Multi-spacecraft analysis of the solar coronal plasma Von der Fakultät für Elektrotechnik, Informationstechnik, Physik der Technischen Universität Carolo-Wilhelmina zu Braunschweig zur Erlangung des Grades einer Doktorin der Naturwissenschaften (Dr. rer. nat.) genehmigte Dissertation von Iulia Ana Maria Chifu aus Bukarest, Rumänien eingereicht am: 11.02.2015 Disputation am: 07.05.2015 1. Referent: Prof. Dr. Sami K. Solanki 2. Referent: Prof. Dr. Karl-Heinz Glassmeier Druckjahr: 2016 Bibliografische Information der Deutschen Nationalbibliothek Die Deutsche Nationalbibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über http://dnb.d-nb.de abrufbar. Dissertation an der Technischen Universität Braunschweig, Fakultät für Elektrotechnik, Informationstechnik, Physik ISBN uni-edition GmbH 2016 http://www.uni-edition.de © Iulia Ana Maria Chifu This work is distributed under a Creative Commons Attribution 3.0 License Printed in Germany Vorveröffentlichung der Dissertation Teilergebnisse aus dieser Arbeit wurden mit Genehmigung der Fakultät für Elektrotech- nik, Informationstechnik, Physik, vertreten durch den Mentor der Arbeit, in folgenden Beiträgen vorab veröffentlicht: Publikationen • Mierla, M., Chifu, I., Inhester, B., Rodriguez, L., Zhukov, A., 2011, Low polarised emission from the core of coronal mass ejections, Astronomy and Astrophysics, 530, L1 • Chifu, I., Inhester, B., Mierla, M., Chifu, V., Wiegelmann, T., 2012, First 4D Recon- struction of an Eruptive Prominence Using Three Simultaneous View Directions, Solar Physics, 281, 121-135 • Mierla, M.; Seaton, D. B.; Berghmans, D.; Chifu, I.; De Groof, A.; Inhester, B.; Rodriguez, L.; Stenborg, G.; Zhukov, A. N., 2013, Study of a Prominence Eruption using PROBA2/SWAP and STEREO/EUVI Data, Solar Physics, 286, 241-253 • Chifu, I., Inhester, B., Wiegelmann, T., 2015, Coronal magnetic field modeling using stereoscopy constraints, Astronomy and Astrophysics, 577, 123 Tagungsbeiträge • Chiricuta O., Chifu I., Besliu-Ionescu D., Mierla M., Studies of Solar - Terrestrial Connections: Geomagnetic Storms Induced by Coronal Mass Ejections in: Mod- ern Topics in Astronomy Conference, Bucharest, Romania, 19 November 2010, (poster); • Chiricuta O., Chifu I., Mierla M., Maris G., Study of Earth-directed Halo Coronal Mass Ejections observed between 1996 and 2008, Assessment and Validation of Space Weather Models, Alcala de Henares, Spain, 14 - 18 March 2011, (poster); • Chifu I., Inhester B., 3D reconstruction of a prominence from three views, in: 4th SOLAIRE network meeting, Teistungen, Germany, 9 - 13 May 2011, (poster) • Chifu I., Inhester B., 3D reconstruction of the eruptive prominence on 1 August 2010 from three views in Stereo4/SDO2/SOHO25 workshop, Kiel, Germany, 25- 29 July 2011, (poster) 3 Vorveröffentlichung der Dissertation • Oprea C., Chifu I., Mierla M., The Dynamics of the 8 April 2010 Coronal Mass Ejection into the Interplanetary Space in AOGS - AGU (WPGM) Joint Assembly, Sentosa, Singapore, 13 - 17 August, 2012, (poster) • Mierla M, Chifu I, Inhester B., Rodriguez L., Zhukov A., Low polarised emission from the core of coronal mass ejections in Nature of Prominences and their role in Space Weather, Paris, France, 10-14 June 2013, (oral) • Chifu I., Inhester B., Wiegelmann Th, Coronal magnetic field modeling using stere- oscopy constraints in IAUS300, Nature of Prominences and their role in Space Weather, Paris, France, 10-14 June 2013, (poster) 4 Contents Abstract 7 Glossary 9 1 Physics of the solar corona 10 1.1 Introduction................................. 10 1.2 Magnetohydrodynamics . 12 1.3 Plasmabeta ................................. 14 1.4 Creationandtheemergenceofthemagneticflux . .... 15 1.5 Themagneticfieldinthesolarcorona . .. 19 1.5.1 Activeregionloops. 19 1.5.2 Prominences ............................ 24 1.5.3 CoronalMassEjections(CMEs) . 31 2 3D reconstruction in the solar corona 43 2.1 Introduction................................. 43 2.2 Stereoscopy ................................. 44 2.2.1 Introduction............................. 44 2.2.2 Theepipolargeometry . 45 2.2.3 Reconstruction ........................... 47 2.3 Multi-view B-spline Stereoscopic Reconstruction (MBSR) ........ 52 2.3.1 B-splinecurve ........................... 53 2.4 3D modeling of the magnetic field through extrapolation . ........ 54 2.4.1 NLFFFoptimizationmethod . 56 2.5 3Dreconstructionofcoronalloops . ... 58 2.5.1 S-NLFFF:AmethodwhichcombinesMBSRandNLFFF . 60 3 Instrumentation 63 3.1 Solar Terrestrial Relation Observatory (STEREO) mission ................................... 63 3.1.1 ExtremeUltravioletImaging(EUVI)telescope . .... 65 3.1.2 Innerandoutercoronagraph . 65 3.2 SolarDynamicObservatory(SDO). 67 3.2.1 AtmosphericImagingAssembly(AIA) . 