V We analyse data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the observed solar active region and discover the appearance of very distinctive small-scale and short-lived dark features in Ca II H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading. Three complete series of these events are detected with remarkably similar properties, i.e. lifetime of ≈ 12 min, maximum length and area of 2 - 4 Mm and 1.6 - 4 Mm2, respectively, and all with associated brightenings. In time series of magnetograms a diverging bipolar configuration is observed accompanying the appearance of the dark features and the brightenings. The observed phenomena are explained as evidencing elementary flux emergence in the solar atmosphere, i.e. small-scale arch filament systems rising up from the photosphere to the lower chromosphere with a length scale of a few solar granules. Brightenings are explained as being the signatures of chromospheric heating triggered by reconnection of the rising loops (once they have reached chromospheric heights) with pre-existing magnetic fields, as well as being due to reconnection/cancellation events in U-loop segments of emerging serpentine fields. The characteristic length scale, area and lifetime of these elementary flux emergence events agree well with those of the serpentine field observed in emerging active regions. We study the temporal evolution and dynamics of the events and compare them with the emergence of magnetic loops detected in quiet Sun regions and serpentine flux emergence signatures in active regions. The physical processes of the emergence of granular-scale magnetic loops seem to be the same in the quiet Sun and active regions. The difference is the reduced chromospheric emission in the quiet Sun attributed to the fact that loops are emerging in a region of lower ambient magnetic field density, making interactions and reconnection less likely to occur. Incorporating the novel features of granular-scale flux emergence presented in this study, we advance the scenario for serpentine flux emergence. Title: Observation, inversion and numerical simulation of single-lobed Stokes V profiles in the quiet sun. Authors: Sainz Dalda, A.; Martínez-Sykora, J.; Bellot Rubio, L.; Title, A. Bibcode: 2012decs.confE..89S Altcode: We have studied characteristics and statistics of strong asymmetric profiles in Stokes V, i.e., single-lobed profiles, in quiet sun using Hinode/SOT. These profiles require the existence of a velocity gradient along the line-of-sight, possibly associated with gradients of magnetic field strength, inclination and/or azimuth. For a better understanding, observations, inversions and numerical simulations are compared. We focus our analysis of the observations on the statistical properties of the single-lobed Stokes V profiles and the results provided by the inversions using SIRJUMP, which is an LTE inversion code that can reproduce sharp discontinuities or jump in the magnetic field and line-of-sight velocity of the atmosphere model. In the quiet sun, magnetic field is continuously appearing and disappearing at small scales due to the convective motions and the input of new flux from deeper layers. From radiative MHD 3D simulations, using Bifrost code, we note that most of these small scale processes have stratifications with gradients of magnetic field strength, inclination and velocities. As result, those stratifications showing jumps in the magnetic field configuration are associated with the existence of single-lobe Stokes V profiles in the solar photosphere, as we previously assumed for the inversions. We show that most of these profiles come from emerging and disappearance magnetic flux in small scales in the simulations. Finally, we emphasize importance of the comparison between the synthetic profiles from the simulations with the observed ones and the atmospheres that produce them. This comparison will ultimately improve the realism of the simulations and quantify the emerging and disappearance flux in the quiet sun. Title: Study of Single-lobed Circular Polarization Profiles in the Quiet Sun Authors: Sainz Dalda, A.; Martínez-Sykora, J.; Bellot Rubio, L.; Title, A. Bibcode: 2012ApJ...748...38S Altcode: 2012arXiv1202.0593S The existence of asymmetries in the circular polarization (Stokes V) profiles emerging from the solar photosphere has been known since the 1970s. These profiles require the presence of a velocity gradient along the line of sight (LOS), possibly associated with gradients of magnetic field strength, inclination, and/or azimuth. We have focused our study on the Stokes V profiles showing extreme asymmetry in the form of only one lobe. Using Hinode spectropolarimetric measurements, we have performed a statistical study of the properties of these profiles in the quiet Sun. We show their spatial distribution, their main physical properties, how they are related with several physical observables, and their behavior with respect to their position on the solar disk. The single-lobed Stokes V profiles occupy roughly 2% of the solar surface. For the first time, we have observed their temporal evolution and have retrieved the physical conditions of the atmospheres from which they emerged using an inversion code implementing discontinuities of the atmospheric parameters along the LOS. In addition, we use synthetic Stokes profiles from three-dimensional magnetoconvection simulations to complement the results of the inversion. The main features of the synthetic single-lobed profiles are in general agreement with the observed ones, lending support to the magnetic and dynamic topologies inferred from the inversion. The combination of all these different analyses suggests that most of the single-lobed Stokes V profiles are signals coming from the magnetic flux emergence and/or submergence processes taking place in small patches in the photosphere of the quiet Sun. Title: The Frontier between Small-scale Bipoles and Ephemeral Regions in the Solar Photosphere: Emergence and Decay of an Intermediate-scale Bipole Observed with SUNRISE/IMaX Authors: Guglielmino, S. L.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.; Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M. Bibcode: 2012ApJ...745..160G Altcode: 2011arXiv1110.1405G We report on the photospheric evolution of an intermediate-scale (≈4 Mm footpoint separation) magnetic bipole, from emergence to decay, observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s) resolution. The observations were acquired by the Imaging Magnetograph Experiment imaging magnetograph during the first science flight of the SUNRISE balloon-borne solar observatory. The bipole flux content is 6 × 1017 Mx, representing a structure bridging the gap between granular scale bipoles and the smaller ephemeral regions. Footpoints separate at a speed of 3.5 km s-1 and reach a maximum distance of 4.5 Mm before the field dissolves. The evolution of the bipole is revealed to be very dynamic: we found a proper motion of the bipole axis and detected a change of the azimuth angle of 90° in 300 s, which may indicate the presence of some writhe in the emerging structure. The overall morphology and behavior are in agreement with previous analyses of bipolar structures emerging at the granular scale, but we also found several similarities with emerging flux structures at larger scales. The flux growth rate is 2.6 × 1015 Mx s-1, while the mean decay rate is one order of magnitude smaller. We describe in some detail the decay phase of the bipole footpoints that includes break up into smaller structures, and interaction with preexisting fields leading to cancellation, but it appears to be dominated by an as-yet unidentified diffusive process that removes most of the flux with an exponential flux decay curve. The diffusion constant (8 × 102 km2 s-1) associated with this decay is similar to the values used to describe the large-scale diffusion in flux transport models. Title: Magnetic field emergence in mesogranular-sized exploding granules observed with sunrise/IMaX data Authors: Palacios, J.; Blanco Rodríguez, J.; Vargas Domínguez, S.; Domingo, V.; Martínez Pillet, V.; Bonet, J. A.; Bellot Rubio, L. R.; Del Toro Iniesta, J. C.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Berkefeld, T.; Schmidt, W.; Knölker, M. Bibcode: 2012A&A...537A..21P Altcode: 2011arXiv1110.4555P We report on magnetic field emergences covering significant areas of exploding granules. The balloon-borne mission Sunrise provided high spatial and temporal resolution images of the solar photosphere. Continuum images, longitudinal and transverse magnetic field maps and Dopplergrams obtained by IMaX onboard Sunrise are analyzed by local correlation traking (LCT), divergence calculation and time slices, Stokes inversions and numerical simulations are also employed. We characterize two mesogranular-scale exploding granules where ~1018 Mx of magnetic flux emerges. The emergence of weak unipolar longitudinal fields (~100 G) start with a single visible magnetic polarity, occupying their respective granules' top and following the granular splitting. After a while, mixed polarities start appearing, concentrated in downflow lanes. The events last around 20 min. LCT analyses confirm mesogranular scale expansion, displaying a similar pattern for all the physical properties, and divergence centers match between all of them. We found a similar behaviour with the emergence events in a numerical MHD simulation. Granule expansion velocities are around 1 kms-1 while magnetic patches expand at 0.65 kms-1. One of the analyzed events evidences the emergence of a loop-like structure. Advection of the emerging magnetic flux features is dominated by convective motion resulting from the exploding granule due to the magnetic field frozen in the granular plasma. Intensification of the magnetic field occurs in the intergranular lanes, probably because of being directed by the downflowing plasma.

Movies associated to Figs. 2-4 are available in electronic form at http://www.aanda.org Title: Spectropolarimetric Study of Sea-serpent Penumbral Filaments and a Naked Sunspot Authors: Sainz Dalda, Alberto; Tarbell, T.; Title, A.; Vargas Dominguez, S.; Bellot Rubio, L. R. Bibcode: 2011SPD....42.0303S Altcode: 2011BAAS..43S.0303S We present a spectropolarimetric study of the sea-serpent penumbral filaments in AR NOAA 10944 and of a naked sunspot (i.e. a sunspot-like feature without penumbra) in AR NOAA 10977. Both active regions were observed by Hinode-SOT/SP in the photospheric lines Fe I 6301 & 6302 [[Unable to Display Character: &#506]]. The high spatial and temporal resolution combined with the high polarimetric sensitivity of these observations enables us to get a better understanding of the dynamics of the penumbra and the moving magnetic feature (herafter MMF) activity in and around both traditional and naked sunspots. Our results show how the temporal evolution of the sea-serpent filaments fits very well with the thin-tube flux model for the penumbra presented by Schlichenmaier (2003). In addition, the spectropolarmetric analysis of the naked sunspot addresses the issue posed by Zuccarello et al. (2009) about the existence of bipolar MMFs around naked sunspots even when they cannot be explained as an extension of the penumbral filaments. Title: Mesogranulation and the Solar Surface Magnetic Field Distribution Authors: Yelles Chaouche, L.; Moreno-Insertis, F.; Martínez Pillet, V.; Wiegelmann, T.; Bonet, J. A.; Knölker, M.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Barthol, P.; Gandorfer, A.; Schmidt, W.; Solanki, S. K. Bibcode: 2011ApJ...727L..30Y Altcode: 2010arXiv1012.4481Y The relation of the solar surface magnetic field with mesogranular cells is studied using high spatial (≈100 km) and temporal (≈30 s) resolution data obtained with the IMaX instrument on board SUNRISE. First, mesogranular cells are identified using Lagrange tracers (corks) based on horizontal velocity fields obtained through local correlation tracking. After ≈20 minutes of integration, the tracers delineate a sharp mesogranular network with lanes of width below about 280 km. The preferential location of magnetic elements in mesogranular cells is tested quantitatively. Roughly 85% of pixels with magnetic field higher than 100 G are located in the near neighborhood of mesogranular lanes. Magnetic flux is therefore concentrated in mesogranular lanes rather than intergranular ones. Second, magnetic field extrapolations are performed to obtain field lines anchored in the observed flux elements. This analysis, therefore, is independent of the horizontal flows determined in the first part. A probability density function (PDF) is calculated for the distribution of distances between the footpoints of individual magnetic field lines. The PDF has an exponential shape at scales between 1 and 10 Mm, with a constant characteristic decay distance, indicating the absence of preferred convection scales in the mesogranular range. Our results support the view that mesogranulation is not an intrinsic convective scale (in the sense that it is not a primary energy-injection scale of solar convection), but also give quantitative confirmation that, nevertheless, the magnetic elements are preferentially found along mesogranular lanes. Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise Balloon-Borne Solar Observatory Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.; Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández, L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.; Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer, T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.; Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.; Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.; Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez, P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.; Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S. Bibcode: 2011SoPh..268...57M Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter built by four institutions in Spain that flew on board the Sunrise balloon-borne solar observatory in June 2009 for almost six days over the Arctic Circle. As a polarimeter, IMaX uses fast polarization modulation (based on the use of two liquid crystal retarders), real-time image accumulation, and dual-beam polarimetry to reach polarization sensitivities of 0.1%. As a spectrograph, the instrument uses a LiNbO3 etalon in double pass and a narrow band pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four Stokes parameters at various points inside the spectral line. This allows vector magnetograms, Dopplergrams, and intensity frames to be produced that, after reconstruction, reach spatial resolutions in the 0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time cadences vary between 10 and 33 s, although the shortest one only includes longitudinal polarimetry. The spectral line is sampled in various ways depending on the applied observing mode, from just two points inside the line to 11 of them. All observing modes include one extra wavelength point in the nearby continuum. Gauss equivalent sensitivities are 4 G for longitudinal fields and 80 G for transverse fields per wavelength sample. The line-of-sight velocities are estimated with statistical errors of the order of 5 - 40 m s−1. The design, calibration, and integration phases of the instrument, together with the implemented data reduction scheme, are described in some detail. Title: Supersonic Downflows at the Umbra-Penumbra Boundary of Sunspots Authors: Louis, Rohan E.; Bellot Rubio, Luis R.; Mathew, Shibu K.; Venkatakrishnan, P. Bibcode: 2011ApJ...727...49L Altcode: 2010arXiv1010.0519L High-resolution spectropolarimetric observations of three sunspots taken with Hinode demonstrate the existence of supersonic downflows at or close to the umbra-penumbra boundary which have not been reported before. These downflows are confined to large patches, usually encompassing bright penumbral filaments, and have lifetimes of more than 14 hr. The presence of strong downflows in the center-side penumbra near the umbra rules out an association with the Evershed flow. Chromospheric filtergrams acquired close to the time of the spectropolarimetric measurements show large, strong, and long-lived brightenings in the neighborhood of the downflows. The photospheric intensity also exhibits persistent brightenings comparable to the quiet Sun. Interestingly, the orientation of the penumbral filaments at the site of the downflows is similar to that resulting from the reconnection process described by Ryutova et al. The existence of such downflows in the inner penumbra represents a challenge for numerical models of sunspots because they have to explain them in terms of physical processes likely affecting the chromosphere. Title: Searching for Overturning Convection in Penumbral Filaments: Slit Spectroscopy at 0farcs2 Resolution Authors: Bellot Rubio, L. R.; Schlichenmaier, R.; Langhans, K. Bibcode: 2010ApJ...725...11B Altcode: 2010arXiv1009.5650B Recent numerical simulations of sunspots suggest that overturning convection is responsible for the existence of penumbral filaments and the Evershed flow, but there is little observational evidence of this process. Here, we carry out a spectroscopic search for small-scale convective motions in the penumbra of a sunspot located 5° away from the disk center. The position of the spot is very favorable for the detection of overturning downflows at the edges of penumbral filaments. Our analysis is based on measurements of the Fe I 709.0 nm line taken with the Littrow spectrograph of the Swedish 1 m Solar Telescope under excellent seeing conditions. We compute line bisectors at different intensity levels and derive Doppler velocities from them. The velocities are calibrated using a nearby telluric line, with systematic errors smaller than 150 m s-1. Deep in the photosphere, as sampled by the bisectors at the 80%-88% intensity levels, we always observe blueshifts or zero velocities. The maximum blueshifts reach 1.2 km s-1 and tend to be cospatial with bright penumbral filaments. In the line core, we detect blueshifts for the most part, with small velocities not exceeding 300 m s-1. Redshifts also occur, but at the level of 100-150 m s-1, and only occasionally. The fact that they are visible in high layers casts doubts on their convective origin. Overall, we do not find indications of downflows that could be associated with overturning convection at our detection limit of 150 m s-1. Either no downflows exist, or we have been unable to observe them because they occur beneath τ = 1 or the spatial resolution/height resolution of the measurements is still insufficient. Title: Multiwavelength Observations of Small-scale Reconnection Events Triggered by Magnetic Flux Emergence in the Solar Atmosphere Authors: Guglielmino, S. L.; Bellot Rubio, L. R.; Zuccarello, F.; Aulanier, G.; Vargas Domínguez, S.; Kamio, S. Bibcode: 2010ApJ...724.1083G Altcode: 2010arXiv1007.4657G The interaction between emerging magnetic flux and the pre-existing ambient field has become a "hot" topic for both numerical simulations and high-resolution observations of the solar atmosphere. The appearance of brightenings and surges during episodes of flux emergence is believed to be a signature of magnetic reconnection processes. We present an analysis of a small-scale flux emergence event in NOAA 10971, observed simultaneously with the Swedish 1 m Solar Telescope on La Palma and the Hinode satellite during a joint campaign in 2007 September. Extremely high-resolution G-band, Hα, and Ca II H filtergrams, Fe I and Na I magnetograms, EUV raster scans, and X-ray images show that the emerging region was associated with chromospheric, transition region and coronal brightenings, as well as with chromospheric surges. We suggest that these features were caused by magnetic reconnection at low altitude in the atmosphere. To support this idea, we perform potential and linear force-free field extrapolations using the FROMAGE service. The extrapolations show that the emergence site is cospatial with a three-dimensional null point, from which a spine originates. This magnetic configuration and the overall orientation of the field lines above the emerging flux region are compatible with the structures observed in the different atmospheric layers and remain stable against variations of the force-free field parameter. Our analysis supports the predictions of recent three-dimensional numerical simulations that energetic phenomena may result from the interaction between emerging flux and the pre-existing chromospheric and coronal field. Title: Retrieval of solar magnetic fields from high-spatial resolution filtergraph data: the Imaging Magnetograph eXperiment (IMaX) Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Martínez Pillet, V.; Bonet, J. A.; Vargas Domínguez, S.; Del Toro Iniesta, J. C. Bibcode: 2010A&A...522A.101O Altcode: 2010arXiv1006.5510O Context. The design of modern instruments does not only imply thorough studies of instrumental effects but also a good understanding of the scientific analysis planned for the data.
Aims: We investigate the reliability of Milne-Eddington (ME) inversions of high-resolution magnetograph measurements such as those to be obtained with the Imaging Magnetograph eXperiment (IMaX) aboard the Sunrise balloon. We also provide arguments to choose either Fe I 525.02 or 525.06 nm as the most suitable line for IMaX.
Methods: We reproduce an IMaX observation using magnetoconvection simulations of the quiet Sun and synthesizing the four Stokes profiles emerging from them. The profiles are degraded by spatial and spectral resolution, noise, and limited wavelength sampling, just as real IMaX measurements. We invert these data and estimate the uncertainties in the retrieved physical parameters caused by the ME approximation and the spectral sampling.
Results: It is possible to infer the magnetic field strength, inclination, azimuth, and line-of-sight velocity from standard IMaX measurements (4 Stokes parameters, 5 wavelength points, and a signal-to-noise ratio of 1000) applying ME inversions to any of the Fe I lines at 525 nm. We also find that telescope diffraction has important effects on the spectra coming from very high resolution observations of inhomogeneous atmospheres. Diffration reduces the amplitude of the polarization signals and changes the asymmetry of the Stokes profiles.
Conclusions: The two Fe I lines at 525 nm meet the scientific requirements of IMaX, but Fe I 525.02 nm is to be preferred because it leads to smaller uncertainties in the retrieved parameters and offers a better detectability of the weakest (linear) polarization signals prevailing in the quiet Sun. Title: Two-dimensional solar spectropolarimetry with the KIS/IAA Visible Imaging Polarimeter Authors: Beck, C.; Bellot Rubio, L. R.; Kentischer, T. J.; Tritschler, A.; Del Toro Iniesta, J. C. Bibcode: 2010A&A...520A.115B Altcode: 2010arXiv1007.1153B Context. Spectropolarimetry at high spatial and spectral resolution is a basic tool to characterize the magnetic properties of the solar atmosphere.
