Author name code: orozco-suarez ADS astronomy entries on 2022-09-14 author:"Orozco Suarez, David" ------------------------------------------------------------------------ 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: 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 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: DeSIRe: Departure coefficient aided Stokes Inversion based on Response functions Authors: Ruiz Cobo, B.; Quintero Noda, C.; Gafeira, R.; Uitenbroek, H.; Orozco Suárez, D.; Páez Mañá, E. Bibcode: 2022A&A...660A..37R Altcode: 2022arXiv220202226R Future ground-based telescopes, such as the 4-metre class facilities DKIST and EST, will dramatically improve on current capabilities for simultaneous multi-line polarimetric observations in a wide range of wavelength bands, from the near-ultraviolet to the near-infrared. As a result, there will be an increasing demand for fast diagnostic tools, i.e., inversion codes, that can infer the physical properties of the solar atmosphere from the vast amount of data these observatories will produce. The advent of substantially larger apertures, with the concomitant increase in polarimetric sensitivity, will drive an increased interest in observing chromospheric spectral lines. Accordingly, pertinent inversion codes will need to take account of line formation under general non-local thermodynamic equilibrium (NLTE) conditions. Several currently available codes can already accomplish this, but they have a common practical limitation that impairs the speed at which they can invert polarised spectra, namely that they employ numerical evaluation of the so-called response functions to changes in the atmospheric parameters, which makes them less suitable for the analysis of very large data volumes. Here we present DeSIRe (Departure coefficient aided Stokes Inversion based on Response functions), an inversion code that integrates the well-known inversion code SIR with the NLTE radiative transfer solver RH. The DeSIRe runtime benefits from employing analytical response functions computed in local thermodynamic equilibrium (through SIR), modified with fixed departure coefficients to incorporate NLTE effects in chromospheric spectral lines. This publication describes the operating fundamentals of DeSIRe and describes its behaviour, robustness, stability, and speed. The code is ready to be used by the solar community and is being made publicly available. Title: A modified Milne-Eddington approximation for a qualitative interpretation of chromospheric spectral lines Authors: Dorantes-Monteagudo, A. J.; Siu-Tapia, A. L.; Quintero-Noda, C.; Orozco Suárez, D. Bibcode: 2022A&A...659A.156D Altcode: 2021arXiv211214536D Context. The Milne-Eddington approximation provides an analytic and simple solution to the radiative transfer equation. It can be easily implemented in inversion codes used to fit spectro-polarimetric observations and infer average values of the magnetic field vector and the line-of-sight velocity of the solar plasma. However, in principle, it is restricted to spectral lines that are formed under local thermodynamic conditions, namely, photospheric and optically thin lines.
Aims: We show that a simple modification to the Milne-Eddington approximation is sufficient to infer relevant physical parameters from spectral lines that deviate from local thermodynamic equilibrium, such as those typically observed in the solar chromosphere.
Methods: We modified the Milne-Eddington approximation by including several exponential terms in the source function to reproduce the prototypical shape of chromospheric spectral lines. To check the validity of such an approximation, we first studied the influence of these new terms on the profile shape by means of the response functions. Then we tested the performance of an inversion code including the modification against the presence of noise. The approximation was also tested with realistic spectral lines generated with the RH numerical radiative transfer code. Finally, we confronted the code with synthetic profiles generated from magneto-hydrodynamic simulations carried out with the Bifrost code. For the various tests, we focused on the vector magnetic field and the line-of-sight velocity. We compared our results with the weak-field approximation and center of gravity technique as well.
Results: The response function corresponding to the new terms in the source function have no trade-offs with the response to the different components of the magnetic field vector and line-of-sight velocity. This allows us to perform a robust inference of the physical parameters from the interpretation of spectral line shapes. The strategy has been successfully applied to synthetic chromospheric Stokes profiles generated with both standard models and realistic magnetohydrodynamic (MHD) simulations. The magnetic field vector and velocity can be successfully recovered with the modified Milne-Eddington approximation.
Conclusions: Milne-Eddington model atmospheres that include exponential terms are not new to the solar community but have been overlooked for quite some time. We show that our modification to the Milne-Eddington approximation succeeds in reproducing the profile shape of two chromospheric spectral lines, namely, the Mg I b2 line and the Ca II at 854.2 nm. The results obtained with this approach are in good agreement with the results obtained from the weak field approximation (for magnetic field) and the center of gravity (for velocity). However, the Milne-Eddington approximation possesses a great advantage over classical methods since it is not limited to weak magnetic fields or to a restricted range of velocities. 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: Probing Upflowing Regions in the Quiet Sun and Coronal Holes Authors: Schwanitz, Conrad; Harra, Louise; Raouafi, Nour E.; Sterling, Alphonse C.; Moreno Vacas, Alejandro; del Toro Iniesta, Jose Carlos; Orozco Suárez, David; Hara, Hirohisa Bibcode: 2021SoPh..296..175S Altcode: 2021arXiv211012753S Recent observations from Parker Solar Probe have revealed that the solar wind has a highly variable structure. How this complex behaviour is formed in the solar corona is not yet known, since it requires omnipresent fluctuations, which constantly emit material to feed the wind. In this article we analyse 14 upflow regions in the solar corona to find potential sources for plasma flow. The upflow regions are derived from spectroscopic data from the EUV Imaging Spectrometer (EIS) on board Hinode determining their Doppler velocity and defining regions which have blueshifts stronger than −6 kms−1. To identify the sources of these blueshift data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI), on board the Solar Dynamics Observatory (SDO), and the X-ray Telescope (XRT), on board Hinode, are used. The analysis reveals that only 5 out of 14 upflows are associated with frequent transients, like obvious jets or bright points. In contrast to that, seven events are associated with small-scale features, which show a large variety of dynamics. Some resemble small bright points, while others show an eruptive nature, all of which are faint and only live for a few minutes; we cannot rule out that several of these sources may be fainter and, hence, less obvious jets. Since the complex structure of the solar wind is known, this suggests that new sources have to be considered or better methods used to analyse the known sources. This work shows that small and frequent features, which were previously neglected, can cause strong upflows in the solar corona. These results emphasise the importance of the first observations from the Extreme-Ultraviolet Imager (EUI) on board Solar Orbiter, which revealed complex small-scale coronal structures. Title: Diagnostic capabilities of spectropolarimetric observations for understanding solar phenomena. I. Zeeman-sensitive photospheric lines Authors: Quintero Noda, C.; Barklem, P. S.; Gafeira, R.; Ruiz Cobo, B.; Collados, M.; Carlsson, M.; Martínez Pillet, V.; Orozco Suárez, D.; Uitenbroek, H.; Katsukawa, Y. Bibcode: 2021A&A...652A.161Q Altcode: 2021arXiv210605084Q Future ground-based telescopes will expand our capabilities for simultaneous multi-line polarimetric observations in a wide range of wavelengths, from the near-ultraviolet to the near-infrared. This creates a strong demand to compare candidate spectral lines to establish a guideline of the lines that are most appropriate for each observation target. We focused in this first work on Zeeman-sensitive photospheric lines in the visible and infrared. We first examined their polarisation signals and response functions using a 1D semi-empirical atmosphere. Then we studied the spatial distribution of the line core intensity and linear and circular polarisation signals using a realistic 3D numerical simulation. We ran inversions of synthetic profiles, and we compared the heights at which we obtain a high correlation between the input and the inferred atmosphere. We also used this opportunity to revisit the atomic information we have on these lines and computed the broadening cross-sections due to collisions with neutral hydrogen atoms for all the studied spectral lines. The results reveal that four spectral lines stand out from the rest for quiet-Sun and network conditions: Fe I 5250.2, 6302, 8468, and 15 648 Å. The first three form higher in the atmosphere, and the last line is mainly sensitive to the atmospheric parameters at the bottom of the photosphere. However, as they reach different heights, we strongly recommend using at least one of the first three candidates together with the Fe I 15 648 Å line to optimise our capabilities for inferring the thermal and magnetic properties of the lower atmosphere. Title: Machine learning initialization to accelerate Stokes profile inversions Authors: Gafeira, R.; Orozco Suárez, D.; Milić, I.; Quintero Noda, C.; Ruiz Cobo, B.; Uitenbroek, H. Bibcode: 2021A&A...651A..31G Altcode: 2021arXiv210309651G Context. At present, an exponential growth in scientific data from current and upcoming solar observatories is expected. Most of the data consist of high spatial and temporal resolution cubes of Stokes profiles taken in both local thermodynamic equilibrium (LTE) and non-LTE spectral lines. The analysis of such solar observations requires complex inversion codes. Hence, it is necessary to develop new tools to boost the speed and efficiency of inversions and reduce computation times and costs.
Aims: In this work we discuss the application of convolutional neural networks (CNNs) as a tool to advantageously initialize Stokes profile inversions.
Methods: To demonstrate the usefulness of CNNs, we concentrate in this paper on the inversion of LTE Stokes profiles. We use observations taken with the spectropolarimeter on board the Hinode spacecraft as a test bench mark. First, we carefully analyse the data with the SIR inversion code using a given initial atmospheric model. The code provides a set of atmospheric models that reproduce the observations well. These models are then used to train a CNN. Afterwards, the same data are again inverted with SIR but using the trained CNN to provide the initial guess atmospheric models for SIR.
Results: The CNNs allow us to significantly reduce the number of inversion cycles when used to compute initial guess model atmospheres (`assisted inversions'), therefore decreasing the computational time for LTE inversions by a factor of two to four. CNNs alone are much faster than assisted inversions, but the latter are more robust and accurate. CNNs also help to automatically cluster pixels with similar physical properties, allowing the association with different solar features on the solar surface, which is useful when inverting huge datasets where completely different regimes are present. The advantages and limitations of machine learning techniques for estimating optimum initial atmospheric models for spectral line inversions are discussed. Finally, we describe a python wrapper for the SIR and DeSIRe codes that allows for the easy setup of parallel inversions. The tool implements the assisted inversion method described in this paper. The parallel wrapper can also be used to synthesize Stokes profiles with the RH code.
