Author name code: degroof ADS astronomy entries on 2022-09-14 author:"De Groof, Anik" ------------------------------------------------------------------------ Title: Solar Orbiter's first close encounter with the Sun: preparation of the coordinated science campaigns Authors: de Groof, Anik; Müller, Daniel; Zouganelis, Yannis; Walsh, Andrew; Williams, David Bibcode: 2022cosp...44.1537D Altcode: After a Cruise Phase of 21 months, Solar Orbiter entered its first scientific orbit on 27 November 2021 after a Gravity Assist Manoeuvre (GAM) by the Earth. The spacecraft entered a highly elliptical orbit that will bring it up to its first close perihelion on 17 March 2022, at 0.32AU from the Sun. In the following years, further GAMs by Venus will lead it even closer to the Sun and also out of the ecliptic plane. Solar Orbiter's main goal is to study the connection between the solar activity close to the star's surface and its effects as seen in the heliosphere, the bubble-like region of space under the Sun's influence including all solar planets. Therefore, its main scientific goals can only be achieved by coordinated observations of both the 6 remote-sensing telescopes onboard, observing the dynamic Sun, and the 4 in-situ instruments measuring the effects in the solar wind surrounding the spacecraft. This coordination takes careful planning and optimisation of the mission resources, in order to fully exploit the capabilities of this exciting mission. In this contribution, we present the science operations as planned for the first year of Nominal mission phase, i.e. the first two orbits. By the time of the COSPAR meeting, Solar Orbiter will have made its first close encounter and most of the data from the perihelion will have arrived! 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: Coordination of the in situ payload of Solar Orbiter Authors: Walsh, A. P.; Horbury, T. S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Wimmer-Schweingruber, R. F.; Zouganelis, I.; Anekallu, C.; Bonnin, X.; Bruno, R.; Carrasco Blázquez, I.; Cernuda, I.; Chust, T.; De Groof, A.; Espinosa Lara, F.; Fazakerley, A. N.; Gilbert, H. R.; Gómez-Herrero, R.; Ho, G. C.; Krucker, S.; Lepri, S. T.; Lewis, G. R.; Livi, S.; Louarn, P.; Müller, D.; Nieves-Chinchilla, T.; O'Brien, H.; Osuna, P.; Plasson, P.; Raines, J. M.; Rouillard, A. P.; St Cyr, O. C.; Sánchez, L.; Soucek, J.; Varsani, A.; Verscharen, D.; Watson, C. J.; Watson, G.; Williams, D. R. Bibcode: 2020A&A...642A...5W Altcode: Solar Orbiter's in situ coordination working group met frequently during the development of the mission with the goal of ensuring that its in situ payload has the necessary level of coordination to maximise science return. Here we present the results of that work, namely how the design of each of the in situ instruments (EPD, MAG, RPW, SWA) was guided by the need for coordination, the importance of time synchronisation, and how science operations will be conducted in a coordinated way. We discuss the mechanisms by which instrument sampling schemes are aligned such that complementary measurements will be made simultaneously by different instruments, and how burst modes are scheduled to allow a maximum overlap of burst intervals between the four instruments (telemetry constraints mean different instruments can spend different amounts of time in burst mode). We also explain how onboard autonomy, inter-instrument communication, and selective data downlink will be used to maximise the number of transient events that will be studied using high-resolution modes of all the instruments. Finally, we briefly address coordination between Solar Orbiter's in situ payload and other missions. 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 Solar Orbiter SPICE instrument. An extreme UV imaging spectrometer Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.; Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini, K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.; Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.; Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau, J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.; Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest, S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler, D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller, S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall, G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris, N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.; Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.; Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy, B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.; Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial, J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward, S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D. Bibcode: 2020A&A...642A..14S Altcode: 2019arXiv190901183A; 2019arXiv190901183S
Aims: The Spectral Imaging of the Coronal Environment (SPICE) instrument is a high-resolution imaging spectrometer operating at extreme ultraviolet wavelengths. In this paper, we present the concept, design, and pre-launch performance of this facility instrument on the ESA/NASA Solar Orbiter mission.
Methods: The goal of this paper is to give prospective users a better understanding of the possible types of observations, the data acquisition, and the sources that contribute to the instrument's signal.
Results: The paper discusses the science objectives, with a focus on the SPICE-specific aspects, before presenting the instrument's design, including optical, mechanical, thermal, and electronics aspects. This is followed by a characterisation and calibration of the instrument's performance. The paper concludes with descriptions of the operations concept and data processing.
Conclusions: The performance measurements of the various instrument parameters meet the requirements derived from the mission's science objectives. The SPICE instrument is ready to perform measurements that will provide vital contributions to the scientific success of the Solar Orbiter mission. Title: Understanding the origins of the heliosphere: integrating observations and measurements from Parker Solar Probe, Solar Orbiter, and other space- and ground-based observatories Authors: Velli, M.; Harra, L. K.; Vourlidas, A.; Schwadron, N.; Panasenco, O.; Liewer, P. C.; Müller, D.; Zouganelis, I.; St Cyr, O. C.; Gilbert, H.; Nieves-Chinchilla, T.; 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.; Wimmer-Schweingruber, R. F.; Bale, S.; Kasper, J.; McComas, D. J.; Raouafi, N.; Martinez-Pillet, V.; Walsh, A. P.; De Groof, A.; Williams, D. Bibcode: 2020A&A...642A...4V Altcode: Context. The launch of Parker Solar Probe (PSP) in 2018, followed by Solar Orbiter (SO) in February 2020, has opened a new window in the exploration of solar magnetic activity and the origin of the heliosphere. These missions, together with other space observatories dedicated to solar observations, such as the Solar Dynamics Observatory, Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations from WIND and ACE, and ground based multi-wavelength observations including the DKIST observatory that has just seen first light, promise to revolutionize our understanding of the solar atmosphere and of solar activity, from the generation and emergence of the Sun's magnetic field to the creation of the solar wind and the acceleration of solar energetic particles.
Aims: Here we describe the scientific objectives of the PSP and SO missions, and highlight the potential for discovery arising from synergistic observations. Here we put particular emphasis on how the combined remote sensing and in situ observations of SO, that bracket the outer coronal and inner heliospheric observations by PSP, may provide a reconstruction of the solar wind and magnetic field expansion from the Sun out to beyond the orbit of Mercury in the first phases of the mission. In the later, out-of-ecliptic portions of the SO mission, the solar surface magnetic field measurements from SO and the multi-point white-light observations from both PSP and SO will shed light on the dynamic, intermittent solar wind escaping from helmet streamers, pseudo-streamers, and the confined coronal plasma, and on solar energetic particle transport.
Methods: Joint measurements during PSP-SO alignments, and magnetic connections along the same flux tube complemented by alignments with Earth, dual PSP-Earth, and SO-Earth, as well as with STEREO-A, SOHO, and BepiColumbo will allow a better understanding of the in situ evolution of solar-wind plasma flows and the full three-dimensional distribution of the solar wind from a purely observational point of view. Spectroscopic observations of the corona, and optical and radio observations, combined with direct in situ observations of the accelerating solar wind will provide a new foundation for understanding the fundamental physical processes leading to the energy transformations from solar photospheric flows and magnetic fields into the hot coronal plasma and magnetic fields and finally into the bulk kinetic energy of the solar wind and solar energetic particles.
Results: We discuss the initial PSP observations, which already provide a compelling rationale for new measurement campaigns by SO, along with ground- and space-based assets within the synergistic context described above. Title: The Solar Orbiter mission. Science overview Authors: Müller, D.; St. Cyr, O. C.; Zouganelis, I.; Gilbert, H. R.; Marsden, R.; Nieves-Chinchilla, T.; Antonucci, E.; Auchère, F.; Berghmans, D.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.; Owen, C. J.; Rochus, P.; Rodriguez-Pacheco, J.; Romoli, M.; Solanki, S. K.; Bruno, R.; Carlsson, M.; Fludra, A.; Harra, L.; Hassler, D. M.; Livi, S.; Louarn, P.; Peter, H.; Schühle, U.; Teriaca, L.; del Toro Iniesta, J. C.; Wimmer-Schweingruber, R. F.; Marsch, E.; Velli, M.; De Groof, A.; Walsh, A.; Williams, D. Bibcode: 2020A&A...642A...1M Altcode: 2020arXiv200900861M
Aims: Solar Orbiter, the first mission of ESA's Cosmic Vision 2015-2025 programme and a mission of international collaboration between ESA and NASA, will explore the Sun and heliosphere from close up and out of the ecliptic plane. It was launched on 10 February 2020 04:03 UTC from Cape Canaveral and aims to address key questions of solar and heliospheric physics pertaining to how the Sun creates and controls the Heliosphere, and why solar activity changes with time. To answer these, the mission carries six remote-sensing instruments to observe the Sun and the solar corona, and four in-situ instruments to measure the solar wind, energetic particles, and electromagnetic fields. In this paper, we describe the science objectives of the mission, and how these will be addressed by the joint observations of the instruments onboard.