Aims: We introduce the KIS/IAA Visible Imaging Polarimeter (VIP), a new post-focus instrument that upgrades the TESOS spectrometer at the German Vacuum Tower Telescope (VTT) into a full vector polarimeter. VIP is a collaboration between the Kiepenheuer Institut für Sonnenphysik (KIS) and the Instituto de Astrofísica de Andalucía (IAA-CSIC).
Methods: We describe the optical setup of VIP, the data acquisition procedure, and the calibration of the spectropolarimetric measurements. We show examples of data taken between 2005 and 2008 to illustrate the potential of the instrument.
Results: VIP is capable of measuring the four Stokes profiles of spectral lines in the range from 420 to 700 nm with a spatial resolution better than 0farcs5. Lines can be sampled at 40 wavelength positions in 60 s, achieving a noise level of about 2 × 10-3 with exposure times of 300 ms and pixel sizes of 0farcs17 × 0farcs17 (2 × 2 binning). The polarization modulation is stable over periods of a few days, ensuring high polarimetric accuracy. The excellent spectral resolution of TESOS allows the use of sophisticated data analysis techniques such as Stokes inversions. One of the first scientific results of VIP presented here is that the ribbon-like magnetic structures of the network are associated with a distinct pattern of net circular polarization away from disk center.
Conclusions: VIP performs spectropolarimetric measurements of solar magnetic fields at a spatial resolution that is only slightly worse than that of the Hinode spectropolarimeter, while providing a 2D field field of view and the possibility to observe up to four spectral regions sequentially with high cadence. VIP can be used as a stand-alone instrument or in combination with other spectropolarimeters and imaging systems of the VTT for extended wavelength coverage. Title: Upflows in the Central Dark Lane of Sunspot Light Bridges Authors: Rouppe van der Voort, L.; Bellot Rubio, L. R.; Ortiz, A. Bibcode: 2010ApJ...718L..78R Altcode: 2010arXiv1006.4578R We use high spatial and spectral resolution observations obtained with the CRisp Imaging SpectroPolarimeter at the Swedish 1 m Solar Telescope to analyze the velocity profile of granular light bridges (LBs) in a sunspot. We find upflows associated with the central dark lanes of the LBs. From bisectors in the Fe I 630.15 nm line we find that the magnitude of the upflows varies with height, with the strongest upflows being deeper in the atmosphere. Typical upflow velocities measured from the 70% bisector are around 500 m s-1 with peaks above 1 km s-1. The upflows in the central dark lane are surrounded by downflows of weaker magnitude, sometimes concentrated in patches with enhanced velocities reaching up to 1.1 km s-1. A small spatial offset between the upflows and the continuum dark lane is interpreted as a line-of-sight effect due to the elevated nature of the dark lane and the LB above the umbral surroundings. Our observations show that the central dark lane in granular LBs is not equivalent to the intergranular lanes of normal photospheric granulation that host convective downflows. These results support recent MHD simulations of magneto-convection in sunspot atmospheres. Title: Milne-Eddington inversion of the Fe I line pair at 630 nm Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Del Toro Iniesta, J. C. Bibcode: 2010A&A...518A...3O Altcode: 2010arXiv1005.5013S; 2010arXiv1005.5013O Context. The iron lines at 630.15 and 630.25 nm are often used to determine the physical conditions of the solar photosphere. A common approach is to invert them simultaneously under the Milne-Eddington approximation. The same thermodynamic parameters are employed for the two lines, except for their opacities, which are assumed to have a constant ratio.
Aims: We aim at investigating the validity of this assumption, since the two lines are not exactly the same.
Methods: We use magnetohydrodynamic simulations of the quiet Sun to examine the behavior of the ME thermodynamic parameters and their influence on the retrieval of vector magnetic fields and flow velocities.
Results: Our analysis shows that the two lines can be coupled and inverted simultaneously using the same thermodynamic parameters and a constant opacity ratio. The inversion of two lines is significantly more accurate than single-line inversions because of the larger number of observables. Title: Applicability of Milne-Eddington inversions to high spatial resolution observations of the quiet Sun Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Vögler, A.; Del Toro Iniesta, J. C. Bibcode: 2010A&A...518A...2O Altcode: 2010arXiv1005.5012O Context. The physical conditions of the solar photosphere change on very small spatial scales both horizontally and vertically. Such a complexity may pose a serious obstacle to the accurate determination of solar magnetic fields.
Aims: We examine the applicability of Milne-Eddington (ME) inversions to high spatial resolution observations of the quiet Sun. Our aim is to understand the connection between the ME inferences and the actual stratifications of the atmospheric parameters.
Methods: We use magnetoconvection simulations of the solar surface to synthesize asymmetric Stokes profiles such as those observed in the quiet Sun. We then invert the profiles with the ME approximation. We perform an empirical analysis of the heights of formation of ME measurements and analyze the uncertainties brought about by the ME approximation. We also investigate the quality of the fits and their relationship with the model stratifications.
Results: The atmospheric parameters derived from ME inversions of high-spatial resolution profiles are reasonably accurate and can be used for statistical analyses of solar magnetic fields, even if the fit is not always good. We also show that the ME inferences cannot be assigned to a specific atmospheric layer: different parameters sample different ranges of optical depths, and even the same parameter may trace different layers depending on the physical conditions of the atmosphere. Despite this variability, ME inversions tend to probe deeper layers in granules than in intergranular lanes.

Figure 10 and appendix are only available in electronic form at http://www.aanda.org Title: Explanation of the Sea-serpent Magnetic Structure of Sunspot Penumbrae Authors: Kitiashvili, I. N.; Bellot Rubio, L. R.; Kosovichev, A. G.; Mansour, N. N.; Sainz Dalda, A.; Wray, A. A. Bibcode: 2010ApJ...716L.181K Altcode: 2010arXiv1003.0049K Recent spectro-polarimetric observations of a sunspot showed the formation of bipolar magnetic patches in the mid-penumbra and their propagation toward the outer penumbral boundary. The observations were interpreted as being caused by sea-serpent magnetic fields near the solar surface. In this Letter, we develop a three-dimensional radiative MHD numerical model to explain the sea-serpent structure and the wave-like behavior of the penumbral magnetic field lines. The simulations reproduce the observed behavior, suggesting that the sea-serpent phenomenon is a consequence of magnetoconvection in a strongly inclined magnetic field. It involves several physical processes: filamentary structurization, high-speed overturning convective motions in strong, almost horizontal magnetic fields with partially frozen field lines, and traveling convective waves. The results demonstrate a correlation of the bipolar magnetic patches with high-speed Evershed downflows in the penumbra. This is the first time that a three-dimensional numerical model of the penumbra results in downward-directed magnetic fields, an essential ingredient of sunspot penumbrae that has eluded explanation until now. Title: Sea-Serpent Magnetic Structure of Sunspot Penumbrae: Observations and MHD Simulations Authors: Kitiashvili, Irina; Bellot Rubio, L. R.; Kosovichev, A. G.; Mansour, N. N.; Sainz Dalda, A.; Wray, A. A. Bibcode: 2010AAS...21631706K Altcode: 2010BAAS...41..899K Recent high-resolution spectro-polarimetric observations of a sunspot detected formation of bipolar magnetic patches in the mid penumbra and propagation of these patches toward the outer penumbral boundary. The observations have been interpreted as an evidence of sea-serpent field lines near the solar surface. Using a radiative 3D MHD code, we model the behavior of solar magnetoconvection in strongly inclined magnetic field of penumbra. The numerical simulation results reproduce the moving bipolar magnetic elements observed in high-resolution SOHO/MDI and Hinode/SOT data and also their physical properties, supporting the sea-serpent model. The simulations explain the sea-serpent structure and dynamics of the penumbral field as a consequence of turbulent magnetoconvection in a highly inclined, strong magnetic field, which forms filamentary structures and has properties of traveling convective wave. The model also shows that the appearance of the sea-serpent magnetic field lines is closely related to high-speed patches ("Evershed clouds") of the penumbra radial outflow. Title: Small Magnetic Loops Connecting the Quiet Surface and the Hot Outer Atmosphere of the Sun Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos, A.; Bellot Rubio, L. R. Bibcode: 2010ApJ...714L..94M Altcode: 2010arXiv1003.1255M Sunspots are the most spectacular manifestation of solar magnetism, yet 99% of the solar surface remains "quiet" at any time of the solar cycle. The quiet sun is not void of magnetic fields, though; they are organized at smaller spatial scales and evolve relatively fast, which makes them difficult to detect. Thus, although extensive quiet Sun magnetism would be a natural driver to a uniform, steady heating of the outer solar atmosphere, it is not clear what the physical processes involved would be, due to lack of observational evidence. We report on the topology and dynamics of the magnetic field in very quiet regions of the Sun from spectropolarimetric observations of the Hinode satellite, showing a continuous injection of magnetic flux with a well-organized topology of Ω-loop from below the solar surface into the upper layers. At first stages, when the loop travels across the photosphere, it has a flattened (staple-like) geometry and a mean velocity ascent of ~3 km s-1. When the loop crosses the minimum temperature region, the magnetic fields at the footpoints become almost vertical and the loop topology resembles a potential field. The mean ascent velocity at chromospheric height is ~12 km s-1. The energy input rate of these small-scale loops in the lower boundary of the chromosphere is (at least) of 1.4 × 106-2.2 × 107 erg cm-2 s-1. Our findings provide empirical evidence for solar magnetism as a multi-scale system, in which small-scale low-flux magnetism plays a crucial role, at least as important as active regions, coupling different layers of the solar atmosphere and being an important ingredient for chromospheric and coronal heating models. Title: Scattering Polarization in the Fe I 630 nm Emission Lines at the Extreme Limb of the Sun Authors: Lites, B. W.; Casini, R.; Manso Sainz, R.; Jurčák, J.; Ichimoto, K.; Ishikawa, R.; Okamoto, T. J.; Tsuneta, S.; Bellot Rubio, L. Bibcode: 2010ApJ...713..450L Altcode: Spectro-polarimetric observations with the Solar Optical Telescope onboard Hinode reveal the emission spectrum of the Fe I 630 nm lines at the solar limb. The emission shell extends for less than 1'' thereby making it extremely difficult to detect from ground-based observatories viewing the limb through the Earth's atmosphere. The linear polarization signal is clearly due to scattering and it is predominantly oriented in the radial direction. Using a comprehensive atomic model of iron, we are able to interpret qualitatively the observed signals, including the radial orientation of the linear polarization. The Hanle effect causes the linear polarization of the Fe I 630 nm lines to be sensitive to magnetic fields between ~0.1 G and ~40 G, and also to be sensitive to the field's topology for stronger fields. The overall degree of observed polarization can be reproduced by randomly oriented horizontal magnetic fields of strength ≈2 G. The discovery of their scattering polarization signals thus opens a new diagnostic opportunity for these lines. Title: Downflows in Sunspot Umbral Dots Authors: Ortiz, A.; Bellot Rubio, L. R.; Rouppe van der Voort, L. Bibcode: 2010ApJ...713.1282O Altcode: 2010arXiv1003.1897O We study the velocity field of umbral dots (UDs) at a resolution of 0farcs14. Our analysis is based on full Stokes measurements of a pore taken with the Crisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope. We determine the flow velocity at different heights in the photosphere from a bisector analysis of the Fe I 630 nm lines. In addition, we use the observed Stokes Q, U, and V profiles to characterize the magnetic properties of these structures. We find that most UDs are associated with strong upflows in deep photospheric layers. Some of them also show concentrated patches of downflows at their edges, with sizes of about 0farcs25, velocities of up to 1000 m s-1, and enhanced net circular polarization signals. The downflows evolve rapidly and have lifetimes of only a few minutes. These results appear to validate numerical models of magnetoconvection in the presence of strong magnetic fields. Title: The stochastic, intermittent nature of quiet Sun magnetism Authors: Martinez González, M. J.; Manso Sainz, R.; López Ariste, A.; Bellot Rubio, L. R.; Bianda, M. Bibcode: 2010iac..talk....1M Altcode: 2010iac..talk..153M No abstract at ADS Title: On Spectropolarimetric Measurements with Visible Lines Authors: del Toro Iniesta, J. C.; Orozco Suárez, D.; Bellot Rubio, L. R. Bibcode: 2010ApJ...711..312D Altcode: 2010arXiv1001.3022D The ability of new instruments for providing accurate inferences of vector magnetic fields and line-of-sight velocities of the solar plasma depends a great deal on the sensitivity to these physical quantities of the spectral lines chosen to be measured. Recently, doubts have been raised about visible Stokes profiles to provide a clear distinction between weak fields and strong ones filling a small fraction of the observed area. The goal of this paper is to give qualitative and quantitative arguments that help in settling the debate since several instruments that employ visible lines are either operating or planned for the near future. The sensitivity of the Stokes profiles is calculated through the response functions (RFs), for e.g., by Ruiz Cobo & Del Toro Iniesta. Both theoretical and empirical evidences are gathered in favor of the reliability of visible Stokes profiles. The RFs are also used for estimating the uncertainties in the physical quantities due to noise in observations. A useful formula has been derived that takes into account the measurement technique (number of polarization measurements, polarimetric efficiencies, and number of wavelength samples), the model assumptions (number of free parameters and the filling factor), and the radiative transfer (RFs). We conclude that a scenario with a weak magnetic field can reasonably be distinguished with visible lines from another with a strong field but a similar Stokes V amplitude, provided that the Milne-Eddington approximation is good enough to describe the solar atmosphere and the polarization signal is at least 3 or 4 times larger than the typical rms noise of 10-3 I c reached in the observations. Title: The Evershed Flow and the Brightness of the Penumbra Authors: Bellot Rubio, L. R. Bibcode: 2010ASSP...19..193B Altcode: 2010ASSP...19..193R; 2010mcia.conf..193B; 2009arXiv0903.3619B The Evershed flow is a systematic motion of gas that occurs in the penumbra of all sunspots. Discovered in 1909, it still lacks a satisfactory explanation. We know that the flow is magnetized, often supersonic, and that it shows conspicuous fine structure on spatial scales of 0.2″-0.3″, but its origin remains unclear. The hope is that a good observational understanding of the relation between the flow and the penumbral magnetic field will help us determine its nature. Here I review advances in the characterization of the Evershed flow and sunspot magnetic fields from high-resolution spectroscopic and spectropolarimetric measurements. Using this information as input for 2D heat transfer simulations, it has been demonstrated that hot Evershed upflows along nearly horizontal field lines are capable of explaining one of the most intriguing aspects of sunspots: the surplus brightness of the penumbra relative to the umbra. They also explain the existence of penumbral filaments with dark cores. These results support the idea that the Evershed flow is largely responsible for the transport of energy in the penumbra. Title: Structure and Dynamics of Penumbral Filaments Authors: Ruiz Cobo, B.; Bellot Rubio, L. R. Bibcode: 2010ASSP...14..461R Altcode: 2010hsa5.conf..461R; 2010ASSP...14..461C; 2008arXiv0810.2463R High-resolution observations of sunspots have revealed the existence of dark cores inside the bright filaments of the penumbra. Here we present the stationary solution of the heat transfer equation in a stratified penumbra consisting of nearly horizontal magnetic flux tubes embedded in a stronger and more vertical field. The tubes and the external medium are in horizontal mechanical equilibrium. This model produces bright filaments with dark cores as a consequence of the higher density of the plasma inside the flux tube, which shifts the surface of optical depth unity toward higher (cooler) layers. Our results suggest that the surplus brightness of the penumbra is a natural consequence of the Evershed flow, and that magnetic flux tubes about 250 km in diameter can explain the morphology of sunspot penumbra. Title: High-resolution observations of interactions during the emergence of magnetic flux from the photosphere to the corona Authors: Guglielmino, S. L.; Bellot Rubio, L. R.; Zuccarello, F.; Romano, P.; Vargas Domínguez, S. Bibcode: 2010MSAIS..14..184G Altcode: Interactions occurring at sites where new flux emerges and an old flux system is already present can trigger various phenomena, such as flux cancellation, reconnection events, and even flaring. We analyze high-resolution observations of a small-scale flux emergence event in NOAA 10971, observed simultaneously by the Hinode satellite and the Swedish Solar Telescope in La Palma Island during a joint campaign. G-band, Halpha , and Ca II H filtergrams were acquired together with Fe I and Na I magnetograms. The data show that the emerging region seen in the photosphere is associated with Ca II H brightenings and a Halpha chromospheric surge. Moreover, EUV raster scans and XRT filtergrams show cospatial brightenings. Comparing our results with recent 3D simulations, we interpret our observations in the context of the low-altitude magnetic reconnection model, suggesting that interactions between the emerging flux and the pre-existing magnetic field can explain the observed coupling. Title: Supersonic Downflows in a Sunspot Light Bridge Authors: Louis, Rohan E.; Bellot Rubio, Luis R.; Mathew, Shibu K.; Venkatakrishnan, P. Bibcode: 2009ApJ...704L..29L Altcode: 2009arXiv0908.3465L We report the discovery of supersonic downflows in a sunspot light bridge using measurements taken with the spectropolarimeter onboard the Hinode satellite. The downflows occur in small patches close to regions where the vector magnetic field changes orientation rapidly, and are associated with anomalous circular polarization profiles. An inversion of the observed Stokes spectra reveals velocities of up to 10 km s-1, making them the strongest photospheric flows ever measured in light bridges. Some (but not all) of the downflowing patches are cospatial and cotemporal with brightness enhancements in chromospheric Ca II H filtergrams. We suggest that these flows are due to magnetic reconnection in the upper photosphere/lower chromosphere, although other mechanisms cannot be ruled out. Title: Emergence of Small-scale Magnetic Loops Through the Quiet Solar Atmosphere Authors: Martínez González, M. J.; Bellot Rubio, L. R. Bibcode: 2009ApJ...700.1391M Altcode: 2009arXiv0905.2691M We investigate the emergence of magnetic flux in the quiet Sun at very small spatial scales, focusing on the magnetic connection between the photosphere and chromosphere. The observational data consist of spectropolarimetric measurements and filtergrams taken with the Hinode satellite and the Dutch Open Telescope. We find that a significant fraction of the magnetic flux present in internetwork regions appears in the form of Ω-shaped loops. The emergence rate is 0.02 loops per hour and arcsec-2, which brings 1.1 × 1012 Mx s-1 arcsec-2 of new flux to the solar surface. Initially, the loops are observed as small patches of linear polarization above a granular cell. Shortly afterward, two footpoints of opposite polarity become visible in circular polarization within or at the edges of the granule and start moving toward the adjacent intergranular space. The orientation of the footpoints does not seem to obey Hale's polarity rules. The loops are continuously buffeted by convective motions, but they always retain a high degree of coherence. Interestingly, 23% of the loops that emerge in the photosphere reach the chromosphere (16 cases out of 69). They are first detected in Fe I 630 nm magnetograms and 5 minutes later in Mg I b 517.3 nm magnetograms. After about 8 minutes, some of them are also observed in Ca II H line-core images, where the footpoints produce small brightness enhancements. Title: Imaging Spectropolarimetry with IBIS: Evolution of Bright Points in the Quiet Sun Authors: Viticchié, B.; Del Moro, D.; Berrilli, F.; Bellot Rubio, L.; Tritschler, A. Bibcode: 2009ApJ...700L.145V Altcode: 2009arXiv0906.2663V We present the results from first spectropolarimetric observations of the solar photosphere acquired at the Dunn Solar Telescope with the Interferometric Bidimensional Spectrometer. Full Stokes profiles were measured in the Fe I 630.15 nm and Fe I 630.25 nm lines with high spatial and spectral resolutions for 53 minutes, with a Stokes V noise of 3 × 10-3 the continuum intensity level. The data set allows us to study the evolution of several magnetic features associated with G-band bright points (BPs) in the quiet Sun. Here we focus on the analysis of three distinct processes, namely the coalescence, fragmentation, and cancellation of G-band BPs. Our analysis is based on an SIR inversion of the Stokes I and V profiles of both Fe I lines. The high spatial resolution of the G-band images combined with the inversion results helps to interpret the undergoing physical processes. The appearance (dissolution) of high-contrast G-band BPs is found to be related to the local increase (decrease) of the magnetic filling factor, without appreciable changes in the field strength. The cancellation of opposite-polarity BPs can be the signature of either magnetic reconnection or the emergence/submergence of magnetic loops. Title: Detection of Supersonic Horizontal Flows in the Solar Granulation Authors: Bellot Rubio, L. R. Bibcode: 2009ApJ...700..284B Altcode: 2009arXiv0905.3719B Hydrodynamic simulations of granular convection predict the existence of supersonic flows covering ~3%-4% of the solar surface at any time, but these flows have not been detected unambiguously as yet. Using data from the spectropolarimeter aboard the Hinode satellite, I present direct evidence of fast horizontal plasma motions in quiet-Sun granules. Their visibility increases toward the limb due to more favorable viewing conditions. At the resolution of Hinode, the horizontal flows give rise to asymmetric intensity profiles with very inclined blue wings and even line satellites located blueward of the main absorption feature. Doppler shifts of up to 9 km s-1 are observed at the edges of bright granules, demonstrating that the flows reach supersonic speeds. The strongest velocities occur in patches of 0farcs5 or less. They tend to be associated with enhanced continuum intensities, line widths, and equivalent widths, but large values of these parameters do not necessarily imply the existence of supersonic flows. Time series of spectropolarimetric measurements in regions away from the disk center show the transient nature of the strong horizontal motions, which last only for a fraction of the granule lifetime. Supersonic flows are expected to produce shocks at the boundaries between granules and intergranular lanes, and may also play a role in the emergence of small-scale magnetic fields in quiet-Sun internetwork regions. Title: Observations of small-scale flux evolution with HINODE Authors: Guglielmino, S. L.; Romano, P.; Zuccarello, F.; Bellot Rubio, L. R. Bibcode: 2009MmSAI..80..278G Altcode: We present observations of NOAA 10971 acquired by the Solar Optical Telescope onboard the HINODE satellite. We have inverted spectropolarimetric data of SOT/SP along Fe I doublet at 630.15 nm and 630.25 nm, using the SIR inversion code in order to get magnetic field strength, inclination, azimuth, Doppler velocity and temperature from the observed Stokes profiles. We compare these first results with SOT/FG broad-band observations in the Ca II H line (396.85 ± 0.3 nm) and G-band (430.5 ±± 0.8 nm), and with magnetograms obtained from the narrow-band shuttered Stokes I and V in the wings of the Na I D1 line (589.6 nm). Small-scale events of flux emergence and flux cancellation have been singled out. Title: Hinode Observations of Chromospheric Brightenings in the Ca II H Line during Small-Scale Flux Emergence Events Authors: Guglielmino, S. L.; Zuccarello, F.; Romano, P.; Bellot Rubio, L. R. Bibcode: 2008ApJ...688L.111G Altcode: 2008arXiv0810.2494G Ca II H emission is a well-known indicator of magnetic activity in the Sun and other stars. It is also viewed as an important signature of chromospheric heating. However, the Ca II H line has not been used as a diagnostic of magnetic flux emergence from the solar interior. Here we report on Hinode observations of chromospheric Ca II H brightenings associated with a repeated, small-scale flux emergence event. We describe this process and investigate the evolution of the magnetic flux, G-band brightness, and Ca II H intensity in the emerging region. Our results suggest that energy is released in the chromosphere as a consequence of interactions between the emerging flux and the preexisting magnetic field, in agreement with recent 3D numerical simulations. Title: Chromospheric Brightenings during Small-scale Flux Emergence Events Authors: Guglielmino, S. L.; Zuccarello, F.; Romano, P.; Bellot Rubio, L. R. Bibcode: 2008ESPM...12.2.46G Altcode: We present multi-wavelength high-resolution observations of active region NOAA 10971, performed by the Solar Optical Telescope aboard the Hinode satellite. Small-scale events of flux emergence occurring in this region have been singled out. In particular, we report observations of chromospheric Ca II H brightenings associated with a repeated emergence event. We describe this process and investigate the evolution of the magnetic flux, G-band brightness, and Ca II H intensity in the emerging region. We compare these observations with simultaneous spectropolarimetric measurements, using the SIR code to retrieve the thermal, dynamical, and magnetic properties of the emerging region. We discuss our results in the context of the chromospheric heating problem. Magnetic reconnection between the emerging flux and the pre-existing chromospheric field would be able to explain the observed chromospheric brightness enhancements. The reconnection releases energy, and this could be an efficient source of local heating for the chromosphere, as suggested by recent 3D numerical simulations. Title: Heat transfer in sunspot penumbrae. Origin of dark-cored penumbral filaments Authors: Ruiz Cobo, B.; Bellot Rubio, L. R. Bibcode: 2008A&A...488..749R Altcode: 2008arXiv0806.0804R Context: Observations at 0.1 arcsec have revealed the existence of dark cores in the bright filaments of sunspot penumbrae. Expectations are high that such dark-cored filaments are the basic building blocks of the penumbra, but their nature remains unknown.
