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Onboard the Solar Orbiter spacecraft is the Polarimetric and Helioseismic Imager (SO/PHI), which has two telescopes, a high resolution telescope (HRT) and the full disk telescope (FDT). The instrument is designed to infer the photospheric magnetic field through differential imaging of the polarised light emitted from the Sun. It is the first magnetograph to move out of the Sun-Earth Line, providing excellent stereoscopic opportunities with other ground and space based instruments. Of particular interest is the comparison between SO/PHI-HRT and the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory (SDO/HMI). They probe the same magnetically sensitive line of Fe1: 6173 Å and have the same aperture diameter. In March 2022 Solar Orbiter crossed the Sun-Earth line, providing an excellent opportunity for a comparison. Here a comparison between the magnetic fields, both line-of-sight and all three vector components, inferred by SDO/HMI and SO/PHI-HRT during the conjunction, are presented.

We developed a scan mirror mechanism (SMM) that enable a slit-based spectrometer or spectropolarimeter to precisely and quickly map an astronomical object. The SMM, designed to be installed in the optical path preceding the entrance slit, tilts a folding mirror and then moves the reflected image laterally on the slit plane, thereby feeding a different one-dimensional image to be dispersed by the spectroscopic equipment. In general, the SMM is required to scan quickly and broadly while precisely placing the slit position across the field-of-view (FOV). These performances are in high demand for near-future observations, such as studies on the magnetohydrodynamics of the photosphere and the chromosphere. Our SMM implements a closed-loop control system by installing electromagnetic actuators and gap-based capacitance sensors. Our optical test measurements confirmed that the SMM fulfills the following performance criteria: i) supreme scan-step uniformity (linearity of 0.08%) across the wide scan range (±1005′′), ii) high stability (3σ=0.1′′), where the angles are expressed in mechanical angle, and iii) fast stepping speed (26 ms). The excellent capability of the SMM will be demonstrated soon in actual use by installing the mechanism for a near-infrared spectropolarimeter onboard the balloon-borne solar observatory for the third launch, SUNRISE III. © 2022, The Author(s), under exclusive licence to Springer Nature B.V., The balloon-borne solar observatory SUNRISE III is a mission of the Max Planck Institute for Solar System Research (MPS, Germany), and the Johns Hopkins Applied Physics Laboratory (APL, USA). SUNRISE III looks at the Sun from the stratosphere using a 1-meter telescope, three scientific instruments, and an image stabilization system. Significant contributors to the mission are a Spanish consortium, the National Astronomical Observatory of Japan (NAOJ, Japan), and the Leibniz Institute for Solar Physics (KIS, Germany). The Spanish consortium is led by the Instituto de Astrofísica de Andalucía (IAA, Spain) and includes the Instituto Nacional de Técnica Aeroespacial (INTA), Universitat de València (UV), Universidad Politécnica de Madrid (UPM) and the Instituto de Astrofísica de Canarias (IAC). Other partners include NASA’s Wallops Flight Facility Balloon Program Office (WFF-BPO) and the Swedish Space Corporation (SSC). SUNRISE III is supported by funding from the Max Planck Foundation, NASA under Grant #80NSSC18K0934, Spanish FEDER/AEI/MCIU (RTI2018-096886-C5) and a “Center of Excellence Severo Ochoa” award to IAA-CSIC (SEV-2017-0709), and the ISAS/JAXA Small Mission-of-Opportunity program and JSPS KAKENHI JP18H05234, and NAOJ Research Coordination Committee, NINS. We would also thank significant technical support from the Advanced Technology Center (ATC), NAOJ. We would like to thank Editage (www.editage.com) for English language editing.

The ESA/NASA Solar Orbiter mission, launched in February 2020, has just completed its cruise phase. During its nominal mission, it will explore the Sun and heliosphere from close up and from out of the ecliptic plane. It aims to address the overarching questions of how the Sun creates and controls the heliosphere, and why solar activity changes with time. Among the instruments onboard Solar Orbiter is the Polarimetric and Helioseismic Imager (SO/PHI), which is the first magnetograph to leave the Sun-Earth line and to observe the Sun from different directions. Already during the cruise phase of Solar Orbiter, SO/PHI has provided a few glimpses of its capabilities, including the excellent quality of the data. In spite of the very limited amount of data gathered during cruise, a few interesting results have already been obtained. A selection of such results will be presented.