Methods: The paper first summarises the mission-level science objectives, followed by an overview of the spacecraft and payload. We report the observables and performance figures of each instrument, as well as the trajectory design. This is followed by a summary of the science operations concept. The paper concludes with a more detailed description of the science objectives.
Results: Solar Orbiter will combine in-situ measurements in the heliosphere with high-resolution remote-sensing observations of the Sun to address fundamental questions of solar and heliospheric physics. The performance of the Solar Orbiter payload meets the requirements derived from the mission's science objectives. Its science return will be augmented further by coordinated observations with other space missions and ground-based observatories.

ARRAY(0x207ce98) Title: Solar Orbiter's Science Activity Plan: Translating Questions into Action Authors: Zouganelis, Y.; Mueller, D.; De Groof, A.; Walsh, A. P.; Williams, D. Bibcode: 2019AGUFMSH21D3315Z Altcode: Solar Orbiter is a mission, scheduled for launch in February 2020, with as main goal to observe solar activity from close by, both in and out of the ecliptic, and to link it to the solar wind as sensed by its in-situ sensors. The payload consists of 6 remote-sensing and 4 in-situ instrument suites, which will have to coordinate their operations in order to address the four mission objectives: (1) What drives the solar wind and where does the heliospheric 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? We have to consider, however, that each orbit around the Sun has different characteristics, including the relative positions of the Earth and spacecraft (affecting downlink rates and communications blackouts), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, each orbit's science telemetry will be downloaded during the next, so orbits cannot be planned individually. So how will those science questions be translated into an actual plan of observations that will fit into the mission? First, the component questions are broken down into answerable questions along with the observations they need from the payload. Then, in order to address this, the so-called Science Activity Plan (SAP) has been developed. The SAP groups together objectives that require similar observations into Solar Orbiter Observing Plans (SOOPs), resulting in a strategic, top-level view of the optimal opportunities for science observations across the mission lifetime, allowing all four mission objectives to be addressed. In this presentation, we introduce Solar Orbiter's SAP through a series of examples and the strategy being followed. Title: An Unusual Widespread Solar Energetic Particle Event Authors: Rodriguez-Garcia, L.; Gomez-Herrero, R.; Zouganelis, Y.; Rodriguez-Pacheco, J.; Dresing, N.; Williams, D.; De Groof, A. Bibcode: 2019AGUFMSH23C3355R Altcode: Over the course of several hours, a Solar Energetic Particle (SEP) event was observed by the twin spacecraft of the Solar TErrestrial RElations Observatory (STEREO A and B), by several near-Earth spacecraft like the SOlar and Heliospheric Observatory (SOHO), and by the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) in orbit around Mercury. These multiple observation points covered a considerable angular span of 222 degrees in the ecliptic plane. The widespread SEP event was associated with a halo Coronal Mass Ejection (CME) passing through the SOHO/ Large Angle and Spectrometric Coronagraph ( LASCO) field of view, with a plane-of-sky speed of 877 km/s. The CME was accompanied by type III and type II radio bursts but, surprisingly , in spite of the 360 degree remote-sensing coverage of the solar disk at different wavelengths, no major solar flare was observed. The SEP event showed a very gradual rise of particle intensities at STEREO-A, STEREO-B and the Earth, and the particle onset at STEREO-B and the Earth were delayed by several hours with respect to the estimated lift-off time of the CME. Unexpectedly, this was also the case for STEREO-A, relatively well connected to the source. However, MESSENGER, located closer to the Sun and slightly better connected to the source than STEREO-A, observed a clear electron increase with much shorter temporal delay. It is remarkable that all the spacecraft-observed electron increases approach relativistic energies and proton increases reach energies beyond 50 MeV. To disentangle the possible scenarios for particle acceleration and propagation during this unusual widespread SEP event, particles anisotropies, onset-timing dispersion and act ive r egion m agnetic foot-point separation are discussed. To understand their possible effect on the SEP interplanetary propagation conditions, the identification and 3D geometric characterisation of the CME, as well as of previously ejected Interplanetary Coronal Mass Ejections (ICME) and shocks, are analysed. Different physical scenarios explaining the wide spread of the SEP such as, a wide coronal shock, cross-field diffusion and particle confinement in the interplanetary medium are discussed and compared with the observational signatures. Title: Solar Orbiter Science Operations: Not A Typical Heliophysics Mission Authors: Walsh, A. P.; De Groof, A.; Williams, D.; Sánchez, L.; Zouganelis, Y. Bibcode: 2019AGUFMSH21D3314W Altcode: ESA's Solar Orbiter is scheduled for launch in February 2020, and will approach the Sun to a distance of 0.28 AU, in an orbit progressively more inclined to the Ecliptic plane. Solar Orbiter will provide landmark new views of a star, up-close, often observing its poles, while measuring the coupling of the solar phenomena and features to the relatively pristine solar wind that it will measure in situ. The unique orbit of the spacecraft and the arrangement and composition of its scientific payload impose unique constraints on how scientific operations can be conducted. These operations involve long- to very short-term planning in carefully arranged steps, which have much more in common with planetary encounter missions than preceding heliophysics missions. In this presentation, we explain the details of how science observations will be arranged and conducted, often very far from Earth, and how data from the mission will be returned and distributed. Title: The Energy Spectrum of the Solar Wind Core Authors: Walsh, A. P.; Toledo Redondo, S.; Osuna, P.; Zouganelis, Y.; Masson, A.; De Groof, A.; Perrone, D.; Roberts, O. W.; Taylor, M. Bibcode: 2017AGUFMSH23D2685W Altcode: The solar wind electron distribution is typically characterised as having three components, a broadly isotropic core at the lowest energies, an isotropic halo at higher energies and a field-aligned strahl at energies similar to those of the halo. Historically, the core has been described by a Maxwellian distribution function while the halo and strahl are known to be suprathermal and have been described using kappa functions. We use high energy resolution Cluster PEACE measurements to re-examine the spectral shape of the observed distributions at core energies and find that, at least some of the time, a kappa function better describes them than a Maxwellian. During these times, no spectral break is found at typical halo energies. We discuss the causes and implications of this in the context of Solar Orbiter and Parker Solar Probe. Title: Performances of swap on-board PROBA-2 Authors: Halain, J. -P.; Berghmans, D.; Defise, J. -F.; Rochus, P.; Nicula, B.; de Groof, A.; Seaton, D. Bibcode: 2017SPIE10565E..0SH Altcode: The PROBA2 mission has been launched on 2nd November2009 with a Rockot launcher to a Sunsynchronous orbit at an altitude of 725 km. Its nominal operation duration is two years with possible extension of 2 years. PROBA2 is a small satellite developed under an ESA General Support Technology Program (GSTP) contract to perform an in-flight demonstration of new space technologies and support a scientific mission for a set of selected instruments. The mission is tracked by the ESA Redu Mission Operation Center. Title: Solar Orbiter Science Operations: Not A Typical Heliophysics Mission Authors: Williams, David R.; De Groof, Anik; Walsh, Andrew Bibcode: 2017SPD....4811408W Altcode: ESA’s Solar Orbiter is scheduled for launch in February 2019, and will approach the Sun to a distance of 0.28 AU, in an orbit progressively more inclined to the Ecliptic plane. Solar Orbiter will provide landmark new views of a star, up-close, often observing its poles, while measuring the coupling of the solar phenomena and features to the relatively pristine solar wind that it measure in situ. The unique orbit of the spacecraft and the arrangement and composition of its scientific payload impose unique constraints on how scientific operations can be conducted. These operations involve long- to very short-term planning in carefully arranged steps, which have much in common with planetary-encounter missions than preceding heliophysics missions. In this presentation, we explain