Aims: We investigate the origin of dark cores in penumbral filaments and the surplus brightness of the penumbra. To that end we use an uncombed penumbral model.
Methods: The 2D stationary heat transfer equation is solved in a stratified atmosphere consisting of nearly horizontal magnetic flux tubes embedded in a stronger and more vertical field. The tubes carry an Evershed flow of hot plasma.
Results: This model produces bright filaments with dark cores as a consequence of the higher density of the plasma inside the tubes, which shifts the surface of optical depth unity toward higher (cooler) layers. Our calculations suggest that the surplus brightness of the penumbra is a natural consequence of the Evershed flow, and that magnetic flux tubes about 250 km in diameter can explain the morphology of sunspot penumbrae. Title: Solar spectropolarimetry at high spatial resolution: Quiet-Sun magnetic fields Authors: Bellot Rubio, L. R.; Borrero, J. M. Bibcode: 2008ESPM...12..2.4B Altcode: Spectropolarimetry permits quantitative inferences of solar magnetic fields to be carried out. It is in fact the only means at our disposal to characterize the physical properties of small magnetic structures from low spatial-resolution observations. The accuracy of the results derived from spectropolarimetric measurements has improved dramatically with the advent of simultaneous observations in different spectral regions and high angular resolution measurements. The main advantage brought about by high spatial resolution is that there is less need to model complex scenarios involving different fields and/or flows coexisting in the pixel. Currently it is possible to achieve resolutions of 0.3 arcsec from space (with the Hinode satellite) and 0.15 arcsec from the ground (with the 1-m Swedish Solar Telescope). In this talk we will show examples of high spatial resolution spectropolarimetric observations and how they are challenging our understanding of quiet Sun magnetic fields and sunspot penumbrae. In addition, we will describe previously unknown issues that affect diffraction-limited observations. Proper interpretations of the measurements require these effects to be taken into account. Title: Erratum: The Analysis of Penumbral Fine Structure Using an Advanced Inversion Technique Authors: Jurcák, Jan; Bellot Rubio, Luis; Ichimoto, Kiyoshi; Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.; Tsuneta, Saku Bibcode: 2008PASJ...60..933J Altcode: In the article [PASJ 59, S601-S606 (2007)], the word ''CSIC'' was omitted from the affiliation of Dr. Luis Bellot Rubio. The correct affiliation is : 2Instituto de Astrofísica de Andalucía (CSIC), Apdo. de Correos 3004, 18080 Granada, Spain Title: Detection of sea-serpent field lines in sunspot penumbrae Authors: Sainz Dalda, A.; Bellot Rubio, L. R. Bibcode: 2008A&A...481L..21S Altcode: 2007arXiv0712.2983S Aims:We investigate the spatial distribution of magnetic polarities in the penumbra of a spot observed very close to disk center.
Methods: High angular and temporal resolution magnetograms taken with the Narrowband Filter Imager aboard Hinode are used in this study. They provide continuous and stable measurements in the photospheric Fe I 630.25 line for long periods of time.
Results: Our observations show small-scale, elongated, bipolar magnetic structures that appear in the mid penumbra and move radially outward. They occur in between the more vertical fields of the penumbra, and can be associated with the horizontal fields that harbor the Evershed flow. Many of them cross the outer penumbral boundary, becoming moving magnetic features in the sunspot moat. We determine the properties of these structures, including their sizes, proper motions, footpoint separation, and lifetimes.
Conclusions: The bipolar patches can be interpreted as being produced by sea-serpent field lines that originate in the mid penumbra and eventually leave the spot in the form moving magnetic features. The existence of such field lines has been inferred from Stokes inversions of spectropolarimetric measurements at lower angular resolution, but this is the first time they are imaged directly. Our observations add another piece of evidence in favor of the uncombed structure of penumbral magnetic fields.

A movie is only available in electronic form at http://www.aanda.org Title: Magnetic field emergence in quiet Sun granules Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Tsuneta, S. Bibcode: 2008A&A...481L..33O Altcode: 2007arXiv0712.2663O Aims:We describe a new form of small-scale magnetic flux emergence in the quiet Sun. This process seems to take vertical magnetic fields from subsurface layers to the photosphere, where they appear above granular convection cells.
Methods: High-cadence time series of spectropolarimetric measurements obtained by Hinode in a quiet region near disk center are analyzed. We extract line parameters from the observed Stokes profiles and study their evolution with time.
Results: The circular polarization maps derived from the observed Fe I 630 nm lines show clear magnetic signals emerging at the center of granular cells. We do not find any evidence for linear polarization signals associated with these events. The magnetic flux patches grow with time, occupying a significant fraction of the granular area. The signals then fade until they disappear completely. The typical lifetime of these events is of the order of 20 min. No significant changes in the chromosphere are seen to occur in response to the emergence, as revealed by co-spatial Ca II H filtergrams. The Stokes I and V profiles measured in the emerging flux concentrations show strong asymmetries and Doppler shifts.
Conclusions: The origin of these events is unclear at present, but we suggest that they may represent the emergence of vertical fields lines from the bottom of the photosphere, possibly dragged by the convective upflows of granules. Preliminary inversions of the Stokes spectra indicate that this scenario is compatible with the observations, although the emergence of vertical field lines is not free from conceptual problems. Title: Formation of Solar Magnetic Flux Tubes with Kilogauss Field Strength Induced by Convective Instability Authors: Nagata, Shin'ichi; Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Katsukawa, Yukio; Shimizu, Toshifumi; Yokoyama, Takaaki; Tarbell, Theodore D.; Lites, Bruce W.; Shine, Richard A.; Berger, Thomas E.; Title, Alan M.; Bellot Rubio, Luis R.; Orozco Suárez, David Bibcode: 2008ApJ...677L.145N Altcode: Convective instability has been a mechanism used to explain the formation of solar photospheric flux tubes with kG field strength. However, the turbulence of the Earth's atmosphere has prevented ground-based observers from examining the hypothesis with precise polarimetric measurement on the subarcsecond scale flux tubes. Here we discuss observational evidence of this scenario based on observations with the Solar Optical Telescope (SOT) aboard Hinode. The cooling of an equipartition field strength flux tube precedes a transient downflow reaching 6 km s-1 and the intensification of the field strength to 2 kG. These observations agree very well with the theoretical predictions. Title: Penumbral models in the light of Hinode spectropolarimetric observations Authors: Jurčák, J.; Bellot Rubio, L. R. Bibcode: 2008A&A...481L..17J Altcode: 2007arXiv0711.1692J Aims:The realism of current models of the penumbra is assessed by comparing their predictions with the plasma properties of penumbral filaments as retrieved from spectropolarimetric observations.
Methods: The spectropolarimeter onboard Hinode allows us, for the first time, to distinguish the fine structure of the penumbra. Therefore, we can use one-component inversions to obtain the stratifications of plasma parameters in each pixel. The correlations between the plasma parameters and the continuum intensity are studied.
Results: We find that, in the outer penumbra, the stronger flows and higher values of magnetic field inclination tend to be located in dark filaments. This finding does not seem to be compatible with the scenario of a field-free gappy penumbra. Title: Spectropolarimetry of a Decaying Sunspot Penumbra Authors: Bellot Rubio, L. R.; Tritschler, A.; Martínez Pillet, V. Bibcode: 2008ApJ...676..698B Altcode: 2007arXiv0712.2937B We report on high angular resolution, high-precision spectropolarimetric measurements of a decaying sunspot. The spot gradually lost its penumbra during the course of 3 days. In the late stages of evolution, where the only remnant of the spot is a naked umbra, we find small-scale inhomogeneities in the magnetic canopy surrounding it. The inhomogeneities are observed as finger-like structures of weak and nearly horizontal magnetic fields extending 1''-2'' from the border of the umbra. These fields are not associated with filamentary structures in continuum intensity or with conspicuous Evershed flows. The Stokes profiles emerging from the fingers exhibit blueshifts, which we interpret as upward motions. This previously unknown fine structure may be related to penumbral field lines that no longer carry strong Evershed flows and rise to the chromosphere, producing the disappearance of the penumbra at photospheric levels. Title: Temporal evolution of the Evershed flow in sunspots. II. Physical properties and nature of Evershed clouds Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Borrero, J. M.; Del Toro Iniesta, J. C. Bibcode: 2008A&A...477..273C Altcode: 2007arXiv0709.1601C Context: Evershed clouds (ECs) represent the most conspicuous variation of the Evershed flow in sunspot penumbrae.
Aims: We determine the physical properties of ECs from high spatial and temporal resolution spectropolarimetric measurements. This information is used to investigate the nature of the EC phenomenon.
Methods: The Stokes profiles of four visible and three infrared spectral lines are subject to inversions based on simple one-component models as well as more sophisticated realizations of penumbral flux tubes embedded in a static ambient field (uncombed models).
Results: According to the one-component inversions, the EC phenomenon can be understood as a perturbation of the magnetic and dynamic configuration of the penumbral filaments along which the ECs move. The uncombed inversions, on the other hand, suggest that ECs are the result of enhancements in the visibility of penumbral flux tubes. We conjecture that these enhancements are caused by a perturbation of the thermodynamic properties of the tubes, rather than by changes in the vector magnetic field. This mechanism is investigated performing numerical experiments of thick penumbral tubes in mechanical equilibrium with a background field.
Conclusions: While the one-component inversions confirm many of the properties indicated by a simple line parameter analysis (Paper I of this series), we give more credit to the results of the uncombed inversions because they take into account, at least in an approximate manner, the fine structure of the penumbra.

Appendix A is only available in electronic form at http://www.aanda.org Title: Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; Del Toro Iniesta, J. C. Bibcode: 2007A&A...475.1067C Altcode: 2007arXiv0707.2629C Context: The magnetic and kinematic properties of the photospheric Evershed flow are relatively well known, but not completely understood. The evolution of the flow with time, which is mainly due to the appearance of velocity packets called Evershed clouds (ECs), may provide information to further constrain its origin.
Aims: We undertake a detailed analysis of the evolution of the Evershed flow by studying the properties of ECs. In this first paper we determine the sizes, proper motions, location in the penumbra, and frequency of appearance of ECs, as well as their typical Doppler velocities, linear and circular polarization signals, Stokes V area asymmetries, and continuum intensities.
Methods: High-cadence, high-resolution, full vector spectropolarimetric measurements in visible and infrared lines are used to characterize the EC phenomenon through a simple line-parameter analysis.
Results: ECs appear in the mid penumbra and propagate outward along filaments having large linear polarization signals and enhanced Evershed flows. The frequency of appearance of ECs varies between 15 and 40 min in different filaments. ECs exhibit the largest Doppler velocities and linear-to-circular polarization ratios of the whole penumbra. In addition, lines formed deeper in the atmosphere show larger Doppler velocities, much in the same way as the “quiescent” Evershed flow. According to our observations, ECs can be classified in two groups: type I ECs, which vanish in the outer penumbra, and type II ECs, which cross the outer penumbral boundary and enter the sunspot moat. Most of the observed ECs belong to type I. On average, type II ECs can be detected as velocity structures outside of the spot for only about 14 min. Their proper motions in the moat are significantly reduced with respect to the ones they had in the penumbra.