Conclusions: The assisted inversions can speed up the inversion process, but the efficiency and accuracy of the inversion results depend strongly on the solar scene and the data used for the CNN training. This method (assisted inversions) will not obviate the need for analysing individual events with the utmost care but will provide solar scientists with a much better opportunity to sample large amounts of inverted data, which will undoubtedly broaden the physical discovery space. Title: On Fabry-Pérot Etalon-based Instruments. IV. Analytical Formulation of Telecentric Etalons Authors: Bailén, F. J.; Orozco Suárez, D.; del Toro Iniesta, J. C. Bibcode: 2021ApJS..254...18B Altcode: 2022arXiv220506026B Fabry-Pérot etalons illuminated with collimated beams have been analytically characterized in detail since their invention. Meanwhile, most of the features of etalons located in telecentric planes have been studied only numerically, despite the wide use of this configuration in astrophysical instrumentation for decades. In this work we present analytical expressions for the transmitted electric field and its derivatives that are valid for etalons placed in slow telecentric beams, like the ones commonly employed in solar instruments. We use the derivatives to infer the sensitivity of the electric field to variations in the optical thickness for different reflectivities and apertures of the incident beam, and we compare them to the collimated case. This allows us to estimate the wavefront degradation produced by roughness errors on the surfaces of the Fabry-Pérot etalons and to establish the maximum allowed rms value of the cavity irregularities across the footprint of the incident beam on the etalons that ensures diffraction-limited performance. We also evaluate the wavefront degradation intrinsic to these mounts, which is produced only by the finite aperture of the beam and that must be added to the one produced by defects. Finally, we discuss the differences in performance of telecentric and collimated etalon-based instruments and we generalize our formulation to anisotropic etalons. Title: First results from SO/PHI's on-board data reduction Authors: Albert, K.; Hirzberger, J.; Kolleck, M.; Albelo Jorge, N.; Busse, D.; Blanco Rodriguez, J.; Cobos Carrascosa, J. P.; Fiethe, B.; Gandorfer, A.; Germerott, D.; Guan, Y.; Guerrero, L.; Gutierrez-Marques, P.; Hernández Expósito, D.; Lange, T.; Michalik, H.; Orozco Suárez, D.; Schou, J.; Solanki, S. K.; Woch, J. G. Bibcode: 2020AGUFMSH038..05A Altcode: The Polarimetric and Helioseismic Imager (PHI), on-board Solar Orbiter (SO), is a spectropolarimeter imaging the solar photosphere at the wavelengths of the Fe I 617.3 nm Zeeman sensitive absorption line. SO/PHI's aim is to provide data about the magnetic structures and the line-of-sight (LOS) velocity in the solar atmosphere. For this, it takes time series of data sets consisting of 2048 x 2048 pixel images of the Sun at 6 wavelengths, each in 4 different polarisation states. With the minimum necessary 17 bits pixel depth, one data set amounts to approx. 0.2 GB. The guaranteed data telemetry for PHI, in contrast, is only 50 GiB/orbit which would also need to contain any calibration data obtained on-board, i.e. our flat and dark fields. To cope with this discrepancy, SO/PHI is performing full data reduction on-board, including the inversion of the radiative transfer equation. The downloaded results are science ready data, containing 5 final images: a total intensity image from nearby the spectral line, the magnetic field strength, azimuth and inclination (describing the magnetic vector) and the LOS velocity. This process maximises the science return by reducing the number of necessary images in a data set, as well as rendering the download of calibration data unessential. In the commissioning phase of SO/PHI we used the on-board data reduction system successfully for the first time. We have calibrated the instrument to its optimal operational parameters (calculation of exposure time, focus, etc.), acquired and processed calibration data (dark and flat fields), removed the most significant instrumental artefacts from the data (dark field, flat field, polarimetric modulation and polarimetric cross-talk), and performed the inversion of the radiative transfer equation. The data have then been compressed to further maximise the use of our telemetry. This contribution presents and discusses the final results from this process. Title: Power spectrum of turbulent convection in the solar photosphere Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.; Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2020A&A...644A..44Y Altcode: 2020arXiv201009037Y The solar photosphere provides us with a laboratory for understanding turbulence in a layer where the fundamental processes of transport vary rapidly and a strongly superadiabatic region lies very closely to a subadiabatic layer. Our tools for probing the turbulence are high-resolution spectropolarimetric observations such as have recently been obtained with the two balloon-borne SUNRISE missions, and numerical simulations. Our aim is to study photospheric turbulence with the help of Fourier power spectra that we compute from observations and simulations. We also attempt to explain some properties of the photospheric overshooting flow with the help of its governing equations and simulations. We find that quiet-Sun observations and smeared simulations are consistent with each other and exhibit a power-law behavior in the subgranular range of their Doppler velocity power spectra with a power-law index of ≈ - 2. The unsmeared simulations exhibit a power law that extends over the full range between the integral and Taylor scales with a power-law index of ≈ - 2.25. The smearing, reminiscent of observational conditions, considerably reduces the extent of the power-law-like portion of the power spectra. This suggests that the limited spatial resolution in some observations might eventually result in larger uncertainties in the estimation of the power-law indices. The simulated vertical velocity power spectra as a function of height show a rapid change in the power-law index (at the subgranular range) from roughly the optical depth unity layer, that is, the solar surface, to 300 km above it. We propose that the cause of the steepening of the power-law index is the transition from a super- to a subadiabatic region, in which the dominant source of motions is overshooting convection. A scale-dependent transport of the vertical momentum occurs. At smaller scales, the vertical momentum is more efficiently transported sideways than at larger scales. This results in less vertical velocity power transported upward at small scales than at larger scales and produces a progressively steeper vertical velocity power law below 180 km. Above this height, the gravity work progressively gains importance at all relevant scales, making the atmosphere progressively more hydrostatic and resulting in a gradually less steep power law. Radiative heating and cooling of the plasma is shown to play a dominant role in the plasma energetics in this region, which is important in terms of nonadiabatic damping of the convective motions. Title: Sunrise Chromospheric Infrared SpectroPolarimeter (SCIP) for sunrise III: system design and capability Authors: Katsukawa, Y.; del Toro Iniesta, J. C.; Solanki, S. K.; Kubo, M.; Hara, H.; Shimizu, T.; Oba, T.; Kawabata, Y.; Tsuzuki, T.; Uraguchi, F.; Nodomi, Y.; Shinoda, K.; Tamura, T.; Suematsu, Y.; Ishikawa, R.; Kano, R.; Matsumoto, T.; Ichimoto, K.; Nagata, S.; Quintero Noda, C.; Anan, T.; Orozco Suárez, D.; Balaguer Jiménez, M.; López Jiménez, A. C.; Cobos Carrascosa, J. P.; Feller, A.; Riethmueller, T.; Gandorfer, A.; Lagg, A. Bibcode: 2020SPIE11447E..0YK Altcode: The Sunrise balloon-borne solar observatory carries a 1 m aperture optical telescope and provides us a unique platform to conduct continuous seeing-free observations at UV-visible-IR wavelengths from an altitude of higher than 35 km. For the next flight planned for 2022, the post-focus instrumentation is upgraded with new spectro- polarimeters for the near UV (SUSI) and the near-IR (SCIP), whereas the imaging spectro-polarimeter Tunable Magnetograph (TuMag) is capable of observing multiple spectral lines within the visible wavelength. A new spectro-polarimeter called the Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is under development for observing near-IR wavelength ranges of around 770 nm and 850 nm. These wavelength ranges contain many spectral lines sensitive to solar magnetic fields and SCIP will be able to obtain magnetic and velocity structures in the solar atmosphere with a sufficient height resolution by combining spectro-polarimetric data of these lines. Polarimetric measurements are conducted using a rotating waveplate as a modulator and polarizing beam splitters in front of the cameras. The spatial and spectral resolutions are 0.2" and 2 105, respectively, and a polarimetric sensitivity of 0.03 % (1σ) is achieved within a 10 s integration time. To detect minute polarization signals with good precision, we carefully designed the opto-mechanical system, polarization optics and modulation, and onboard data processing. Title: Coordination within the remote sensing payload on the Solar Orbiter mission Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.; Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade, S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.; Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy, S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.; Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.; Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey, B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.; Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi, M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.; Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.; Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.; Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.; Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams, D.; Woch, J.; Zhukov, A. N.; Zouganelis, I. Bibcode: 2020A&A...642A...6A Altcode: Context. To meet the scientific objectives of the mission, the Solar Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing (RS) instruments designed for joint operations with inter-instrument communication capabilities. Indeed, previous missions have shown that the Sun (imaged by the RS instruments) and the heliosphere (mainly sampled by the IS instruments) should be considered as an integrated system rather than separate entities. Many of the advances expected from Solar Orbiter rely on this synergistic approach between IS and RS measurements.
Aims: Many aspects of hardware development, integration, testing, and operations are common to two or more RS instruments. In this paper, we describe the coordination effort initiated from the early mission phases by the Remote Sensing Working Group. We review the scientific goals and challenges, and give an overview of the technical solutions devised to successfully operate these instruments together.
Methods: A major constraint for the RS instruments is the limited telemetry (TM) bandwidth of the Solar Orbiter deep-space mission compared to missions in Earth orbit. Hence, many of the strategies developed to maximise the scientific return from these instruments revolve around the optimisation of TM usage, relying for example on onboard autonomy for data processing, compression, and selection for downlink. The planning process itself has been optimised to alleviate the dynamic nature of the targets, and an inter-instrument communication scheme has been implemented which can be used to autonomously alter the observing modes. We also outline the plans for in-flight cross-calibration, which will be essential to the joint data reduction and analysis.
Results: The RS instrument package on Solar Orbiter will carry out comprehensive measurements from the solar interior to the inner heliosphere. Thanks to the close coordination between the instrument teams and the European Space Agency, several challenges specific to the RS suite were identified and addressed in a timely manner. 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: 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: 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 Fabry-Pérot Etalon-based Instruments. III. Instrument Applications Authors: Bailén, F. J.; Orozco Suárez, D.; del Toro Iniesta, J. C. Bibcode: 2020ApJS..246...17B Altcode: 2020arXiv200200599B The spectral, imaging, and polarimetric behavior of Fabry-Pérot etalons have an influence on imaging vector magnetograph instruments based on these devices. The impact depends on the optical configuration (collimated or telecentric), on the relative position of the etalon with respect to the polarimeter, on the type of etalon (air-gapped or crystalline), and even on the polarimetric technique to be used (single-beam or dual-beam). In this paper, we evaluate the artificial line-of-sight velocities and magnetic field strengths that arise in etalon-based instruments, attending to the factors mentioned. We differentiate between signals that are implicit to telecentric mounts due to the wavelength dependence of the point-spread function and those emerging in both collimated and telecentric setups from the polarimetric response of birefringent etalons. For the anisotropic case, we consider two possible locations of the etalon—between the modulator and the analyzer or after it—and we include the effect on different channels when dual-beam polarimetry is employed. We also evaluate the impact of the loss of symmetry produced in telecentric mounts due to imperfections in the illumination and/or to a tilt of the etalon relative to the incident beam. Title: A flexible and heterogeneous framework for scientific image data processing on-board the Solar Orbiter PHI instrument Authors: Lange, Tobias; Fiethe, Björn; Guan, Yejun; Michalik, Harald; Albert, Kinga; Hirzberger, Johann; Orozco Suárez, David; Rodríguez-Valido, Manuel Bibcode: 2019SPIE11155E..06L Altcode: Present scientific space instruments generate a high amount of raw data while deep-space missions only have a very limited telemetry rate. Because the computation of the scientific relevant parameters is usually accompanied with the reduction of the data, the processing is desired to be carried out already on-board. To accomplish this, the following paper presents a flexible image processing framework which makes use of a heterogeneous data processing module consisting of a space-grade General Purpose Processor (GPP) as well as two dynamically reconfigurable Field-Programmable Gate Arrays used for hardware acceleration. The flexibility and capabilities of the presented framework are proven by means of three exemplary processing tasks of the Polarimetric and Helioseismic Imager (PHI) on-board Solar Orbiter. Title: Chromospheric polarimetry through multiline observations of the 850 nm spectral region III: Chromospheric jets driven by twisted magnetic fields Authors: Quintero Noda, C.; Iijima, H.; Katsukawa, Y.; Shimizu, T.; Carlsson, M.; de la Cruz Rodríguez, J.; Ruiz Cobo, B.; Orozco Suárez, D.; Oba, T.; Anan, T.; Kubo, M.; Kawabata, Y.; Ichimoto, K.; Suematsu, Y. Bibcode: 2019MNRAS.486.4203Q Altcode: 2019MNRAS.tmp.1081N; 2019arXiv190409151Q We investigate the diagnostic potential of the spectral lines at 850 nm for understanding the magnetism of the lower atmosphere. For that purpose, we use a newly developed 3D simulation of a chromospheric jet to check the sensitivity of the spectral lines to this phenomenon as well as our ability to infer the atmospheric information through spectropolarimetric inversions of noisy synthetic data. We start comparing the benefits of inverting the entire spectrum at 850 nm versus only the Ca II 8542 Å spectral line. We found a better match of the input atmosphere for the former case, mainly at lower heights. However, the results at higher layers were not accurate. After several tests, we determined that we need to weight more the chromospheric lines than the photospheric ones in the computation of the goodness of the fit. The new inversion configuration allows us to obtain better fits and consequently more accurate physical parameters. Therefore, to extract the most from multiline inversions, a proper set of weights needs to be estimated. Besides that, we conclude again that the lines at 850 nm, or a similar arrangement with Ca II 8542 Å plus Zeeman-sensitive photospheric lines, pose the best-observing configuration for examining the thermal and magnetic properties of the lower solar atmosphere. Title: On Fabry-Pérot Etalon-based Instruments. II. The Anisotropic (Birefringent) Case Authors: Bailén, F. J.; Orozco Suárez, D.; del Toro Iniesta, J. C. Bibcode: 2019ApJS..242...21B Altcode: 2019arXiv190610361B Crystalline etalons present several advantages with respect to other types of filtergraphs when employed in magnetographs, especially that they can be tuned by only applying electric fields. However, anisotropic crystalline etalons can also introduce undesired birefringent effects that corrupt the polarization of the incoming light. In particular, uniaxial Fabry-Pérots, such as LiNbO3 etalons, are birefringent when illuminated with an oblique beam. The farther the incidence from the normal, the larger the induced retardance between the two orthogonal polarization states. The application of high voltages, as well as fabrication defects, can also change the direction of the optical axis of the crystal, introducing birefringence even at normal illumination. Here we obtain analytical expressions for the induced retardance and for the Mueller matrix of uniaxial etalons located in both collimated and telecentric configurations. We also evaluate the polarimetric behavior of Z-cut crystalline etalons with the incident angle, with the orientation of the optical axis, and with the f-number of the incident beam for the telecentric case. We study artificial signals produced in the output Stokes vector in the two configurations. Last, we discuss the polarimetric dependence of the imaging response of the etalon for both collimated and telecentric setups. Title: Photospheric Magnetic Fields of the Trailing Sunspots in Active Region NOAA 12396 Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer, C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2019ASPC..526..291V Altcode: 2018arXiv180507752V The solar magnetic field is responsible for all aspects of solar activity. Sunspots are the main manifestation of the ensuing solar activity. Combining high-resolution and synoptic observations has the ambition to provide a comprehensive description of the sunspot growth and decay processes. Active region NOAA 12396 emerged on 2015 August 3 and was observed three days later with the 1.5-meter GREGOR solar telescope on 2015 August 6. High-resolution spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together with the chromospheric He I λ1083.0 nm triplet. These near-infrared spectropolarimetric observations were complemented by synoptic line-of-sight magnetograms and continuum images of the Helioseismic and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Title: On Fabry-Pérot Etalon-based Instruments. I. The Isotropic Case Authors: Bailén, F. J.; Orozco Suárez, D.; del Toro Iniesta, J. C. Bibcode: 2019ApJS..241....9B Altcode: 2019arXiv190306403B Here we assess the spectral and imaging properties of Fabry-Pérot etalons when located in solar magnetographs. We discuss the chosen configuration (collimated or telecentric) for both ideal and real cases. For the real cases, we focus on the effects caused by the polychromatic illumination of the filter by the irregularities in the optical thickness of the etalon and by deviations from the ideal illumination in both setups. We first review the general properties of Fabry-Pérots and we then address the different sources of degradation of the spectral transmission profile. We review and extend the general treatment of defects followed by different authors. We discuss the differences between the point spread functions (PSFs) of the collimated and telecentric configurations for both monochromatic and (real) quasi-monochromatic illumination of the etalon. The PSF corresponding to collimated mounts is shown to have a better performance, although it varies from point to point due to an apodization of the image inherent to this configuration. This is in contrast to the (perfect) telecentric case, where the PSF remains constant but produces artificial velocities and magnetic field signals because of its strong spectral dependence. We find that the unavoidable presence of imperfections in the telecentrism produces a decrease of flux of photons and a shift, a broadening and a loss of symmetrization of both the spectral and PSF profiles over the field of view, thus compromising their advantages over the collimated configuration. We evaluate these effects for different apertures of the incident beam. 