the details of how science observations will be arranged and conducted, often very far from Earth, and how data from the mission will be returned and distributed. Title: Solar signatures and eruption mechanism of the August 14, 2010 coronal mass ejection (CME) Authors: D'Huys, Elke; Seaton, Daniel B.; De Groof, Anik; Berghmans, David; Poedts, Stefaan Bibcode: 2017JSWSC...7A...7D Altcode: 2017arXiv170108814D On August 14, 2010 a wide-angled coronal mass ejection (CME) was observed. This solar eruption originated from a destabilized filament that connected two active regions and the unwinding of this filament gave the eruption an untwisting motion that drew the attention of many observers. In addition to the erupting filament and the associated CME, several other low-coronal signatures that typically indicate the occurrence of a solar eruption were associated with this event. However, contrary to what was expected, the fast CME (v > 900 km s-1) was accompanied by only a weak C4.4 flare. We investigate the various eruption signatures that were observed for this event and focus on the kinematic evolution of the filament in order to determine its eruption mechanism. Had this solar eruption occurred just a few days earlier, it could have been a significant event for space weather. The risk of underestimating the strength of this eruption based solely on the C4.4 flare illustrates the need to include all eruption signatures in event analyses in order to obtain a complete picture of a solar eruption and assess its possible space weather impact. Title: Solar Wind Core Electrons: Kappa or Maxwellian? Authors: Walsh, A. P.; Osuna, P.; Toledo Redondo, S.; Zouganelis, Y.; Masson, A.; De Groof, A.; Mueller, D.; Perrone, D.; Roberts, O. W.; Taylor, M. G.; Turc, L. Bibcode: 2016AGUFMSH51D2608W Altcode: Solar wind core electrons are typically considered to have a Maxwellian velocity distribution function. However, most measurements made of them to date don't have sufficient energy resolution to distinguish between a Maxwellian and a kappa distribution at low energies. Here we present a survey of solar wind electron velocity distribution functions observed by Cluster PEACE in its highest energy resolution mode, which is sufficient to distinguish between Maxwellian and kappa distributions for energies below 15eV. Initial results suggest that a kappa distribution better fits the data than a Maxwellian in all cases; in the majority of cases the difference in goodness of fit between a kappa and Maxwellian is small but in some cases, a kappa distribution fits the data significantly better. Title: A virtual appliance as proxy pipeline for the Solar Orbiter/Metis coronagraph Authors: Pancrazzi, M.; Straus, T.; Andretta, V.; Spadaro, D.; Haugan, S. V.; de Groof, A.; Carr, R.; Focardi, M.; Nicolini, G.; Landini, F.; Baccani, C.; Romoli, M.; Antonucci, E. Bibcode: 2016SPIE.9913E..4LP Altcode: Metis is the coronagraph on board Solar Orbiter, the ESA mission devoted to the study of the Sun that will be launched in October 2018. Metis is designed to perform imaging of the solar corona in the UV at 121.6 nm and in the visible range where it will accomplish polarimetry studies thanks to a variable retarder plate. Due to mission constraints, the telemetry downlink on the spacecraft will be limited and data will be downloaded with delays that could reach, in the worst case, several months. In order to have a quick overview on the ongoing operations and to check the safety of the 10 instruments on board, a high-priority downlink channel has been foreseen to download a restricted amount of data. These so-called Low Latency Data will be downloaded daily and, since they could trigger possible actions, they have to be quickly processed on ground as soon as they are delivered. To do so, a proper processing pipeline has to be developed by each instrument. This tool will then be integrated in a single system at the ESA Science Operation Center that will receive the downloaded data by the Mission Operation Center. This paper will provide a brief overview of the on board processing and data produced by Metis and it will describe the proxy-pipeline currently under development to deal with the Metis low-latency data. Title: PROBA2/SWAP EUV images of the large-scale EUV corona up to 3 solar radii: Can we close the gap in coronal magnetic field structure between 1.3 and 2.5 solar radii? Authors: De Groof, Anik; Seaton, Daniel B.; Rachmeler, Laurel; Berghmans, David Bibcode: 2015TESS....140901D Altcode: The EUV telescope PROBA2/SWAP has been observing the solar corona in a bandpass near 17.4 nm since February 2010. SWAP's wide field-of-view provides a unique and continuous view of the extended EUV corona up to 2-3 solar radii. By carefully processing and combining multiple SWAP images, low-noise composites were produced that reveal large-scale, EUV-emitting, coronal structures. These extended structures appear mainly above or at the edges of active regions and typically curve towards the poles. As they persist for multiple Carrington rotations and cannot easily be related to white-light features, they give an interesting view on how the coronal magnetic field is structured between 1.3 and 2-3 solar radii, in the gap between SDO/AIA’s FOV and typical lower boundaries of coronagraph FOVs. With the help of magnetic field models, we analyse the geometry of the extended EUV structures in more detail and compare with sporadic EUV coronagraph measurements up to as close as 1.5Rs. The opportunities that Solar Orbiter’s future observations will bring are explored. Title: SWAP Observations of the Long-term, Large-scale Evolution of the Extreme-ultraviolet Solar Corona Authors: Seaton, Daniel B.; De Groof, Anik; Shearer, Paul; Berghmans, David; Nicula, Bogdan Bibcode: 2013ApJ...777...72S Altcode: 2013arXiv1309.1345S The Sun Watcher with Active Pixels and Image Processing (SWAP) EUV solar telescope on board the Project for On-Board Autonomy 2 spacecraft has been regularly observing the solar corona in a bandpass near 17.4 nm since 2010 February. With a field of view of 54 × 54 arcmin, SWAP provides the widest-field images of the EUV corona available from the perspective of the Earth. By carefully processing and combining multiple SWAP images, it is possible to produce low-noise composites that reveal the structure of the EUV corona to relatively large heights. A particularly important step in this processing was to remove instrumental stray light from the images by determining and deconvolving SWAP's point-spread function from the observations. In this paper, we use the resulting images to conduct the first-ever study of the evolution of the large-scale structure of the corona observed in the EUV over a three year period that includes the complete rise phase of solar cycle 24. Of particular note is the persistence over many solar rotations of bright, diffuse features composed of open magnetic fields that overlie polar crown filaments and extend to large heights above the solar surface. These features appear to be related to coronal fans, which have previously been observed in white-light coronagraph images and, at low heights, in the EUV. We also discuss the evolution of the corona at different heights above the solar surface and the evolution of the corona over the course of the solar cycle by hemisphere. Title: The SWAP EUV Imaging Telescope Part I: Instrument Overview and Pre-Flight Testing Authors: Seaton, D. B.; Berghmans, D.; Nicula, B.; Halain, J. -P.; De Groof, A.; Thibert, T.; Bloomfield, D. S.; Raftery, C. L.; Gallagher, P. T.; Auchère, F.; Defise, J. -M.; D'Huys, E.; Lecat, J. -H.; Mazy, E.; Rochus, P.; Rossi, L.; Schühle, U.; Slemzin, V.; Yalim, M. S.; Zender, J. Bibcode: 2013SoPh..286...43S Altcode: 2012SoPh..tmp..217S; 2012arXiv1208.4631S The Sun Watcher with Active Pixels and Image Processing (SWAP) is an EUV solar telescope onboard ESA's Project for Onboard Autonomy 2 (PROBA2) mission launched on 2 November 2009. SWAP has a spectral bandpass centered on 17.4 nm and provides images of the low solar corona over a 54×54 arcmin field-of-view with 3.2 arcsec pixels and an imaging cadence of about two minutes. SWAP is designed to monitor all space-weather-relevant events and features in the low solar corona. Given the limited resources of the PROBA2 microsatellite, the SWAP telescope is designed with various innovative technologies, including an off-axis optical design and a CMOS-APS detector. This article provides reference documentation for users of the SWAP image data. Title: Preface Authors: Berghmans, D.; De Groof, A.; Dominique, M.; Hochedez, J. -F.; Leibacher, J. W. Bibcode: 2013SoPh..286....1B Altcode: No abstract at ADS Title: SoFAST: Automated Flare Detection with the PROBA2/SWAP EUV Imager Authors: Bonte, K.; Berghmans, D.; De Groof, A.; Steed, K.; Poedts, S. Bibcode: 2013SoPh..286..185B Altcode: 2012SoPh..tmp..288B The Sun Watcher with Active Pixels and Image Processing (SWAP) EUV imager onboard PROBA2 provides