Appendices A and B are only available in electronic form at http://www.aanda.org Title: Quiet-Sun Internetwork Magnetic Fields from the Inversion of Hinode Measurements Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Tsuneta, S.; Lites, B. W.; Ichimoto, K.; Katsukawa, Y.; Nagata, S.; Shimizu, T.; Shine, R. A.; Suematsu, Y.; Tarbell, T. D.; Title, A. M. Bibcode: 2007ApJ...670L..61O Altcode: 2007arXiv0710.1405O We analyze Fe I 630 nm observations of the quiet Sun at disk center taken with the spectropolarimeter of the Solar Optical Telescope aboard the Hinode satellite. A significant fraction of the scanned area, including granules, turns out to be covered by magnetic fields. We derive field strength and inclination probability density functions from a Milne-Eddington inversion of the observed Stokes profiles. They show that the internetwork consists of very inclined, hG fields. As expected, network areas exhibit a predominance of kG field concentrations. The high spatial resolution of Hinode's spectropolarimetric measurements brings to an agreement the results obtained from the analysis of visible and near-infrared lines. Title: Strategy for the Inversion of Hinode Spectropolarimetric Measurements in the Quiet Sun Authors: Orozco Suárez, David; Bellot Rubio, Luis R.; Del Toro Iniesta, Jose Carlos; Tsuneta, Saku; Lites, Bruce; Ichimoto, Kiyoshi; Katsukawa, Yukio; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine, Richard A.; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M. Bibcode: 2007PASJ...59S.837O Altcode: 2007arXiv0709.2033O In this paper we propose an inversion strategy for the analysis of spectropolarimetric measurements taken by Hinode in the quiet Sun. The Spectro-Polarimeter of the Solar Optical Telescope aboard Hinode records the Stokes spectra of the FeI line pair at 630.2nm with unprecendented angular resolution, high spectral resolution, and high sensitivity. We discuss the need to consider a local stray-light contamination to account for the effects of telescope diffraction. The strategy is applied to observations of a wide quiet Sun area at disk center. Using these data we examine the influence of noise and initial guess models in the inversion results. Our analysis yields the distributions of magnetic field strengths and stray-light factors. They show that quiet Sun internetwork regions consist mainly of hG fields with stray-light contamination of about 0.8. Title: The Analysis of Penumbral Fine Structure Using an Advanced Inversion Technique Authors: Jurcák, Jan; Bellot Rubio, Luis; Ichimoto, Kiyoshi; Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.; Tsuneta, Saku Bibcode: 2007PASJ...59S.601J Altcode: 2007arXiv0707.1560J We present a method to study the penumbral fine structure using data obtained by the spectropolarimeter on board Hinode. For the first time, the penumbral filaments can be considered as being resolved in spectropolarimetric measurements. This enables us to use inversion codes with only one-component model atmospheres, and thus to assign the obtained stratifications of the plasma parameters directly to the penumbral fine structure. This approach was applied to the limb-side part of the penumbra in the active region NOAA10923. Preliminary results show a clear dependence of the plasma parameters on the continuum intensity in the inner penumbra, i.e., a weaker and horizontal magnetic field along with an increased line-of-sight velocity are found in the low layers of the bright filaments. The results in the mid penumbra are ambiguous, and future analyses are necessary to unveil the magnetic field structure and other plasma parameters there. Title: Vector Spectropolarimetry of Dark-cored Penumbral Filaments with Hinode Authors: Bellot Rubio, L. R.; Tsuneta, S.; Ichimoto, K.; Katsukawa, Y.; Lites, B. W.; Nagata, S.; Shimizu, T.; Shine, R. A.; Suematsu, Y.; Tarbell, T. D.; Title, A. M.; del Toro Iniesta, J. C. Bibcode: 2007ApJ...668L..91B Altcode: 2007arXiv0708.2791B We present spectropolarimetric measurements of dark-cored penumbral filaments taken with Hinode at a resolution of 0.3". Our observations demonstrate that dark-cored filaments are more prominent in polarized light than in continuum intensity. Far from disk center, the Stokes profiles emerging from these structures are very asymmetric and show evidence for magnetic fields of different inclinations along the line of sight, together with strong Evershed flows of at least 6-7 km s-1. In sunspots closer to disk center, dark-cored penumbral filaments exhibit regular Stokes profiles with little asymmetries due to the vanishing line-of-sight component of the horizontal Evershed flow. An inversion of the observed spectra indicates that the magnetic field is weaker and more inclined in the dark cores as compared with the surrounding bright structures. This is compatible with the idea that dark-cored filaments are the manifestation of flux tubes carrying hot Evershed flows. Title: Flux Tubes as the Origin of Net Circular Polarization in Sunspot Penumbrae Authors: Borrero, J. M.; Bellot Rubio, L. R.; Müller, D. A. N. Bibcode: 2007ApJ...666L.133B Altcode: 2007arXiv0707.4145B We employ a three-dimensional magnetohydrostatic model of a horizontal flux tube, embedded in a magnetic surrounding atmosphere, to successfully reproduce the azimuthal and center-to-limb variations of the net circular polarization observed in sunspot penumbrae. This success is partly due to the realistic modeling of the interaction between the flux tube and the surrounding magnetic field. Title: Magnetic properties of G-band bright points in a sunspot moat Authors: Beck, C.; Bellot Rubio, L. R.; Schlichenmaier, R.; Sütterlin, P. Bibcode: 2007A&A...472..607B Altcode: 2007arXiv0707.1232B We present simultaneous spectropolarimetric observations of four visible (630 nm) and three infrared (1565 nm) spectral lines from the German Vacuum Tower Telescope, together with speckle-reconstructed filtergrams in the G-band and the Ca II H line core from the Dutch Open Telescope. After alignment of the data sets, we used the G-band intensity to locate bright points (BPs) in the moat of a regular sunspot. With the cospatial and cotemporal information provided by the polarimetric data, we characterize the magnetic, kinematic, and thermal properties of the BPs. We find that (a) 94% of the BPs are associated with magnetic fields; (b) their field strengths range between 500 and 1400 G, with a rather flat distribution; (c) the contrast of BPs in the G-band depends on the angle between the vector magnetic field and the line of sight; (d) the BPs harbor downflows of magnetized plasma and exhibit Stokes V profiles with large area and amplitude asymmetries; (e) the magnetic interior of BPs is hotter than the immediate field-free surroundings by about 1000 K at equal optical depth; and (f) the mean effective diameter of BPs in our data set is 150 km, with very few BPs larger than 300 km. Most of these properties can be explained by the classical magnetic flux tube model. However, the wide range of BP parameters found in this study indicates that not all G-band BPs are identical to stable long-lived flux tubes or sheets of kG strength.

Appendices A-C are only available in electronic form at http://www.aanda.org Title: Quiet-Sun Magnetic Fields from Space-borne Observations: Simulating Hinode's Case Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta, J. C. Bibcode: 2007ApJ...662L..31O Altcode: 2007arXiv0705.0096O We examine whether it is possible to derive the field strength distribution of quiet-Sun internetwork regions from very high spatial resolution polarimetric observations in the visible. In particular, we consider the case of the spectropolarimeter attached to the Solar Optical Telescope aboard Hinode. Radiative magnetoconvection simulations are used to synthesize the four Stokes profiles of the Fe I 630.2 nm lines. Once the profiles are degraded to a spatial resolution of 0.32" and added noise, we infer the atmospheric parameters by means of Milne-Eddington inversions. The comparison of the derived values with the real ones indicates that the visible lines yield correct internetwork field strengths and magnetic fluxes, with uncertainties smaller than ~150 G, when a stray-light contamination factor is included in the inversion. Contrary to the results of ground-based observations at 1", weak fields are retrieved wherever the field is weak in the simulation. Title: Multi-wavelength observations at the German VTT on Tenerife Authors: Beck, C.; Mikurda, K.; Bellot Rubio, L. R.; Kentischer, T.; Collados, M. Bibcode: 2007msfa.conf...55B Altcode: To study the small-scale dynamic processes of magneto-convection in the solar photosphere in more detail than currently achieveable, not only the spatial resolution has to be increased, but also the information content of observations. In order to do so, several wavelengths and spectral lines must be observed simultaneously. This is often achieved by coordinated campaigns at several telescopes with different post-focus instrumentation. The German Vacuum Tower Telescope (VTT) on Tenerife offers the possibility to operate several dedicated instruments spectrometers, polarimeters, imaging systems at the same time. We describe some of the possible combinations of post-focus instruments, and present examples of multi-wavelength data obtained recently. Title: S im ulation And Analysis Of VIM Measurements: Feedback On Design Parameters Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Vargas, S.; Bonet, J. A.; Martíez Pillet, V.; del Toro Iniesta, J. C. Bibcode: 2007ESASP.641E..49O Altcode: 2006astro.ph.11443O The Visible-light Imager and Magnetograph (VIM) proposed for the ESA Solar Orbiter mission will observe a photo spheric spectral line at high spatial resolution. Here we simulate and interpret VIM measurements. Realistic MHD models are used to synthesize "observed" Stokes profiles of the photospheric Fe I 617.3 nm line. The profiles are degraded by telescope diffraction and detector pixel size to a spatial resolution of 162 km on the solar surface. We stufy the influence of spectral resolving power, noise, and limited wavelength sampling on the vector magnetic fields and line-of-sight velocities derived from Milne-Eddington inversions of the simulated measurements. VIM will provide reasonably accurate values of the atmospheric parametes even with the filter widths of 120 Å and 3 wavelength positions plus continuum, as long as the noise level is kept below 10-3 Ic. Title: A Look into the Guts of Sunspots Authors: Bellot Rubio, L. R. Bibcode: 2007hsa..conf..271B Altcode: 2006astro.ph.11471B Advances in instrumentation have made it possible to study sunspots with unprecedented detail. New capabilities include imaging observations at a resolution of 0.1" (70 km on the sun), spectroscopy at ~0.2", and simultaneous spectropolarimetry in visible and infrared lines at resolutions well below 1". In spite of these advances, we still have not identified the building blocks of the penumbra and the mechanism responsible for the Evershed flow. Three different models have been proposed to explain the corpus of observations gathered over the years. The strengths and limitations of these models are reviewed in this contribution. Title: Magnetic properties of G-band bright points Authors: Beck, C.; Mikurda, K.; Bellot Rubio, L. R.; Schlichenmaier, R.; Sütterlin, P. Bibcode: 2007msfa.conf..165B Altcode: Bright points (BPs) visible in the G band at 430 nm are commonly used as tracers of magnetic fields, indicating the location of kG flux concentrations. To study the actual magnetic properties of G-band BPs, we took observations in 2003 and 2005, employing simultaneously a speckle setup in the G band and vector spectropolarimetry to derive the magnetic field vector. From the analysis of the co-aligned polarimetric data we find that the BPs show a broad range of field strengths, magnetic fluxes, and field inclinations. Many G-band BPs are not co-spatial with the central part of the nearby flux concentrations. Even at the small heliocentric angle of only 12°, the BPs appear projected on adjacent granules, whereas the magnetic field is concentrated in the intergranular lanes. Our findings support the view that the G-band BPs are a result of the "hot wall effect". The downward shift of the optical depth scale in the presence of magnetic fields allows to see deeper and hotter layers in the hot granules next to the field concentrations, where CH dissociates. Thus, information drawn from imaging observations of BPs has limited use to investigate the actual magnetic field structure, when the BPs are not co-spatial with the central part of the flux concentrations. Title: Polarimetric Observations of the Formation of a G-Band Bright Point Authors: Beck, C.; Schmidt, W.; Bellot Rubio, L. R.; Schlichenmaier, R.; Sütterlin, P.; Lites, B. W. Bibcode: 2006ASPC..358...72B Altcode: We investigate the kinematic and magnetic properties of G-band bright points in the moat of a regular sunspot. The analysis is based on vector polarimetric measurements made at the German Vacuum Tower Telescope in visible (630 nm) and infrared (1565 nm) spectral lines, complemented by high-resolution filtergrams in the G-band at 430.6 nm and the core of the Ca II H line at 396.7 nm from the Dutch Open Telescope. The spectro-polarimetric data has been inverted to derive the magnetic field properties of the observed region. We witness the formation of a G-band bright point from a patch of diffuse flux with an initial field strength of 0.4 kG. The magnetic field strength increases to 0.9 kG in the course of several minutes, accompanied by a downflow of magnetized plasma. A few minutes after the field intensification, a G-band bright point is seen at the location of the flux concentration. The formation of the bright point shows the signatures of convective collapse. Title: Stokes Inversion Techniques: Recent Advances and New Challenges Authors: Bellot Rubio, L. R. Bibcode: 2006ASPC..358..107B Altcode: 2006astro.ph..1483B Inversion techniques (ITs) allow us to infer the magnetic, dynamic, and thermal properties of the solar atmosphere from polarization line profiles. In recent years, major progress has come from the application of ITs to state-of-the-art observations. This paper summarizes the main results achieved both in the photosphere and in the chromosphere. It also discusses the challenges facing ITs in the near future. Understanding the limitations of spectral lines, implementing more complex atmospheric models, and devising efficient strategies of data analysis for upcoming ground-based and space-borne instruments, are among the most important issues that need to be addressed. It is argued that proper interpretations of diffraction-limited Stokes profiles will not be possible without accounting for gradients of the atmospheric parameters along the line of sight. The feasibility of determining gradients in real time from space-borne observations is examined. Title: First Steps Towards the Electronic Inversion of the Radiative Transfer Equation Authors: Castillo Lorenzo, J. L.; Orozco Suárez, D.; Bellot Rubio, L. R.; Jiménez, L.; Del Toro Iniesta, J. C. Bibcode: 2006ASPC..358..177C Altcode: The radiative transfer equation (RTE) gives us information about how the light streams through the medium. It must be inverted in order to obtain the properties of the medium that generated the observation. While there are a number of well discussed methods to approach the solution of the inversion, none of them is suitable for the real-time analysis of high-resolution images due to their computational requirements. This document introduces an electronic inverter for the RTE, suitable for real-time inversion and mainly intended for space missions and on-line ground-based observations. Title: Inversion of Visible and IR Stokes Profiles in Sunspots Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; Del Toro Iniesta, J. C. Bibcode: 2006ASPC..358...25C Altcode: We present an analysis of simultaneous observations of a sunspot in two different spectral ranges (630 nm and 1565 nm). The dataset was acquired with the POlarimetric LIttrow Spectrograph (POLIS) and the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT) of Observatorio del Teide. Inversions of both sets of lines are carried out to retrieve physical quantities such as temperature and magnetic fields. We find that: a) the differences between the atmospheric parameters inferred from the two ranges are small, demonstrating that inversion techniques provide unique results; b) there is a cross-talk between temperature and stray light for visible lines; c) a more realistic treatment of the stray light contamination is required. Making use of both visible and infrared lines we obtain < dB/dz >=-2.3±0.6 G km-1 and < dγ/dz >=-0.019±0.015 deg km-1 in the umbra. Finally, we show how simultaneous spectro-polarimetric observations of the Sun in visible and infrared wavelengths improve the diagnostic capabilities of a single spectral range alone. Title: Milne-Eddington Response Functions and Their Applications Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Del Toro Iniesta, J. C. Bibcode: 2006ASPC..358..197O Altcode: We examine the errors in the atmospheric parameters recovered from the inversion of spectro-polarimetric data with limited wavelength sampling. We suggest that response functions evaluated in Milne-Eddington atmospheres may be useful as diagnostic tools that allow, for instance, the selection of the optimum wavelength positions to be observed by vector magnetographs. Title: Evershed Clouds as Precursors of Moving Magnetic Features around Sunspots Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; del Toro Iniesta, J. C. Bibcode: 2006ApJ...649L..41C Altcode: 2006astro.ph..9108C The relation between the Evershed flow and moving magnetic features (MMFs) is studied using high-cadence, simultaneous spectropolarimetric measurements of a sunspot in visible (630.2 nm) and near-infrared (1565 nm) lines. Doppler velocities, magnetograms, and total linear polarization maps are calculated from the observed Stokes profiles. We follow the temporal evolution of two Evershed clouds that move radially outward along the same penumbral filament. Eventually, the clouds cross the visible border of the spot and enter the moat region, where they become MMFs. The flux patch farther from the sunspot has the same polarity of the spot, while the MMF closer to it has opposite polarity and exhibits abnormal circular polarization profiles. Our results provide strong evidence that at least some MMFs are the continuation of the penumbral Evershed flow into the moat. This, in turn, suggests that MMFs are magnetically connected to sunspots. Title: The flow field in the sunspot canopy Authors: Rezaei, R.; Schlichenmaier, R.; Beck, C.; Bellot Rubio, L. R. Bibcode: 2006A&A...454..975R Altcode: 2006astro.ph..4301R Aims.We investigate the flow field in the sunspot canopy using simultaneous Stokes vector spectropolarimetry of three sunspots (θ=27°, 50°, 75°) and their surroundings in visible (630.15 and 630.25 nm) and near infrared (1564.8 and 1565.2 nm) neutral iron lines.
Methods: .To calibrate the Doppler shifts, we compare an absolute velocity calibration using the telluric O_2-line at 630.20 nm and a relative velocity calibration using the Doppler shift of Stokes V profiles in the umbra under the assumption that the umbra is at rest. Both methods yield the same result within the calibration uncertainties (~150 m s-1). We study the radial dependence of Stokes V profiles in the directions of disk center and limb side.
Results: .Maps of Stokes V profile shifts, polarity, amplitude asymmetry, field strength and magnetic field azimuth provide strong evidence for the presence of a magnetic canopy and for the existence of a radial outflow in the canopy.