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: Study of the polarization produced by the Zeeman effect in the solar Mg I b lines Authors: Quintero Noda, C.; Uitenbroek, H.; Carlsson, M.; Orozco Suárez, D.; Katsukawa, Y.; Shimizu, T.; Ruiz Cobo, B.; Kubo, M.; Oba, T.; Kawabata, Y.; Hasegawa, T.; Ichimoto, K.; Anan, T.; Suematsu, Y. Bibcode: 2018MNRAS.481.5675Q Altcode: 2018arXiv181001067Q; 2018MNRAS.tmp.2566Q The next generation of solar observatories aim to understand the magnetism of the solar chromosphere. Therefore, it is crucial to understand the polarimetric signatures of chromospheric spectral lines. For this purpose, we here examine the suitability of the three Fraunhofer Mg I b1, b2, and b4 lines at 5183.6, 5172.7, and 5167.3 Å, respectively. We start by describing a simplified atomic model of only six levels and three line transitions for computing the atomic populations of the 3p-4s (multiplet number 2) levels involved in the Mg I b line transitions assuming non-local thermodynamic conditions and considering only the Zeeman effect using the field-free approximation. We test this simplified atom against more complex ones finding that, although there are differences in the computed profiles, they are small compared with the advantages provided by the simple atom in terms of speed and robustness. After comparing the three Mg I lines, we conclude that the most capable one is the b2 line as b1 forms at similar heights and always shows weaker polarization signals, while b4 is severely blended with photospheric lines. We also compare Mg I b2 with the K I D1 and Ca II 8542 Å lines finding that the former is sensitive to the atmospheric parameters at heights that are in between those covered by the latter two lines. This makes Mg I b2 an excellent candidate for future multiline observations that aim to seamlessly infer the thermal and magnetic properties of different features in the lower solar atmosphere. Title: SOPHISM: Software Instrument Simulator Authors: Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Orozco Suárez, D.; Martínez Pillet, V.; Bonet, J. A.; Feller, A.; Hirzberger, J.; Lagg, A.; Piqueras, J.; Gasent Blesa, J. L. Bibcode: 2018ascl.soft10017B Altcode: SOPHISM models astronomical instrumentation from the entrance of the telescope to data acquisition at the detector, along with software blocks dealing with, for example, demodulation, inversion, and compression. The code performs most analyses done with light in astronomy, such as differential photometry, spectroscopy, and polarimetry. The simulator offers flexibility and implementation of new effects and subsystems, making it user-adaptable for a wide variety of instruments. SOPHISM can be used for all stages of instrument definition, design, operation, and lifetime tracking evaluation. Title: SOPHISM: An End-to-end Software Instrument Simulator Authors: Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Orozco Suárez, D.; Martínez Pillet, V.; Bonet, J. A.; Feller, A.; Hirzberger, J.; Lagg, A.; Piqueras, J.; Gasent Blesa, J. L. Bibcode: 2018ApJS..237...35B Altcode: We present a software simulator for the modeling of astronomical instrumentation, which includes platform effects and software processing. It is an end-to-end simulator, from the entrance of the telescope to the data acquisition at the detector, along with software blocks dealing, e.g., with demodulation, inversion, and compression. Developed following the Solar Orbiter/Polarimetric and Helioseismic Imager (SO/PHI) instrument, it comprises elements such as a filtergraph, polarimetric modulator, detector, vibrations, and accumulations. Through these, the simulator performs most of the analyses that can be done with light in astronomy, such as differential photometry, spectroscopy, and polarimetry. The simulator is coded with high flexibility and ease of implementation of new effects and subsystems. Thus, it allows for the user to adapt it to a wide variety of instruments, even not exclusively solar ones, as illustrated with an example of application to a night-time observation. The simulator can provide support in the phase of instrument design and help assess tolerances and test solutions to underperformances arising during the instrument operations. All this makes SOPHISM a very valuable tool for all the stages of astronomical instrument definition, design, operation, and lifetime tracking evaluation. Title: Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) for the SUNRISE balloon-borne solar observatory Authors: Suematsu, Yoshinori; Katsukawa, Yukio; Hara, Hirohisa; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito; Barthol, Peter; Riethmueller, Tino; Gandorfer, Achim; Feller, Alex; Orozco Suárez, David; Del Toro Iniesta, Jose Carlos; Kano, Ryouhei; Ishikawa, Shin-nosuke; Ishikawa, Ryohko; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Quintero Noda, Carlos; Tamura, Tomonori; Oba, Takayoshi; Kawabata, Yusuke; Nagata, Shinichi; Anan, Tetsu; Cobos Carrascosa, Juan Pedro; Lopez Jimenez, Antonio Carlos; Balaguer Jimenez, Maria; Solanki, Sami Bibcode: 2018cosp...42E3285S Altcode: The SUNRISE balloon-borne solar observatory carries a 1 m aperture optical telescope, and allows us to perform seeing-free continuous observations at visible-IR wavelengths from an altitude higher than 35 km. In the past two flights, in 2009 and 2013, observations mainly focused on fine structures of photospheric magnetic fields. For the third flight planned for 2021, we are developing a new instrument for conducting spectro-polarimetry of spectral lines formed over a larger height range in the solar atmosphere from the photosphere to the chromosphere. Targets of the spectro-polarimetric observation are (1) to determine 3D magnetic structure from the photosphere to the chromosphere, (2) to trace MHD waves from the photosphere to the chromosphere, and (3) to reveal the mechanism driving chromospheric jets, by measuring height- and time-dependent velocities and magnetic fields. To achieve these goals, a spectro-polarimeter called SCIP (Sunrise Chromospheric Infrared spectroPolarimeter) is designed to observe near-infrared spectrum lines sensitive to solar magnetic fields. The spatial and spectral resolutions are 0.2 arcsec and 200,000, respectively, while 0.03% polarimetric sensitivity is achieved within a 10 sec integration time. The optical system employs an Echelle grating and off-axis aspheric mirrors to observe the two wavelength ranges centered at 850 nm and 770 nm simultaneously by two cameras. Polarimetric measurements are performed using a rotating waveplate and polarization beam-splitters in front of the cameras. For detecting minute polarization signals with good precision, we carefully assess the temperature dependence of polarization optics, and make the opto-structural design that minimizes the thermal deformation of the spectrograph optics. Another key technique is to attain good (better than 30 msec) synchronization among the rotating phase of the waveplate, read-out timing of cameras, and step timing of a slit-scanning mirror. On-board accumulation and data processing are also critical because we cannot store all the raw data read-out from the cameras. We demonstrate that we can reduce the data down to almost 10% with loss-less image compression and without sacrificing polarimetric information in the data. The SCIP instrument is developed by internal collaboration among Japanese institutes including Japan Aerospace Exploration Agency (JAXA), the Spanish Sunrise consortium, and the German Max Planck Institute for Solar System Research (MPS) with a leadership of the National Astronomical Observatory of Japan (NAOJ). Title: The quick RTE inversion on FPGA for DKIST Authors: Cobos Carrascosa, J. P.; Ramos Mas, J. L.; Aparicio del Moral, B.; Hernández Expósito, D.; Sánchez Gómez, A.; Balaguer, M.; López Jiménez, A. C.; Orozco Suárez, D.; del Toro Iniesta, J. C. Bibcode: 2018SPIE10707E..0LC Altcode: In this contribution we present a multi-core system-on-chip, embedded on FPGA, for real-time data processing, to be used in the Daniel K. Inouye Solar Telescope (DKIST). Our system will provide "quick-look" magnetic field vector and line-of-sight velocity maps to help solar physicists to react to specific solar events or features during observations or to address specific phenomena while analyzing the data off line. The stand-alone device will be installed at the National Solar Observatory (NSO) Data Center. It will be integrated in the processing data pipeline through a software interface, and is competitive in computing speed to complex computer clusters. Title: Image compression on reconfigurable FPGA for the SO/PHI space instrument Authors: Hernández Expósito, D.; Cobos Carrascosa, J. P.; Ramos Mas, J. L.; Rodríguez Valido, M.; Orozco Suárez, D.; Hirzberger, J.; Woch, J.; Solanki, S.; del Toro Iniesta, J. C. Bibcode: 2018SPIE10707E..2FH Altcode: In this paper we present a novel FPGA implementation of the Consultative Committee for Space Data Systems Image Data Compression (CCSDS-IDC 122.0-B-1) for performing image compression aboard the Polarimetric Helioseismic Imager instrument of the ESA's Solar Orbiter mission. This is a System-On-Chip solution based on a light multicore architecture combined with an efficient ad-hoc Bit Plane Encoder core. This hardware architecture performs an acceleration of 30 times with respect to a software implementation running into space-qualified processors, like LEON3. The system stands out over other FPGA implementations because of the low resource usage, which does not use any external memory, and of its configurability. Title: Getting Ready for the Third Science Flight of SUNRISE Authors: Barthol, Peter; Katsukawa, Yukio; Lagg, Andreas; Solanki, Sami K.; Kubo, Masahito; Riethmueller, Tino; Martínez Pillet, Valentin; Gandorfer, Achim; Feller, Alex; Berkefeld, . Thomas; Orozco Suárez, David; Del Toro Iniesta, Jose Carlos; Bernasconi, Pietro; Álvarez-Herrero, Alberto; Quintero Noda, Carlos Bibcode: 2018cosp...42E.215B Altcode: SUNRISE is a balloon-borne, stratospheric solar observatory dedicated to the investigation of the structure and dynamics of the Sun's magnetic field and its interaction with convective plasma flows and waves. The previous science flights of SUNRISE in 2009 and 2013 have led to many new scientific results, so far described in around 90 refereed publications. This success has shown the huge potential of the SUNRISE concept and the recovery of the largely intact payload offers the opportunity for a third flight.The scientific instrumentation of SUNRISE 3 will have extended capabilities in particular to measure magnetic fields, plasma velocities and temperatures with increased sensitivity and over a larger height range in the solar atmosphere, from the convectively dominated photosphere up to the still poorly understood chromosphere. The latter is the key interaction region between magnetic field, waves and radiation and plays a central role in transporting energy to the outer layers of the solar atmosphere including the corona.SUNRISE 3 will carry 2 new grating-based spectro-polarimeters with slit-scanning and context imaging with slitjaw cameras. The SUNRISE UV Spectro-polarimeter and Imager (SUSI) will explore the rich near-UV range between 300 nm and 430 nm which is poorly accessible from the ground. The SUNRISE Chromospheric Infrared spectro-Polarimeter (SCIP) will sample 2 spectral windows in the near-infrared, containing many spectral lines highly sensitive to magnetic fields at different formation heights. In addition to the two new instruments the Imaging Magnetograph eXperiment (IMaX), an etalon-based tunable filtergraph and spectro-polarimeter flown on both previous missions, will be upgraded to IMaX+, enhancing its cadence and giving access to 2 spectral lines in the visible spectral range. All three instruments will allow investigating both the photosphere and the chromosphere and will ideally complement each other in terms of sensitivity, height coverage and resolution.A new gondola with a sophisticated attitude control system including roll damping will provide improved pointing/tracking performance. Upgraded image stabilization with higher bandwidth will further reduce residual jitter, maximizing the quality of the science data.SUNRISE 3 is a joint project of the German Max-Planck-Institut für Sonnensystemforschung together with the Spanish SUNRISE consortium, the Johns Hopkins University Applied Physics Laboratory, USA, the German Kiepenheuer Institut für Sonnenphysik, the National Astronomical Observatory of Japan and the Japan Aerospace eXploraion Agency (JAXA). Title: Autonomous on-board data processing and instrument calibration software for the SO/PHI Authors: Albert, K.; Hirzberger, J.; Busse, D.; Lange, T.; Kolleck, M.; Fiethe, B.; Orozco Suárez, D.; Woch, J.; Schou, J.; Blanco Rodriguez, J.; Gandorfer, A.; Guan, Y.; Cobos Carrascosa, J. P.; Hernández Expósito, D.; del Toro Iniesta, J. C.; Solanki, S. K.; Michalik, H. Bibcode: 2018SPIE10707E..0OA Altcode: 2018arXiv181003493A The extension of on-board data processing capabilities is an attractive option to reduce telemetry for scientific instruments on deep space missions. The challenges that this presents, however, require a comprehensive software system, which operates on the limited resources a data processing unit in space allows. We implemented such a system for the Polarimetric and Helioseismic Imager (PHI) on-board the Solar Orbiter (SO) spacecraft. It ensures autonomous operation to handle long command-response times, easy changing of the processes after new lessons have been learned and meticulous book-keeping of all operations to ensure scientific accuracy. This contribution presents the requirements and main aspects of the software implementation, followed by an example of a task implemented in the software frame, and results from running it on SO/PHI. The presented example shows that the different parts of the software framework work well together, and that the system processes data as we expect. The flexibility of the framework makes it possible to use it as a baseline for future applications with similar needs and limitations as SO/PHI. Title: Solar polarimetry in the K I D2 line : A novel possibility for a stratospheric balloon Authors: Quintero Noda, C.; Villanueva, G. L.; Katsukawa, Y.; Solanki, S. K.; Orozco Suárez, D.; Ruiz Cobo, B.; Shimizu, T.; Oba, T.; Kubo, M.; Anan, T.; Ichimoto, K.; Suematsu, Y. Bibcode: 2018A&A...610A..79Q Altcode: 2018arXiv180101655Q Of the two solar lines, K I D1 and D2, almost all attention so far has been devoted to the D1 line, as D2 is severely affected by an O2 atmospheric band. This, however, makes the latter appealing for balloon and space observations from above (most of) the Earth's atmosphere. We estimate the residual effect of the O2 band on the K I D2 line at altitudes typical for stratospheric balloons. Our aim is to study the feasibility of observing the 770 nm window. Specifically, this paper serves as a preparation for the third flight of the Sunrise balloon-borne observatory. The results indicate that the absorption by O2 is still present, albeit much weaker, at the expected balloon altitude. We applied the obtained O2 transmittance to K I D2 synthetic polarimetric spectra and found that in the absence of line-of-sight motions, the residual O2 has a negligible effect on the K I D2 line. On the other hand, for Doppler-shifted K I D2 data, the residual O2 might alter the shape of the Stokes profiles. However, the residual O2 absorption is sufficiently weak at stratospheric levels that it can be divided out if appropriate measurements are made, something that is impossible at ground level. Therefore, for the first time with Sunrise III, we will be able to perform polarimetric observations of the K I D2 line and, consequently, we will have improved access to the thermodynamics and magnetic properties of the upper photosphere from observations of the K I lines. Title: Detection of emission in the Si I 1082.7 nm line core in sunspot umbrae Authors: Orozco Suárez, D.; Quintero Noda, C.; Ruiz Cobo, B.; Collados Vera, M.; Felipe, T. Bibcode: 2017A&A...607A.102O Altcode: 2017arXiv170906773O Context. Determining empirical atmospheric models for the solar chromosphere is difficult since it requires the observation and analysis of spectral lines that are affected by non-local thermodynamic equilibrium (NLTE) effects. This task is especially difficult in sunspot umbrae because of lower continuum intensity values in these regions with respect to the surrounding brighter granulation. Umbral data is therefore more strongly affected by the noise and by the so-called scattered light, among other effects.