67 5 Contents 4 Application of the Multi-view B-spline Stereoscopic Reconstruction method for the analysis of two erupting prominences 68 4.1 Previous work on 3D reconstruction of prominences . ....... 68 4.2 Previousworkonthe3DreconstructionofCMEs . .... 69 4.2.1 ForwardModeling ......................... 69 4.2.2 Geometriclocalization . 71 4.2.3 Maskfitting............................. 71 4.2.4 Polarizationratio . 72 4.2.5 Stereoscopy............................. 74 4.2.6 Localcorrelationtrackingplustie-pointing . ...... 75 4.2.7 Hybridmethods .......................... 76 4.3 3DreconstructionofaCMEcore. 76 4.3.1 Introduction............................. 76 4.3.2 Observations ............................ 77 4.3.3 Dataanalysis ............................ 79 4.3.4 Discussion ............................. 82 4.4 4D reconstruction of a prominence-CME from two and three views. 85 4.4.1 Introduction............................. 85 4.4.2 Observationaldataandthe3Dreconstruction . .... 87 4.4.3 Dataanalysisandresults . 91 4.4.4 Discussionandsummary. 101 5 Coronal magnetic field modeling using stereoscopy constraints 104 5.1 Introduction................................. 104 5.2 Testing the S-NLFFF (Stereoscopic-NonLinear Force Free Field) method 104 5.2.1 TestingthemethodforCaseI . 107 5.2.2 TestingthemethodforCaseII . 114 5.3 Discussionsandconclusions . 119 6 Summary and outlook 121 A Appendix 124 Bibliography 127 Publications 137 Acknowledgements 139 Curriculum vitae 141 6 Abstract The thesis “Multi-spacecraft analysis of the solar coronal plasma” deals with two different approaches in the analysis of the solar corona: an observational and a theoretical one. The first approach aims at the reconstruction of the 3D structure of phenomena in the solar corona using data obtained by multiple spacecraft. We used observations from three spacecraft: Solar Terrestrial Relation Observatory (STEREO) A and B and Solar Dynamic Observatory. The observed and analyzed solar phenomena were prominences and CMEs. For the analysis of the observed phenomena we extended and applied a 3D stereoscopic reconstruction method, called MBSR (Multi-view B-spline Stereoscopic Reconstruction) which was developed as part of this thesis. The MBSR method has a large spectrum of possible applications to solar phenomena, from coronal loops to coronal mass ejections (CME). We applied the MBSR method to two eruptive prominences which evolved into CMEs. In one of the events a bright patch of low polarized radiation was observed in corona- graph images of the CME core, which was presumably caused by a Hα resonant scatter- ing. This effect is not common since at the usual coronal temperatures at the height of the analyzed CME, one expects the plasma to be fully ionized. The polarization ratio method failed to retrieve a meaningful location of the bright patch. Therefore, we applied the MBSR method and determined its probable 3D position in the CME core. For the second event we make use of simultaneous data from three space probes to reconstruct the 3D location of the highest ridge of a rising prominence and the core and leading edge of the CME which evolved from it. We follow the evolution of the eruption from the time of the initial rise of the prominence until the CME core leaves the field of view of the COR1 coronagraph. We calculate various parameters which characterize the 3D curves, such as the propagation direction, the rise velocity, the angular width of the prominence and of the CME core and their rotation. The second approach is related to the extrapolation of the coronal magnetic field from a photospheric magnetogram using the NLFFF (non-linear force-free field) model. It is generally accepted that coronal loops observed in EUV images outline magnetic field lines. The results from many conventional magnetic field extrapolations show, however, large discrepancies between the extrapolated magnetic field lines and the observed coronal loops, typically they deviate by angles of the order of 20 degrees. We therefore introduced an additional observational constraint to the extrapolation scheme by requiring the field also reproduces 3D reconstructed coronal loops. This is achieved by minimizing the local angles between the extrapolated magnetic field and the tangents to the coronal loops. We call this new method stereoscopic - nonlinear force-free field (S-NLFFF) extrapolation method because the shape of the coronal loops is reconstructed from EUV images by stereoscopy. In the thesis we present the S-NLFFF method and tests of it with synthetic 7 Contents data. The thesis is structured in six chapters: in Chapter 1 we give an introduction to the studied solar coronal phenomena; in Chapter 2 we present the methods which we devel-