Conclusions: .Our findings indicate that the Evershed flow does not cease abruptly at the white-light spot boundary, but that at least a part of the penumbral Evershed flow continues into the magnetic canopy. Title: VIP - 2D Vector Spectropolarimetry of the Solar Atmosphere near the Diffraction Limit Authors: Bellot Rubio, L. R.; Tritschler, A.; Kentischer, T.; Beck, C.; Del Toro Iniesta, J. C. Bibcode: 2006IAUJD...3E..58B Altcode: The KIS/IAA Vector Imaging Polarimeter (VIP) is a new instrument for two-dimensional spectropolarimetry of the solar atmosphere. It is used with TESOS, the triple etalon Fabry-Perot interferometer installed at the German Vacuum Tower Telescope of Observatorio del Teide (Tenerife, Spain). The polarimeter is based on a pair of nematic liquid crystal retarders and a Wollaston prism. VIP and TESOS are able to observe any spectral line in the range from 450 nm to 750 nm with a spectral resolving power of about 250000 and spatial resolutions better than 0.5" (thanks to the Kiepenheuer Adaptive Optics System). Typically, the four Stokes parameters of a line can be measured at 40 wavelength points in less than 60 s, with a noise level of 1-2 x 10^-3 and a pixel size of 0.18" x 0.18" (2x2 binning). The modulation matrix of VIP is derived using the polarimetric calibration unit installed at the telescope. Here we present first-light observations of VIP carried out in November 2005. We recorded the full Stokes profiles of the 630.1 and 630.2 nm Fe I lines emerging from a solar pore and its surroundings at a spatial resolution of ~0.4". Based on these data, we discuss the performance and capabilities of VIP as a powerful instrument for high spatial and temporal resolution measurements of vector magnetic fields in the solar atmosphere. Title: Two-dimensional spectroscopy of a sunspot. III. Thermal and kinematic structure of the penumbra at 0.5 arcsec resolution Authors: Bellot Rubio, L. R.; Schlichenmaier, R.; Tritschler, A. Bibcode: 2006A&A...453.1117B Altcode: 2006astro.ph..1423B We investigate the thermal and kinematic configuration of a sunspot penumbra using high spectral and spatial resolution intensity profiles of the non-magnetic Fe I 557.6 nm line. The data set was acquired with the 2D solar spectrometer TESOS. The profiles are inverted using a one-component model atmosphere with gradients of the physical quantities. From this inversion we obtain the stratification with depth of temperature, line-of-sight velocity, and microturbulence across the penumbra. Our results suggest that the physical mechanism(s) responsible for the penumbral filaments operate preferentially in the lower photosphere. The spot, located at an heliocentric angle of 23°, exhibits larger continuum intensities in the center-side penumbra as compared with the limb side, which translates into an average temperature difference of 100-150 K at log τ500 = 0. We investigate the nature of the bright ring that appears in the inner penumbra when sunspots are observed in the wing of spectral lines. It is suggested that the bright ring does not reflect a temperature enhancement in the mid photospheric layers. The line-of-sight velocities retrieved from the inversion are used to determine the flow geometry at different heights in the photosphere. Both the flow speed and flow angle increase with optical depth and radial distance. Downflows are detected in the mid and outer penumbra, but only in deep layers (log τ500 ≥ -1.4). We demonstrate that the velocity stratifications retrieved from the inversion are consistent with the idea of penumbral flux tubes channeling the Evershed flow. Finally, we show that larger Evershed flows are associated with brighter continuum intensities in the inner center-side penumbra. Dark structures, however, are also associated with significant Evershed flows. This leads us to suggest that the bright and dark filaments seen at 0.5 arcsec resolution are not individual flow channels, but a collection of them. Our analysis highlights the importance of very high spatial resolution spectroscopic and spectropolarimetric measurements for a better understanding of sunspot penumbrae. Title: Dynamical Properties of Photospheric Flux Tubes at the Footpoints of Hot and Cool Coronal Loops Authors: Nagata, Shin'ichi; Bellot Rubio, Luis R.; Katsukawa, Yukio Bibcode: 2006ApJ...638..539N Altcode: The dynamical properties of photospheric flux tubes at the footpoints of hot (T>2 MK) and cool (T=1-2 MK) coronal loops in active region plages are investigated by analyzing the Stokes V profile parameters of Fe I λ6302. We show that the footpoints of both hot and cool loops are located at the periphery of small magnetic concentrations, such as pores and azimuth centers, having a field strength of 1-1.8 kG and a spatial size of 2"-5". The footpoints of cool loops seem to be associated with more densely packed and higher field strength pores and azimuth centers than those of hot loops. Enhanced Stokes V asymmetries, redshifted zero-crossing velocities, and small magnetic filling factors are found at the footpoints of both types of loops, as compared with outside the footpoints. However, the largest asymmetries and more redshifted zero-crossing velocities are observed at the footpoints of hot loops, where the filling factor is smaller than at the footpoints of cool loops. The differences between the profiles emerging from the footpoints of hot and cool coronal loops suggest that heating of the coronal loops could be related to the dynamical properties of photospheric flux tubes. Title: A polarization model for the German Vacuum Tower Telescope from in situ and laboratory measurements Authors: Beck, C.; Schlichenmaier, R.; Collados, M.; Bellot Rubio, L.; Kentischer, T. Bibcode: 2005A&A...443.1047B Altcode: It is essential to properly calibrate the polarimetric properties of telescopes, if one wants to take advantage of the capabilities of high precision spectro-polarimeters. We have constructed a model for the German Vacuum Tower Telescope (VTT) that describes its time-dependent polarization properties. Since the coelostat of the telescope changes the polarization state of the light by introducing cross talk among different polarization states, such a model is necessary to correct the measurements, in order to retrieve the true polarization as emitted from the Sun. The telescope model is quantified by a time-dependent Mueller matrix that depends on the geometry of the light beam through the telescope, and on material properties: the refractive indices of the coelostat mirrors, and the birefringence of the entrance window to the vacuum tube. These material properties were determined experimentally in-situ by feeding the telescope with known states of polarization (including unpolarized light) and by measuring its response, and from measurements of an aluminum-coated sample in the laboratory. Accuracy can in our case be determined only for the combination of telescope and spectro-polarimeter used; for the instrument POLIS at the VTT, we estimate an accuracy of ±4-5× 10-3 for the cross talk correction coefficients. Title: Multi-line spectroscopy of dark-cored penumbral filaments Authors: Bellot Rubio, L. R.; Langhans, K.; Schlichenmaier, R. Bibcode: 2005A&A...443L...7B Altcode: Dark-cored filaments could be the basic building blocks of sunspot penumbrae. Yet, their nature and physical conditions are unknown. In an attempt to improve this situation, we present the first high-resolution spectra of dark-cored penumbral filaments. Several such filaments were observed near the umbra/penumbra boundary of a sunspot located at heliocentric angles of 5° and 20°. Our data reveal (a) significantly larger Doppler shifts in the dark cores as compared to their lateral brightenings; (b) Doppler shifts that increase with depth in the photosphere, up to 1.5 km s-1; and (c) Doppler shifts that increase with increasing heliocentric distance. The Doppler velocities measured in the dark cores are almost certainly produced by upflows. In addition, dark-cored penumbral filaments exhibit weaker fields than their surroundings (by 100-300 G). These results provide new constraints for models of dark-cored penumbral filaments. Title: Chromospheric and Coronal Signatures of Magnetic Flux Cancellation in a Sunspot's Moat Authors: Beck, C.; Bellot Rubio, L. R.; Nagata, S. Bibcode: 2005ESASP.596E..51B Altcode: 2005ccmf.confE..51B No abstract at ADS Title: Sensitivity of spectral lines to temperature, velocity, and magnetic field Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; del Toro Iniesta, J. C. Bibcode: 2005A&A...439..687C Altcode: We present an analytical and numerical study of the sensitivity of weak solar photospheric lines to temperature, velocity, and magnetic fields. Our investigation is based on the concept of response functions (Landi degl'Innocenti & Landi degl'Innocenti 1977; Ruiz Cobo & del Toro Iniesta 1994). Lines commonly used in solar spectropolarimetry, like Fe I 630.25 nm in the visible and Fe I 1564.85 nm in the infrared, are examined in detail as emerging from reference quiet Sun and sunspot models. We develop a simple phenomenological model capable of describing the response of any given line to these atmospheric parameters. We find that: (a) the sensitivity of the lines to velocity and magnetic fields increases with the sharpness of the intensity and circular polarization profiles; (b) the sensitivity to temperature is determined mainly by the variation of the source function with temperature, which is smaller at longer wavelengths; and (c) lines quoted to be insensitive to temperature, like Fe I 1564.85 nm and Fe I 557.61 nm, exhibit larger changes in equivalent width than lines presumed to have higher sensitivities to T, such as Fe I 630.25 nm. The relations provided by our model are universal and can be used to decide which line is better suited to measuring a given atmospheric parameter. The results of this study are of practical interest for the design of new instruments and for better exploitation of existing ones. Title: Magnetic Flux Cancellation in the Moat of Sunspots: Results from Simultaneous Vector Spectropolarimetry in the Visible and the Infrared Authors: Bellot Rubio, Luis R.; Beck, Christian Bibcode: 2005ApJ...626L.125B Altcode: We analyze multiwavelength observations of the cancellation of a moving magnetic feature and a plage element at the outer edge of the moat of an isolated, round sunspot. The event lasted for some 35 minutes until the smaller flux concentration disappeared completely from the photosphere. The data set consists of high-resolution, full vector spectropolarimetric measurements of four visible lines and two near-infrared lines, along with speckle-reconstructed G-band and Ca II H filtergrams. The observations reveal strong chromospheric emission at the neutral line separating the two magnetic poles; it becomes visible 18 minutes after the cancellation has started and persists for 25 minutes. We have carried out an inversion of the observed Stokes profiles to determine the variation of the vector magnetic field, temperature, and line-of-sight velocity during the cancellation. No significant changes in field strength, field inclination, or temperature are observed in either of the two opposite-polarity patches. The decrease in magnetic flux is primarily due to a decrease in magnetic filling factor, which is accompanied by strong upflows (of at least 1.1 km s-1) in the smaller flux concentration. These results suggest that the cancellation is due to magnetic reconnection in the photosphere. Title: Flow filaments linking bright and dark filaments in a sunspot penumbra Authors: Tritschler, A.; Schlichenmaier, R.; Bellot Rubio, L. R. Bibcode: 2005AGUSMSP11A..08T Altcode: We present two-dimensional spectroscopic sunspot observations of high spatial (≍ 0.5 arcsec) and high spectral resolution (λ/Δλ = 250000). The observations were taken with the Telecentric Solar Spectrometer (TESOS) operated at the German Vacuum Tower Telescope on Tenerife. We examine a single scan taken in the popular non-magnetic neutral iron line at 557.6 nm and concentrate our analysis on the unsettled issue of the relation between the Evershed flow and the intensity structure in a sunspot penumbra. At the end of the 20th century, observers concluded that the highest flow velocities are connected to the dark filaments which harbour more horizontal magnetic fields than the bright filaments. Based on a correlation analysis we find that the correlation between flows and intensity varies from the inner to the outer penumbra, from the center-side to the limb-side penumbra, and depends on the length of the trace used to perform the correlation. The line-of-sight velocity maps reveal that the Evershed flow on the center-side penumbra appears highly organised in narrow flow filaments, while the flows in the red-shifted limb-side penumbra do not show a filamentary fine-structure. A high correlation between flow speed and intensity is only observed over small spatial scales, i.e. considering short traces cutting individual features. The correlation is positive in the inner centre and limb-side penumbra, and tends to be negative in the outer penumbra. Our results imply that the Evershed flow is present in bright and dark filaments. In individual cases we find that flow filaments connect bright and dark filaments supporting the moving tube model for the penumbral fine structure. Title: On the relation between penumbral intensity and flow filaments Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Tritschler, A. Bibcode: 2005AN....326..301S Altcode: Taking advantage of high spatial (≈ 0.5 arcsec) and high spectral (λ/δλ = 250 000) resolution observations obtained with the 2D spectrometer TESOS, we analyze a sunspot located at a heliocentric angle of 23o. We elaborate on the issue of a correlation between dark filaments and the Evershed flow in sunspot penumbrae. Controversies on the existence of such a correlation are resolved: It varies from the inner to the outer penumbra, from the center-side to the limb-side penumbra, and depends on the length of the trace which is used to perform the correlation. The flow map exhibits flow filaments in the center-side penumbra while the red-shifted limb-side penumbra does not show filamentary fine-structure. High correlation coefficients, |C| ≈ 0.9 are only found if small scales, i.e. short traces cutting individual features are considered. C is positive in the inner center and limb-side penumbra, and tends to be negative in the outer penumbra. Our results imply that the Evershed flow is present in bright and dark filaments. In individual cases we find that bright and dark intensities are connected by a flow filament supporting the moving tube model for the penumbral fine structure. Title: Two magnetic components in sunspot penumbrae Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M. Bibcode: 2004A&A...427..319B Altcode: The magnetic and kinematic configuration of sunspot penumbrae is investigated by performing an inversion of the Stokes profiles of three infrared lines at 1565 nm. We use a two-component model atmosphere to describe, at least to first order, the unresolved structure of the penumbra. The observed Stokes profiles are successfully fitted, including those exhibiting abnormal shapes. The results of the inversion are consistent with the idea that the penumbra is formed by almost horizontal flux tubes embedded in a more vertical background magnetic field, as proposed by Solanki & Montavon (\cite{Sol93}). The tubes possess weaker fields than the background except in the very outer penumbra, and carry most of the Evershed flow. We characterize the radial variation of the magnetic field vector and the velocity vector in these atmospheric components. In the middle penumbra and beyond, the magnetic field and the flow in the tubes are seen to return to the solar surface. Everywhere in the penumbra, there is a perfect alignment of the magnetic field vector and the velocity vector in the component describing the penumbral flux tubes. We find that the Evershed flow is supercritical in many places of the outer penumbra, and supersonic at some locations near the outer sunspot boundary. Based on these inversions, we suggest that the azimuthal fluctuations in the average magnetic field inclination and strength inferred from simple one-component models are caused by fluctuations in the filling factor (i.e., the fractional area of the resolution element occupied by flux tubes), not by changes in the intrinsic magnetic and kinematic properties of the background or the flux-tube atmospheres. Also, we confirm the jump of magnetic field azimuth proposed by Müller et al. (\cite{Mul02}) to explain the observed net circular polarization of infrared lines. Title: Asymmetrical appearance of dark-cored filaments in sunspot penumbrae Authors: Sütterlin, P.; Bellot Rubio, L. R.; Schlichenmaier, R. Bibcode: 2004A&A...424.1049S Altcode: Recent sunspot observations at unprecedented resolution have led to the discovery of dark cores in the bright filaments that form the penumbra (\citealt{scharmer02_Nat420}). The discovery paper considered spots at disk center only, so the properties of the dark-cored filaments remain largely unknown. Here we analyze a speckle-reconstructed time series of G-band and blue continuum images of a sunspot acquired with the Dutch Open Telescope. The target was located at an heliocentric angle of 27 deg. We confirm the existence of dark-cored penumbral filaments also in spots outside the disk center, and report on distinct differences between the center and limb-side penumbra. In the inner center-side penumbra, filaments are detected as two narrow bright streaks separated by a central obscuration. These structures move together as a single entity. On the limb side, dark cores are hardly seen. The time series is used to determine the sizes (∼200-250 km), proper motions (∼280 m s-1), and lifetimes (⪉45 min) of typical dark-cored filaments. Title: On the fine structure of sunspot penumbrae. I. A quantitative comparison of two semiempirical models with implications for the Evershed effect Authors: Borrero, J. M.; Solanki, S. K.; Bellot Rubio, L. R.; Lagg, A.; Mathew, S. K. Bibcode: 2004A&A...422.1093B Altcode: Sunspot penumbrae exhibit prominent fine structure. Different interpretations of spectropolarimetric observations suggest different, sometimes contradictory, properties of this fine structure. In this paper we show that the results of inversions of penumbral infrared profiles based on one-component models with gradients of the atmospheric parameters and two-component models without gradients are compatible with each other. Our analysis reconciles the results of previous investigations and provides further support for the picture that sunspot penumbrae are composed of penumbral flux tubes embedded in a magnetic background. The magnetic field in the tubes is more horizontal and weaker than that of the background atmosphere. While the tubes carry most of the Evershed flow, the background is essentially at rest. We notice also that the magnetic field strength in the flux tubes drops much more slowly with radial distance than the background field. This finding is discussed as a possible driver for the Evershed flow. Title: Towards 2D-Spectropolarimetry with TESOS and Adaptive Optics Authors: Tritschler, A.; Bellot Rubio, L. R.; Kentischer, T. J. Bibcode: 2004AAS...204.6902T Altcode: 2004BAAS...36Q.794T The TElecentric SOlar Spectrometer (TESOS) is a 2D tunable filtergraph installed at the Vacuum Tower Telescope of Teide Observatory (Tenerife, Spain). The instrument features a high spectral resolution (λ /Δ λ ∼ 250000 at 633 nm) and is capable of scanning solar lines over a broad wavelength range (430 - 700 nm). Together with the Kiepenheuer-Institute Adaptive Optics System (KAOS), it is able to achieve spatial resolutions of the order of 0.5 arcsec on a regular basis. Here we present the first spectropolarimetric observations of a sunspot and its immediate surroundings using TESOS. We describe the optical setup, characterize the performance of TESOS operated in the polarimetric mode, and investigate the appearance of the sunspot as seen in circular polarized light with an angular resolution better than 0.5 arcsec. Our results demonstrate the feasibility of using TESOS as a polarimeter, and may be of interest for the design of a TESOS-like multiple-etalon magnetograph for the 4-m NSO/Advanced Technology Solar Telescope. Title: Two-dimensional spectroscopy of a sunspot. II. Penumbral line asymmetries Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Tritschler, A. Bibcode: 2004A&A...415..731S Altcode: We present, analyse, and interpret line asymmetries from Fe I 557.6 nm of a sunspot penumbra at a heliocentric angle of 23o with high spatial (0.5 arcsec) and spectral (λ/\triangleλ=250 000) resolution. The data set is described and presented in the first paper of this series \citep{tritschler+etal2003}. Line bisectors are used to quantify the line asymmetries. Our findings are: (1) For averaged limb and center side bisectors the shift increases linearly with the bisector intensity level, but the limb side bisector is more inclined than the center side bisector. (2) Individual bisectors exhibit kinks, such that the bisector at high intensity levels is shifted towards the red for both, limb and center side bisectors. Some of the kinks produce bisector reversals in the outer center side penumbra. The bisector properties and their intriguing differences between center and limb side can be explained if one assumes downflows in deep atmospheric layers (\log τ > -1). This is demonstrated by synthetic bisectors. The differences between the two penumbral sides are due to projection effects of non-horizontal flow channels. Our findings also imply that bisectors reversals are not due to elevated channels, but due to the presence of downflows. Along a specific center side flow filament the bisector shift is found to be largest in the line wing, except for the outer end of the filament, where a kink at high bisector intensities toward the red is found. This is consistent with an upflow at the inner footpoint, a deep lying horizontal flow, and, after a spatial distance of 4 arcsec, with a downflow at the end of the flow filament. Title: Two-dimensional spectroscopy of a sunspot. I. Properties of the penumbral fine structure Authors: Tritschler, A.; Schlichenmaier, R.; Bellot Rubio, L. R.; KAOS Team; Berkefeld, T.; Schelenz, T. Bibcode: 2004A&A...415..717T Altcode: We investigate the properties of the fine structure of a sunspot penumbra based on spectroscopic