Aims: The purpose of this study is to analyze spectropolarimetric sunspot umbra observations taken in the near-infrared Si I 1082.7 nm line taking NLTE effects into account. Interestingly, we detected emission features at the line core of the Si I 1082.7 nm line in the sunspot umbra. Here we analyze the data in detail and offer a possible explanation for the Si I 1082.7 nm line emission.
Methods: Full Stokes measurements of a sunspot near disk center in the near-infrared spectral range were obtained with the GRIS instrument installed at the German GREGOR telescope. A point spread function (PSF) including the effects of the telescope, the Earth's atmospheric seeing, and the scattered light was constructed using prior Mercury observations with GRIS and the information provided by the adaptive optics system of the GREGOR telescope during the observations. The data were then deconvolved from the PSF using a principal component analysis deconvolution method and were analyzed via the NICOLE inversion code, which accounts for NLTE effects in the Si I 1082.7 nm line. The information of the vector magnetic field was included in the inversion process.
Results: The Si I 1082.7 nm line seems to be in emission in the umbra of the observed sunspot after the effects of scattered light (stray light coming from wide angles) are removed. We show how the spectral line shape of umbral profiles changes dramatically with the amount of scattered light. Indeed, the continuum levels range, on average, from 44% of the quiet Sun continuum intensity to about 20%. Although very low, the inferred levels are in line with current model predictions and empirical umbral models. The Si I 1082.7 nm line is in emission after adding more that 30% of scattered light so that it is very sensitive to a proper determination of the PSF. Additionally, we have thoroughly investigated whether the emission is a byproduct of the particular deconvolution technique but have not found any evidence to the contrary. Only the circular polarization signals seem to be more sensitive to the deconvolution strategy because of the larger amount of noise in the umbra. Interestingly, current umbral empirical models are not able to reproduce the emission in the deconvolved umbral Stokes profiles. The results of the NLTE inversions suggests that to obtain the emission in the Si I 1082.7 nm line, the temperature stratification should first have a hump located at about log τ = -2 and start rising at lower heights when moving into the transition region.
Conclusions: This is, to our knowledge, the first time the Si I 1082.7 nm line is seen in emission in sunspot umbrae. The results show that the temperature stratification of current umbral models may be more complex than expected with the transition region located at lower heights above sunspot umbrae. Our finding might provide insights into understanding why the sunspot umbra emission in the millimeter spectral range is less than that predicted by current empirical umbral models. Title: Chromospheric polarimetry through multiline observations of the 850-nm spectral region - II. A magnetic flux tube scenario Authors: Quintero Noda, C.; Kato, Y.; Katsukawa, Y.; Oba, T.; de la Cruz Rodríguez, J.; Carlsson, M.; Shimizu, T.; Orozco Suárez, D.; Ruiz Cobo, B.; Kubo, M.; Anan, T.; Ichimoto, K.; Suematsu, Y. Bibcode: 2017MNRAS.472..727Q Altcode: 2017arXiv170801333Q In this publication, we continue the work started in Quintero Noda et al., examining this time a numerical simulation of a magnetic flux tube concentration. Our goal is to study if the physical phenomena that take place in it, in particular, the magnetic pumping, leaves a specific imprint on the examined spectral lines. We find that the profiles from the interior of the flux tube are periodically doppler shifted following an oscillation pattern that is also reflected in the amplitude of the circular polarization signals. In addition, we analyse the properties of the Stokes profiles at the edges of the flux tube discovering the presence of linear polarization signals for the Ca II lines, although they are weak with an amplitude around 0.5 per cent of the continuum intensity. Finally, we compute the response functions to perturbations in the longitudinal field, and we estimate the field strength using the weak-field approximation. Our results indicate that the height of formation of the spectral lines changes during the magnetic pumping process, which makes the interpretation of the inferred magnetic field strength and its evolution more difficult. These results complement those from previous works, demonstrating the capabilities and limitations of the 850-nm spectrum for chromospheric Zeeman polarimetry in a very dynamic and complex atmosphere. Title: The Maximum Entropy Limit of Small-scale Magnetic Field Fluctuations in the Quiet Sun Authors: Gorobets, A. Y.; Berdyugina, S. V.; Riethmüller, T. L.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2017ApJS..233....5G Altcode: 2017arXiv171008361G The observed magnetic field on the solar surface is characterized by a very complex spatial and temporal behavior. Although feature-tracking algorithms have allowed us to deepen our understanding of this behavior, subjectivity plays an important role in the identification and tracking of such features. In this paper, we continue studies of the temporal stochasticity of the magnetic field on the solar surface without relying either on the concept of magnetic features or on subjective assumptions about their identification and interaction. We propose a data analysis method to quantify fluctuations of the line-of-sight magnetic field by means of reducing the temporal field’s evolution to the regular Markov process. We build a representative model of fluctuations converging to the unique stationary (equilibrium) distribution in the long time limit with maximum entropy. We obtained different rates of convergence to the equilibrium at fixed noise cutoff for two sets of data. This indicates a strong influence of the data spatial resolution and mixing-polarity fluctuations on the relaxation process. The analysis is applied to observations of magnetic fields of the relatively quiet areas around an active region carried out during the second flight of the Sunrise/IMaX and quiet Sun areas at the disk center from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory satellite. Title: Flows along arch filaments observed in the GRIS `very fast spectroscopic mode' Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.; Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier, R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2017IAUS..327...28G Altcode: 2017arXiv170102206G A new generation of solar instruments provides improved spectral, spatial, and temporal resolution, thus facilitating a better understanding of dynamic processes on the Sun. High-resolution observations often reveal multiple-component spectral line profiles, e.g., in the near-infrared He i 10830 Å triplet, which provides information about the chromospheric velocity and magnetic fine structure. We observed an emerging flux region, including two small pores and an arch filament system, on 2015 April 17 with the `very fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS) situated at the 1.5-meter GREGOR solar telescope at Observatorio del Teide, Tenerife, Spain. We discuss this method of obtaining fast (one per minute) spectral scans of the solar surface and its potential to follow dynamic processes on the Sun. We demonstrate the performance of the `very fast spectroscopic mode' by tracking chromospheric high-velocity features in the arch filament system. Title: Solar polarimetry through the K I lines at 770 nm Authors: Quintero Noda, C.; Uitenbroek, H.; Katsukawa, Y.; Shimizu, T.; Oba, T.; Carlsson, M.; Orozco Suárez, D.; Ruiz Cobo, B.; Kubo, M.; Anan, T.; Ichimoto, K.; Suematsu, Y. Bibcode: 2017MNRAS.470.1453Q Altcode: 2017arXiv170510002Q We characterize the K I D1 & D2 lines in order to determine whether they could complement the 850 nm window, containing the Ca II infrared triplet lines and several Zeeman sensitive photospheric lines, that was studied previously. We investigate the effect of partial redistribution on the intensity profiles, their sensitivity to changes in different atmospheric parameters, and the spatial distribution of Zeeman polarization signals employing a realistic magnetohydrodynamic simulation. The results show that these lines form in the upper photosphere at around 500 km, and that they are sensitive to the line-of-sight velocity and magnetic field strength at heights where neither the photospheric lines nor the Ca II infrared lines are. However, at the same time, we found that their sensitivity to the temperature essentially comes from the photosphere. Then, we conclude that the K I lines provide a complement to the lines in the 850 nm window for the determination of atmospheric parameters in the upper photosphere, especially for the line-of-sight velocity and the magnetic field. Title: Erratum: Morphological Properties of Slender CaII H Fibrils Observed by sunrise II (ApJS 229, 1, 6) Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.; van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.; Riethmüller, T. L.; Schmidt, W. Bibcode: 2017ApJS..230...11G Altcode: No abstract at ADS Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low Solar Chromosphere Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.; Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez, J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez, D.; Schmidt, W. Bibcode: 2017ApJS..229...11J Altcode: 2016arXiv161003104J A dense forest of slender bright fibrils near a small solar active region is seen in high-quality narrowband Ca II H images from the SuFI instrument onboard the Sunrise balloon-borne solar observatory. The orientation of these slender Ca II H fibrils (SCF) overlaps with the magnetic field configuration in the low solar chromosphere derived by magnetostatic extrapolation of the photospheric field observed with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are qualitatively aligned with small-scale loops computed from a novel inversion approach based on best-fit numerical MHD simulation. Such loops are organized in canopy-like arches over quiet areas that differ in height depending on the field strength near their roots. Title: Magneto-static Modeling from Sunrise/IMaX: Application to an Active Region Observed with Sunrise II Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2017ApJS..229...18W Altcode: 2017arXiv170101458N; 2017arXiv170101458W Magneto-static models may overcome some of the issues facing force-free magnetic field extrapolations. So far they have seen limited use and have faced problems when applied to quiet-Sun data. Here we present a first application to an active region. We use solar vector magnetic field measurements gathered by the IMaX polarimeter during the flight of the Sunrise balloon-borne solar observatory in 2013 June as boundary conditions for a magneto-static model of the higher solar atmosphere above an active region. The IMaX data are embedded in active region vector magnetograms observed with SDO/HMI. This work continues our magneto-static extrapolation approach, which was applied earlier to a quiet-Sun region observed with Sunrise I. In an active region the signal-to-noise-ratio in the measured Stokes parameters is considerably higher than in the quiet-Sun and consequently the IMaX measurements of the horizontal photospheric magnetic field allow us to specify the free parameters of the model in a special class of linear magneto-static equilibria. The high spatial resolution of IMaX (110-130 km, pixel size 40 km) enables us to model the non-force-free layer between the photosphere and the mid-chromosphere vertically by about 50 grid points. In our approach we can incorporate some aspects of the mixed beta layer of photosphere and chromosphere, e.g., taking a finite Lorentz force into account, which was not possible with lower-resolution photospheric measurements in the past. The linear model does not, however, permit us to model intrinsic nonlinear structures like strongly localized electric currents. Title: The Second Flight of the Sunrise Balloon-borne Solar Observatory: Overview of Instrument Updates, the Flight, the Data, and First Results Authors: Solanki, S. K.; Riethmüller, T. L.; Barthol, P.; Danilovic, S.; Deutsch, W.; Doerr, H. -P.; Feller, A.; Gandorfer, A.; Germerott, D.; Gizon, L.; Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.; Lagg, A.; Meller, R.; Tomasch, G.; van Noort, M.; Blanco Rodríguez, J.; Gasent Blesa, J. L.; Balaguer Jiménez, M.; Del Toro Iniesta, J. C.; López Jiménez, A. C.; Orozco Suarez, D.; Berkefeld, T.; Halbgewachs, C.; Schmidt, W.; Álvarez-Herrero, A.; Sabau-Graziati, L.; Pérez Grande, I.; Martínez Pillet, V.; Card, G.; Centeno, R.; Knölker, M.; Lecinski, A. Bibcode: 2017ApJS..229....2S Altcode: 2017arXiv170101555S The Sunrise balloon-borne solar observatory, consisting of a 1 m aperture telescope that provides a stabilized image to a UV filter imager and an imaging vector polarimeter, carried out its second science flight in 2013 June. It provided observations of parts of active regions at high spatial resolution, including the first high-resolution images in the Mg II k line. The obtained data are of very high quality, with the best UV images reaching the diffraction limit of the telescope at 3000 Å after Multi-Frame Blind Deconvolution reconstruction accounting for phase-diversity information. Here a brief update is given of the instruments and the data reduction techniques, which includes an inversion of the polarimetric data. Mainly those aspects that evolved compared with the first flight are described. A tabular overview of the observations is given. In addition, an example time series of a part of the emerging active region NOAA AR 11768 observed relatively close to disk center is described and discussed in some detail. The observations cover the pores in the trailing polarity of the active region, as well as the polarity inversion line where flux emergence was ongoing and a small flare-like brightening occurred in the course of the time series. The pores are found to contain magnetic field strengths ranging up to 2500 G, and while large pores are clearly darker and cooler than the quiet Sun in all layers of the photosphere, the temperature and brightness of small pores approach or even exceed those of the quiet Sun in the upper photosphere. Title: A Tale of Two Emergences: Sunrise II Observations of Emergence Sites in a Solar Active Region Authors: Centeno, R.