a non-stop stream of coronal extreme-ultraviolet (EUV) images at a cadence of typically 130 seconds. These images show the solar drivers of space-weather, such as flares and erupting filaments. We have developed a software tool that automatically processes the images and localises and identifies flares. On one hand, the output of this software tool is intended as a service to the Space Weather Segment of ESA's Space Situational Awareness (SSA) program. On the other hand, we consider the PROBA2/SWAP images as a model for the data from the Extreme Ultraviolet Imager (EUI) instrument prepared for the future Solar Orbiter mission, where onboard intelligence is required for prioritising data within the challenging telemetry quota. In this article we present the concept of the software, the first statistics on its effectiveness and the online display in real time of its results. Our results indicate that it is not only possible to detect EUV flares automatically in an acquired dataset, but that quantifying a range of EUV dynamics is also possible. The method is based on thresholding of macropixelled image sequences. The robustness and simplicity of the algorithm is a clear advantage for future onboard use. Title: The Projects for Onboard Autonomy (PROBA2) Science Centre: Sun Watcher Using APS Detectors and Image Processing (SWAP) and Large-Yield Radiometer (LYRA) Science Operations and Data Products Authors: Zender, J.; Berghmans, D.; Bloomfield, D. S.; Cabanas Parada, C.; Dammasch, I.; De Groof, A.; D'Huys, E.; Dominique, M.; Gallagher, P.; Giordanengo, B.; Higgins, P. A.; Hochedez, J. -F.; Yalim, M. S.; Nicula, B.; Pylyser, E.; Sanchez-Duarte, L.; Schwehm, G.; Seaton, D. B.; Stanger, A.; Stegen, K.; Willems, S. Bibcode: 2013SoPh..286...93Z Altcode: 2012SoPh..tmp..142Z The PROBA2 Science Centre (P2SC) is a small-scale science operations centre supporting the Sun observation instruments onboard PROBA2: the EUV imager Sun Watcher using APS detectors and image Processing (SWAP) and Large-Yield Radiometer (LYRA). PROBA2 is one of ESA's small, low-cost Projects for Onboard Autonomy (PROBA) and part of ESA's In-Orbit Technology Demonstration Programme. The P2SC is hosted at the Royal Observatory of Belgium, co-located with both Principal Investigator teams. The P2SC tasks cover science planning, instrument commanding, instrument monitoring, data processing, support of outreach activities, and distribution of science data products. PROBA missions aim for a high degree of autonomy at mission and system level, including the science operations centre. The autonomy and flexibility of the P2SC is reached by a set of web-based interfaces allowing the operators as well as the instrument teams to monitor quasi-continuously the status of the operations, allowing a quick reaction to solar events. In addition, several new concepts are implemented at instrument, spacecraft, and ground-segment levels allowing a high degree of flexibility in the operations of the instruments. This article explains the key concepts of the P2SC, emphasising the automation and the flexibility achieved in the commanding as well as the data-processing chain. Title: Temperature Response of the 171 Å Passband of the SWAP Imager on PROBA2, with a Comparison to TRACE, SOHO, STEREO, and SDO Authors: Raftery, Claire L.; Bloomfield, D. Shaun; Gallagher, Peter T.; Seaton, Daniel B.; Berghmans, David; De Groof, Anik Bibcode: 2013SoPh..286..111R Altcode: We calculated the temperature response of the 171 Å passbands of the Sun Watcher using APS detectors and image Processing (SWAP) instrument onboard the PRoject for OnBoard Autonomy 2 (PROBA2) satellite. These results were compared to the temperature responses of the Extreme Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO), the Transition Region and Coronal Explorer (TRACE), the twin Extreme Ultraviolet Imagers (EUVI) onboard the Solar TErrestrial RElations Observatory (STEREO) A and B spacecraft, and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). Multiplying the wavelength-response functions for each instrument by a series of isothermal synthetic spectra and integrating over the range 165 - 195 Å produced temperature-response functions for the six instruments. Each temperature response was then multiplied by sample differential emission-measure functions for four different solar conditions. For any given plasma condition (e.g. quiet Sun, active region), it was found that the overall variation with temperature agreed remarkably well across the six instruments, although the wavelength responses for each instrument have some distinctly different features. Deviations were observed, however, when we compared the response of any one instrument to different solar conditions, particularly for the case of solar flares. Title: The SWAP EUV Imaging Telescope. Part II: In-flight Performance and Calibration Authors: Halain, J. -P.; Berghmans, D.; Seaton, D. B.; Nicula, B.; De Groof, A.; Mierla, M.; Mazzoli, A.; Defise, J. -M.; Rochus, P. Bibcode: 2013SoPh..286...67H Altcode: 2012SoPh..tmp..317H; 2012arXiv1210.3551H The Sun Watcher with Active Pixel System detector and Image Processing (SWAP) telescope was launched on 2 November 2009 onboard the ESA PROBA2 technological mission and has acquired images of the solar corona every one to two minutes for more than two years. The most important technological developments included in SWAP are a radiation-resistant CMOS-APS detector and a novel onboard data-prioritization scheme. Although such detectors have been used previously in space, they have never been used for long-term scientific observations on orbit. Thus SWAP requires a careful calibration to guarantee the science return of the instrument. Since launch we have regularly monitored the evolution of SWAP's detector response in-flight to characterize both its performance and degradation over the course of the mission. These measurements are also used to reduce detector noise in calibrated images (by subtracting dark-current). Because accurate measurements of detector dark-current require large telescope off-points, we also monitored straylight levels in the instrument to ensure that these calibration measurements are not contaminated by residual signal from the Sun. Here we present the results of these tests and examine the variation of instrumental response and noise as a function of both time and temperature throughout the mission. Title: PROBA2: Mission and Spacecraft Overview Authors: Santandrea, S.; Gantois, K.; Strauch, K.; Teston, F.; Proba2 Project Team; Tilmans, E.; Baijot, C.; Gerrits, D.; Proba2 Industry Team; de Groof, A.; Schwehm, G.; Zender, J. Bibcode: 2013SoPh..286....5S Altcode: Within the European Space Agency's (ESA) General Support and Technology Programme (GSTP), the Project for On-Board Autonomy (PROBA) missions provide a platform for in-orbit technology demonstration. Besides the technology demonstration goal, the satellites allow to provide services to, e.g., scientific communities. PROBA1 has been providing multi-spectral imaging data to the Earth observation community for a decade, and PROBA2 provides imaging and irradiance data from our Sun to the solar community. This article gives an overview of the PROBA2 mission history and provides an introduction to the flight segment, the ground segment, and the payload operated onboard. Important aspects of the satellite's design, including onboard software autonomy and the functionality of the navigation and guidance, are discussed. PROBA2 successfully proved again within the GSTP concept that it is possible to provide a fast and cost-efficient satellite design and to combine advanced technology objectives from industry with focussed objectives from the science community. Title: Study of a Prominence Eruption using PROBA2/SWAP and STEREO/EUVI Data Authors: Mierla, M.; Seaton, D. B.; Berghmans, D.; Chifu, I.; De Groof, A.; Inhester, B.; Rodriguez, L.; Stenborg, G.; Zhukov, A. N. Bibcode: 2013SoPh..286..241M Altcode: 2012SoPh..tmp...66M; 2012arXiv1203.6732M Observations of the early rise and propagation phases of solar eruptive prominences can provide clues about the forces acting on them through the behavior of their acceleration with height. We have analyzed such an event, observed on 13 April 2010 by SWAP on PROBA2 and EUVI on STEREO. A feature at the top of the erupting prominence was identified and tracked in images from the three spacecraft. The triangulation technique was used to derive the true direction of propagation of this feature. The reconstructed points were fitted with two mathematical models: i) a power-law polynomial function and ii) a cubic smoothing spline, in order to derive the accelerations. The first model is characterized by five degrees of freedom while the second one is characterized by ten degrees of freedom. The results show that the acceleration increases smoothly, and it is continuously increasing with height. We conclude that the prominence is not accelerated immediately by