measurements with high spectral (λ/δλ=250 000) and high spatial (≈0.5 arcsec) resolution. The magnetically insensitive Fe I 557.6 nm line is used to probe the penumbral atmosphere. The data was taken at the German Vacuum Tower Telescope with the 2D-spectrometer TESOS, taking advantage of the recently installed Kiepenheuer Adaptive Optics System (KAOS). The field of view covers a sunspot located at 23o off the disk center and its immediate surroundings. The penumbral structure is studied by means of maps computed for the line-of-sight velocity, the line width, the equivalent width and the line depression. Line-of-sight velocities are derived from the Doppler shifts at different bisector levels. From these maps we infer the flow field geometry and study the azimuthal and radial dependences of the line parameters. Our findings can be summarized as follows: (a) the flow pattern has a conspicuous filamentary structure in the deep photospheric layers and is rather diffuse in the high layers. (b) The flow field slightly spreads and fans out with height. (c) The flow geometry confirms the presence of an upflow component in the inner penumbra and a downflow component in the middle and outer penumbra. (d) We find an enhanced brightness of the mid-penumbra (``bright ring'') in the line wings, but not in the continuum or line core. (e) The azimuthal average of the equivalent width, the line width and the absolute flow velocity increase with radial distance within the penumbra. (f) Small-scale variations of the equivalent width and the line width on the center-side penumbra are co-spatial and correlated with (blue-shifted) fluctuations in the line-of-sight velocity. (g) Inner limb-side penumbral grains are associated with blue-shifts of v≤-400 m s-1, indicating upflows. (h) One umbral dot in our sample is associated with a blue-shift of v=-200 m s-1. Title: Ludwig Biermann Award Lecture: Sunspots as seen in Polarized Light (With 14 Figures) Authors: Bellot Rubio, Luis R. Bibcode: 2004RvMA...17...21B Altcode: No abstract at ADS Title: Velocity field in the intergranular atmosphere Authors: Kučera, A.; Koza, J.; Bellot Rubio, L. R.; Hanslmeier, A.; Rybák, J.; Wöhl, H. Bibcode: 2004HvaOB..28...19K Altcode: The line-of-sight velocity ľand macroturbulent velocity are studied in the centre of the intergranular space in the solar photosphere. An inversion method is applied to a 4-min time sequence of Stokes I spectra of the 5, 6 and 7 lines observed with high spatial and temporal resolutions at solar disk centre. The results are presented in the form of the functional dependence of ľ(logτ5,t) and (t) on the continuum optical depth τ5 at 500 nm and time t. A ľof several hundreds of meters per second was found in the upper photosphere (logτ5≤-1.5), where the plasma flows away from the observer. On the contrary, upflows directed toward the observer were found in deeper layers (logτ5>-1.5). The typical value of in the centre of the intergranular space is found to be ∼1.7 kms, which is about 0.5 kms greater than in the adjacent granule. Title: Thermal Kinematic Structure of a Sunspot at 0.5 arcsec Resolution Authors: Bellot Rubio, L. R.; Schlichenmaier, R.; Tritschler, A. Bibcode: 2003ANS...324..104B Altcode: 2003ANS...324..P10B No abstract at ADS Title: Penumbral Line Asymmetries of Fe I 557.6 nm: Implications on the Flow Geometry of a Sunspot Penumbra Authors: Schlichenmaier, P.; Bellot Rubio, L.; Tritschler, A. Bibcode: 2003ANS...324..105S Altcode: 2003ANS...324..P11S No abstract at ADS Title: Understanding internetwork magnetic fields as determined from visible and infrared spectral lines Authors: Bellot Rubio, L. R.; Collados, M. Bibcode: 2003A&A...406..357B Altcode: We present numerical experiments aimed at understanding why near-infrared observations systematically deliver weak magnetic fields in the internetwork, whereas analyses based on visible lines indicate that kG fields are ubiquitous. Synthetic noisy Stokes V profiles of the iron lines at 6302 Å and 1.565 mu m have been produced under varying conditions in an effort to simulate polarized spectra coming from the internetwork. An inversion technique has been applied to the profiles, as it is usually done with real observations, in order to derive the distribution of magnetic fields in the simulated region. Our results show that infrared lines yield distributions which are very similar to those used as input for the simulation, while visible lines are to a large extent affected by noise. Analyses based on the Fe I lines at 6302 Å may lead to an overabundance of kG fields if the signal-to-noise ratio in Stokes V is poorer than about 10. A particular example is shown where strong fields are retrieved in nearly 30% of the pixels of a simulated internetwork region in which only fields of 200 G exist. Title: Accurate atomic parameters for near-infrared spectral lines Authors: Borrero, J. M.; Bellot Rubio, L. R.; Barklem, P. S.; del Toro Iniesta, J. C. Bibcode: 2003A&A...404..749B Altcode: A realistic two-component model of the quiet solar photosphere is used to fit the intensity spectrum of the Sun in the wavelength range 0.98-1.57 mu m. Our approach differs from earlier attempts in many respects: proper account of convective inhomogeneities is made, accurate collisional broadening parameters from quantum mechanical computations are used, and the effects of possible blends in the local continuum are corrected empirically. This allows us to derive oscillator strengths and central wavelengths for virtually any unblended line of the solar spectrum. The accuracy of the inferred atomic parameters, about 0.06 dex for oscillator strengths and 5 mÅ at 1 mu m for central wavelengths, is similar to that of the best laboratory measurements. We apply our method to 83 near-infrared lines belonging to 6 different atomic species. The availability of accurate oscillator strengths and central wavelengths for lines of different species is essential for the interpretation of high resolution spectroscopic observations. The method is especially useful in the infrared, a wavelength domain where laboratory measurements are scarce. Title: Magnetoacoustic Waves in Sunspots Authors: Khomenko, E. V.; Collados, M.; Bellot Rubio, L. R. Bibcode: 2003ApJ...588..606K Altcode: Observed variations of the magnetic field strength in sunspot umbrae consist of intrinsic oscillations and ``false'' oscillations due to time-dependent opacity effects. Here we present an approach intended for the separation of these components. We develop a mathematical formalism based on the analytical solution of the MHD equations including gravity, inclination of the magnetic field, and effects of nonadiabaticity. The theoretical results are compared with observations in the near-infrared at 1.56 μm by Bellot Rubio and coworkers using the Tenerife Infrared Polarimeter. It is shown that part of the detected field strength variations can be intrinsic magnetic field oscillations caused by magnetoacoustic waves. Title: Field-aligned Evershed flows in the photosphere of a sunspot penumbra Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M.; Schlichenmaier, R. Bibcode: 2003A&A...403L..47B Altcode: We determine the inclinations of the vector magnetic field and flow velocity in a sunspot penumbra by interpreting full Stokes profiles of three infrared lines observed with the Tenerife Infrared Polarimeter. It is shown that analyses based on one-component atmospheres deliver flow velocities which are more horizontal than the average magnetic field by up to 10 deg. This apparent violation of the concept of frozen-in magnetic fields is solved as soon as two magnetic atmospheres are allowed to coexist in the resolution element. The magnetic field and velocity in the atmospheric component carrying the Evershed flow are found to be aligned to within +/- 2 deg all the way from the inner to the outer penumbra. This is the first observational confirmation of magnetic fields being frozen into the plasma in sunspots. Our results indicate that sunspot penumbrae can be understood in terms of inclined flux tubes embedded in a more vertical background field. The flux tubes carry most of the Evershed flows and return to the solar surface in the middle penumbra and beyond. The background atmosphere is essentially at rest in the inner penumbra, and harbors small flows in the outer penumbra. Title: The structure of the penumbra Authors: Balthasar, H.; Bellot Rubio, L.; Collados, M. Bibcode: 2003AN....324..390B Altcode: No abstract at ADS Title: Fluctuations in the Activity Curve of the 2002 Leonids Authors: Ruiz Herrera, Lola; Bellot Rubio, Luis R.; Serra-Ricart, Miquel Bibcode: 2003IAUJD..19E..55R Altcode: We present observations of the 2002 Leonid meteor shower taken with four intensified video cameras from Teide Observatory (Tenerife Spain) on November 19 2002. The cameras fitted with f/1.4 85 mm objectives were aimed at 6 deg above the horizon in order to monitor the largest atmospheric volume possible. The most sensitive camera detected 1300 meteors between 0312 and 0456 UT i.e. the period covering the European Leonid storm of 2002. The activity curve constructed from these data peaks at 0401 UT about 9 minutes earlier than indicated by the visual observations analyzed by the International Meteor Organization. Our results thus favor the model of Lyytinen and van Flandern who predicted the first maximum at 0402 UT. We find statistically significant oscillations in the activity curve. A Fourier analysis delivers a period of about 7 minutes. These observations confirm the discovery of Singer et al. (2000) that density fluctuations exist in the Leonid dust trails at spatial scales of 10000-30000 km. The oscillations we observe are very similar to those detected by Singer et al. the only difference being that the dust trail is 132 years older. Title: The Fine Structure of the Penumbra: from Observations to Realistic Physical Models Authors: Bellot Rubio, L. R. Bibcode: 2003ASPC..307..301B Altcode: No abstract at ADS Title: Evolution of temperature in granule and intergranular space Authors: Koza, J.; Bellot Rubio, L. R.; Kučera, A.; Hanslmeier, A.; Rybák, J.; Wöhl, H. Bibcode: 2003AN....324..349K Altcode: The temporal evolution of temperature in a dissolving granule and in an adjacent intergranular space is presented. The semi-empirical evolutionary models have been calculated using an inversion method applied to 4-min time series of Stokes I spectral line profiles. The models are presented in the form of the functional dependence of temperature T(log tau_5 ,t) on optical depth tau_5 at 500 nm and time t. The observed disappearance of the granule is accompanied with overall cooling of the granular photosphere. Temperature changes greater than 100 K have been found in deeper (log tau_5 >=0) and upper layers (log tau_5 <=-2) whereas the intermediate layers are thermally stable. The intergranular space, which is 2 arcsec off the granule, keeps the temperature structure of the layers from log tau_5 =0.5 to log tau_5 =-2 without global evolutionary changes except short-term and spatially confined heating. Finally, the significant temperature changes in the upper layers (log tau_5 <=-2.5) observed during the time interval of 4 min are found to be typical for the granular and intergranular photosphere. Title: 2D Solar Spectroscopy with a Triple Fabry-Perot Filtergraph Authors: Bellot Rubio, Luis R.; Tritschler, Alexandra; Schlichenmaier, Rolf Bibcode: 2003IAUJD..20E..27B Altcode: TESOS is a tunable narrow-band filter based on three Fabry-Perot etalons operated in a telecentric configuration. Installed at the German Vacuum Tower Telescope (VTT) of Teide Observatory (Spain) it is used regularly for 2D spectroscopy of the solar atmosphere. Its spectral resolution of 250000 is similar to that of grating spectrographs. In the high resolution mode the field of view of TESOS is 42 arcsec in diameter and the image scale is 0.09 arcsec/pixel. Due to the high quantum efficiency of the detector above 500 nm exposure times of a few tens of msec can be used. As a result TESOS is able to measure the intensity profiles of a given spectral line across the field of view in less than 40 sec (assuming 100 wavelength positions). Recently TESOS has been combined with KAOS the adaptive optics system of the VTT to improve the spatial resolution of the observations up to 0.4 arcsec. Here we present the first science results of TESOS+KAOS based on observations of a sunspot penumbra. Maps of various spectroscopic parameters are computed and the line asymmetries induced by the Evershed flows are investigated by means of a bisector analysis of the FeI line at 557.6 nm. Title: Two-Component Modeling of Convective Motions in the Solar Photosphere and Determination of Atomic Parameters Authors: Borrero, J. M.; Bellot Rubio, L. R. Bibcode: 2003IAUS..210P..C9B Altcode: No abstract at ADS Title: Accurate Atomic Parameters from the Solar Spectrum Authors: Bellot Rubio, Luis Ramon; Borrero, Juan Manuel; Barklem, Paul; del Toro Iniesta, Jose Carlos Bibcode: 2003IAUJD..20E..16B Altcode: A realistic two-component model of the quiet solar photosphere is used to fit the full shape of the intensity profiles of unblended lines in the solar spectrum. Our approach differs from previous attempts in many respects: proper account of granulation inhomogeneities is made accurate collisional broadening parameters from quantum mechanical computations are used and possible absorptions in the local continuum due to blends are corrected empirically. This allows us to derive oscillator strengths and central wavelengths for any clean line with an accuracy comparable with that of the best laboratory measurements. The availability of very precise atomic parameters for lines of different species is essential for the interpretation of high resolution spectroscopic observations. Abundance determinations and investigations of granular motions in stellar atmospheres are among the applications that would benefit from such accurate atomic data. As an example we determine the oscillator strengths and central wavelengths of 100 unblended lines in the near-infrared (0.99-1.56 microns) a wavelength domain where laboratory measurements are particularly scarce. Title: Modeling the Fine Structure of a Sunspot Penumbra through the Inversion of Stokes Profiles Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Frutiger, C.; Collados, M.; Bellot Rubio, L. R. Bibcode: 2003ASPC..286..235B Altcode: 2003ctmf.conf..235B No abstract at ADS Title: Line-of-sight velocity in a semiempirical model of a disappearing granule Authors: Koza, J.; Bellot Rubio, L. R.; Kučera, A.; Hanslmeier, A.; Rybák, J.; Wöhl, H. Bibcode: 2002ESASP.506..443K Altcode: 2002svco.conf..443K; 2002ESPM...10..443K The behaviour of the line-of-sight velocity in the centre of a disappearing granule is analyzed using an inversion method applied to a time-series of spectra containing the Fe I 522.5 nm, 557.6 nm and 557.7 nm lines. The temporal evolution of the line-of-sight velocity vLOS is presented in the form of the functional dependence of vLOS(logτ5, t) on the optical depth τ5 at 500 nm and time t. An oscillatory behaviour is found in the velocity stratification with nearly constant phase through the photosphere. The amplitude of variations increases from logτ5 = -0.3 to logτ5 = -2.5 reaching a maximum of ~1.2 km s-1. A zero velocity layer is detected in every instantaneous model of the velocity stratification. The results suggest, that the zero velocity may occur in a considerable range of the optical depths from logτ5 ~ -2 to logτ5 ~ -3.5. Title: Observations of the 2001 Leonid meteor storm from northern Australia with the Teide imaging meteor system Authors: Bellot Rubio, L. R.; Martínez-Delgado, D.; López-Sánchez, A. R.; Ruiz Herrera, L.; Serra-Ricart, M.; Rodríguez Gil, P.; Oscoz, A. Bibcode: 2002ESASP.500..221B Altcode: 2002acm..conf..221B We describe the Teide Imaging MEteor System (TIMES), a fully automatic experiment consisting of two fixed image-intensified video cameras which are operated from Teide Observatory (Tenerife, Spain). A second station equipped with an identical system is located in Maspalomas (Gran Canaria, Spain). TIMES has been designed to work with the MetRec detection software for efficient video observations of meteors with a minimum of human interaction. The system will be used to monitor the shower and sporadic meteor activity for at least three years. In addition, double-station observations will be made on every clear night for orbital calculations and light curve analyses. We also present preliminary results on the 2001 Leonid storm observed by TIMES during the scientific mission organized by the Instituto de Astrofisica de Canarias (Spain). Double-station observations were carried out in Central Australia from 16 to 18 November 2001. In this contribution we concentrate on the night of maximum activity and construct the activity curve and magnitude distribution of the Leonid meteors detected by our video system in the interval from 18 to 19 UT, 18 November 2001. Title: Spectropolarimetry and magnetography from the ground Authors: Bellot Rubio, Luis R. Bibcode: 2002ESASP.505....3B Altcode: 2002solm.conf....3B; 2002IAUCo.188....3B Most of what we know today about solar magnetic fields has been learned through the measurement and interpretation of the polarization of spectral lines. In this contribution, I review the different instruments used for solar polarimetry, the techniques we apply to extract information from the measurements, and the advantages and disadvantages of polarization studies from the ground. I will describe some recent results obtained from high precision, full Stokes spectropolarimetry in order to illustrate the potential of ground-based observations. In particular, I will discuss advances in the understanding of the structure of sunspot penumbrae, a topic of active research these days. Finally, expected developments and applications of solar polarimetry from the ground will be briefly mentioned. Title: Observation and Interpretation of Leonid Impact Flashes on the Moon in 2001 Authors: Ortiz, J. L.; Quesada, J. A.; Aceituno, J.; Aceituno, F. J.; Bellot Rubio, L. R. Bibcode: 2002ApJ...576..567O Altcode: We present observations of lunar Leonid impact flashes recorded in 2001 November from Spain. Four impact flashes were detected on November 18. Another flash was also recorded on the same night, which appears to be impact related, and two more on that night are possibly, but not unambiguously, of impact nature. On November 19 another flash was detected, which very likely resulted from an impact. The brightest impact flash reached a peak brightness of 5.2+/-0.3 mag in V; it had a very dim precursor just 0.02 s prior to peak brightness and had a very long lasting afterglow that remained visible for more than 600 ms with oscillations in brightness; this unique and unexpected behavior challenges current models of impact flashes. The other flashes did not show such a behavior and remained visible for a few tens of milliseconds. Adopting the luminous efficiency derived for the 1999 lunar Leonids (2×10-3), our observations can be used to estimate meteoroid fluxes. The observations are compatible with a flux of 0.1 meteoroids of mass larger than 2×10-8 kg km-2 hr-1 on November 18 at 18:15 UT, provided that a mass index of 1.69 is used. Both the flux and the mass index agree with meteor observations carried out in 2001 from several locations on Earth. Title: Iron abundance in the solar photosphere. Application of a two-component model atmosphere Authors: Bellot Rubio, L. R.; Borrero, J. M. Bibcode: 2002A&A...391..331B Altcode: A realistic two-component model of the quiet Sun is used to determine the solar abundance of iron from the inversion of a number of Fe I and Fe II spectral lines for which accurate atomic parameters (oscillator strengths, central wavelengths, and collisional broadening cross sections) exist. From 33 Fe I lines we infer an abundance of A_Fe = 7.43 +/- 0.06, whereas we estimate A_Fe = 7.45 +/- 0.08 from 10 Fe II lines. These values are in excellent agreement with the results of analyses based on realistic 3D hydrodynamical simulations of the solar granulation, and imply a low photospheric iron abundance. We investigate the effects of convective motions and granular temperatures and conclude that both are important for reliable abundance determinations. For Fe I lines, the effects of convective motions can be simulated by using a microturbulent velocity of about 1 km s-1, whereas it is possible to account for temperature inhomogeneities by adopting an average temperature stratification which is cooler than the Holweger & Müller model in the upper layers. Title: Modeling the photometric and dynamical behavior of Super-Schmidt meteors in the Earth's atmosphere Authors: Bellot Rubio, L. R.; Martínez González, M. J.; Ruiz Herrera, L.; Licandro, J.; Martínez-Delgado, D.; Rodríguez-Gil, P.; Serra-Ricart, M. Bibcode: 2002A&A...389..680B Altcode: Faint meteors observed with Super-Schmidt cameras are re-examined in order to assess whether their dynamical and photometric behavior can be described by means of the single body theory. Velocities, decelerations and magnitudes are fitted simultaneously to synthetic curves resulting from integration of the appropriate set of differential equations. The parameters determined by this procedure are the ablation coefficient, the shape-density coefficient and the preatmospheric mass of each individual meteoroid. It turns out that 73% of the meteors analyzed here (with magnitudes in the range from +2.5 to -5) are reasonably well described by this theory, suggesting that they did not undergo significant fragmentation during their atmospheric flight. Nevertheless, we identify some systematic differences between observed and theoretical light curves of meteors for which the fit is good. Meteoroid bulk densities are estimated from the retrieved shape-density coefficients. The distributions of individual values are broad, indicating that objects of different densities coexist within the same meteoroid population. The average density is found to be 2400, 1400, and 400 kg m-3 for A-type, B-type and C-type meteoroids, respectively. These results do not confirm the large values determined from quasicontinuous fragmentation models. Title: A two-component model of the solar photosphere from the inversion of spectral lines Authors: Borrero, J. M.; Bellot Rubio, L. R. Bibcode: 2002A&A...385.1056B Altcode: A two-component model of the solar photosphere is obtained from the inversion of the intensity profiles of 22 Fe I spectral lines for which very accurate