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.; Orozco Suárez, D.; Berkefeld, T.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2017ApJS..229....3C Altcode: 2016arXiv161003531C In 2013 June, the two scientific instruments on board the second Sunrise mission witnessed, in detail, a small-scale magnetic flux emergence event as part of the birth of an active region. The Imaging Magnetograph Experiment (IMaX) recorded two small (∼ 5\prime\prime ) emerging flux patches in the polarized filtergrams of a photospheric Fe I spectral line. Meanwhile, the Sunrise Filter Imager (SuFI) captured the highly dynamic chromospheric response to the magnetic fields pushing their way through the lower solar atmosphere. The serendipitous capture of this event offers a closer look at the inner workings of active region emergence sites. In particular, it reveals in meticulous detail how the rising magnetic fields interact with the granulation as they push through the Sun’s surface, dragging photospheric plasma in their upward travel. The plasma that is burdening the rising field slides along the field lines, creating fast downflowing channels at the footpoints. The weight of this material anchors this field to the surface at semi-regular spatial intervals, shaping it in an undulatory fashion. Finally, magnetic reconnection enables the field to release itself from its photospheric anchors, allowing it to continue its voyage up to higher layers. This process releases energy that lights up the arch-filament systems and heats the surrounding chromosphere. Title: Photospheric Response to an Ellerman Bomb-like Event—An Analogy of Sunrise/IMaX Observations and MHD Simulations Authors: Danilovic, S.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2017ApJS..229....5D Altcode: 2016arXiv160903817D Ellerman Bombs are signatures of magnetic reconnection, which is an important physical process in the solar atmosphere. How and where they occur is a subject of debate. In this paper, we analyze Sunrise/IMaX data, along with 3D MHD simulations that aim to reproduce the exact scenario proposed for the formation of these features. Although the observed event seems to be more dynamic and violent than the simulated one, simulations clearly confirm the basic scenario for the production of EBs. The simulations also reveal the full complexity of the underlying process. The simulated observations show that the Fe I 525.02 nm line gives no information on the height where reconnection takes place. It can only give clues about the heating in the aftermath of the reconnection. However, the information on the magnetic field vector and velocity at this spatial resolution is extremely valuable because it shows what numerical models miss and how they can be improved. Title: Transverse Oscillations in Slender Ca II H Fibrils Observed with Sunrise/SuFI Authors: Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.; van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.; Riethmüller, T. L.; Schmidt, W. Bibcode: 2017ApJS..229....9J Altcode: 2016arXiv161007449J We present observations of transverse oscillations in slender Ca II H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high- (spatial and temporal-) resolution seeing-free observations in a 1.1 Å wide passband covering the line core of Ca II H 3969 Å from the second flight of the Sunrise balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 2.4 ± 0.8 km s-1 and 83 ± 29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9 ± 14 km s-1. While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvénic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapid high-frequency transverse waves, often produced in the lower photosphere, can penetrate into the chromosphere with an estimated energy flux of ≈15 kW m-2. Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere. Title: Kinematics of Magnetic Bright Features in the Solar Photosphere Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez, D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M. Bibcode: 2017ApJS..229....8J Altcode: 2016arXiv161007634J Convective flows are known as the prime means of transporting magnetic fields on the solar surface. Thus, small magnetic structures are good tracers of turbulent flows. We study the migration and dispersal of magnetic bright features (MBFs) in intergranular areas observed at high spatial resolution with Sunrise/IMaX. We describe the flux dispersal of individual MBFs as a diffusion process whose parameters are computed for various areas in the quiet-Sun and the vicinity of active regions from seeing-free data. We find that magnetic concentrations are best described as random walkers close to network areas (diffusion index, γ =1.0), travelers with constant speeds over a supergranule (γ =1.9{--}2.0), and decelerating movers in the vicinity of flux emergence and/or within active regions (γ =1.4{--}1.5). The three types of regions host MBFs with mean diffusion coefficients of 130 km2 s-1, 80-90 km2 s-1, and 25-70 km2 s-1, respectively. The MBFs in these three types of regions are found to display a distinct kinematic behavior at a confidence level in excess of 95%. Title: Spectropolarimetric Evidence for a Siphon Flow along an Emerging Magnetic Flux Tube Authors: Requerey, Iker S.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2017ApJS..229...15R Altcode: 2016arXiv161106732R We study the dynamics and topology of an emerging magnetic flux concentration using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board the sunrise balloon-borne solar observatory. We obtain the full vector magnetic field and the line of sight (LOS) velocity through inversions of the Fe I line at 525.02 nm with the SPINOR code. The derived vector magnetic field is used to trace magnetic field lines. Two magnetic flux concentrations with different polarities and LOS velocities are found to be connected by a group of arch-shaped magnetic field lines. The positive polarity footpoint is weaker (1100 G) and displays an upflow, while the negative polarity footpoint is stronger (2200 G) and shows a downflow. This configuration is naturally interpreted as a siphon flow along an arched magnetic flux tube. Title: Morphological Properties of Slender Ca II H Fibrils Observed by SUNRISE II Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.; van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.; Riethmüller, T. L.; Schmidt, W. Bibcode: 2017ApJS..229....6G Altcode: 2016arXiv161200319G We use seeing-free high spatial resolution Ca II H data obtained by the SUNRISE observatory to determine properties of slender fibrils in the lower solar chromosphere. In this work we use intensity images taken with the SuFI instrument in the Ca II H line during the second scientific flight of the SUNRISE observatory to identify and track elongated bright structures. After identification, we analyze theses structures to extract their morphological properties. We identify 598 slender Ca II H fibrils (SCFs) with an average width of around 180 km, length between 500 and 4000 km, average lifetime of ≈400 s, and average curvature of 0.002 arcsec-1. The maximum lifetime of the SCFs within our time series of 57 minutes is ≈2000 s. We discuss similarities and differences of the SCFs with other small-scale, chromospheric structures such as spicules of type I and II, or Ca II K fibrils. Title: A New MHD-assisted Stokes Inversion Technique Authors: Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2017ApJS..229...16R Altcode: 2016arXiv161105175R We present a new method of Stokes inversion of spectropolarimetric data and evaluate it by taking the example of a Sunrise/IMaX observation. An archive of synthetic Stokes profiles is obtained by the spectral synthesis of state-of-the-art magnetohydrodynamics (MHD) simulations and a realistic degradation to the level of the observed data. The definition of a merit function allows the archive to be searched for the synthetic Stokes profiles that best match the observed profiles. In contrast to traditional Stokes inversion codes, which solve the Unno-Rachkovsky equations for the polarized radiative transfer numerically and fit the Stokes profiles iteratively, the new technique provides the full set of atmospheric parameters. This gives us the ability to start an MHD simulation that takes the inversion result as an initial condition. After a relaxation process of half an hour solar time we obtain physically consistent MHD data sets with a target similar to the observation. The new MHD simulation is used to repeat the method in a second iteration, which further improves the match between observation and simulation, resulting in a factor of 2.2 lower mean {χ }2 value. One advantage of the new technique is that it provides the physical parameters on a geometrical height scale. It constitutes a first step toward inversions that give results consistent with the MHD equations. Title: Oscillations on Width and Intensity of Slender Ca II H Fibrils from Sunrise/SuFI Authors: Gafeira, R.; Jafarzadeh, S.; Solanki, S. K.; Lagg, A.; van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.; Riethmüller, T. L.; Schmidt, W. Bibcode: 2017ApJS..229....7G Altcode: 2017arXiv170102801G We report the detection of oscillations in slender Ca II H fibrils (SCFs) from high-resolution observations acquired with the Sunrise balloon-borne solar observatory. The SCFs show obvious oscillations in their intensity, but also their width. The oscillatory behaviors are investigated at several positions along the axes of the SCFs. A large majority of fibrils show signs of oscillations in intensity. Their periods and phase speeds are analyzed using a wavelet analysis. The width and intensity perturbations have overlapping distributions of the wave period. The obtained distributions have median values of the period of 32 ± 17 s and 36 ± 25 s, respectively. We find that the fluctuations of both parameters propagate in the SCFs with speeds of {11}-11+49 km s-1 and {15}-15+34 km s-1, respectively. Furthermore, the width and intensity oscillations have a strong tendency to be either in anti-phase or, to a smaller extent, in phase. This suggests that the oscillations of both parameters are caused by the same wave mode and that the waves are likely propagating. Taking all the evidence together, the most likely wave mode to explain all measurements and criteria is the fast sausage mode. Title: Solar Coronal Loops Associated with Small-scale Mixed Polarity Surface Magnetic Fields Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2017ApJS..229....4C Altcode: 2016arXiv161007484C How and where are coronal loops rooted in the solar lower atmosphere? The details of the magnetic environment and its evolution at the footpoints of coronal loops are crucial to understanding the processes of mass and energy supply to the solar corona. To address the above question, we use high-resolution line-of-sight magnetic field data from the Imaging Magnetograph eXperiment instrument on the Sunrise balloon-borne observatory and coronal observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory of an emerging active region. We find that the coronal loops are often rooted at the locations with minor small-scale but persistent opposite-polarity magnetic elements very close to the larger dominant polarity. These opposite-polarity small-scale elements continually interact with the dominant polarity underlying the coronal loop through flux cancellation. At these locations we detect small inverse Y-shaped jets in chromospheric Ca II H images obtained from the Sunrise Filter Imager during the flux cancellation. Our results indicate that magnetic flux cancellation and reconnection at the base of coronal loops due to mixed polarity fields might be a crucial feature for the supply of mass and energy into the corona. Title: Moving Magnetic Features around a Pore Authors: Kaithakkal, A. J.; Riethmüller, T. L.; Solanki, S. K.; Lagg, A.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; vanNoort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2017ApJS..229...13K Altcode: 2016arXiv160905664K Spectropolarimetric observations from Sunrise/IMaX, obtained in 2013 June, are used for a statistical analysis to determine the physical properties of moving magnetic features (MMFs) observed near a pore. MMFs of the same and opposite polarity, with respect to the pore, are found to stream from its border at an average speed of 1.3 km s-1 and 1.2 km s-1, respectively, with mainly same-polarity MMFs found further away from the pore. MMFs of both polarities are found to harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs are blueshifted, whereas same-polarity MMFs do not show any preference for up- or downflows. Most of the MMFs are found to be of sub-arcsecond size and carry a mean flux of ∼1.2 × 1017 Mx. Title: Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.; Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.; Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe, O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.; Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H. Bibcode: 2016A&A...596A...2B Altcode: 2016arXiv160708165B Context. Some models for the topology of the magnetic field in sunspot penumbrae predict regions free of magnetic fields or with only dynamically weak fields in the deep photosphere.
Aims: We aim to confirm or refute the existence of weak-field regions in the deepest photospheric layers of the penumbra.