local reconnection, but rather is swept away as part of a large-scale relaxation of the coronal magnetic field. Title: Solar TErrestrial Relations Observatory-A (STEREO-A) and PRoject for On-Board Autonomy 2 (PROBA2) Quadrature Observations of Reflections of Three EUV Waves from a Coronal Hole Authors: Kienreich, I. W.; Muhr, N.; Veronig, A. M.; Berghmans, D.; De Groof, A.; Temmer, M.; Vršnak, B.; Seaton, D. B. Bibcode: 2013SoPh..286..201K Altcode: 2012SoPh..tmp..138K We investigate the interaction of three consecutive large-scale coronal waves with a polar coronal hole, simultaneously observed on-disk by the Solar TErrestrial Relations Observatory (STEREO)-A spacecraft and on the limb by the PRoject for On-Board Autonomy 2 (PROBA2) spacecraft on 27 January 2011. All three extreme ultraviolet (EUV) waves originate from the same active region, NOAA 11149, positioned at N30E15 in the STEREO-A field of view and on the limb in PROBA2. For the three primary EUV waves, we derive starting velocities in the range of ≈ 310 km s−1 for the weakest up to ≈ 500 km s−1 for the strongest event. Each large-scale wave is reflected at the border of the extended coronal hole at the southern polar region. The average velocities of the reflected waves are found to be smaller than the mean velocities of their associated direct waves. However, the kinematical study also reveals that in each case the ending velocity of the primary wave matches the initial velocity of the reflected wave. In all three events, the primary and reflected waves obey the Huygens-Fresnel principle, as the incident angle with ≈ 10° to the normal is of the same magnitude as the angle of reflection. The correlation between the speed and the strength of the primary EUV waves, the homologous appearance of both the primary and the reflected waves, and in particular the EUV wave reflections themselves suggest that the observed EUV transients are indeed nonlinear large-amplitude MHD waves. Title: Quasi-Periodic Pulsations during the onset of solar flares: multi-instrumental comparison Authors: West, M. J.; Dolla, L.; Marque, C.; Seaton, D. B.; Van Doorsselaere, T.; Dominique, M.; Berghmans, D.; Cabanas, C.; De Groof, A.; Schmutz, W.; Verdini, A.; Zender, J.; Zhukov, A. N. Bibcode: 2013enss.confE..82W Altcode: Quasi-periodic pulsations have been observed in the rising phase of solar flares for many years. Observations have been made over a wide spectral range, extending from X-rays to radio wavelengths. The current generation of spacebourne instruments, especially SDO, EVE and ESP, have exceptionally high sampling rates and allow us to make more detailed observations of this phenomena. In this work, we compare short-period oscillations (around 10 s) observed in flare events by multiple instruments: the radiometer channels of SDO/EVE-ESP (soft X-ray, coronal and chromospheric passbands), the EUV channels of the radiometer PROBA2/LYRA, the RHESSI passbands and short-wavelength radio observations. Title: Plasmoid Ejection at a Solar Total Eclipse Authors: Koutchmy, S.; Bazin, C.; Berghmans, D.; De Groof, A.; Druckmüller, M.; Tavabi, E.; Engell, A.; Filippov, B.; Golub, L.; Lamy, Ph.; Linker, J.; Mikic, Z.; Mouette, J.; Nitschelm, Ch.; Seaton, D.; Slemzin, V. Bibcode: 2012EAS....55..223K Altcode: The existence of coronal plasmoids has been postulated for many years in order to supply material to streamers and possibly to the solar wind (SW). The W-L SoHO C2 Lasco coronagraph observations were made under the 2.2 solar radii (R0) occulting disk to look at the ultimate sources of the SW; EUV imagers are preferably devoted to the analysis of the corona on and very near the solar disk. Here, in addition to eclipse white-light (W-L) snapshots, we used the new SWAP space-borne imager designed for the systematic survey of coronal activity in the EUV lines near 17.4 nm, over a field of view (FOV) up to 2 R0. Using summed and co-aligned images, the corona can then be evaluated for the 1st time up to the limit of this FOV. At the time of the July 11, 2010, solar total eclipse a 20h continuous run of observations was collected, including images taken during eclipse totality from several ground observing locations where W-L data were collected. A plasmoid-like off-limb event was followed using the SWAP summed Title: STEREO-A and PROBA2 Quadrature Observations of Reflections of three EUV Waves from a Coronal Hole Authors: Kienreich, Ines Waltraud; Muhr, Nicole; Veronig, Astrid; Berghmans, David; de Groof, Anik; Temmer, Manuela; Vršnak, Bojan; Seaton, Dan Bibcode: 2012arXiv1204.6472K Altcode: 2012arXiv1204.6472W We investigate the interaction of three consecutive large-scale coronal waves with a polar coronal hole, simultaneously observed on-disk by the Solar TErrestrial Relations Observatory (STEREO)-A spacecraft and on the limb by the PRoject for On-Board Autonomy 2 (PROBA2) spacecraft on January 27, 2011. All three extreme-ultraviolet(EUV) waves originate from the same active region NOAA 11149 positioned at N30E15 in the STEREO-A field-of-view and on the limb in PROBA2. We derive for the three primary EUV waves start velocities in the range of ~310 km/s for the weakest up to ~500 km/s for the strongest event. Each large-scale wave is reflected at the border of the extended coronal hole at the southern polar region. The average velocities of the reflected waves are found to be smaller than the mean velocities of their associated direct waves. However, the kinematical study also reveals that in each case the end velocity of the primary wave matches the initial velocity of the reflected wave. In all three events the primary and reflected waves obey the Huygens-Fresnel principle, as the incident angle with ~10° to the normal is of the same size as the angle of reflection. The correlation between the speed and the strength of the primary EUV waves, the homologous appearance of both the primary and the reflected waves, and in particular the EUV wave reflections themselves implicate that the observed EUV transients are indeed nonlinear large-amplitude MHD waves. Title: Time Delays in Quasi-periodic Pulsations Observed during the X2.2 Solar Flare on 2011 February 15 Authors: Dolla, L.; Marqué, C.; Seaton, D. B.; Van Doorsselaere, T.; Dominique, M.; Berghmans, D.; Cabanas, C.; De Groof, A.; Schmutz, W.; Verdini, A.; West, M. J.; Zender, J.; Zhukov, A. N. Bibcode: 2012ApJ...749L..16D Altcode: 2012arXiv1203.6223D We report observations of quasi-periodic pulsations (QPPs) during the X2.2 flare of 2011 February 15, observed simultaneously in several wavebands. We focus on fluctuations on timescale 1-30 s and find different time lags between different wavebands. During the impulsive phase, the Reuven Ramaty High Energy Solar Spectroscopic Imager channels in the range 25-100 keV lead all the other channels. They are followed by the Nobeyama RadioPolarimeters at 9 and 17 GHz and the extreme-ultraviolet (EUV) channels of the Euv SpectroPhotometer (ESP) on board the Solar Dynamic Observatory. The zirconium and aluminum filter channels of the Large Yield Radiometer on board the Project for On-Board Autonomy satellite and the soft X-ray (SXR) channel of ESP follow. The largest lags occur in observations from the Geostationary Operational Environmental Satellite, where the channel at 1-8 Å leads the 0.5-4 Å channel by several seconds. The time lags between the first and last channels is up to ≈9 s. We identified at least two distinct time intervals during the flare impulsive phase, during which the QPPs were associated with two different sources in the Nobeyama RadioHeliograph at 17 GHz. The radio as well as the hard X-ray channels showed different lags during these two intervals. To our knowledge, this is the first time that time lags are reported between EUV and SXR fluctuations on these timescales. We discuss possible emission mechanisms and interpretations, including flare electron trapping. Title: LYRA and SWAP, the two Solar Instruments on-board PROBA2 Authors: Dominique, M.; Berghmans, D.; Schmutz, W. K.; Dammasch, I.; De Groof, A.; Halain, J.; Hochedez, J.; Kretzschmar, M.; Seaton, D. B. Bibcode: 2011AGUFMSH13B1949D Altcode: PROBA2 (http://proba2.sidc.be) is an ESA micro-satellite that was launched in November 2009. Two instruments on-board, SWAP and LYRA, are devoted to solar observations. SWAP (PI: D. Berghmans) is an EUV imager observing the corona with a bandpass centered on 174 Å at a cadence of 1-2 min. Its high contrast images, large FOV and flexible off-pointing capabilities make SWAP particularly well suited for the study of coronal eruptions. LYRA (PI: M. Dominique) is a UV-EUV radiometer observing in four spectral channels, chosen for their relevance in solar physics and aeronomy. Its very fast acquisition cadence (up to 100 Hz) allows scientists to perform detailed analysis of solar flares. We discuss the characteristics of both instruments, review their performance and evolution, and highlight their complementarity to other missions. We also present