The Earth-Sun Lagrangian point 4 is a meta-stable location at 1 AU from the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of the solar photosphere centered on W60, the Earth's nominal magnetic field connection to the Sun. Such a mission on its own would serve as a solar remote sensing observatory that would oversee the entire solar radiation hemisphere with significant relevance for protecting Moon and Mars explorers from radiation exposure. In combination with appropriately planned observatories at L1 and L5, the three spacecraft would provide 300° longitude coverage of photospheric magnetic field structure, and allow continuous viewing of both solar poles, with >3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun with a 7.2° inclination out of the heliographic equator, 14.5° out of the ecliptic plane. We discuss the impact of extending solar magnetic field observations in both longitude and latitude to improve global solar wind modeling and, with the development of local helioseismology, the potential for long-term solar activity forecasting. Such a mission would provide a unique opportunity for interplanetary and interstellar dust science. It would significantly add to reliability of operational observations on fast coronal mass ejections directed at Earth and for human Mars explorers on their round-trip journey. The L4 mission concept is technically feasible, and is scientifically compelling. ISSN:1542-7390

The Solar Orbiter Polarimetric and Helioseismic Imager (SO/PHI) will provide maps of the magnetic vector and of the line-of-sight velocities in the solar photosphere. For reaching its science goals, SO/PHI is equipped with two telescopes: the high resolution channel (HRT) and the full disk channel (FDT). Since both optical channels are fed into a common path including the camera, the need arises for a highly precise mechanism, which selects only one telescope at a time: the Feed-Select Mechanism (FSM). The mechanism therefore needs to serve two purposes: (1) directing one channel towards the camera, (2) shutting the second channel to not disturb the measurement of the observing channel. In this paper we will describe the different design features, as well as the design verification and qualification of the mechanism.

Sunrise is a balloon-borne solar observatory dedicated to the investigation of key processes of the magnetic field and the plasma flows in the lower solar atmosphere. The observatory operates in the stratosphere at an altitude of around 37 km in order to avoid image degradation due to turbulence in the Earth’s atmosphere and to access the UV range. The third science flight of Sunrise will carry new instrumentation which samples the solar spectrum over a broad wavelength domain from the UV to the near IR and covers an extended height range in the solar atmosphere. A key feature of the Sunrise UV Spectropolarimeter and Imager (SUSI) operating between 309 nm and 417 nm, is its capability to simultaneously record a large number of spectral lines. By combining the spectral and polarization information of many individual lines with different formation heights and sensitivities, the accuracy and the height resolution of the inferred atmospheric parameters can be significantly increased. The spectral bands of SUSI are selected one at a time by rotating a diffraction grating with respect to a fixed polarimetry unit. The spatial and spectral field of view on the 2k x 2k cameras is 59” and 2.0 - 2.3 nm, respectively. A further innovation is the numerical restoration of the spectrograph scans by means of synchronized 2D context imaging, a technique that has recently produced impressive results at ground-based solar observatories.

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.

The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is a near-IR spectro-polarimeter instrument newly designed for Sunrise III, which is a balloon-borne solar observatory equipped with a 1 m optical telescope. To acquire high-quality 3D magnetic and velocity fields, SCIP selects the two wavelength bands centered at 850 nm and 770 nm, which contain many spectrum lines that are highly sensitive to magnetic fields permeating the photosphere and chromosphere. To achieve high spatial and spectral resolution (0.21 arcsec and 2 × 105), SCIP optics adopt a quasi-Littrow configuration based on an echelle grating and two high-order aspheric mirrors. Using different diffraction orders of the echelle grating, dichroic beam splitter, and polarizing beam-splitters, SCIP can obtain s- and p-polarization signals in the two wavelength bands simultaneously within a relatively small space. We established the wavefront error budget based on tolerance analysis, surface figure errors, alignment errors, and environmental changes. In addition, we performed stray light analysis, and designed light traps and baffles needed to suppress unwanted reflections and diffraction by the grating. In this paper, we present the details of this optical system and its performance.

The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is a near-IR spectro-polarimeter instrument newly designed for Sunrise III, a balloon-borne solar observatory with a 1-m diameter telescope. In order to achieve the strict requirements the SCIP wavefront error, it is necessary to quantify the errors due to environmen- tal effects such as gravity and temperature variation under the observation conditions. We therefore conducted an integrated opto-mechanical analysis incorporating mechanical and thermal disturbances into a finite element model of the entire SCIP structure to acquire the nodal displacements of each optical element, then fed them back to the optical analysis software in the form of rigid body motion and surface deformation fitted by polynomials. This method allowed us to determine the error factors having a significant influence on optical performance. For example, no significant wavefront degradation was associated with the structural mountings because the optical element mounts were well designed based on quasi-kinematic constraints. In contrast, we found that the main factor affecting wavefront degradation was the rigid body motions of the optical elements, which must be mini- mized within the allowable level. Based on these results, we constructed the optical bench using a sandwich panel as the optical bench consisting of an aluminum-honeycomb core and carbon fiber reinforced plastic skins with a high stiffness and low coefficient of thermal expansion. We then confirmed that the new opto-mechanical model achieved the wavefront error requirement. In this paper, we report the details of this integrated opto-mechanical analysis, including the wavefront error budgeting and the design of the opto-mechanics.