Methods: We investigated the magnetic field at log τ5 = 0 is by inverting spectropolarimetric data of two different sunspots located very close to disk center with a spatial resolution of approximately 0.4-0.45''. The data have been recorded using the GRIS instrument attached to the 1.5-m solar telescope GREGOR at the El Teide observatory. The data include three Fe I lines around 1565 nm, whose sensitivity to the magnetic field peaks half a pressure scale height deeper than the sensitivity of the widely used Fe I spectral line pair at 630 nm. Before the inversion, the data were corrected for the effects of scattered light using a deconvolution method with several point spread functions.
Results: At log τ5 = 0 we find no evidence of regions with dynamically weak (B< 500 Gauss) magnetic fields in sunspot penumbrae. This result is much more reliable than previous investigations made on Fe I lines at 630 nm. Moreover, the result is independent of the number of nodes employed in the inversion, is independent of the point spread function used to deconvolve the data, and does not depend on the amount of stray light (I.e., wide-angle scattered light) considered. Title: Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.; Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.; Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1050B Altcode: 2016arXiv160901514B Arch filament systems occur in active sunspot groups, where a fibril structure connects areas of opposite magnetic polarity, in contrast to active region filaments that follow the polarity inversion line. We used the GREGOR Infrared Spectrograph (GRIS) to obtain the full Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0 nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line to investigate the photospheric magnetic field and velocities, and use the line core intensities and velocities of the helium line to study the chromospheric plasma. The individual fibrils of the arch filament system connect the sunspot with patches of magnetic polarity opposite to that of the spot. These patches do not necessarily coincide with pores, where the magnetic field is strongest. Instead, areas are preferred not far from the polarity inversion line. These areas exhibit photospheric downflows of moderate velocity, but significantly higher downflows of up to 30 km s-1 in the chromospheric helium line. Our findings can be explained with new emerging flux where the matter flows downward along the field lines of rising flux tubes, in agreement with earlier results. Title: Upper chromospheric magnetic field of a sunspot penumbra: observations of fine structure Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados, M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar, H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.; Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A...8J Altcode: 2016arXiv160801988J
Aims: The fine-structure of the magnetic field in a sunspot penumbra in the upper chromosphere is to be explored and compared to that in the photosphere.
Methods: Spectropolarimetric observations with high spatial resolution were recorded with the 1.5-m GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The observed spectral domain includes the upper chromospheric Hei triplet at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å spectral lines. The upper chromospheric magnetic field is obtained by inverting the Hei triplet assuming a Milne-Eddington-type model atmosphere. A height-dependent inversion was applied to the Sii 10 827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic field.
Results: We find that the inclination of the magnetic field varies in the azimuthal direction in the photosphere and in the upper chromosphere. The chromospheric variations coincide remarkably well with the variations in the inclination of the photospheric field and resemble the well-known spine and interspine structure in the photospheric layers of penumbrae. The typical peak-to-peak variations in the inclination of the magnetic field in the upper chromosphere are found to be 10°-15°, which is roughly half the variation in the photosphere. In contrast, the magnetic field strength of the observed penumbra does not vary on small spatial scales in the upper chromosphere.
Conclusions: Thanks to the high spatial resolution of the observations that is possible with the GREGOR telescope at 1.08 microns, we find that the prominent small-scale fluctuations in the magnetic field inclination, which are a salient part of the property of sunspot penumbral photospheres, also persist in the chromosphere, although at somewhat reduced amplitudes. Such a complex magnetic configuration may facilitate penumbral chromospheric dynamic phenomena, such as penumbral micro-jets or transient bright dots. Title: Probing deep photospheric layers of the quiet Sun with high magnetic sensitivity Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González, M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.; Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.; Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.; Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier, K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.; Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.; Schmidt, D.; Kiess, C.; Nicklas, H. Bibcode: 2016A&A...596A...6L Altcode: 2016arXiv160506324L Context. Investigations of the magnetism of the quiet Sun are hindered by extremely weak polarization signals in Fraunhofer spectral lines. Photon noise, straylight, and the systematically different sensitivity of the Zeeman effect to longitudinal and transversal magnetic fields result in controversial results in terms of the strength and angular distribution of the magnetic field vector.
Aims: The information content of Stokes measurements close to the diffraction limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of spatial straylight and photon noise into account.
Methods: Highly sensitive full Stokes measurements of a quiet-Sun region at disk center in the deep photospheric Fe I lines in the 1.56 μm region were obtained with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise statistics and Stokes V asymmetries were analyzed and compared to a similar data set of the Hinode spectropolarimeter (SOT/SP). Simple diagnostics based directly on the shape and strength of the profiles were applied to the GRIS data. We made use of the magnetic line ratio technique, which was tested against realistic magneto-hydrodynamic simulations (MURaM).
Results: About 80% of the GRIS spectra of a very quiet solar region show polarimetric signals above a 3σ level. Area and amplitude asymmetries agree well with small-scale surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss range with some concentrations of kilo-Gauss fields.
Conclusions: The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4 are so far unique in the combination of high spatial resolution scans and high magnetic field sensitivity. Nevertheless, the unavoidable effect of spatial straylight and the resulting dilution of the weak Stokes profiles means that inversion techniques still bear a high risk of misinterpretating the data. Title: Flow and magnetic field properties in the trailing sunspots of active region NOAA 12396 Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer, C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados, M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1090V Altcode: Improved measurements of the photospheric and chromospheric three-dimensional magnetic and flow fields are crucial for a precise determination of the origin and evolution of active regions. We present an illustrative sample of multi-instrument data acquired during a two-week coordinated observing campaign in August 2015 involving, among others, the GREGOR solar telescope (imaging and near-infrared spectroscopy) and the space missions Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS). The observations focused on the trailing part of active region NOAA 12396 with complex polarity inversion lines and strong intrusions of opposite polarity flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV spectral profiles in the photospheric Si I λ1082.7 nm line, the chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I λ1083.9 nm line. Carefully calibrated GRIS scans of the active region provided maps of Doppler velocity and magnetic field at different atmospheric heights. We compare quick-look maps with those obtained with the ``Stokes Inversions based on Response functions'' (SIR) code, which furnishes deeper insight into the magnetic properties of the region. We find supporting evidence that newly emerging flux and intruding opposite polarity flux are hampering the formation of penumbrae, i.e., a penumbra fully surrounding a sunspot is only expected after cessation of flux emergence in proximity to the sunspots. Title: Three-dimensional structure of a sunspot light bridge Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.; Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A..59F Altcode: 2016arXiv161104803F Context. Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation are fundamental problems in solar physics. Light bridges are commonly present during sunspot decay, but a comprehensive picture of their role in the removal of the photospheric magnetic field is still lacking.
Aims: We study the three-dimensional configuration of a sunspot, and in particular, its light bridge, during one of the last stages of its decay.
Methods: We present the magnetic and thermodynamical stratification inferred from full Stokes inversions of the photospheric Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR Infrared Spectrograph of the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The analysis is complemented by a study of continuum images covering the disk passage of the active region, which are provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory.
Results: The sunspot shows a light bridge with penumbral continuum intensity that separates the central umbra from a smaller umbra. We find that in this region the magnetic field lines form a canopy with lower magnetic field strength in the inner part. The photospheric light bridge is dominated by gas pressure (high-β), as opposed to the surrounding umbra, where the magnetic pressure is higher. A convective flow is observed in the light bridge. This flow is able to bend the magnetic field lines and to produce field reversals. The field lines merge above the light bridge and become as vertical and strong as in the surrounding umbra. We conclude that this occurs because two highly magnetized regions approach each other during the sunspot evolution.

Movies associated to Figs. 2 and 13 are available at http://www.aanda.org Title: Fitting peculiar spectral profiles in He I 10830Å absorption features Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.; Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.; Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1057G Altcode: 2016arXiv160300679G The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He I 10830 Å triplet presents such peculiar spectral profiles, which give information on the velocity and magnetic fine structure of the upper chromosphere. The purpose of this investigation is to describe a technique to efficiently fit the two blended components of the He I 10830 Å triplet, which are commonly observed when two atmospheric components are located within the same resolution element. The observations used in this study were taken on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar telescope, located at the Observatorio del Teide, Tenerife, Spain. We apply a double-Lorentzian fitting technique using Levenberg-Marquardt least-squares minimization. This technique is very simple and much faster than inversion codes. Line-of-sight Doppler velocities can be inferred for a whole map of pixels within just a few minutes. Our results show sub- and supersonic downflow velocities of up to 32 km s-1 for the fast component in the vicinity of footpoints of filamentary structures. The slow component presents velocities close to rest. 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: Spatial deconvolution of spectropolarimetric data: an application to quiet Sun magnetic elements Authors: Quintero Noda, C.; Asensio Ramos, A.; Orozco Suárez, D.; Ruiz Cobo, B. Bibcode: 2015A&A...579A...3Q Altcode: 2015arXiv150503219Q Context. One of the difficulties in extracting reliable information about the thermodynamical and magnetic properties of solar plasmas from spectropolarimetric observations is the presence of light dispersed inside the instruments, known as stray light.
Aims: We aim to analyze quiet Sun observations after the spatial deconvolution of the data. We examine the validity of the deconvolution process with noisy data as we analyze the physical properties of quiet Sun magnetic elements.
Methods: We used a regularization method that decouples the Stokes inversion from the deconvolution process, so that large maps can be quickly inverted without much additional computational burden. We applied the method on Hinode quiet Sun spectropolarimetric data. We examined the spatial and polarimetric properties of the deconvolved profiles, comparing them with the original data. After that, we inverted the Stokes profiles using the Stokes Inversion based on Response functions (SIR) code, which allow us to obtain the optical depth dependence of the atmospheric physical parameters.
Results: The deconvolution process increases the contrast of continuum images and makes the magnetic structures sharper. The deconvolved Stokes I profiles reveal the presence of the Zeeman splitting while the Stokes V profiles significantly change their amplitude. The area and amplitude asymmetries of these profiles increase in absolute value after the deconvolution process. We inverted the original Stokes profiles from a magnetic element and found that the magnetic field intensity reproduces the overall behavior of theoretical magnetic flux tubes, that is, the magnetic field lines are vertical in the center of the structure and start to fan when we move far away from the center of the magnetic element. The magnetic field vector inferred from the deconvolved Stokes profiles also mimic a magnetic flux tube but in this case we found stronger field strengths and the gradients along the line-of-sight are larger for the magnetic field intensity and for its inclination. Moreover, the discontinuity between the magnetic and non magnetic environment in the flux tube gets sharper.
Conclusions: The deconvolution process used in this paper reveals information that the smearing induced by the point spread function (PSF) of the telescope hides. Additionally, the deconvolution is done with a low computational load, making it appealing for its use on the analysis of large data sets.

A copy of the IDL code is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A3 Title: VizieR Online Data Catalog: Spatial deconvolution code (Quintero Noda+, 2015) Authors: Quintero Noda, C.; Asensio Ramos, A.; Orozco Suarez, D.; Ruiz Cobo, B. Bibcode: 2015yCat..35790003Q Altcode: This deconvolution method follows the scheme presented in Ruiz Cobo & Asensio Ramos (2013A&A...549L...4R) The Stokes parameters are projected onto a few spectral eigenvectors and the ensuing maps of coefficients are deconvolved using a standard Lucy-Richardson algorithm. This introduces a stabilization because the PCA filtering reduces the amount of noise.

(1 data file). Title: Height Variation of the Vector Magnetic Field in Solar Spicules Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J. Bibcode: 2015ApJ...803L..18O Altcode: 2015arXiv150404637O Proving the magnetic configuration of solar spicules has hitherto been difficult due to the lack of spatial resolution and image stability during off-limb ground-based observations. We report spectropolarimetric observations of spicules taken in the He i 1083 nm spectral region with the Tenerife Infrared Polarimeter II at the German Vacuum Tower Telescope of the Observatorio del Teide (Tenerife, Canary Islands, Spain). The data provide the variation with geometrical height of the Stokes I, Q, U, and V profiles, whose encoded information allows the determination of the magnetic field vector by means of the HAZEL inversion code. The inferred results show that the average magnetic field strength at the base of solar spicules is about 80 gauss, and then it decreases rapidly with height to about 30 gauss at a height of 3000 km above the visible solar surface. Moreover, the magnetic field vector is close to vertical at the base of the chromosphere and has mid-inclinations (about 50°) above 2 Mm height. 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: High speed magnetized flows in the quiet Sun Authors: Quintero Noda, C.; Borrero, J. M.; Orozco Suárez, D.; Ruiz Cobo, B. Bibcode: 2014A&A...569A..73Q Altcode: 2014arXiv1407.7477Q Context. We analyzed spectropolarimetric data recorded with Hinode/SP in quiet-Sun regions located at the disk center. We found single-lobed Stokes V profiles showing highly blue- and red-shifted signals. Oftentimes both types of events appear to be related to each other.
Aims: We aim to set constraints on the nature and physical causes of these highly Doppler-shifted signals, as well as to study their spatial distribution, spectropolarimetric properties, size, and rate of occurrence. Also, we plan to retrieve the variation of the physical parameters with optical depth through the photosphere.