the data products that can be downloaded from the mission website and give an overview of the various investigations for which SWAP and LYRA data are currently used (CMEs, flares, solar variability, and many others). Title: LYRA Observations of Two Oscillation Modes in a Single Flare Authors: Van Doorsselaere, T.; De Groof, A.; Zender, J.; Berghmans, D.; Goossens, M. Bibcode: 2011ApJ...740...90V Altcode: We analyze light curves from the LYRA irradiance experiment on board PROBA2 during the flare of 2010 February 8. We see both long- and short-period oscillations during the flare. The long-period oscillation is interpreted in terms of standing slow sausage modes; the short-period oscillation is thought to be a standing fast sausage mode. The simultaneous presence of two oscillation modes in the same flaring structure allows for new coronal seismological applications. The periods are used to find seismological estimates of the plasma-β and the density contrast of the flaring loop. Also the wave mode number is estimated from the observed periods. Title: Validation of CME Detection Software (CACTus) by Means of Simulated Data, and Analysis of Projection Effects on CME Velocity Measurements Authors: Bonte, K.; Jacobs, C.; Robbrecht, E.; De Groof, A.; Berghmans, D.; Poedts, S. Bibcode: 2011SoPh..270..253B Altcode: 2011SoPh..tmp...52B; 2011SoPh..tmp...72B In the context of space weather forecasting, an automated detection of coronal mass ejections (CMEs) becomes more and more important for efficiently handling a large data flow which is expected from recently-launched and future solar missions. In this paper we validate the detection software package "CACTus" by applying the program to synthetic data from our 3D time-dependent CME simulations instead of observational data. The main strength of this study is that we know in advance what should be detected. We describe the sensitivities and strengths of automated detection, more specific for the CACTus program, resulting in a better understanding of CME detection on one hand and the calibration of the CACTus software on the other hand, suggesting possible improvements of the package. In addition, the simulation is an ideal tool to investigate projection effects on CME velocity measurements. Title: First light of SWAP on-board PROBA2 Authors: Halain, Jean-Philippe; Berghmans, David; Defise, Jean-Marc; Renotte, Etienne; Thibert, Tanguy; Mazy, Emmanuel; Rochus, Pierre; Nicula, Bogdan; de Groof, Anik; Seaton, Dan; Schühle, Udo Bibcode: 2010SPIE.7732E..0PH Altcode: 2010SPIE.7732E..18H The SWAP telescope (Sun Watcher using Active Pixel System detector and Image Processing) is an instrument launched on 2nd November 2009 on-board the ESA PROBA2 technological mission. SWAP is a space weather sentinel from a low Earth orbit, providing images at 174 nm of the solar corona. The instrument concept has been adapted to the PROBA2 mini-satellite requirements (compactness, low power electronics and a-thermal opto-mechanical system). It also takes advantage of the platform pointing agility, on-board processor, Packetwire interface and autonomous operations. The key component of SWAP is a radiation resistant CMOS-APS detector combined with onboard compression and data prioritization. SWAP has been developed and qualified at the Centre Spatial de Liège (CSL) and calibrated at the PTBBessy facility. After launch, SWAP has provided its first images on 14th November 2009 and started its nominal, scientific phase in February 2010, after 3 months of platform and payload commissioning. This paper summarizes the latest SWAP developments and qualifications, and presents the first light results. Title: SWAP onboard PROBA2: An Innovative EUV Imager Designed for Space Weather Authors: de Groof, A.; Berghmans, D.; Defise, J. M.; Nicula, B.; Schuehle, U. Bibcode: 2008ESPM...122.116D Altcode: PROBA2 (PRoject for OnBoard Autonomy) is an ESA micro-satellite that is being prepared for launch in 2009. Its primary goal is the demonstration of new technologies in the space environment. Furthermore, the satellite carries an ambitious suite of both in-situ and remote sensing instruments for monitoring space weather, despite the modest onboard resources. Both the spacecraft and the remote sensing instruments are mainly developed within Belgium.

One of the main instruments, SWAP (Sun Watcher with APS detectors and image Processing), is a compact EUV imager. It carries the first APS detector with an EUV sensitive scintillator coating to be flown in orbit. In addition to the new detector, the PROBA2/SWAP design is innovative in the sense that the instrument will make heavy use of on-board data processing and autonomous operations. These will range from automatic off-pointing and tracking of appropriate solar events, to pre-downlink data prioritisation, and feature and event recognition procedures.

We discuss the first results of the SWAP pre-flight calibration and the strengths and weaknesses of the instrument [2]. With a narrow spectral bandpass centred around 17.4nm, a FOV of 54 arcmin and an image cadence of 1 min, its design is ideal for monitoring most CME associated phenomena on the solar disk and close to the limb.

[1] Defise J., Halain J., Berghmans D., et al. 2007, In: Proc. SPIE, 6689, 66890S

[2] De Groof A., Berghmans D., Nicula B., et al. 2008, Solar Phys. 249, 147-163 Title: CMOS-APS Detectors for Solar Physics: Lessons Learned during the SWAP Preflight Calibration Authors: De Groof, A.; Berghmans, D.; Nicula, B.; Halain, J. -P.; Defise, J. -M.; Thibert, T.; Schühle, U. Bibcode: 2008SoPh..249..147D Altcode: 2008SoPh..tmp...62D CMOS-APS imaging detectors open new opportunities for remote sensing in solar physics beyond what classical CCDs can provide, offering far less power consumption, simpler electronics, better radiation hardness, and the possibility of avoiding a mechanical shutter. The SWAP telescope onboard the PROBA2 technology demonstration satellite of the European Space Agency will be the first actual implementation of a CMOS-APS detector for solar physics in orbit. One of the goals of the SWAP project is precisely to acquire experience with the CMOS-APS technology in a real-live space science context. Such a precursor mission is essential in the preparation of missions such as Solar Orbiter where the extra CMOS-APS functionalities will be hard requirements. The current paper concentrates on specific CMOS-APS issues that were identified during the SWAP preflight calibration measurements. We will discuss the different readout possibilities that the CMOS-APS detector of SWAP provides and their associated pros and cons. In particular we describe the "image lag" effect, which results in a contamination of each image with a remnant of the previous image. We have characterised this effect for the specific SWAP implementation and we conclude with a strategy on how to successfully circumvent the problem and actually take benefit of it for solar monitoring. Title: SWAP: a novel EUV telescope for space weather Authors: Defise, Jean-Marc; Halain, Jean-Philippe; Berghmans, David; Denis, François; Mazy, Emmanuel; Thibert, Tanguy; Lecat, Jean-Hervé; Rochus, Pierre; Nicula, Bogdan; De Groof, Anik; Hochedez, Jean-François; Schühle, Udo; Ravet, Marie-Françoise; Delmotte, Frank Bibcode: 2007SPIE.6689E..0SD Altcode: 2007SPIE.6689E..24D The SWAP telescope (Sun Watcher using Active Pixel System detector and Image Processing) is being developed to be part of the PROBA2 payload, an ESA technological mission to be launched in early 2008. SWAP is directly derived from the concept of the EIT telescope that we developed in the '90s for the SOHO mission. Several major innovations have been introduced in the design of the instrument in order to be compliant with the requirements of the PROBA2 mini-satellite: compactness with a new of-axis optical design, radiation resistance with a new CMOS-APS detector, a very low power electronics, an athermal opto-mechanical system, optimized onboard compression schemes combined with prioritization of collected data, autonomy with automatic triggering of observation and off-pointing procedures in case of Solar event occurrence, ... All these new features result from the low resource requirements (power, mass, telemetry) of the mini-satellite, but also take advantage of the specificities of a modern technological platform, such as quick pointing agility, new powerful on-board processor, Packetwire interface and autonomous operations. These new enhancements will greatly improve the operations of SWAP as a space weather sentinel from a low Earth orbit while the downlink capabilities are limited. This paper summarizes the conceptual design, the development and the qualification of the instrument, the autonomous operations and the expected performances for science exploitation. Title: a Multi-Wavelength View on Coronal Rain Authors: Müller, D. A. N.; de Groof, A.; de Pontieu, B.; Hansteen, V. H. Bibcode: 2005ESASP.600E..30M Altcode: 