Authors: F. Carcaboso (Postdoctoral Program Fellow - NPP / NASA GSFC / CUA),
M. Dumbović (Hvar Observatory, Faculty of Geodesy, University of Zagreb),
C. Kay (NASA GSFC / CUA) ,
D. Lario (NASA GSFC),
L. K. Jian (NASA GSFC),
L. B. Wilson III (NASA GSFC),
R. Gómez-Herrero (Universidad de Alcalá, Space Research Group),
M. Temmer (Institute of Physics, University of Graz),
S. G. Heinemann (University of Helsinki),
T. Nieves-Chinchilla (NASA GSFC),
A. M. Veronig (Institute of Physics / University of Graz, Kanzelhöhe Observatory for Solar and Environmental Research)
Context. A fast (∼2000 km/s) and wide (>110º) Coronal Mass Ejection (CME) erupted from the Sun on March 13, 2012. Its interplanetary counterpart was detected in situ two days later by STEREO-A and near-Earth spacecraft, such as ACE, Wind and Cluster. We suggest that at 1 au the CME extended at least 110º in longitude, with Earth crossing its east flank and STEREO-A crossing its west flank. Despite their separation, measurements from both positions showed similar in-situ CME signatures. The solar source region where the CME erupted was surrounded by three coronal holes (CHs). Their locations with respect to the CME launch site were east (negative polarity), southwest (positive polarity) and west (positive polarity). The solar magnetic field polarity of the area covered by each CH matches that observed at 1 au in situ. Suprathermal electrons at each location showed mixed signatures with only some intervals presenting clear counterstreaming flows as the CME transits both locations. The strahl population coming from the shortest magnetic connection of the structure to the Sun showed more intensity.
Aims. The aim of this work is to understand the propagation and evolution of the CME and its interaction with the surrounding CHs, to explain the similarities and differences between the observations at different spacecraft, and report that it would be one of the most expanded in longitude CME structures observed in situ.
Methods. Known properties of the large-scale structures from a variety of catalogues and previous studies are used to have a better overview of this particular event. In addition, multipoint observations are used to reconstruct the 3D geometry of the CME, and determine the context of the solar and heliospheric conditions before the CME eruption and during its propagation. The graduated cylindrical shell model (GCS) is used to reproduce the orientation, size and speed of the structure with a simple geometry. Also, the Drag-Based Model (DBM) is utilised to understand better the conditions of the interplanetary medium in terms of the drag undergone by the structure while propagating in different directions. Finally, a comparative analysis of the different regions of the structure through the different observatories has been made in order to directly compare the in-situ plasma and magnetic field properties at each location.
Results. The study presents important findings regarding the in-situ measured CME on March 15, 2012, detected at a longitudinal separation of 110º in the ecliptic plane despite its initial inclination being around 45º when erupted (March 13). This suggests that the CME may have bent, allowing it to be observed near its legs with spacecraft at a separation angle greater than 100º. The CME structure interacts with high-speed streams generated by the surrounding CHs. The piled-up plasma in the sheath region exhibits an unexpected correlation in magnetic field strength despite the large separation in longitude. In-situ observations reveal that at both locations, the spacecraft cross the CME near its central axis, encounter ambient solar wind, and pass through the legs of the structure.
Conclusions. A scenario covering all evidence is proposed for both locations with a general view of the whole structure and solar wind conditions. Also, the study shows the necessity of having multipoint observations of large-scale structures in the heliosphere.