Methods: We have examined the spatial and polarimetric properties of these events using a variety of data from the Hinode spacecraft. We have also inferred the atmospheric stratification of the physical parameters by means of the inversion of the observed Stokes profiles employing the Stokes Inversion based on Response functions (SIR) code. Finally, we analyzed their evolution using a time series from the same instrument.
Results: Blue-shifted events tend to appear over bright regions at the edge of granules, while red-shifted events are seen predominantly over dark regions on intergranular lanes. Large linear polarization signals can be seen in the region that connects them. The magnetic structure inferred from the time series revealed that the structure corresponds to a Ω-loop, with one footpoint always over the edge of a granule and the other inside an intergranular lane. The physical parameters obtained from the inversions of the observed Stokes profiles in both events show an increase with respect to the Harvard-Smithonian reference atmosphere in the temperature at log τ500 ∈ (-1, -3) and a strong magnetic field, B ≥ 1 kG, at the bottom of the atmosphere that quickly decreases upward until vanishing at log τ500 ≈ -2. In the blue-shifted events, the LOS velocities change from upflows at the bottom to downflows at the top of the atmosphere. Red-shifted events display the opposite velocity stratification. The change of sign in LOS velocity happens at the same optical depth in which the magnetic field becomes zero.
Conclusions: The physical mechanism that best explains the inferred magnetic field configuration and flow motions is a siphon flow along an arched magnetic flux tube. Further investigation is required, however, as the expected features of a siphon flow cannot be unequivocally identified. Title: The magnetic field configuration of a solar prominence inferred from spectropolarimetric observations in the He i 10 830 Å triplet Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J. Bibcode: 2014A&A...566A..46O Altcode: 2014arXiv1403.7976O Context. Determining the magnetic field vector in quiescent solar prominences is possible by interpreting the Hanle and Zeeman effects in spectral lines. However, observational measurements are scarce and lack high spatial resolution.
Aims: We determine the magnetic field vector configuration along a quiescent solar prominence by interpreting spectropolarimetric measurements in the He i 1083.0 nm triplet obtained with the Tenerife Infrared Polarimeter installed at the German Vacuum Tower Telescope of the Observatorio del Teide.
Methods: The He i 1083.0 nm triplet Stokes profiles were analyzed with an inversion code that takes the physics responsible for the polarization signals in this triplet into account. The results are put into a solar context with the help of extreme ultraviolet observations taken with the Solar Dynamic Observatory and the Solar Terrestrial Relations Observatory satellites.
Results: For the most probable magnetic field vector configuration, the analysis depicts a mean field strength of 7 gauss. We do not find local variations in the field strength except that the field is, on average, lower in the prominence body than in the prominence feet, where the field strength reaches ~25 gauss. The averaged magnetic field inclination with respect to the local vertical is ~77°. The acute angle of the magnetic field vector with the prominence main axis is 24° for the sinistral chirality case and 58° for the dextral chirality. These inferences are in rough agreement with previous results obtained from the analysis of data acquired with lower spatial resolutions.

A movie is available in electronic form at http://www.aanda.org Title: Photospheric downward plasma motions in the quiet Sun Authors: Quintero Noda, C.; Ruiz Cobo, B.; Orozco Suárez, D. Bibcode: 2014A&A...566A.139Q Altcode: 2014arXiv1405.1561Q Context. We analyze spectropolarimetric data taken with the Hinode spacecraft in quiet solar regions at the disk center. Distorted redshifted Stokes V profiles are found that show a characteristic evolution that always follows the same sequence of phases.
Aims: We aim to characterize the statistical properties of these events and recover the stratification of the relevant physical quantities to understand the nature of the mechanism behind them.
Methods: We studied the statistical properties of these events using spectropolarimetric data from Hinode/SP. We also examined the upper photosphere and the low chromosphere using Mg i b2 and Ca ii h data from Hinode. Finally, we applied the SIRGAUSS inversion code to the polarimetric data to infer the atmospheric stratification of the physical parameters. We also obtained these physical parameters taking into account dynamical terms in the equation of motion.
Results: The Stokes V profiles display a bump that evolves in four different time steps, and the total process lasts 108 seconds. The Stokes I shows a strongly bent red wing and the continuum signal exhibits a bright point inside an intergranular lane. This bright point is correlated with a strong redshift in the Mg i b2 line and a bright feature in Ca ii h images. The model obtained from the inversion of the Stokes profiles is hotter than the average quiet-Sun model, with a vertical magnetic field configuration and field strengths in the range of kG values. It also presents a line of sight velocity stratification with a Gaussian perturbation, the center of which is moving to deeper layers with time. The Gaussian perturbation is also found in the gas pressure and density stratification obtained taking into account dynamical terms in the equation of motion.
Conclusions: We have examined a particular type of event that can be described as a plasmoid of hot plasma that is moving downward from the top of the photosphere, placed over intergranular lanes and always related to strong magnetic field concentrations. We argue that the origin of this plasmoid might be magnetic reconnection that is taking place in the chromosphere.

Appendix A is available in electronic form at http://www.aanda.org Title: Time Evolution of Plasma Parameters during the Rise of a Solar Prominence Instability Authors: Orozco Suárez, D.; Díaz, A. J.; Asensio Ramos, A.; Trujillo Bueno, J. Bibcode: 2014ApJ...785L..10O Altcode: 2014arXiv1403.5640O We present high-spatial resolution spectropolarimetric observations of a quiescent hedgerow prominence taken in the He I 1083.0 nm triplet. The observation consisted of a time series in sit-and-stare mode of ~36 minutes duration. The spectrograph's slit crossed the prominence body and we recorded the time evolution of individual vertical threads. Eventually, we observed the development of a dark Rayleigh-Taylor plume that propagated upward with a velocity, projected onto the plane of the sky, of 17 km s-1. Interestingly, the plume apex collided with the prominence threads pushing them aside. We inferred Doppler shifts, Doppler widths, and magnetic field strength variations by interpreting the He I Stokes profiles with the HAZEL code. The Doppler shifts show that clusters of threads move coherently while individual threads have oscillatory patterns. Regarding the plume we found strong redshifts (~9-12 km s-1) and large Doppler widths (~10 km s-1) at the plume apex when it passed through the prominence body and before it disintegrated. We associate the redshifts with perspective effects while the Doppler widths are more likely due to an increase in the local temperature. No local variations of the magnetic field strength associated with the passage of the plume were found; this leads us to conclude that the plumes are no more magnetized than the surroundings. Finally, we found that some of the threads' oscillations are locally damped, what allowed us to apply prominence seismology techniques to infer additional prominence physical parameters. 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: A first look into the magnetic field configuration of prominence threads using spectropolarimetric data Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J. Bibcode: 2014IAUS..300..112O Altcode: 2014IAUS..300..112S; 2013arXiv1310.0257O We show preliminary results of an ongoing investigation aimed at determining the configuration of the magnetic field vector in the threads of a quiescent hedgerow solar prominence using high-spatial resolution spectropolarimetric observations taken in the He I 1083.0 nm multiplet. The data consist of a two-dimensional map of a quiescent hedgerow prominence showing vertical threads. The observations were obtained with the Tenerife Infrared Polarimeter attached to the German Vacuum Tower Telescope at the Observatorio del Teide (Spain). The He I 1083.0 nm Stokes signals are interpreted with an inversion code, which takes into account the key physical processes that generate and/or modify circular and linear polarization signals in the He I 1083.0 nm triplet: the Zeeman effect, anisotropic radiation pumping, and the Hanle effect. We present initial results of the inversions, i.e, the strength and orientation of the magnetic field vector along the prominence and in prominence threads. 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: Measuring vector magnetic fields in solar prominences Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J. Bibcode: 2013hsa7.conf..786O Altcode: 2012arXiv1211.2119O We present spectropolarimetric observations in the He I 1083.0 nm multiplet of a quiescent, hedgerow solar prominence. The data were taken with the Tenerife Infrared Polarimeter attached to the German Vacuum Tower Telescope at the Observatorio del Teide (Tenerife; Canary Islands; Spain). The observed He I circular and linear polarization signals are dominated by the Zeeman effect and by atomic level polarization and the Hanle effect, respectively. These observables are sensitive to the strength and orientation of the magnetic field vector at each spatial point of the field of view. We determine the magnetic field vector of the prominence by applying the HAZEL inversion code to the observed Stokes profiles. We briefly discuss the retrieved magnetic field vector configuration. Title: Polar Field Reversal Observations with Hinode Authors: Shiota, D.; Tsuneta, S.; Shimojo, M.; Sako, N.; Orozco Suarez, D.; Ishikawa, R. Bibcode: 2012AGUFMSH13C2274S Altcode: We have been monitoring yearly variation in the Sun's polar magnetic fields with the Solar Optical Telescope aboard Hinode to record their evolution and expected reversal near the solar maximum. All magnetic patches in the magnetic flux maps are automatically identified to obtain the number density and magnetic flux density as a function of the total magnetic flux per patch. The detected magnetic flux per patch ranges over four orders of magnitude (10^15 -- 10^20 Mx). The higher end of the magnetic flux in the polar regions is about one order of magnitude larger than that of the quiet Sun, and nearly that of pores. Almost all large patches ( > 10^18 Mx) have the same polarity, while smaller patches have a fair balance of both polarities. The polarity of the polar region as a whole is consequently determined only by the large magnetic concentrations. A clear decrease in the net flux of the polar region is detected in the slow rising phase of the current solar cycle. The decrease is more rapid in the north polar region than in the south. The decrease in the net flux is caused by a decrease in the number and size of the large flux concentrations as well as the appearance of patches with opposite polarity at lower latitudes. In contrast, we do not see temporal change in the magnetic flux associated with the smaller patches ( < 10^18 Mx) and that of the horizontal magnetic fields during the years 2008--2012. Title: Evidence for Rotational Motions in the Feet of a Quiescent Solar Prominence Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J. Bibcode: 2012ApJ...761L..25O Altcode: 2012arXiv1211.6980O We present observational evidence of apparent plasma rotational motions in the feet of a solar prominence. Our study is based on spectroscopic observations taken in the He I 1083.0 nm multiplet with the Tenerife Infrared Polarimeter attached to the German Vacuum Tower Telescope. We recorded a time sequence of spectra with 34 s cadence placing the slit of the spectrograph almost parallel to the solar limb and crossing two feet of an intermediate size, quiescent hedgerow prominence. The data show opposite Doppler shifts, ±6 km s-1, at the edges of the prominence feet. We argue that these shifts may be interpreted as prominence plasma rotating counterclockwise around the vertical axis to the solar surface as viewed from above. The evolution of the prominence seen in EUV images taken with the Solar Dynamics Observatory provided us with clues to interpret the results as swirling motions. Moreover, time-distance images taken far from the central wavelength show plasma structures moving parallel to the solar limb with velocities of about 10-15 km s-1. Finally, the shapes of the observed intensity profiles suggest the presence of, at least, two components at some locations at the edges of the prominence feet. One of them is typically Doppler shifted (up to ~20 km s-1) with respect to the other, thus suggesting the existence of supersonic counter-streaming flows along the line of sight. 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: 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: Power Spectra of Velocities and Magnetic Fields on the Solar Surface and their Dependence on the Unsigned Magnetic Flux Density Authors: Katsukawa, Y.; Orozco Suárez, D. Bibcode: 2012ApJ...758..139K Altcode: 2012arXiv1209.0548K We have performed power spectral analysis of surface temperatures, velocities, and magnetic fields, using spectropolarimetric data taken with the Hinode Solar Optical Telescope. When we make power spectra in a field of view covering the supergranular scale, kinetic and thermal power spectra have a prominent peak at the granular scale while the magnetic power spectra have a broadly distributed power over various spatial scales with weak peaks at both the granular and supergranular scales. To study the power spectra separately in internetwork and network regions, power spectra are derived in small subregions extracted from the field of view. We examine slopes of the power spectra using power-law indices, and compare them with the unsigned magnetic flux density averaged in the subregions. The thermal and kinetic spectra are steeper than the magnetic ones at the subgranular scale in the internetwork regions, and the power-law indices differ by about 2. The power-law indices of the magnetic power spectra are close to or smaller than -1 at that scale, which suggests the total magnetic energy mainly comes from either the granular scale magnetic structures or both the granular scale and smaller ones contributing evenly. The slopes of the thermal and kinetic power spectra become less steep with increasing unsigned flux density in the network regions. The power-law indices of all the thermal, kinetic, and magnetic power spectra become similar when the unsigned flux density is larger than 200 Mx cm-2. 