All 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., 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. © 2020 ESO., Solar Orbiter is a space mission of international collaboration between ESA and NASA with contributions from national agencies of ESA member states. The spacecraft has been developed by Airbus and is being operated by ESA from the European Space Operations Centre (ESOC) in Darmstadt, Germany. Science operations are carried out at ESA's European Space Astronomy Centre (ESAC) in Villafranca del Castillo, Spain. SWA is an international collaboration which has been funded by the UKSA, CNES, ASI, NASA and the Czech contribution to the ESA PRODEX programme. UAH authors want to thanks the Spanish MINECO-FPI-2016 predoctoral grant with FSE, and its project FEDER/MCIU-AEEI/Proyecto ESP2017-88436-R. The Spanish contribution to SO/PHI has been funded by the Spanish Ministry of Science and Innovation through several projects, the last one being RTI2018-096886-B-C5, and by "Centro de Excelencia Severo Ochoa" programme under grant SEV-2017-0709. RAH, RCC, DMM, SPP, and AV acknowledge the support of the NASA Heliophysics Division, Solar Orbiter Collaboration Office under IAT NNG09EK11I. JEP acknowledges grant UKRI/STFC ST/N000692/1. All French involvements are supported by CNES and CNRS. DV is supported by the STFC Ernest Rutherford Fellowship ST/P003826/1 and STFC Consolidated Grant ST/S000240/1. The authors thank the referee for her constructive comments and suggestions, which led to the substantial improvement of this paper.

22nd EGU General Assembly, held online 4-8 May, 2020, id.17904, A central instrument of Solar Orbiter is the Polarimetric and Helioseismic Imager, SO/PHI. It is a vector magnetograph that also provides data for helioseismology. SO/PHI is composed of two telescopes, a full-disk telescope (FDT) and a high-resolution telescope (HRT). The HRT will observe at a resolution as high as 200 km on the solar surface, while the FDT will obtain the magnetic field and velocity of the full solar disc whenever it observes. SO/PHI will be the first solar spectro-polarimeter to leave the Sun-Earth line, opening up some unique perspectives, such as the first detailed view of the solar poles. This will allow not just a more precise and exact mapping of the polar magnetic field than possible so far, but will also enable us to follow the dynamics of individual magnetic features at high latitudes and to determine solar surface and sub-surface flows right up to the poles. In addition to its standard data products (vector magnetograms, continuum images and maps of the line-of-sight velocity), SO/PHI will also provide higher-level data products. These will include synoptic charts, local magnetic field extrapolations starting from HRT data and global magnetic field extrapolations (from FDT data) with potential field source-surface (PFSS) models and possibly also non-potential models such as NLFFF (non-linear force-free fields), magnetostatics and MHD. The SO/PHI data products will usefully complement the data taken by other instruments on Solar Orbiter and on Solar Probe, as well as instruments on the ground or in Earth orbit. Combining with observations by Earth-based and near-Earth telescopes will enable new types of investigations, such as stereoscopic polarimetry and stereoscopic helioseismology.

This is an open access article. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI., A frequent problem arising for deep space missions is the discrepancy between the amount of data desired to be transmitted to the ground and the available telemetry bandwidth. A part of these data consists of scientific observations, being complemented by calibration data to help remove instrumental effects. We present our solution for this discrepancy, implemented for the Polarimetric and Helioseismic Imager on-board the Solar Orbiter mission, the first solar spectropolarimeter in deep space. We implemented an on-board data reduction system that processes calibration data, applies them to the raw science observables, and derives science-ready physical parameters. This process reduces the raw data for a single measurement from 24 images to five, thus reducing the amount of downlinked data, and in addition, renders the transmission of the calibration data unnecessary. Both these on-board actions are completed autonomously. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI., This work was carried out in the framework of the International Max Planck Research School for Solar System Science at the Max Planck Institute for Solar System Research. Solar Orbiter is a mission led by the European Space Agency with contribution from the National Aeronautics and Space Administration (NASA). The Polarimetric and Helioseismic Imager instrument is supported by the German Aerospace Center (DLR) under grant Nos. 50 OT 1201 and 50 OT 1901. The Spanish contribution has been partly funded by the Spanish Research Agency under projects under grant Nos. ESP2016-77548-C5 and RTI2018-096886-B-C5, partially including European FEDER funds. IAA-CSIC members acknowledge and funds from the Spanish Ministry of Science and Innovation “Centro de Excelencia Severo Ochoa” Program under grant No. SEV-2017-0709. The solar data used in the tests are the courtesy of NASA/SDO HMI science team. Parts of the work shown in this paper have been introduced at the SPIE Astronomical Telescopes + Instrumentation conference.42 Editorial