atomic data (oscillator strengths, central wavelengths, and collisional broadening parameters) exist. The model is meant to describe the effects of convective motions in the solar photosphere. It has been subject to various tests to confront its predictions with observations of the solar spectrum. The model is able to reproduce the observed line shifts and equivalent widths of about 800 spectral lines of iron and other species. It is also capable of matching the observed center-to-limb variation of the continuum intensity with unprecedented accuracy. This allows us to determine line-transition parameters from the fitting of the solar spectrum. Exploratory calculations demonstrate that the model can be used to derive transition probabilities and central wavelengths of Fe I and Fe II lines, as well as other elements, within the uncertainties of the best laboratory measurements. Title: Modeling the dynamical and photometric behavior of faint meteors in the Earth's atmosphere Authors: Bellot Rubio, Luis R.; Martínez González, María Jesús; Ruiz Herrera, Lola; Licandro, Javier; Martínez Delgado, David; Rodríguez Gil, Pablo; Serra-Ricart, Miquel Bibcode: 2001ESASP.495..525B Altcode: 2001mete.conf..525B Faint meteors observed with Super-Schmidt cameras are re-examined in order to assess whether their dynamical and photometric behavior can be described by means of the single body theory. Velocities, decelerations and magnitudes are fitted simultaneously to synthetic curves resulting from integration of the appropriate set of differential equations. The parameters determined by this procedure are the ablation coefficient, the shape-density coefficient and the preatmospheric mass of the meteoroids. It turns out that 64% of the meteors analyzed here are reasonably well described by this theory, suggesting that they did not undergo significant fragmentation during their atmospheric flight. We identify some systematic differences between observed and theoretical light curves of meteors for which the fit is good. From the retrieved shape-density coefficients we derive meteoroid bulk densities. The average density turns out to be 1.0 g cm-3, with individual values ranging from 0.2 g cm-3 to 1.4 g cm-3. This work represent a first step toward the analysis of low-light level video observations of very small meteoroids. Title: Observation of Convective Collapse and Upward-moving Shocks in the Quiet Sun Authors: Bellot Rubio, Luis R.; Rodríguez Hidalgo, Inés; Collados, Manuel; Khomenko, Elena; Ruiz Cobo, Basilio Bibcode: 2001ApJ...560.1010B Altcode: We present spectropolarimetric evidence of convective collapse and destruction of magnetic flux by upward-moving fronts in the quiet Sun. The observational material consists of time series of the full Stokes vector of two infrared spectral lines emerging from regions associated with Ca II K network points. The amplitude of the circular polarization profiles of a particular spatial point is seen to increase while the profiles are redshifted. It then decreases during a much shorter phase characterized by large blueshifts. Inspection of the data indicates that the blueshift occurs because of the sudden appearance of a new, strongly displaced Stokes V profile of the same polarity. The amplification of the magnetic signal takes place in a time interval of about 13 minutes, while blueshifts and the concomitant decreasing Stokes V amplitudes last for only 2 minutes. An inversion code based on the thin flux-tube scenario has been applied to the data in order to derive the thermal, magnetic, and dynamic structures of the atmosphere. According to our results, the field strength undergoes a moderate increase from 400 to 600 G at z=0 km during the phase in which redshifts are present. The observed redshifts are produced by internal downflows of up to 6 km s-1 at z=0 km. After ~13 minutes, the material falling down inside the tube appears to bounce off in the deeper layers, originating an upward-propagating front whose manifestation on the Stokes V profiles is a large blueshift. The front moves with a speed of 2.3 km s-1 and has a downflow-to-upflow velocity difference of about 7 km s-1 initially and some 4 km s-1 after 2 minutes. It strongly weakens the magnetic field strength and may be responsible for the complete destruction of the magnetic feature. The observed behavior is in general agreement with theoretical predictions of flux expulsion, convective collapse, and development of shocks within magnetic flux tubes. Title: Cold, Supersonic Evershed Downflows in a Sunspot Authors: del Toro Iniesta, Jose Carlos; Bellot Rubio, Luis R.; Collados, Manuel Bibcode: 2001ApJ...549L.139D Altcode: We report here on the discovery of supersonic Evershed downflows in the penumbra of a sunspot. These flows are shown to occur along spatially unresolved, very cold magnetic flux tubes whose downflowing footpoints are found from the middle penumbra outward. Evershed flows along magnetic field lines returning to the solar surface were discovered by Westendorp Plaza and coworkers, but only in the outer parts of the penumbra and beyond its visible boundary; on the other hand, no supersonic flows of any type have ever been reported in the photosphere of sunspots, except for the very different case of the delta spot analyzed by Martínez Pillet and coworkers. We present unequivocal evidence of such supersonic motions, already predicted theoretically by the siphon-flow model, from the interpretation of infrared spectropolarimetric observations of a sunspot with unprecedented spatial resolution. Title: Spectropolarimetric Signatures of Convective Collapse Authors: Rodrígues Hidalgo, I.; Bellot Rubio, L. R.; Collados, M.; Ruiz Cobo, B. Bibcode: 2001ASPC..236..415R Altcode: 2001aspt.conf..415R No abstract at ADS Title: The IAC Stokes Profile Inversion Codes based on Response Functions (CD-ROM Directory: contribs/bellot) Authors: Bellot Rubio, L. R. Bibcode: 2001ASPC..223..569B Altcode: 2001csss...11..569B No abstract at ADS Title: Lagrangian and Eulerian Stratifications of Acoustic Oscillations through the Solar Photosphere Authors: Rodríguez Hidalgo, Inés; Ruiz Cobo, Basilio; Collados, Manuel; Bellot Rubio, Luis R. Bibcode: 2001ApJ...547..491R Altcode: We evaluate the stratification of acoustic oscillations in the solar photosphere in both the Lagrangian (comoving) frame of reference and the Eulerian (inertial) frame of reference, from a temporal sequence of model atmospheres in an optical depth scale obtained after a quasi-non-LTE inversion of the radiative transfer equation applied to spectral observations of the K I 7699 Å line. Our results suggest that, to first order, the photosphere moves up and down as a whole with amplitudes ranging from ~8 km in deep layers (around 0 km) to ~19 km in the upper layers (around 640 km). In Lagrangian coordinates, we observe numerous short-lived, local temperature and velocity amplitude enhancements in medium-high layers, together with asymmetric waveforms in the oscillation of these two physical quantities. The Lagrangian temperature oscillation clearly shows two nodes associated with sharp phase jumps of about 180°, whereas the velocity amplitude shows the well-known increase with geometrical height, at nearly constant phase. In Eulerian coordinates, the perturbations are dominated by the coherent oscillation of the entire photosphere. Title: Photospheric acoustic oscillations in a Langrangian reference system Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados Vera, M.; Bellot Rubio, L. R. Bibcode: 2001ESASP.464..239R Altcode: 2001soho...10..239R The stratification of acoustic oscillations through the solar photosphere in Lagrangian (comoving) coordinates has been evaluated from a quasi-NLTE inversion of the radiative transfer equation (RTE) applied to a temporal sequence of K I 7699 Å line spectra. The stratifications of amplitude and phase of the temperature and line-of-sight (LOS) velocity Lagrangian oscillations have been evaluated. Our results suggest that, to first order, the photosphere moves up and down as a whole with amplitudes ranging from ~8 km in deep layers (around 0 km) to ~19 km in the upper layers (around 640 km). Numerous short-lived, local temperature and velocity amplitude enhancements in medium-high layers are observed, together with an asymmetric waveform in the oscillation of these two physical quantities. Two nodes are clearly seen in the Lagrangian temperature oscillation run, which are associated with sharp phase jumps of about 180°. The velocity amplitude shows the well known increase with geometrical height, keeping practically in phase. Title: Luminous Efficiency in Hypervelocity Impacts from the 1999 Lunar Leonids Authors: Bellot Rubio, L. R.; Ortiz, J. L.; Sada, P. V. Bibcode: 2000ApJ...542L..65B Altcode: An analysis of the optical flashes produced by Leonid meteoroids impacting the Moon in 1999 November is carried out in order to estimate the fraction of kinetic energy converted into radiation, the so-called luminous efficiency η. It is shown that the observational data are consistent with luminous efficiencies of 2×10-3 in the wavelength range of 400-900 nm with an uncertainty of about 1 order of magnitude. This experimental value of η is significantly larger than previous estimates for meteoroids of asteroidal composition based on numerical calculations and scaling laws from laboratory collisions. According to our results, the luminous efficiency might vary with mass, i.e., the smaller impactors converting less kinetic energy into light and vice versa. A comparison with recent numerical simulations for meteoroids of cometary composition is also carried out. Title: Optical detection of meteoroidal impacts on the Moon Authors: Ortiz, J. L.; Sada, P. V.; Bellot Rubio, L. R.; Aceituno, F. J.; Aceituno, J.; Gutiérrez, P. J.; Thiele, U. Bibcode: 2000Natur.405..921O Altcode: Impacts of meteoroids on the Moon should cause detectable optical flashes, but the population of objects that are big enough is very low, and hitherto no unambiguous impact flashes have been recorded. The flux of meteoroids associated with the Leonid meteor shower of 18 November 1999 was predicted to produce observable flashes on the night side of the Moon. Here we report the unambiguous detection of five such impact flashes, three of which were seen simultaneously by other observers. We also observed a possible impact flash on 16 July 1999. All of the flashes were of very brief duration (<0.02s), as expected for high-speed impacts. Title: Structure of Plage Flux Tubes from the Inversion of Stokes Spectra. I. Spatially Averaged Stokes I and V Profiles Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 2000ApJ...535..489B Altcode: We present results of the inversion of spatially averaged Stokes I and V profiles emerging from plage regions near disk center. The observations analyzed in this work were recorded with the Advanced Stokes Polarimeter. All atmospheric quantities determining the radiative transfer in the thin flux-tube approximation are inferred self-consistently with the help of the inversion code described by Bellot Rubio et al. With regard to thermodynamics, the retrieved model atmospheres are found to behave as expected on theoretical grounds. For the first time, velocities inside and outside the tubes have been derived empirically. The magnetic atmospheres resulting from the inversion are characterized by the absence of significant motions in high layers but show strong velocity gradients in deeper layers. These gradients turn out to be essential for reproducing the whole shape of the observed profiles and, in particular, the asymmetries and the extended red tail of Stokes V. Our scenario predicts that the Stokes V zero-crossing wavelengths of Fe I and Fe II lines are redshifted by small but nonnegligible amounts, which is indeed confirmed by observations made with the Fourier Transform Spectrometer. According to recent numerical simulations, the internal downflows derived from the inversion could be produced by the strong shear that takes place in the intermediate layer between the magnetized interior and the ambient medium. Another possible origin is magnetic flux undergoing convective collapse within the resolution element. Title: Oscillations in the Photosphere of a Sunspot Umbra from the Inversion of Infrared Stokes Profiles Authors: Bellot Rubio, L. R.; Collados, M.; Ruiz Cobo, B.; Rodríguez Hidalgo, I. Bibcode: 2000ApJ...534..989B Altcode: We report on the detection of magnetic field strength and velocity oscillations in the photosphere of a sunspot umbra. Our analysis is based on the inversion of the full Stokes vector of three Fe I lines at 15650 Å, from which the stratification with optical depth of the different atmospheric parameters has been derived. This allows us to estimate the amplitude of the oscillations and the phase lag between the fluctuations in the line-of-sight velocity and field strength. Our results suggest that the inferred magnetic field oscillations are caused by opacity fluctuations that move upward and downward the region where the spectral lines are sensitive to magnetic fields. Title: Inversion of Stokes Profiles from Solar Magnetic Elements Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 2000ApJ...535..475B Altcode: We describe a new LTE inversion code for the analysis of Stokes profiles emerging from unresolved magnetic elements. It has been specifically designed to obtain the thermal, dynamic, and magnetic properties of these structures in a self-consistent manner by fitting the whole shape of the observed spectra. The inversion code is based on a previous scheme by Ruiz Cobo & del Toro Iniesta and implements the thin flux-tube model as a reasonable description of reality. All physical parameters considered relevant for the problem (including velocity fields) are retrieved by means of a Marquardt nonlinear least-squares algorithm. We present the results of extensive tests aimed at characterizing the behavior of the code so as to understand its limitations for the analysis of real observations. The code is found to produce accurate results even with only two spectral lines and noisy Stokes I and V profiles. A detailed error treatment, in which the covariances between parameters are explicitly included, is also carried out in order to investigate the uniqueness and reliability of the inferred model atmospheres. Title: Observation and Interpretation of Meteoroid Impact Flashes on the Moon Authors: Bellot Rubio, Luis R.; Ortiz, Jose L.; Sada, Pedro V. Bibcode: 2000lsr..book..575B Altcode: No abstract at ADS Title: Bulletin 15 of the International Leonid Watch: First Global Analysis of the 1999 Leonid Storm Authors: Arlt, R.; Bellot Rubio, L.; Brown, P.; Gyssens, M. Bibcode: 1999JIMO...27..286A Altcode: An overall activity profile of the 1999 Leonid meteor shower is presented based on the observations of 434 observers who reported 277172 Leonids in 10806 observing periods. A storm of Leonid activity was observed from western Asian, European, and African locations at a solar longitude of lambda=235.285+-0.001, corresponding to November 18, 1999, 2h02m+-2m UT with a peak equivalent ZHR of 3700+-100 based on 2.8-minute intervals. Solar longitudes refer to equinox J2000.0. The flux density of particles causing meteors brighter than magnitude +6.5 is 1.4+-0.3 particles per square kilometer and per hour. This corresponds to a number density of 5400+-1200 particles per 10^9 cubic kilometer. Additional maxima were found in the ZHR peak profile; one of them at lambda=235.272 or 1h43m UT can be associated with the cometary ejecta from the 1932 perihelion passage. The time of this peak as well as the main peak, which is caused by particles from the 1899 passage, are reproduced by particle simulations. A clear second activity outburst occurred at lambda=235.87+-0.04 (November 18, 1999, 16h+-1h UT) with a maximum ZHR of 180+-20. The Leonid storm component is found to exhibit an unusual magnitude distribution with a lack of both very bright and very faint meteors. Title: Formation and Destruction of a Weak Magnetic Feature in the Solar Photosphere Authors: Khomenko, E.; Collados, M.; Bellot Rubio, L. R.; Rodríguez Hidalgo, I.; Ruiz Cobo, B. Bibcode: 1999ESASP.448..307K Altcode: 1999mfsp.conf..307K; 1999ESPM....9..307K No abstract at ADS Title: Video Observations Of Leonids 1999 Authors: Molau, Sirko; Rendtel, Jürgen; Bellot-Rubio, Luis Ramon Bibcode: 1999EM&P...87....1M Altcode: We analyse data obtained by different ground-based video camera systems during the 1999 Leonid meteor storm. We observe similar activity profiles at nearby observing sites, but significant differences over distances in the order of 4,000 km. The main peak occured at 02:03 UT (λ=235.286, J2000, corrected for the time of the topocentric stream encounter). At the Iberian peninsula quasi-periodic activity fluctuations with a period of about 7 min were recorded. The camera in Jordan detected a broad plateau of activity at 01:39-01:53 UT, but no periodic variations. The Leonid brightness distribution derived from all cameras shows a lack of faint meteors with a turning point close to +3m, which corresponds to meteoroids of approximately 10-3 g. We find a pin-point radiant at αalpha=153.65 ±0.1, δ=21.80 ±0. (λ=235.290). The radiant positionis identical before and after the storm, and also during the storm no driftis observed. Title: TIP: The Tenerife Infrared Polarimeter Authors: Martínez Pillet, V.; Collados, M.; Bellot Rubio, L. R.; Rodríiguez Hidalgo, I.; Ruiz Cobo, B.; Soltau, D. Bibcode: 1999AGAb...15...89M Altcode: 1999AGM....15..P05M The aim of the IAC Tenerife Infrared Polarimeter is to obtain quantitative measurements of the polarization state of the solar radiation collected in near-infrared wavelengths by the Gregory Coudé Telescope and the Vacuum Tower Telescope of the Observatorio del Teide (Spain). In this contribution we describe the analyzer, instrumental calibration, and detector subsystems of TIP, and give details concerning the specifications of the instrument. Title: Structure of a Facular Region From the Inversion of High Spatial and Temporal Resolution Stokes Spectra Authors: Bellot Rubio, L.; Ruiz Cobo, B.; Collados, M. Bibcode: 1999ASPC..183...61B Altcode: 1999hrsp.conf...61B No abstract at ADS Title: An LTE code for the inversion of Stokes spectra from solar magnetic elements Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1999ASSL..243..271B Altcode: 1999sopo.conf..271B No abstract at ADS Title: TIP (Tenerife Infrared Polarimeter): a near IR full Stokes Polarimeter for the German Solar Telescopes at Observatorio del Teide Authors: Collados, M.; Rodríguez Hidalgo, I.; Bellot Rubio, L.; Ruiz Cobo, B.; Soltau, D. Bibcode: 1999AGAb...15Q..11C Altcode: 1999AGM....15..A13C In this contribution, the main characteristics of the=20 Tenerife Infrared Polarimeter (TIP), recently built at the Instituto de Astrofísica de Canarias, to be operated at the German Solar Telescopes (GCT and VTT) of the Observatorio del Teide (Tenerife) are presented. Especial emphasis is put on the modulation scheme, polarisation efficiencies, signal-to-noise ratio, spatial and spectral resolution, and instrumental polarisation cross-talk. Some examples of data recently obtained are presented, which give an idea of the performance and capabilities of this instrument. Title: The Hermitian solution of the radiative transfer equation for non-LTE problems Authors: Ruiz Cobo, B.; Bellot Rubio, L. R.; Collados, M. Bibcode: 1999ASSL..243..231R Altcode: 1999sopo.conf..231R No abstract at ADS Title: Probing downflows in solar magnetic elements: the Fe II test Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1999A&A...341L..31B Altcode: In an attempt to assess the physical realism of the plage flux tube model derived by Bellot Rubio, Ruiz Cobo & Collados (\cite{brc}, \cite{bellot}) we extend its predictions to the Stokes V zero-crossing shifts of a number of Fe ii lines. For this analysis, accurate Fe ii central wavelengths are required. We have devised a procedure for bringing the available Fe ii laboratory wavelengths to the system of accurate Fe i wavelengths of Nave et al. (\cite{nav}). It is shown that, relative to this system, the Fe ii system of Kurucz (\cite{kur}) is shifted by 6.4 m Angstroms/ towards longer wavelengths. Some lines, however, are displaced by more than 10 m Angstroms/. Corrected central wavelengths have been used to extract the observed Stokes V zero-crossing shifts of 16 Fe ii lines. Comparison with the values resulting from the model of Bellot Rubio et al. (\cite{brc}, \cite{bellot}) suggests that the velocity gradients derived by these authors are esentially correct. Title: The IAC Stokes profile inversion codes Authors: Bellot Rubio, L. R. Bibcode: 1999AGAb...15...90B Altcode: 1999AGM....15..P06B In this contribution I describe the main characteristics of the inversion codes developed at the Instituto de Astrofísica de Canarias for the analisys of Stokes profiles emerging from single (magnetized or non-magnetized) atmospheres and thin flux tubes. Some results of the application of these codes to real data, including infrared Stokes profiles recorded with the Tenerife Infrared Polarimeter, are presented as well. Title: Oscillations in a sunspot umbra from the inversion of infrared Stokes profiles Authors: Bellot Rubio, Luis R.; Collados, Manuel; Ruiz Cobo, Basilio; Rodríguez Hidalgo, Inés; Bogdan, Thomas J. Bibcode: 1999AGM....15..A07B Altcode: We report on the detection of magnetic field strength and velocity oscillations in the photosphere of a sunspot umbra. Our analysis is based on the inversion of the full Stokes profiles of three Fe I lines at 15650 Å, from which the stratification with optical depth of the different atmospheric parameters has been derived. This allows us to estimate the amplitude of the oscillations and the phase lag between the fluctuations in the line-of-sight velocity and field strength. Our results suggest that the inferred magnetic field oscillations are caused by opacity fluctuations that move upward and donward the region where the spectral lines are sensitive to magnetic fields. Title: An Hermitian Method for the Solution of Polarized Radiative Transfer Problems Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1998ApJ...506..805B Altcode: Spectral synthesis calculations in stellar (magnetized) atmospheres are based on the solution of the radiative transfer equation (RTE) for polarized light. The thermodynamic and magnetic properties of the atmospheres, along with the radiation field, completely specify the basic ingredients of the RTE, after which numerical methods have