2005dysu.confE..30M; 2005ESPM...11...30M No abstract at ADS Title: The Dynamic Sun: Challenges for Theory and Observations Authors: Danesy, D.; Poedts, S.; de Groof, A.; Andries, J. Bibcode: 2005ESASP.600E....D Altcode: 2005dysu.confE....D; 2005ESPM...11.....D No abstract at ADS Title: Multiwavelength Analysis of Downflows Along AN Off-Limb Loop Authors: de Groof, A.; Müller, D. A. N.; Poedts, S. Bibcode: 2005ESASP.600E..29D Altcode: 2005ESPM...11...29D; 2005dysu.confE..29D No abstract at ADS Title: Downflows Along AN Off-Limb Loop Seen both in 30.4NM and Hα Authors: de Groof, A.; Müller, D. A. N.; Poedts, S. Bibcode: 2005ESASP.596E..36D Altcode: 2005ccmf.confE..36D No abstract at ADS Title: a Multi-Wavelength View on Coronal Rain Authors: Müller, D. A. N.; de Groof, A.; de Pontieu, B.; Hansteen, V. H. Bibcode: 2005ESASP.596E..37M Altcode: 2005ccmf.confE..37M No abstract at ADS Title: Detailed comparison of downflows seen both in EIT 30.4 nm and Big Bear Hα movies Authors: de Groof, A.; Bastiaensen, C.; Müller, D. A. N.; Berghmans, D.; Poedts, S. Bibcode: 2005A&A...443..319D Altcode: An EIT shutterless campaign was conducted on 11 July 2001 and provided 120 high-cadence (68 s) 30.4 nm images of the north-eastern quarter of the Sun. Systematic intensity variations are seen which appear to propagate along an off-disk loop-like structure. In this paper we study the nature of these intensity variations by confronting the EIT observations studied in De Groof et al. (2004, A&A, 415, 1141) with simultaneous Hα images from Big Bear Solar Observatory. With the goal to carefully co-register the two image sets, we introduce a technique designed to compare data of two different instruments. The image series are first co-aligned and later overplotted in order to visualize and compare the behaviour of the propagating disturbances in both data sets. Since the same intensity variations are seen in the EIT 30.4 nm and in the Hα images, we confirm the interpretation of De Groof et al. (2004, A&A, 415, 1141) that we are observing downflows of relatively cool plasma. The origin of the downflows is explained by numerical simulations of "catastrophic cooling" in a coronal loop which is heated predominantly at its footpoints. Title: High-speed coronal rain Authors: Müller, D. A. N.; De Groof, A.; Hansteen, V. H.; Peter, H. Bibcode: 2005A&A...436.1067M Altcode: At high spatial and temporal resolution, coronal loops are observed to have a highly dynamic nature. Recent observations with SOHO and TRACE frequently show localized brightenings "raining" down towards the solar surface. What is the origin of these features? Here we present for the first time a comparison of observed intensity enhancements from an EIT shutterless campaign with non-equilibrium ionization simulations of coronal loops in order to reveal the physical processes governing fast flows and localized brightenings. We show that catastrophic cooling around the loop apex as a consequence of footpoint-concentrated heating offers a simple explanation for these observations. An advantage of this model is that no external driving mechanism is necessary as the dynamics result entirely from the non-linear character of the problem. Title: Coronal MHD Waves and Theoretical Constraints of Wave Heating Authors: Poedts, S.; de Groof, A. Bibcode: 2004ESASP.575...62P Altcode: 2004soho...15...62P No abstract at ADS Title: Thermal Instability as the Origin of High Speed Coronal Rain Authors: Müller, D. A. N.; de Groof, A.; Hansteen, V. H.; Peter, H. Bibcode: 2004ESASP.575..291M Altcode: 2004soho...15..291M No abstract at ADS Title: Intensity variations in EIT shutterless mode: Waves or flows? Authors: De Groof, A.; Berghmans, D.; van Driel-Gesztelyi, L.; Poedts, S. Bibcode: 2004A&A...415.1141D Altcode: On 11 July 2001 an EIT shutterless campaign was conducted which provided 120 high-cadence (68 s) 304 Å images of the north eastern quarter of the Sun. The most interesting feature seen in the data is an off-limb half loop structure along which systematic intensity variations are seen which appear to propagate from the top of the loop towards its footpoint. We investigate the underlying cause of these propagating disturbances, i.e. whether they are caused by waves or by plasma flows. First we identify 7 blobs with the highest intensities and follow them along the loop. By means of a location-time plot, bulk velocities can be measured at several locations along the loop. The velocity curve found this way is then compared with characteristic wave speeds and with the free-fall speed in order to deduce the nature of the intensity variations. Additional information on density and temperature is derived by measuring the relative intensity enhancements and comparing the EIT 304 Å sequence with Big Bear data and 171 Å data (TRACE/EIT). The combination of all these constraints gives us an insight on the nature and origin of these intensity variations. The idea of slow magneto-acoustic waves is rejected, and we find several arguments supporting that these intensity variations are due to flowing/falling plasma blobs. Title: Active Region Oscillations as Observed by CDS, EIT and TRACE Authors: Banerjee, D.; O'Shea, E.; de Groof, A.; Poedts, S. Bibcode: 2004ESASP.547...39B Altcode: 2004soho...13...39B No abstract at ADS Title: Thermal non-equilibrium in coronal loops: A road to complex evolution Authors: Müller, Daniel; de Groof, A.; Hansteen, V. H.; Peter, H. Bibcode: 2004IAUS..223..289M Altcode: 2005IAUS..223..289M At high spatial and temporal resolution, coronal loops are observed to have a highly dynamic nature. Recent observations with SOHO and TRACE frequently show localized brightening "raining" down towards the solar surface. What is the origin of these features? Here we present for the first time a comparison of observed intensity enhancements from an EIT shutterless campaign with non-equilibrium ionization simulations of coronal loops in order to reveal the physical processes governing fast flows and localized brightening. We show that catastrophic cooling around the loop apex as a consequence of footpoint-concentrated heating offers a simple explanation for these observations. An advantage of this model is that no external driving mechanism is necessary as the dynamics result entirely from the non-linear character of the system. Title: Intensity Variations in EIT Shutterless Mode: Waves or Flows? Authors: de Groof, A.; Berghmans, D.; van Driel-Gesztelyi, L.; Poedts, S. Bibcode: 2004ESASP.547..245D Altcode: 2004soho...13..245D On 11 July 2001 an EIT shutterless campaign was conducted which provided 120 high-cadence (68s) 304 Å images of the north eastern quarter of the Sun. The most interesting feature seen in the data is an off-limb half loop structure along which systematic intensity variations appear to propagate from the top of the loop towards its footpoint. We investigate the underlying cause of these propagating disturbances, i.e. whether they are caused by waves or by plasma flows. First we identify 7 blobs with the highest intensities and follow them along the loop. By means of a location-time plot, bulk velocities can be measured at several locations along the loop. The velocity curve found this way is then compared with characteristic wave speeds and with the free-fall speed in order to deduce the nature of the intensity variations. Additional information is derived by measuring the relative intensity enhancements and comparing the EIT 304 Å sequence with Big Bear and 171 Å data. The idea of slow magneto-acoustic waves is rejected, and we find several arguments supporting that these intensity variations are due to flowing/falling plasma blobs. Title: Waves and oscillations in magnetic fields Authors: Goossens, Marcel; de Groof, Anik; Andries, Jesse Bibcode: 2002ESASP.505..137G Altcode: 2002solm.conf..137G; 2002IAUCo.188..137G This paper gives an overview of the theory of MHD waves in magnetic plasma configurations in the solar atmosphere. The emphasis is on basic properties that are independent of specific equilibrium models but are rather related to the intrinsic structuring and non-uniformity of the plasma. The discussion is confined to MHD waves in uniform and 1-d cylindrical equilibrium models of magnetic flux tubes with a straight magnetic field. These models contain sufficient physics for understanding basic properties of MHD waves and still allow for a relatively straightforward and transparent mathematical analysis. Title: Fast and Alfvén waves driven by azimuthal footpoint motions Authors: de Groof, Anik; Goossens, Marcel Bibcode: 2002ESASP.505..389D Altcode: 2002solm.conf..389D; 2002IAUCo.188..389D The excitation of Alfvén and fast magnetosonic waves in footpoint driven coronal loops is studied in the framework of resonant absorption. Previous studies revealed that in case of radial footpoint motions, quasi-modes are essential for effective wave dissipation in the loops. We now investigate the role they play in azimuthally driven loops. For a