Evidence of a complex structure within the 2013 August 19 CME. ICME
radial and longitudinal evolution in the heliosphere.
Abstract
Context: Late on 2013 August 19, a coronal mass ejection (CME) erupted
from an active region located near the far-side central meridian from
Earth’s perspective. The event and its accompanying shock was remotely
observed by the STEREO-A, STEREO-B and SOHO spacecraft. The
interplanetary (IP) counterpart (ICME) intercepted MESSENGER near 0.3
au, and both STEREO-A and STEREO-B, near 1 au, which were separated by
78 degrees in longitude. Aims: The main objective of this study is to
follow the radial and longitudinal evolution of the ICME throughout the
heliosphere, and to examine possible scenarios for the different
magnetic flux- rope (MFR) signatures observed on the solar disk, and
measured at the locations of MESSENGER and STEREO-A, separated by 15
degrees in heliolongitude, and at STEREO-B, which detected the ICME
flank. Methods: Solar disk observations are used to estimate the ‘MFR
type’ and the graduated cylindrical shell model is used to reconstruct
the CME in the corona. The analysis of in-situ data, namely, plasma and
magnetic field, is used to estimate the global IP shock geometry and to
derive the MFR type at different in-situ locations. The elliptical
cylindrical analytical model is used for the in-situ MFR reconstruction.
Results: The MFR structure detected at STEREO-B belongs to the same
magnetic structure detected at MESSENGER and STEREO-A. The different
helicity deduced at STEREO-B, might be due to the spacecraft
intercepting one of the legs of the MFR, while STEREO-A and MESSENGER
are crossing through the core of the structure. The opposite polarity
measured at MESSENGER and STEREO-A arises because the two spacecraft
measure a curved, highly distorted and rather complex MFR topology. The
ICME may have suffered additional distortion in its evolution in the
heliosphere, resulting in different expansion and arrival time of the IP
shock flanks at 1 au.