Comparing extrapolations of the coronal magnetic field structure at 2.5 R_⊙ with multi-viewpoint coronagraphic observations

¹ INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
e-mail: csasso@oacn.inaf.it
² Institut de Recherche en Astrophysique et Planétologie, University of Toulouse, CNRS, UPS, CNES, 9 Avenue Colonel Roche, BP 44346, 31028 Toulouse Cedex 4A, France
³ Space Science Division, US Naval Research Laboratory, Washington, DC, USA
⁴ Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
⁵ INAF-Turin Astrophysical Observatory, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
⁶ INAF-Catania Astrophysical Observatory, Via Santa Sofia 78, 95123 Catania, Italy
⁷ CNR-Institute of Photonics and Nanotechnologies, Via Trasea 7, 35131 Padova, Italy
⁸ INAF-Arcetri Astrophysical Observatory, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁹ University of Padova, Department of Physics and Astronomy “Galileo Galilei”, Via Marzolo, 8, 35131 Padova, Italy
¹⁰ University of Florence, Dept. of Physics and Astronomy, Largo Enrico Fermi 2, 50125 Firenze, Italy

Received: 23 August 2018
Accepted: 20 May 2019

Abstract

The magnetic field shapes the structure of the solar corona, but we still know little about the interrelationships between the coronal magnetic field configurations and the resulting quasi-stationary structures observed in coronagraphic images (such as streamers, plumes, and coronal holes). One way to obtain information on the large-scale structure of the coronal magnetic field is to extrapolate it from photospheric data and compare the results with coronagraphic images. Our aim is to verify whether this comparison can be a fast method to systematically determine the reliability of the many methods that are available for modeling the coronal magnetic field. Coronal fields are usually extrapolated from photospheric measurements that are typically obtained in a region close to the central meridian on the solar disk and are then compared with coronagraphic images at the limbs, acquired at least seven days before or after to account for solar rotation. This implicitly assumes that no significant changes occurred in the corona during that period. In this work, we combine images from three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) that observe the Sun from different viewing angles to build Carrington maps that cover the entire corona to reduce the effect of temporal evolution to about five days. We then compare the position of the observed streamers in these Carrington maps with that of the neutral lines obtained from four different magnetic field extrapolations to evaluate the performances of the latter in the solar corona. Our results show that the location of coronal streamers can provide important indications to distinguish between different magnetic field extrapolations.