Ground-Based and Airborne Telescopes VIII 2020; Virtual, Online; United States; 14 December 2020 through 22 December 2020; Code 166573.--Proceedings of SPIE - The International Society for Optical Engineering Volume 11445, 2020, Article number 114454F, The SUNRISE Chromospheric Infrared spectroPolarimeter (SCIP) is a balloon-borne long-slit spectrograph for SUNRISE III to precisely measure magnetic fields in the solar atmosphere. The scan mirror mechanism (SMM) is installed in the optical path to the entrance slit of the SCIP to move solar images focused on the slit for 2-dimensional mapping. The SMM is required to have (1) the tilt stability better than 0.035″ (3σ) on the sky angle for the diffraction-limited spatial resolution of 0.2″, (2) step response shorter than 32 msec for rapid scanning observations, and (3) good linearity (i.e. step uniformity) over the entire field-of-view (60″x60″). To achieve these performances, we have developed a flight-model mechanism and its electronics, in which the mirror tilt is controlled by electromagnetic actuators with a closed-loop feedback logic with tilt angles from gap-based capacitance sensors. Several optical measurements on the optical bench verified that the mechanism meets the requirements. In particular, the tilt stability achives better than 0.012″ (3σ). Thermal cycling and thermal vacuum tests have been completed to demonstrate the performance in the vacuum and the operational temperature range expected in the balloon flight. We found a small temperature dependence in the step uniformity and this dependence will be corrected to have 2-demensional maps with the sub-arcsec spatial accuracy in the data post-processing. © COPYRIGHT SPIE., The SUNRISE III project is funded in Japan by the ISAS/JAXA Small Mission-of-Opportunity program for novel solar observations, JSPS KAKENHI Grant Number 18H05234 (PI:Y.Katsukawa), and NAOJ Research Coordination Committee, NINS. We would also thank significant technical support from the Advanced Technology Center (ATC), NAOJ.

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. © 2020 ESO., The German contribution to SUNRISE and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economia y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant number NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea and by the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation program (grand agreements Nos 715947 and 695075).

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. © 2018 SPIE., This work was carried out in the framework of the International Max Planck Research School (IMPRS) for Solar System Science at the Max Planck Institute for Solar System Research (MPS). Solar Orbiter is a mission lead by the European Space Agency (ESA) with significant contribution from National Aeronautics and Space Administration (NASA). The SO/PHI instrument is supported by the German Aerospace Center (DLR) through Grant 50 OT 1201. The Spanish contribution has been partly funded by the Spanish Research Agency under project ESP2016-77548-05, partially including European FEDER funds. The solar data used in the test are the courtesy of NASA/SDO HMI science team.

Solar Orbiter is a joint mission of ESA and NASA scheduled for launch in 2020. Solar Orbiter is a complete and unique heliophysics mission, combining remote sensing and in-situ analysis; its special elliptical orbit allows viewing the Sun from a distance of only 0.28 AU, and - leaving the ecliptic plane - to observe the solar poles from a hitherto unexplored vantage point. One of the key instruments for Solar Orbiter's science is the »Polarimetric and Helioseismic Imager» (PHI), which will provide maps of the solar surface magnetic fields and the gas flows on the visible solar surface. Two telescopes, a full disc imager, and a high resolution channel feed a common Fabry-Perot based tunable filter and thus allow sampling a single Fraunhofer line at 617.3 nm with high spectral resolution; a polarization modulation system makes the system sensitive to the full state of polarization. From the analysis of the Doppler shift and the magnetically induced Zeeman polarization in this line, the magnetic field and the line-of-sight gas motions can be detected for each point in the image. In this paper we describe the opto-mechanical system design of the high resolution telescope. It is based on a decentred Ritchey-Chrétien two-mirror telescope. The telescope includes a Barlow type magnifier lens group, which is used as in-orbit focus compensator, and a beam splitter, which sends a small fraction of the collected light onto a fast camera, which provides the error signals for the actively controlled secondary mirror compensating for spacecraft jitter and other disturbances. The elliptical orbit of the spacecraft poses high demands on the thermo-mechanical stability. The varying size of the solar disk image requires a special false-light suppression architecture, which is briefly described. In combination with a heat-rejecting entrance window, the optical energy impinging on the polarimetric and spectral analysis system is efficiently reduced. We show how the design can preserve the diffraction-limited imaging performance over the design temperature range of -20°C to +60°C. The decentred hyperbolical mirrors require special measures for the inter-alignment and their alignment with respect to the mechanical structure. A system of alignment flats and mechanical references is used for this purpose. We will describe the steps of the alignment procedure, and the dedicated optical ground support equipment, which are needed to reach the diffraction limited performance of the telescope. We will also report on the verification of the telescope performance, both - in ambient condition - and in vacuum at different temperatures. © COPYRIGHT SPIE., Solar Orbiter is a mission led by the European Space Agency (ESA) with signicant contribution from National Aeronautics and Space Administration (NASA). The SO/PHI instrument is supported by the German Aerospace Center (DLR) through grants 50 OT 1201 and 50 OT 1703 (for the ISS) and a grant from the Max Planck Society for Solar Orbiter instrument development. The Spanish contribution has been partly funded by the Spanish Research Agency under project ESP2016-77548-C5 and ESP2014-56169-C6, partially including European FEDER funds.

S. Jafarzadeh et. al., ©2017 The American Astronomical Society. All rights reserved.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., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant number NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. S.J. receives support from the Research Council of Norway. T.W. acknowledges support by DFG-grant WI 3211/4-1. M.S. acknowledges support from the European Research Council under the European Union's Seventh Framework Programme / ERC Grant agreement nr. 291058.

©2017 The American Astronomical Society. All rights reserved.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., This work has been partially funded by the Spanish Ministerio de Economía y Competitividad, through Projects No. ESP2013-47349-C6 and ESP2014-56169-C6, including a percentage from European FEDER funds. The German contribution to sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The National Solar Observatory (NSO) is operated by the Association of Universities for Research in Astronomy (AURA) Inc. under a cooperative agreement with the National Science Foundation. The HAO contribution was partly funded through NASA grant number NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea.