periodic driver, the efficiency of resonant absorption strongly depends on the driving frequency ωd: only for quasi-mode frequencies coupling has a positive effect on the growth of the (single) Alfvén resonance. The problem of single-shell heating can be solved by considering a more realistic, random driver: a variety of resonant Alfvén waves are excited and multiple resonant peaks appear, with length scales which are short enough for effective dissipation. When more realistic loop lengths are considered, the resonant surfaces are even more numerous resulting in globally heated loops. Title: Fast and Alfvén waves driven by azimuthal footpoint motions. I. Periodic driver Authors: De Groof, A.; Paes, K.; Goossens, M. Bibcode: 2002A&A...386..681D Altcode: The excitation of Alfvén and fast magneto-acoustic waves in coronal loops driven by footpoint motions is studied in linear, ideal MHD. The analysis is restricted to azimuthally polarized footpoint motions so that only Alfvén waves are directly excited which couple to fast magneto-acoustic waves at later times. In the present study a periodic driver is applied at one end of the loop. The effects of a more realistic random driver are studied in the companion paper De Groof & Goossens (2002) (hereafter referred to as Paper II). The first part of the paper is devoted to the study of resonant absorption and phase-mixing in the absence of coupling (azimuthal wavenumber ky=0). Since the density varies across the loop, resonances occur at the magnetic surfaces where the driving frequency equals the local Alfvén frequency. In a second part where Alfvén waves with ky !=q 0 coupling to fast waves are taken into account, we find that the behaviour of the MHD waves is strongly dependent on the driving frequency omegad . Especially driving frequencies equal to a quasi-mode frequency seem to make the difference. The fast waves excited in these cases are global oscillations of the system and form quasi-modes as they are damped through the resonant coupling with Alfvén modes. Since these resonances occur at the same location where the original Alfvén wave peaks, the resonant peak is further amplified. While in most cases coupling has a negative effect on the growth of the directly excited Alfvén waves, driving with a quasi-mode frequency leads to a faster growth of the resonant peaks and a more efficient decrease in length scales than in the uncoupled case. Title: Fast and Alfvén waves driven by azimuthal footpoint motions. II. Random driver Authors: De Groof, A.; Goossens, M. Bibcode: 2002A&A...386..691D Altcode: The excitation of Alfvén and fast magneto-acoustic waves in coronal loops driven by footpoint motions is studied in linear, ideal MHD. The analysis is restricted to azimuthally polarized footpoint motions so that only Alfvén waves are directly excited to couple to fast magneto-acoustic waves at later times. In the companion paper De Groof et al. (\cite{Groof02a}) (hereafter referred to as Paper I), the behaviour of the MHD waves is studied in case of a monochromatic driver. In the present study, the effects of a more realistic random driver are investigated.\ First, we consider loops of equal length and width in order to limit the number of quasi-modes in the frequency range of the driver so that the influence of quasi-modes in the system can easily be detected. In contrast to the single resonant surface which was found in case of a periodic driver (see Paper I), a random pulse train excites a variety of resonant Alfvén waves and consequently the small length scales built up are spread over the whole width of the loop. The specific effects of the quasi-modes are not so easily recognized as for radial footpoint motions (De Groof & Goossens \cite{Groof00a}) since the resonances corresponding to directly and indirectly excited Alfvén waves are mixed together. In the second part of the paper, longer loops are considered. Since more quasi-modes are involved, the resonant surfaces are more numerous and widely spread throughout the whole loop volume. On the other hand, it takes more time for the MHD waves to cross the loop and to form standing waves. Nevertheless this negative effect does not have too much impact since the simulations show that after a small time interval, resonant surfaces are created all over the loop, with length scales which are short enough for effective dissipation. Title: Resonant absorption in randomly driven coronal loops Authors: de Groof, Anik; Goossens, Marcel Bibcode: 2000AIPC..537..208D Altcode: 2000wdss.conf..208D De Groof et al. '98 [1] and '00 [2] studied the time evolution of fast magnetosonic and Alfvén waves in a coronal loop driven by radially polarized footpoint motions in linear ideal MHD. Footpoint driving seems to be an efficient way of generating resonant absorption since the input energy is mainly stored in body modes which keep the energy in the loop. The most important feature in this study is the stochastic driving of the loop. While in earlier models with a periodic driver or a single pulse, the loop is only heated at one single layer, we now find multiple resonance layers which results in a more globally heated loop. Moreover, these resonances (created on a realistic time scale) have length scales which are small enough to explain energy dissipation. An important aspect to take into account is the mass transfer between corona and chromosphere since the density becomes time dependent and consequently, the resonant surfaces shift throughout the loop [3]. Combined with the multiple resonances we found in the previous study, this result can lead to the globally heated coronal loops we observe. . Title: Randomly driven fast waves in coronal loops. II. with coupling to Alfvén waves Authors: De Groof, A.; Goossens, M. Bibcode: 2000A&A...356..724D Altcode: We study the time evolution of fast magnetosonic and Alfvén waves in a coronal loop driven by random footpoint motions. The footpoint motions are assumed to be polarized normal to the magnetic flux surfaces in linear ideal MHD. De Groof et al. (1998) (Paper I) showed that the input energy is mainly stored in the body modes when the fast waves are decoupled from the Alfvén waves. Hence driving at the loop's feet forms a good basis for resonant absorption as heating mechanism. In order to determine the efficiency of resonant absorption, we therefore study the energy transfer from the body modes to the resonant Alfvén waves in the case of coupling. We find that the growth of Alfvén mode energy depends on several parameters. Subsequently we check whether the necessary small lengthscales are created on a realistic time scale for the coronal loop. We find that Alfvén resonances are built up at the magnetic surfaces, where local Alfvén frequencies equal the quasi-modes frequencies, on time scales comparable to the lifetime of the loop. Finally we conclude that a random footpoint driving can produce enough resonances to give rise to a globally heated coronal loop. Title: Randomly Driven Fast Waves in Coronal Loops Authors: de Groof, A.; Goossens, M. Bibcode: 1999ESASP.448..251D Altcode: 1999ESPM....9..251D; 1999mfsp.conf..251D No abstract at ADS Title: Random driven fast waves in coronal loops. I. Without coupling to Alfven waves Authors: de Groof, A.; Tirry, W. J.; Goossens, M. Bibcode: 1998A&A...335..329D Altcode: In this paper we study the time evolution of fast MHD waves in a coronal loop driven by footpoint motions in linear ideal MHD. We restrict the analysis to footpoint motions polarized normal to the magnetic flux surfaces such that the fast waves are driven directly. By supposing the azimuthal wave number k_y to be zero, the fast waves are decoupled from the Alfven waves. As a first step to real stochastic driving, we consider the loop to be driven by a train of identical pulses with random time intervals in between. The solution is written as a superposition of eigenmodes whose excitation is determined by the time dependence of the footpoint motion through a convolution and by the spatial dependence of the footpoint motion through a scalar product. An important result from the simulations is that the amount of kinetic energy associated with the body modes is much larger than the amount corresponding to the leaky modes. This means that most of the input energy is stored within the loop. For k_y!=q 0, body modes can resonantly couple to Alfven waves at certain magnetic surfaces and hence the energy of the body modes can then be dissipated around the resonant magnetic surfaces. Using a gamma distribution for the time intervals between the successive pulses, we analytically derive a relation between the mean value of the kinetic energy contribution of each eigenmode, the eigenfrequency, the number of pulses and the width of the pulses. The larger the variance of the distribution, the less the power spectrum reveals fine structure, peaks around certain preferred frequencies. The analytical results confirm the output from the numerical simulations.