Determining the Intrinsic CME Flux Rope Type Using Remote-sensing Solar Disk Observations

Abstract

A key aim in space weather research is to be able to use remote-sensing observations of the solar atmosphere to extend the lead time of predicting the geoeffectiveness of a coronal mass ejection (CME). In order to achieve this, the magnetic structure of the CME as it leaves the Sun must be known. In this article we address this issue by developing a method to determine the intrinsic flux rope type of a CME solely from solar disk observations. We use several well known proxies for the magnetic helicity sign, the axis orientation, and the axial magnetic field direction to predict the magnetic structure of the interplanetary flux rope. We present two case studies: the 2 June 2011 and the 14 June 2012 CMEs. Both of these events erupted from an active region and, despite having clear in situ counterparts, their eruption characteristics were relatively complex. The first event was associated with an active region filament that erupted in two stages, while for the other event the eruption originated from a relatively high coronal altitude and the source region did not feature the presence of a filament. Our magnetic helicity sign proxies include the analysis of magnetic tongues, soft X-ray and/or extreme-ultraviolet sigmoids, coronal arcade skew, filament emission and absorption threads, and filament rotation. Since the inclination of the post-eruption arcades was not clear, we use the tilt of the polarity inversion line to determine the flux rope axis orientation, and coronal dimmings to determine the flux rope footpoints and, therefore, the direction of the axial magnetic field. The comparison of the estimated intrinsic flux rope structure to in situ observations at the Lagrangian point L1 indicated a good agreement with the predictions. Our results highlight the flux rope type determination techniques that are particularly useful for active region eruptions, where most geoeffective CMEs originate.

On-Disc Observations of Flux Rope Formation Prior to Its Eruption

“…Furthermore, the hooked shape of the western flare ribbon is considered a signature of energy deposition along field lines at the periphery of a flux rope (Démoulin, Priest, and Lonie, 1996;Janvier et al, 2014). Our interpretation of the presence of a flux rope in the active region by the time of the CME is matched by the in situ data, which find the interplanetary CME to contain a flux rope with a chirality and axial orientation matching that observed at the Sun (Palmerio et al, 2017).…”

“…The shock preceding the magnetic cloud was first detected at ≈ 19:30 UT on 16 June, and the passage of the magnetic cloud lasted from ≈ 22:00 UT on 16 June until ≈ 12:30 UT on 17 June. The measured magnetic field vector rotated from north to south in the geocentric solar ecliptic (GSE) coordinate system as the cloud passed the spacecraft, and an eastern field component was measured throughout the cloud (see Figure 6 of Palmerio et al, 2017). This is consistent with a flux rope that has an eastern axial field with helical field wrapped around it.…”

“…The helical field at the leading edge of the flux rope is northward and at the trailing edge it is southward, so the measured rotation from north to south is produced as it passes over the spacecraft. The in situ flux rope detection is discussed in more detail by Palmerio et al (2017) in addition to another event, whereas in this article we focus on the pre-eruptive coronal field that generated the magnetic cloud.…”

“…1 Kubicka et al, 2016;Palmerio et al, 2017. For the method used in creating the ICME list, see Richardson, 2003 andCane, 2010).…”

“…Finally, the key conclusions are given in Section 5. A study of the same magnetic cloud was performed by Palmerio et al (2017), in which the compatibility between the in situ measurements and the pre-eruptive configuration was examined.…”