T. Wiegelmann et. al., ©2017 The American Astronomical Society. All rights reserved.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., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant number NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. The used HMI-data are courtesy of NASA/SDO and the HMI science team. TW acknowledges DLR-grant 50 OC 1301 and DFG-grant WI 3211/4-1. T.N. acknowledges support by the UK's Science and Technology Facilities Council via Consolidated Grants ST/K000950/1 and ST/N000609/1. D.N. was supported from GA ČR under grant numbers 16-05011S and 16-13277S. The Astronomical Institute Ondřejov is supported by the project RVO:67985815.

S. Danilovic et. al., ©2017 The American Astronomical Society. All rights reserved.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., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which are all gratefully acknowledged. This work has benefited from the discussions at the meeting "Solar UV bursts—a new insight to magnetic reconnection" at the International Space Science Institute (ISSI) in Bern. The Spanish contribution was funded by the Ministerio de Economia y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant number NNX13AE95G. The National Solar Observatory (NSO) is operated by the Association of Universities for Research in Astronomy (AURA) Inc. under a cooperative agreement with the National Science Foundation. This work was also partly supported by the BK21 plus program through the National Research Foundation (NRF), funded by the Ministry of Education of Korea.

S. Jafarzadeh et. al., ©2017 The American Astronomical Society. All rights reserved. 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., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant number NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea.

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 Gorobets, A. Y., Borrero, J. M., & Berdyugina, S. 2016, ApJL, 825, L18 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., 11 pages, 5 figures, The Astrophysical Journal Supplement Series (accepted)

The {\em Solar Orbiter} is the next solar physics mission of the European Space Agency, ESA, in collaboration with NASA, with a launch planned in 2018. The spacecraft is designed to approach the Sun to within 0.28\,AU at perihelion of a highly eccentric orbit. The proximity with the Sun will also allow its observation at uniformly high resolution at EUV and visible wavelengths. Such observations are central for learning more about the magnetic coupling of the solar atmosphere. At a later phase in the mission the spacecraft will leave the ecliptic and study the enigmatic poles of the Sun from a heliographic latitude of up to 33$^\circ$., Comment: 6 pages, 1 figure

©2017 The American Astronomical Society. All rights reserved. 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 ${\chi }^{2}$ 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., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The National Center for Atmospheric Research is sponsored by the National Science Foundation. The HAO contribution was partly funded through NASA grant number NNX13AE95G. The National Solar Observatory (NSO) is operated by the Association of Universities for Research in Astronomy (AURA) Inc. under a cooperative agreement with the National Science Foundation. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea.

S. Jafarzadeh et. al., ©2017 The American Astronomical Society. All rights reserved.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, $\gamma =1.0$), travelers with constant speeds over a supergranule ($\gamma =1.9\mbox{--}2.0$), and decelerating movers in the vicinity of flux emergence and/or within active regions ($\gamma =1.4\mbox{--}1.5$). 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%., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant number NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. S.J. receives support from the Research Council of Norway.

L. P. Chitta et. al., ©2017 The American Astronomical Society. All rights reserved. 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., L.P.C. acknowledges funding by the Max-Planck-Princeton Center for Plasma Physics and funding from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement No. 707837. The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant number NNX13AE95G. SDO data are the courtesy of NASA/SDO and the AIA, and HMI science teams. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea

A. J. Kaithakkal et. al., ©2017 The American Astronomical Society. All rights reserved.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., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant number NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea.

The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 spacecraft, the first dedicated solar mission of the Indian Space Research Organization (ISRO), which will be put in a halo orbit at the Sun-Earth Langrage point (L1). SUIT has an off-axis Ritchey–Chretien configuration with a combination of 11 narrow and broad bandpass filters which will be used for full-disk solar imaging in the Ultravoilet (UV) wavelength range 200-400 nm. It will provide near simultaneous observations of lower and middle layers of the solar atmosphere, namely the Photosphere and Chromosphere. These observations will help to improve our understanding of coupling and dynamics of various layers of the solar atmosphere, mechanisms responsible for stability, dynamics and eruption of solar prominences and Coronal Mass ejections, and possible causes of solar irradiance variability in the Near and Middle UV regions, which is of central interest for assessing the Sun’s influence on climate.