to be employed to calculate the emergent Stokes spectra. The advent of powerful analysis techniques for the inversion of Stokes spectra has evidenced the need for accurate and fast solutions of the RTE. In this paper we describe a novel Hermitian strategy to integrate the polarized RTE that is based on the Taylor expansion of the Stokes parameter vector to fourth order in depth. Our technique makes use of the first derivatives of the absorption matrix and source vector with respect to the coordinate measured along the ray path. Both analytical and numerical results indicate that the new strategy is superior to other methods in terms of speed and accuracy. It also gives an approximation to the evolution operator at no extra cost, which is of interest for inversion algorithms based on response functions. The Hermitian technique can be straightforwardly particularized to the scalar case, providing a very efficient solution of the RTE in the absence of magnetic fields. We investigate in detail the consequences of the oscillations that appear in the evolution operator for large values of line strength η0. The problems they pose are shared by all integration schemes, but can be minimized by adopting nonequally spaced grids. Title: Observation and Interpretation of Meteoroid Impact Flashes on the Moon Authors: Bellot Rubio, Luis R.; Ortiz, Jose L.; Sada, Pedro V. Bibcode: 1998EM&P...82..575B Altcode: 2000EM&P...82..575B The first unambiguous detection of meteoroids impacting the night side of the Moon was obtained during the 1999 Leonid storm. Up to eight optical flashes were recorded with CCD video cameras attached to small telescopes on November 18, 1999. Six impacts were videotaped by at least two independent observers at the same times and lunar locations, which is perhaps the strongest evidence for their collisional nature. The flashes were clearly above the noise and lasted for less than 0.02 s. Although previous observational efforts did not succeed in detecting impact flashes, additional candidates have been reported in the literature. The evidence accumulated so far implies that small telescopes equipped with high speed cameras can be used as a new tool for studying meteoroid streams, sporadic meteoroids, and hypervelocity collisions. In this review we discuss the various intervening parameters for detectability of flashes on the night side of the Moon (geometrical effects, contamination by scattered light from the day side, and properties of the meteoroids such as speed and flux of particles). Particular emphasis is placed on the analysis of the observations in order to derive relevant physical parameters such as luminous efficiencies, impactor masses, and crater sizes. Some of these parameters are of interest for constraining theoretical impact models. From a simple analysis, it is possible to derive the mass distribution of the impactors in the kg range. A more elaborate analysis of the data permits an estimate of the fraction of kinetic energy converted to radiation (luminous efficiency) if the meteoroid flux on the Moon is known. Applied to the 1999 lunar Leonids, these methods yield a mass index of 1.6 +/- 0.1 and luminous efficiencies of 2 × 10^-3 with an uncertainty of about one order of magnitude. Predictions of visibility of the major annual meteor showers are given for the next few years. These include the forthcoming 2001 Leonid return, for which we estimate detection rates in the visible. Title: Structure of solar magnetic elements from inversion of Stokes spectra Authors: Bellot Rubio, Luis Ramon Bibcode: 1998PhDT........24B Altcode: No abstract at ADS Title: The Rotation of Comet 1995 O1 (Hale-Bopp) at Perihelion Authors: Kidger, M.; Licandro, J.; Sabalisk, N.; Goetz, B.; Santos, P.; Serra-Ricart, M.; Bellot Rubio, L.; Casas, R.; Gomez, A.; Jorda, L.; Tozzi, G. -P.; Osip, D.; Boehnhardt, H.; West, R. Bibcode: 1997AAS...191.8801K Altcode: 1997BAAS...29.1356K Narrow band near infrared images of comet 1995 O1 (Hale-Bopp), where obtained in day-time, during April 1997, using the 1.52m Carlos Sanchez Telescope, at Teide Observatory (Tenerife, Spain), by the Comet Hale Bopp European Team. The comet was observed continuously for up to 11 hours hours each day on a total of 15 days. This allows us to obtain a complete map of the rotation of the comet's nucleus, and the evolution of the structures observed in the inner coma. These observations were part of a long-term monitoring campaign of the comet's inner-coma morphology which started in August 1995. A long-enduring polar fan structure was observed on 76 nights pre-perihelion, from March to September 1996, in broadband R CCD images obtained with the 0.82m IAC-80 and 0.5m Mons telescopes at Teide Observatory. These images allow us to obtain the spin axis orientation of the comet with considerable precision. Preliminary results, combining these data sets, are presented on the rotation period, pole orientation, and evolution of the active zones. Title: Precisely reduced meteoroid trajectories and orbits from the 1995 Leonid meteor outburst Authors: Betlem, Hans; Kuile, Casper Ter; van't Leven, Jaap; de Lignie, Marc; Bellot Rubio, Luis Ramon; Koop, Mike; Angelo, Chris; Wilson, Mike; Jenniskens, Peter Bibcode: 1997P&SS...45..853B Altcode: The discovery of enhanced Leonid activity in 1994 led to the mounting of a multi-station photographic campaign on two continents during the Leonids of 1995. The goal was to determine orbits and trajectories of outburst Leonids. The outburst did recur as predicted, resulting in 23 precisely reduced Leonid orbits and 30 Leonid trajectories. Individual velocities and radiant positions, as well as the average orbit are presented. It is found that the distribution of Leonid radiants contains a dense cluster of seven radiant positions. This clustering is tentatively associated with the visually observed outburst component. These seven meteors provide the first orbital elements of outburst Leonids and put strong constraints on theoretical models of the origin and evolution of the Leonid stream. Title: A Comparison Between Near-Infrared And Visible Imaging Of The Inner Coma Of Comet Hale-Bopp At Perihelion Authors: Santos-Sanz, P.; Sabalisck, N.; Kidger, M. R.; Licandro, J.; Serra-Ricart, M.; Bellot Rubio, L. R.; Casas, R.; Gómez, A.; Sánchez Portero, J.; Osip, D. Bibcode: 1997EM&P...78..235S Altcode: We present a comparison between images of comet C/1995 O1 (Hale-Bopp) obtained from 12 March to 9 May 1997, with two telescopes of the Observatorio del Teide (IAC, Tenerife, Spain) in visible (Johnson-V filter) and three near-infrared narrowband filters (Brγ (2.166 μm), CO (2.295 μm), and Kcon (2.260 μm)). No significant differences are observed between the images in the three near-infrared bands suggesting that any CO emission is very weak, or produced by an extended flat source. We do not find evidence for the existence of an additional infrared component due to emission by warm dust, or to dust grains of diverse composition and/or size. Visible and infrared images of the same rotational phase look almost identical, supporting the view that the observed jets and shells are mainly dust structures. Title: The Spin Axis Position of C/1995 O1 (Hale-Bopp) Authors: Licandro, J.; Bellot Rubio, L. R.; Casas, R.; Gómez, A.; Kidger, M. R.; Sabalisk, N.; Santos-Sanz, P.; Serra-Ricart, M.; Torres-Chico, R.; Oscoz, A.; Jorda, L.; Denicolo, G. Bibcode: 1997EM&P...77..199L Altcode: Monitoring of the near-nucleus activity of C/1995 O1 (Hale-Bopp) began in Teide Observatory in August 1995. During 1996 the comet was observed on 72 nights between March 26 and November 13. A permanent fan structure was observed towards the north during the whole period of observation. The position angle of the axis of this fan was measured and its variations with time were used to determine the position of the North Pole of the cometary nucleus. Title: Flux-Tube Model Atmospheres and Stokes V Zero-crossing Wavelengths Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1997ApJ...478L..45B Altcode: 1997astro.ph..1059B; 1997astro.ph..1059R First results of the inversion of Stokes I and V profiles from plage regions near disk center are presented. Both low and high spatial resolution spectra of Fe I 6301.5 and Fe I 6302.5 Å obtained with the Advanced Stokes Polarimeter (ASP) have been considered for analysis. The thin flux-tube approximation, implemented in an LTE inversion code based on response functions, is used to describe unresolved magnetic elements. The code allows the simultaneous and consistent inference of all atmospheric quantities determining the radiative transfer with the sole assumption of hydrostatic equilibrium. By considering velocity gradients within the tubes, we are able to match the full ASP Stokes profiles. The magnetic atmospheres derived from the inversion are characterized by the absence of significant motions in high layers and strong velocity gradients in deeper layers. These are essential to reproduce the asymmetries of the observed profiles. Our scenario predicts a shift of the Stokes V zero-crossing wavelengths, which is indeed present in observations made with the Fourier Transform Spectrometer. Title: (Erratum) Response functions for the inversion of data from unresolved solar magnetic elements. Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1997A&A...319.1036B Altcode: Erratum to Astron. Astrophys. 306, 960 (1996). Title: Evolution of a Spiral Jet in the Inner Coma of Comet Hale-Bopp (1995 O1) Authors: Kidger, Mark R.; Serra-Ricart, Miquel; Bellot Rubio, Luis R.; Casas, Ricard Bibcode: 1996ApJ...461L.119K Altcode: We present observations of the evolution of a prominent spiral jet in the inner coma of comet Hale-Bopp (1995 O1). The observations, taken with the 82 cm IAC-80 telescope at the Teide Observatory, were made on 1995 August 25, 27, 28, and 31, and on September 4--7, as part of an ongoing program of monitoring the comet in Tenerife. The jet is observed to show a nearly, but not completely, constant position angle over the two weeks of observation. Although it is generally assumed that the jet is a dust event, some aspects of the morphology and behavior mean that the hypothesis that it is a gas jet cannot be ruled out. No single hypothesis is thought to be completely satisfactory. Between our first detection of the jet on August 25 and its disappearance on September 7, we see the point of inflection within the jet expand away from the nucleus at a highly constant velocity. At the same time, the jet fades considerably. This jet event seems different from others that have been observed later because the collimation of the beam is very tight, rather than the highly wound spiral structure shown by some later jets. Title: Response functions for the inversion of data from unresolved solar magnetic elements. Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1996A&A...306..960B Altcode: By adopting the thin flux tube model as representative of spatially unresolved magnetic elements in the photosphere of the Sun, we identify an adequate set of parameters for the model and derive the corresponding response functions (RFs) which inform about the variation of the emergent Stokes spectrum when such parameters are perturbed. We numerically compute these RFs for reasonable values of the parameters and explore their main properties. It turns out that the RFs at a given height often depend on the state of layers above as a result of the constraints imposed by flux tube geometry. As a whole, RFs can be classified into two well defined groups: one containing RFs dominated by local effects and another which contains RFs governed by non-local effects (i.e., contributions coming from layers other than that where the perturbation takes place). In particular, the RFs to the temperature, line of sight velocity and microturbulence of both the internal and the external atmospheres belong to the first group, while the RFs to the magnetic field strength, external gas pressure and radius of the tube at the base of the atmosphere must be ascribed to the second group. The RFs presented in this paper constitute a first step for the inversion of Stokes spectra from faculae and the network. Title: Determination of fragmentation parameters from photographic and video data Authors: Bellot Rubio, L. R. Bibcode: 1996pimo.conf...35B Altcode: In this paper we introduce the modeling of meteor light curves obtained by photographic and video observations. We briefly comment on the physical relevance of the available models for the interaction atmosphere-meteoroid, and select the quasi-continuous fragmentation theory as a best general description. The analysis of light curves makes it possible to derive some parameters of the particles, among them their bulk densities. By producing synthetic light curves we explore a successful analysis. It is concluded that measurements of brightness have to be as accurate as 0.1-0.2 mag to uniquely distinguish fragmenting behavior. Title: Morphology and Evolution of the Spiral Jets Observed in the Inner Coma of Comet Hale-Bopp (1995 O1): the 1995 Teide Observing Campaign Authors: Kidger, M. R.; Serra-Ricart, M.; Bellot Rubio, L.; Torres-Chico, R.; Casas, R.; Chinarro, L. M.; Gomez, A.; Lopez, S.; Manade, L.; Shulman, L. Bibcode: 1995AAS...187.4210K Altcode: 1995BAAS...27.1338K CCD monitoring of Comet Hale-Bopp (1995 O1) has been carried out on more than 50 nights using the 82cm IAC-80 Telescope at Teide Observatory (Tenerife, Spain), operated by the Instituto de Astrofísica de Canarias. A combination of deep exposures of the extended coma in BVRI (up to 2 hours total exposure in a single filter) and near nucleus imaging has been carried out. Major jets were observed in late August, late September and mid-October which were followed from first detection to complete disappearance. We present a video of the evolution of the different events which shows both similarities and important differences between their morphology and evolution. The August and October events feature a structure with a straight, highly collimated jet of increasing projected length with time and a so-called ``spiral arm" which in all three jets ends in a similar PA, close to the anti-solar direction. These jets we interpret on the basis of various models in an attempt to derive basic parameters such as the rotation and axial inclination, as well as the position of the three sites on the nucleus. There is strong evidence that the three events are caused by different active points on the nucleus, sited at different latitudes. We also present light curves of the comet for different apertures (near-nucleus and total coma) which are linked to the different jet events. Title: Alpha Monocerotid Meteors 1995 Authors: Spurny, P.; Borovicka, J.; Gomez, A.; Bellot Rubio, L.; Roman, A.; Reyes, F.; Rendtel, J.; Molau, S.; Forti, G.; Haver, R.; Gorelli, R.; Nagy, Z. A.; Sarenczky, K.; Tepliczky, I.; Gerbos, J.; Rapavy, P.; Hrusovsky, V.; Steyaert, C.; de Meyere, M. Bibcode: 1995IAUC.6265....1S Altcode: Numerous reports have been received, from several locations in Europe, of an excellent display of this occasional, short-lived meteor shower around Nov. 22.06 UT. Mentioned by Olivier (1936, Pop. Astron. 44, 88) as perhaps having a 10-year periodicity, and discussed at length by Kresak (1958, Bull. Astron. Inst. Czech. 9, 88), the shower was widely anticipated to recur in 1995, Jenniskens (1995, WGN 23, No. 3, 84) predicting the brief maximum as occurring some time during Nov. 22.00-22.25 UT. P. Spurny and J. Borovicka, Ondrejov Observatory, report monitoring during Nov. 21.96-22.11, Monocerotids first being detected at 22.050, with more than six during each 2-min interval until 22.067 and some continuing activity to 22.098; during one minute at 22.058 a maximum of seven meteors was observed. A. Gomez, Instituto de Astrofisica de Canarias, reports observations from Almeria by L. Bellot, A. Roman and F. Reyes of as many as 70 Monocerotids during 22.055-22.071; the limiting visual magnitude was about 6.2, and most of the meteors were in the magnitude range 0-2. J. Rendtel, International Meteor Organization, Potsdam, noted 34 shower meteors from a radiant of R.A. = 113 deg, Decl. = -3 deg during 22.042-22.076 (limiting magnitude 6.15), yielding an average ZHR (assuming a population index of r = 2.5) of 90 (with an equivalent ZHR of up to 190 during 10 min centered on 22.062; on combining his results with those of S. Molau in Chemnitz, he revised this to 220 +/- 50). G. Forti, Arcetri Observatory, reports observations by R. Haver and R. Gorelli from Frasso Sabino, indicating a radiant of R.A. = 112.5 deg, Decl. = -3 deg and a peak within 5 min of 22.059, there being a sharp rise and fall and no meteors observed 15 min before or after the peak; the meteors were yellow and blue, and few were brighter than mag 0. Z. A. Nagy, K. Sarenczky and I. Tepliczky, observing from Vertes Mountain (Hungary), collectively recorded Monocerotids during 22.045-22.087, counting 139 shower members during 22.049-22.072 (with maximum activity during 22.060-22.065), 90 percent of them from a compact radiant at R.A. = 116 deg, Decl. = +4 deg, and the others from a diffuse radiant between alpha CMi and delta Mon; several meteors were around mag 0. J. Gerbos, P. Rapavy and V. Hrusovsky, Rimavska Sobota (Slovakia), collectively registered more than 600 Monocerotids during one hour beginning 22.049, the maximum activity in 5 min being centered on 22.058. C. Steyaert reports that M. De Meyere, monitoring in Deurle (Belgium) a 100-kW radio station in Budapest, 1170 km away, at 66.51 MHz, detected a significant (fourfold) enhancement in forward-scattering rates during the hour beginning 22.042, the number of meteor reflections lasting at least 0.027 second being 232. Title: Effects of a dependence of meteor brightness on the entry angle. Authors: Bellot Rubio, L. R. Bibcode: 1995A&A...301..602B Altcode: In this paper we discuss the observational consequences of a dependence of meteor brightness on the entry angle z_R_, namely the decrease of the observed rates of meteors and the reduction of the population indices r for radiant zenith distances larger than zero. These effects, if not properly accounted for, lead to erroneous values of meteor shower activity. The first one is corrected by applying a factor cos^-γ^ z_R_ to the observed rates, while the second one requires a correction of the form r(0deg)=r(z_R_)^b(z_R_)/b(0deg)^. We give general expressions for γ and b(z_R_)/b(0deg) in terms of the coefficients relating the absolute magnitude of the meteor to its physical parameters. High quality photographic data, as well as naked-eye observations, are analyzed. It turns out that γ=1+1.53logr(0deg) describes the photographic behavior quite well. For visual observations, however, an exponent γ=1 should be employed in most cases. We explain this difference on the basis of a larger path of the meteoroids at increasing entry angles, which increases the probability of perception of meteors for visual observers. As regards b(z_R_)/b(0deg), a dependence b(z_R_)/b(0deg)=1.04-0.04cos z_R_ is suitable for both photographic and naked-eye records. These values are compared to predictions resulting from a detailed treatment of the single body theory. It turns out that the single body approach gives a much stronger dependence of the meteor brightness on the entry angle than that obtained from observations. Models including quasicontinuous fragmentation are therefore necessary. Title: LTE polarized radiative transfer through interlaced atmospheres. Authors: del Toro Iniesta, J. C.; Ruiz Cobo, B.; Bellot Rubio, L. R.; Collados, M. Bibcode: 1995A&A...294..855D Altcode: We show that the solution of the radiative transfer equation (RTE) through a line of sight that pierces several times two alternate atmospheres can be obtained in terms of the solutions of the RTE through both single atmospheres separately considered. This also applies to the response functions of the observed Stokes spectrum to perturbations of the physical quantities. The analytic solution of the RTE in case that the single atmospheres are Milne-Eddington is presented. The simplification of the solution in the case of a longitudinal or transversal (with constant azimuth) magnetic field is presented as well. Finally, as a numerical example, we synthesize the Stokes I- and V-spectrum emerging from a thin magnetic flux tube, achieving a considerable decrease in computation time with respect to conventional integrations and without loss of accuracy. Title: An analysis of the Taurid radiants. Authors: Bellot Rubio, L. R. Bibcode: 1994JIMO...22..108B Altcode: 1994WGN....22..108B No abstract at ADS Title: Spatial number densities and errors from photographic meteor observations under very high activity. Authors: Bellot Rubio, L. R. Bibcode: 1994JIMO...22..118B Altcode: 1994WGN....22..118B A procedure to compute meteoroid spatial number densities from photographs is presented. It follows from the visual method of Koschack and Rendtel with slight changes. Some parameters are recomputed and hints are given on how to produce useful photographic observations. Finally, an analysis of the expected errors is performed. Title: Dependence of the population index on the radiant zenithal distance Authors: Bellot Rubio, Luis R. Bibcode: 1994JIMO...22...13B Altcode: 1994WGN....22...13B By integrating the differential equation system of the single-body meteor theory which describes meteor flight in the atmosphere, we show that the population index r depends on the radiant zenithal distance zR. When zR is large, r diminishes, requiring correction in order to obtain reliable number density profiles. A new method is proposed to correct the population index when zR is not zero. Its application to the problem of the 1992 Quadrantids raised by Rendtel et al. shows that corrected values of r vary from r=2.32 to r=2.44 between solar longitudes 283.00 and 283.23 deg. Title: On the presence of trains in meteor showers. Authors: Bellot Rubio, L. R. Bibcode: 1992JIMO...20..140B Altcode: 1992WGN....20..140B Different mechanisms for meteor train generation are reviewed. Train percentages for different showers are calculated and compared. An attempt is made to correlate numbers of trains with train duration. Finally, fireball trains are considered. Title: 1992 Quadrantid and Coma Berenicid activity in Spain. Authors: Bellot Rubio, L. R. Bibcode: 1992JIMO...20...93B Altcode: 1992WGN....20...93B No abstract at ADS Title: The α-Capricornids in 1989. Authors: Bellot Rubio, L. R. Bibcode: 1990JIMO...18...26B Altcode: 1990WGN....18...26B No abstract at ADS