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: Center-to-Limb Variation of the Magnetic Field Vector Distribution in the Internetwork Authors: Orozco Suárez, D. Bibcode: 2012ASPC..454...37O Altcode: 2012ASPC..454...37S I present a comparison between the Probability Density Functions of the magnetic field strength, inclination, azimuth, and filling factor determined at four different heliocentric angles in the quiet Sun internetwork. The data were acquired with the spectropolarimeter attached to the Solar Optical Telescope onboard the Hinode satellite. The signal-to-the-noise ratio corresponds to ∼ 3600, measured at the continuum of Stokes I. To obtain the PDFs, the data were subjected to a simple one component Milne-Eddington inversion. The results show that for strong fields (above 300 G), variations on the shape of the inclination PDF are detected, suggesting that the geometry of the field vector changes with viewing angle. For weaker fields, the distribution of inclinations does not vary, what concurs with the isotropic nature of the internetwork fields. Title: Polar Field Reversal Observations with Hinode Authors: Shiota, D.; Tsuneta, S.; Shimojo, M.; Sako, N.; Orozco Suárez, D.; Ishikawa, R. Bibcode: 2012ApJ...753..157S Altcode: 2012arXiv1205.2154S We have been monitoring yearly variation in the Sun's polar magnetic fields with the Solar Optical Telescope aboard Hinode to record their evolution and expected reversal near the solar maximum. All magnetic patches in the magnetic flux maps are automatically identified to obtain the number density and magnetic flux density as a function of the total magnetic flux per patch. The detected magnetic flux per patch ranges over four orders of magnitude (1015-1020 Mx). The higher end of the magnetic flux in the polar regions is about one order of magnitude larger than that of the quiet Sun, and nearly that of pores. Almost all large patches (>=1018 Mx) have the same polarity, while smaller patches have a fair balance of both polarities. The polarity of the polar region as a whole is consequently determined only by the large magnetic concentrations. A clear decrease in the net flux of the polar region is detected in the slow rising phase of the current solar cycle. The decrease is more rapid in the north polar region than in the south. The decrease in the net flux is caused by a decrease in the number and size of the large flux concentrations as well as the appearance of patches with opposite polarity at lower latitudes. In contrast, we do not see temporal change in the magnetic flux associated with the smaller patches (<1018 Mx) and that of the horizontal magnetic fields during the years 2008-2012. 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: 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: Model Selection for Spectropolarimetric Inversions Authors: Asensio Ramos, A.; Manso Sainz, R.; Martínez González, M. J.; Viticchié, B.; Orozco Suárez, D.; Socas-Navarro, H. Bibcode: 2012ApJ...748...83A Altcode: 2012arXiv1201.5063A Inferring magnetic and thermodynamic information from spectropolarimetric observations relies on the assumption of a parameterized model atmosphere whose parameters are tuned by comparison with observations. Often, the choice of the underlying atmospheric model is based on subjective reasons. In other cases, complex models are chosen based on objective reasons (for instance, the necessity to explain asymmetries in the Stokes profiles) but it is not clear what degree of complexity is needed. The lack of an objective way of comparing models has, sometimes, led to opposing views of the solar magnetism because the inferred physical scenarios are essentially different. We present the first quantitative model comparison based on the computation of the Bayesian evidence ratios for spectropolarimetric observations. Our results show that there is not a single model appropriate for all profiles simultaneously. Data with moderate signal-to-noise ratios (S/Ns) favor models without gradients along the line of sight. If the observations show clear circular and linear polarization signals above the noise level, models with gradients along the line are preferred. As a general rule, observations with large S/Ns favor more complex models. We demonstrate that the evidence ratios correlate well with simple proxies. Therefore, we propose to calculate these proxies when carrying out standard least-squares inversions to allow for model comparison in the future. Title: On the Distribution of Quiet-Sun Magnetic Fields at Different Heliocentric Angles Authors: Orozco Suárez, D.; Katsukawa, Y. Bibcode: 2012ApJ...746..182O Altcode: This paper presents results from the analysis of high signal-to-noise ratio spectropolarimetric data taken at four heliocentric angles in quiet-Sun internetwork regions with the Hinode satellite. First, we find that the total circular and total linear polarization signals vary with heliocentric angle, at least for fields with large polarization signals. We also report changes on the Stokes V amplitude asymmetry histograms with viewing angle for fields weaker than 200 G. Then, we subject the data to a Milne-Eddington inversion and analyze the variation of the field vector probability density functions with heliocentric angle. Weak, highly inclined fields permeate the internetwork at all heliocentric distances. For fields weaker than 200 G, the distributions of field inclinations peak at 90° and do not vary with viewing angle. The inclination distributions change for fields stronger than 200 G. We argue that the shape of the inclination distribution for weak fields partly results from the presence of coherent, loop-like magnetic features at all heliocentric distances and not from tangled fields within the field of view. We also find that the average magnetic field strength is about 180 G (for 75% of the pixels) and is constant with heliocentric angle. The average vertical and horizontal magnetic field components are 70 and 150 G. The latter (former) is slightly greater (smaller) near the limb. Finally, the ratio between the horizontal and vertical components of the fields ranges from ~1 for strong fields to ~3.5 for weak fields, suggesting that the magnetic field vector is not isotropically distributed within the field of view. 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: 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: 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: Size matters Authors: del Toro Iniesta, J. C.; Orozco Suárez, D. Bibcode: 2010AN....331..558D Altcode: 2010arXiv1002.3106D The new generation of ground-based, large-aperture solar telescopes promises to significantly increase our capabilities to understand the many basic phenomena taking place in the Sun at all atmospheric layers and how they relate to each other. A (non-exhaustive) summary of the main scientific arguments to pursue these impressive technological goals is presented. We illustrate how imaging, polarimetry, and spectroscopy can benefit from the new telescopes and how several wavelength bands should be observed to study the atmospheric coupling from the upper convection zone all the way to the corona. The particular science case of sunspot penumbrae is barely discussed as a specific example. 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: Simulation and Analysis of Hinode Spectropolarimetric Observations Authors: Orozco Suárez, D. Bibcode: 2009ASPC..415...57O Altcode: The diffraction-limited observations of the Hinode Spectro-Polarimeter have open exciting possibilities for the analysis of the weak magnetic signals of the solar internetwork (IN). Hinode/SP has demonstrated that the IN is permeated by highly inclined fields with weak flux densities. These observations are important to solve the discrepancy between the IN field strength distributions obtained using visible and infrared ground-based measurements. Recently, it has been argued that the information contained in the Fe I 630 nm spectral region is not sufficient to provide reliable field strength values. In this contribution, radiative magnetoconvection simulations are used to generate synthetic Hinode/SP observations, in an attempt to examine the reliability of Milne-Eddington inversions applied to very high spatial resolution data. The results show that ME inversions deliver reasonably good magnetic field strengths and inclinations from Hinode/SP measurements, provided the effects caused by telescope diffraction are corrected. These effects can be accurately modeled using a local stray-light contamination. If one does not account for the reduction in polarization signals caused by diffraction, the inversion leads to field strengths that are too weak. Finally, the implications that telescope diffraction has on the average magnetic filling factors and flux densities retrieved from Hinode/SP data are discussed. Title: MISMA inversion of HINODE SOT/SP data. Preliminary results Authors: Viticchiè, B.; Berrilli, F.; Sánchez Almeida, J.; Orozco Suárez, D. Bibcode: 2009MmSAI..80..255V Altcode: We analyze full Stokes observations of a quiet Sun region at disk center taken with the spectropolarimeter of the Solar Optical Telescope aboard the HINODE satellite. We present the preliminary results derived from the MISMA inversion of the observed Stokes I and V profiles. The complete analysis has as a final goal the definition of probability density function for the statistical description of the quiet Sun magnetic field vector for a direct comparison with recently published results. Title: The Magnetic Landscape of the Sun's Polar Region Authors: Tsuneta, S.; Ichimoto, K.; Katsukawa, Y.; Lites, B. W.; Matsuzaki, K.; Nagata, S.; Orozco Suárez, D.; Shimizu, T.; Shimojo, M.; Shine, R. A.; Suematsu, Y.; Suzuki, T. K.; Tarbell, T. D.; Title, A. M. Bibcode: 2008ApJ...688.1374T Altcode: 2008arXiv0807.4631T We present observations of the magnetic landscape of the polar region of the Sun that are unprecedented in terms of spatial resolution, field of view, and polarimetric precision. They were carried out with the Solar Optical Telescope aboard Hinode. Using a Milne-Eddington inversion, we find many vertically oriented magnetic flux tubes with field strengths as strong as 1 kG scattered in latitude between 70° and 90°. They all have the same polarity, consistent with the global polarity of the polar region. The field vectors are observed to diverge from the centers of the flux elements, consistent with a view of magnetic fields that are expanding and fanning out with height. The polar region is also found to have ubiquitous horizontal fields. The polar regions are the source of the fast solar wind, which is channeled along unipolar coronal magnetic fields whose photospheric source is evidently rooted in the strong-field, vertical patches of flux. We conjecture that vertical flux tubes with large expansion around the photospheric-coronal boundary serve as efficient chimneys for Alfvén waves that accelerate the solar wind. 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: Diffraction-limited spectropolarimetry of quiet-sun magnetic fields Authors: Orozco Suárez, David Bibcode: 2008PhDT........82O Altcode: No abstract at ADS 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: 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: Attempt to detect Aflven waves with Solar Optical Telescope aboard Hinode Authors: Tsuneta, Saku; Suematsu, Y.; Ichimoto, K.; Katsukawa, Y.; Shimizu, T.; Nagata, S.; Orozco Suárez, D.; Lites, B.; Shine, D.; Tarbell, T.; Title, A. Bibcode: 2007AAS...210.9428T Altcode: 2007BAAS...39..222T Flux tube on the sun may carry linear and torsional Alfven waves generated by photospheric motion. Photospheric motion of 2 km/s would provide magnetic fluctuation of 40G for 1KG tube and for the Alfven speed of 50km/s. This may be close to the detection limit of the Stokes Q and U signals for flux tubes located in the sun center. However, for flux tubes located near the limb, the fluctuation would be seen in the Stokes V signal, and can be detectable.

We also may be able to confirm the 90 degree phase shift between magnetic fluctuation and velocity fluctuation, which is easier to observe for flux tubes near the limb. Detection of waves would be important in terms of coronal heating and solar wind acceleration. An attempt to detect waves along flux tubes will be reported. Title: Magnetic Landscape Of Solar Polar Region With Solar Optical Telescope Aboard Hinode Authors: Tsuneta, Saku; Suematsu, Y.; Ichimoto, K.; Shimizu, T.; Katsukawa, Y.; Nagata, S.; Orozco Suárez, D.; Lites, B.; Shine, D.; Tarbell, T.; Title, A. Bibcode: 2007AAS...210.9405T Altcode: 2007BAAS...39..218T Solar polar region is the final destination for remnant magnetic fields due to meridional flow and granular diffusion, and is very important for the global solar dynamo. Hinode satellite carried out high-resolution spectro-polarimetric observations for the Northern pole on 2006 November 22 as a part of its performance verification program. We find ubiquitous isolated (positive and negative) patches in the Stokes V map (i.e. fields horizontal to local surface) all over the Arctic circle. The Q (vertical to local surface) map indicates scattered vertical flux tubes, which have bipolar feature in the U and V maps. This suggests canopy-like structure of the strong isolated flux tubes. This will be compared with equatorial landscape with similar distance from the sun center. Strong flux tube and weaker ubiquitous horizontal fields as represented by Stokes V would have implication to the current understanding of the global and local dynamo. Title: The usefulness of analytic response functions Authors: Orozco Suárez, D.; Del Toro Iniesta, J. C. Bibcode: 2007A&A...462.1137O Altcode: 2012arXiv1211.1502O Aims:We introduce analytical response functions and their main properties as an important diagnostic tool that help understand Stokes profile formation physics and the meaning of well-known behaviors of standard inversion codes of the radiative transfer equation often used to measure solar magnetic fields.
Methods: A Milne-Eddington model atmosphere is used as an example where response functions are analytical. A sample spectral line has been chosen to show the main qualitative properties.
Results: We show that analytic response functions readily provide explanations for various well-known behaviors of spectral lines, such as the sensitivity of visible lines to weak magnetic fields or the trade-offs often detected in inversion codes between the Milne-Eddington thermodynamic parameters. We also show that response functions are helpful in selecting sample wavelengths optimized for specific parameter diagnostics.

Appendix A is only available in electronic form at http://www.aanda.org 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: 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: Measuring the Magnetic Vector with the He I 10830 Å Line: A Rich New World Authors: Solanki, S. K.; Lagg, A.; Aznar Cuadrado, R.; Orozco Suárez, D.; Collados, M.; Wiegelmann, T.; Woch, J.; Sasso, C.; Krupp, N. Bibcode: 2006ASPC..358..431S Altcode: The triplet of the He I transitions around 10830 Å not only shows a rich variety of Stokes profiles, but also allows the full magnetic vector in the upper chromosphere to be probed, thus revealing the magnetic structure of loops, current sheets, finely structured supersonic downflows, the chromospheric layers of sunspots (supporting the presence of uncombed fields in the penumbra), flares, and the quiet Sun. A very brief overview of some of the observations and results obtained so far is given. 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: Photospheric and Chromospheric Magnetic Structure of a Sunspot Authors: Orozco Suarez, D.; Lagg, A.; Solanki, S. K. Bibcode: 2005ESASP.596E..59O Altcode: 2005ccmf.confE..59O No abstract at ADS