Energetic particles are critical components of plasma populations found throughout the universe. In many cases particles are accelerated to relativistic energies and represent a substantial fraction of the total energy of the system, thus requiring extremely efficient acceleration processes. The production of accelerated particles also appears coupled to magnetic field evolution in astrophysical plasmas through the turbulent magnetic fields produced by diffusive shock acceleration. Particle acceleration is thus a key component in helping to understand the origin and evolution of magnetic structures in, e.g. galaxies. The proximity of the Sun and the range of high-resolution diagnostics available within the solar atmosphere offers unique opportunities to study the processes involved in particle acceleration through the use of a combination of remote sensing observations of the radiative signatures of accelerated particles, and of their plasma and magnetic environment. The SPARK concept targets the broad range of energy, spatial and temporal scales over which particle acceleration occurs in the solar atmosphere, in order to determine how and where energetic particles are accelerated. SPARK combines highly complementary imaging and spectroscopic observations of radiation from energetic electrons, protons and ions set in their plasma and magnetic context. The payload comprises focusing-optics X-ray imaging covering the range from 1 to 60 keV; indirect HXR imaging and spectroscopy from 5 to 200 keV, γ-ray spectroscopic imaging with high-resolution LaBr3 scintillators, and photometry and source localisation at far-infrared wavelengths. The plasma environment of the regions of acceleration and interaction will be probed using soft X-ray imaging of the corona and vector magnetography of the photosphere and chromosphere. SPARK is designed for solar research. However, in addition it will be able to provide exciting new insights into the origin of particle acceleration in other regimes, including terrestrial gamma-ray flashes (TGF), the origin of γ-ray bursts, and the possible existence of axions.

The Sunrise balloon-borne solar observatory consists of a 1m aperture Gregory telescope, a UV filter imager, an imaging vector polarimeter, an image stabilization system and further infrastructure. The first science flight of Sunrise yielded high-quality data that reveal the structure, dynamics and evolution of solar convection, oscillations and magnetic fields at a resolution of around 100 km in the quiet Sun. After a brief description of instruments and data, first qualitative results are presented. In contrast to earlier observations, we clearly see granulation at 214 nm. Images in Ca II H display narrow, short-lived dark intergranular lanes between the bright edges of granules. The very small-scale, mixed-polarity internetwork fields are found to be highly dynamic. A significant increase in detectable magnetic flux is found after phase-diversity-related reconstruction of polarization maps, indicating that the polarities are mixed right down to the spatial resolution limit, and probably beyond., Comment: accepted by ApJL

We present high-resolution images of the Sun in the near-ultraviolet spectral range between 214 nm and 397 nm as obtained from the first science flight of the 1 m SUNRISE balloon-borne solar telescope. The quiet-Sun rms intensity contrasts found in this wavelength range are among the highest values ever obtained for quiet-Sun solar surface structures—up to 32.8% at a wavelength of 214 nm. We compare the rms contrasts obtained from the observational data with theoretical intensity contrasts obtained from numerical magnetohydrodynamic simulations. For 388 nm and 312 nm the observations agree well with the numerical simulations whereas at shorter wavelengths discrepancies between observed and simulated contrasts remain.

The Sunrise balloon-borne solar observatory consists of a 1m aperture Gregory telescope, a UV filter imager, an imaging vector polarimeter, an image stabilization system and further infrastructure. The first science flight of Sunrise yielded high-quality data that reveal the structure, dynamics and evolution of solar convection, oscillations and magnetic fields at a resolution of around 100 km in the quiet Sun. Here we describe very briefly the mission and the first results obtained from the Sunrise data, which include a number of discoveries.

SUNRISE is a balloon-borne telescope with an aperture of one meter. It is equipped with a filter imager for the UV wavelength range between 214 nm and 400 nm (SUFI), and with a spectro-polarimeter that measures the magnetic field of the photosphere using the Fe I line at 525.02 nm that has a Lande factor of 3. SUNRISE performed its first science flight from 8 to 14 June 2009. It was launched at the Swedish ESRANGE Space Center and cruised at an altitude of about 36 km and geographic latitudes between 70 and 74 degrees to Somerset Island in northern Canada. There, all data, the telescope and the gondola were successfully recovered. During its flight, Sunrise achieved high pointing stability during 33 hours, and recorded about 1.8 TB of science data. Already at this early stage of data processing it is clear that SUNRISE recorded UV images of the solar photosphere, and spectropolarimetric measurements of the quiet Sun's magnetic field of unprecedented quality (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

SUNRISE is an international project for the development, construction and operation of a balloon-borne solar telescope with an aperture of 1 m, working in the UV/VIS spectral domain. The main scientific goal of SUNRISE is to understand the structure and dynamics of the magnetic field in the atmosphere of the Sun. SUNRISE will provide near diffraction-limited images of the photosphere and chromosphere with an unprecedented resolution down to 35 km on the solar surface at wavelengths around 220 nm. Active in-flight alignment and image stabilization techniques are used. The focal-plane instrumentation consists of a polarization sensitive spectrograph, a Fabry–Perot filter magnetograph and a phase-diverse filter imager working in the near UV. The first stratospheric long-duration balloon flight of SUNRISE is planned in summer 2009 from the Swedish ESRANGE station. SUNRISE is a joint project of the German Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut fur Sonnenphysik (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin Solar and Astrophysics Laboratory (LMSAL), Palo Alto, USA, and the Spanish IMaX consortium. This paper will give an overview about the mission and a description of its scientific and technological aspects.

Photospheric bright points were investigated in three different wavelength bands using interference filters centered at 436.5 nm (continuum), 430.5 nm (Fraunhofer's G-band dominated by absorption due to CH), and 388.7 nm (absorption band of CN). Such bright points serve as proxies of small-scale solar magnetic elements. Near diffraction limited imaging was achieved by real-time frame selection and subsequent joint phase diverse speckle reconstruction. Comparison of the filtergrams of NOAA0670 taken in CH and CN shows that the contrast of bright points is on average 1.4 times higher in CN than in G-band, which is in good quantitative agreement with the predictions of Berdyugina et al. (2003, A&A, 412, 513) and Rutten et al. (2001, ASP Conf. Ser., 236, 445).

We describe an imaging polarimeter for high sensitivity measurements of solar polarisation signals in the wavelength range from 300 nm to 1 μ m. At higher wavelengths the system is limited by the wavelength cut-off of the silicon CCD sensor used. To the blue the limitation arises from the atmospheric cut-off around 310 nm. The complete system is a modified version of the Z urich Im aging Pol arimeter ZIMPOL ii which has been equipped with a special CCD sensor. The CCD combines for the first time a so-called open electrode structure with on-chip demodulation. The concept as well as the detailed design of the instrument are presented. Examples of observations are shown and interpreted in order to experimentally evaluate the performance of the system.

Over the last decade spectro-polarimetry evolved to ever higher sensitivity levels. New techniques and instruments allow us to address weak polarization signals, which are caused by scattering in the solar atmosphere. In this paper a review on the development of spectro-polarimetric investigations of scattering physics and its coupling to the solar magnetic field will be given. Starting from a technical point of view it will be demonstrated how our understanding of scattering phenomena and their role in solar physics in general has reached its current state. An outlook on future spectro-polarimetry with new large solar telescopes concludes this review.

Spatial mapping of the Hanle and Zeeman eects on the Sun has been done for the rst time, through Stokes vector imaging with a narrow-band (0.2 A) universal lter. It is shown how the polarization signatures of the Hanle and Zeeman eects can be cleanly distinguished from each other by comparing the Stokes images recorded at dierent, specially selected wavelengths within the Na i D2{D1 line system. Examples of the polarization signatures of sunspots, faculae, the supergranulation network, and large-scale canopy elds are shown. The most striking result of our observations is that the scattering polarization has an extremely intermittent structure rather than being a simple function of limb distance. These intermittent scattering polarization signals are cospatial with the facular and supergranulation network seen both in intensity and circular polarization. The observed pattern can be explained in terms of magnetic enhancement of the scattering polarization in the network and/or Hanle depolarization of the scattering polarization outside the network. Since however no magnetic elds are seen in circular polarization outside the network, the relative absence of linear scattering polarization there may be explained by Hanle depolarization only if the volume lling, depolarizing magnetic eld has mixed polarities on a subarcsec scale that is not resolved.

S. K. Solanki et. al., ©2017 The American Astronomical Society. All rights reserved.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., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which is gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The National Center for Atmospheric Research is sponsored by the National Science Foundation. The HAO contribution was partly funded through NASA grant number NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. L.G. acknowledges research funding from the State of Lower Saxony, Germany. SDO is a mission of NASA's Living With a Star (LWS) program. The SDO/HMI data were provided by the Joint Science Operation Center (JSOC). The National Solar Observatory (NSO) is operated by the Association of Universities for Research in Astronomy (AURA) Inc. under a cooperative agreement with the National Science Foundation.

R. Gafeira et. al., ©2017 The American Astronomical Society. All rights reserved. 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., The German contribution to Sunrise and its reflight was funded by the Max Planck Foundation, the Strategic Innovations Fund of the President of the Max Planck Society (MPG), DLR, and private donations by supporting members of the Max Planck Society, which are gratefully acknowledged. The Spanish contribution was funded by the Ministerio de Economía y Competitividad under Projects ESP2013-47349-C6 and ESP2014-56169-C6, partially using European FEDER funds. The HAO contribution was partly funded through NASA grant No. NNX13AE95G. This work was partly supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. S.J. receives support from the Research Council of Norway.

The Solar Orbiter mission, to be launched in July 2017, will carry a suite of remote sensing and in-situ instruments, including the Polarimetric and Helioseismic Imager (PHI). PHI will deliver high-cadence images of the Sun in intensity and Doppler velocity suitable for carrying out novel helioseismic studies. The orbit of the Solar Orbiter spacecraft will reach a solar latitude of up to 21 deg (up to 34 deg by the end of the extended mission) and thus will enable the first local helioseismology studies of the polar regions. Here we consider an array of science objectives to be addressed by helioseismology within the baseline telemetry allocation (51 Gbit per orbit, current baseline) and within the science observing windows (baseline 3 x 10 days per orbit). A particularly important objective is the measurement of large-scale flows at high latitudes (rotation and meridional flow), which are largely unknown but play an important role in flux transport dynamos. The full range of Earth-Sun-spacecraft angles provided by the orbit will enable helioseismology from two vantage points by combining PHI with another instrument: stereoscopic helioseismology will allow the study of the deep solar interior and a better understanding of the physics of solar oscillations in both quiet Sun and sunspots. We have used a model of the PHI instrument to study its performance for helioseismology applications. As input we used a 6 hr time-series of realistic solar magneto-convection simulation (Stagger code) and the SPINOR radiative transfer code to synthesize the observables. The simulated power spectra of solar oscillations show that the instrument is suitable for helioseismology. In particular, the specified point spread function, image jitter, and photon noise are no obstacle to a successful mission., 35 pages, 12 figures. Accepted for publication in Space Science Reviews

Bright points (BPs) in the solar photosphere are radiative signatures of magnetic elements described by slender flux tubes located in the darker intergranular lanes. They contribute to the ultraviolet (UV) flux variations over the solar cycle and hence may influence the Earth's climate. Here we combine high-resolution UV and spectro-polarimetric observations of BPs by the SUNRISE observatory with 3D radiation MHD simulations. Full spectral line syntheses are performed with the MHD data and a careful degradation is applied to take into account all relevant instrumental effects of the observations. It is demonstrated that the MHD simulations reproduce the measured distributions of intensity at multiple wavelengths, line-of-sight velocity, spectral line width, and polarization degree rather well. Furthermore, the properties of observed BPs are compared with synthetic ones. These match also relatively well, except that the observations display a tail of large and strongly polarized BPs not found in the simulations. The higher spatial resolution of the simulations has a significant effect, leading to smaller and more numerous BPs. The observation that most BPs are weakly polarized is explained mainly by the spatial degradation, the stray light contamination, and the temperature sensitivity of the Fe I line at 5250.2 \AA{}. The Stokes $V$ asymmetries of the BPs increase with the distance to their center in both observations and simulations, consistent with the classical picture of a production of the asymmetry in the canopy. This is the first time that this has been found also in the internetwork. Almost vertical kilo-Gauss fields are found for 98 % of the synthetic BPs. At the continuum formation height, the simulated BPs are on average 190 K hotter than the mean quiet Sun, their mean BP field strength is 1750 G, supporting the flux-tube paradigm to describe BPs., Comment: Accepted for publication in Astronomy & Astrophysics on May 30 2014

The migration of magnetic bright point-like features (MBP) in the lower solar atmosphere reflects the dispersal of magnetic flux as well as the horizontal flows of the atmospheric layer they are embedded in. We analyse trajectories of the proper motion of intrinsically magnetic, isolated internetwork Ca II H MBPs (mean lifetime 461 +- 9 s) to obtain their diffusivity behaviour. We use seeing-free high spatial and temporal resolution image sequences of quiet-Sun, disc-centre observations obtained in the Ca II H 3968 {\AA} passband of the Sunrise Filter Imager (SuFI) onboard the Sunrise balloon-borne solar observatory. Small MBPs in the internetwork are automatically tracked. The trajectory of each MBP is then calculated and described by a diffusion index ({\gamma}) and a diffusion coefficient (D). We further explore the distribution of the diffusion indices with the help of a Monte Carlo simulation. We find {\gamma} = 1.69 +- 0.08 and D = 257 +- 32 km^2/s averaged over all MBPs. Trajectories of most MBPs are classified as super-diffusive, i.e., {\gamma} > 1, with the determined {\gamma} being to our knowledge the largest obtained so far. A direct correlation between D and time-scale ({\tau}) determined from trajectories of all MBPs is also obtained. We discuss a simple scenario to explain the diffusivity of the observed, relatively short-lived MBPs while they migrate within a small area in a supergranule (i.e., an internetwork area). We show that the scatter in the {\gamma} values obtained for individual MBPs is due to their limited lifetimes. The super-diffusive MBPs can be well-described as random walkers (due to granular evolution and intergranular turbu- lence) superposed on a large systematic (background) velocity, caused by granular, mesogranular and supergranular flows., Comment: 10 pages, 7 figures, 3 tables

To clarify the physical nature of the enigmatic scattering polarization in the Na i D 1 and D 2 line cores we have explored their behavior with full Stokes vector polarimetry in regions with varying degree of magnetic activity near the solar limb. These observations represent the first time that ZIMPOL II, the second generation of our CCD based imaging polarimeter systems, has been used for a scientific program. With ZIMPOL II the four Stokes images can be demodulated and recorded with a single CCD sensor such that the resulting images of the fractional polarization $Q/I$, $U/I$, and $V/I$ are entirely free from spurious features due to seeing or flat-field effects. The polarization in the cores of the lines, in particular in D 2 , exhibits dramatic and unexpected spatial variations in both $Q/I$ and $U/I$, including polarization self-reversals of the D 2 $Q/I$ core peak. As the fluctuations in the Q , U , and V parameters appear to be relatively uncorrelated, we have parametrized the profiles and made scatter plots of the extracted parameters. Comparison with synthetic scatter plots based on different theoretical models suggests that the polarization signals in the cores of the D 2 and D 1 lines have different physical origins: While the D 1 core is likely to be governed by ground-state atomic polarization, the D 2 core is dominated by the alignment of the excited state and by effects of partial frequency redistribution.