Self‐Similarity of ICME Flux Ropes: Observations by Radially Aligned Spacecraft in the Inner Heliosphere

Abstract

Interplanetary coronal mass ejections (ICMEs) are a significant feature of the heliospheric environment and the primary cause of adverse space weather at the Earth. ICME propagation and the evolution of ICME magnetic field structure during propagation are still not fully understood. We analyze the magnetic field structures of 18 ICME magnetic flux ropes observed by radially aligned spacecraft in the inner heliosphere. Similarity in the underlying flux rope structures is determined through the application of a simple technique that maps the magnetic field profile from one spacecraft to the other. In many cases, the flux ropes show very strong underlying similarities at the different spacecraft. The mapping technique reveals similarities that are not readily apparent in the unmapped data and is a useful tool when determining whether magnetic field time series observed at different spacecraft are associated with the same ICME. Lundquist fitting has been applied to the flux ropes, and the rope orientations have been determined; macroscale differences in the profiles at the aligned spacecraft may be ascribed to differences in flux rope orientation. Assuming that the same region of the ICME was observed by the aligned spacecraft in each case, the fitting indicates some weak tendency for the rope axes to reduce in inclination relative to the solar equatorial plane and to align with the solar east‐west direction with heliocentric distance.

Radial Evolution of Coronal Mass Ejections Between MESSENGER, Venus Express, STEREO, and L1: Catalog and Analysis

“…It is important to note that our findings (scaling of the peak magnetic field strength in the ejecta with heliocentric distance) are in good agreement with previous statistical studies. In a study published after the initial submission of this manuscript, Good et al (2019) performed a static Lundquist flux rope fitting (Burlaga, 1988;Lepping et al, 1990) for 18 interplanetary flux ropes observed in conjunction between radially aligned spacecraft in the inner heliosphere. Applying the same fitting technique for MESSENGER and STEREO measurements, Winslow et al (2015) reported this power law equation to be B max ,ejecta = 12.18 +0.75 −0.71 r −1.89±0.14 .…”

“…However, except for a few studies that used multipoint spacecraft observations (Burlaga et al, 1981;Cane et al, 1997;Farrugia et al, 2011;Good et al, 2015Good et al, , 2018Janvier et al, 2019;Kilpua et al, 2011;Möstl, 2015;Möstl et al, 2009;Prise et al, 2015;Wang et al, 2018;Winslow et al, 2016Winslow et al, , 2018, CME measurements are largely restricted to single-point observations in space (see also discussion in Lugaz et al, 2018). Recently, Good et al (2019) examined the self similarity in the time series profiles of magnetic field structures of 18 interplanetary flux ropes. These lineup events were observed at heliocentric distances ranging from 0.62-9.4 AU, with longitudinal separations between the observing spacecraft being less than 20 • .…”

Radial Evolution of Magnetic Field Fluctuations in an Interplanetary Coronal Mass Ejection Sheath

“…If PMS2 is due to flux rope draping, the plane normal and flux rope axis orientation would likely be separated by large acute angles and this is indeed the case, with separations of ∼ 73 • at MESSENGER and ∼ 57 • at STEREO-B. The flux rope orientations used to make this comparison were determined by Good et al (2019).…”

An Observationally Constrained Analytical Model for Predicting the Magnetic Field Vectors of Interplanetary Coronal Mass Ejections at 1 au

“…We also do not consider any CME-CME interaction in the interplanetary space which may change the propagation trajectory of the CME. Assuming that the CMEs expand in a self-similar (Subramanian et al 2014;Good et al 2019;Vršnak et al 2019) way during its interplanetary propagation, we estimate the geometrical parameters of the CME upon its arrival at 1 AU. Using the conservation principle of the magnetic flux and helicity, we determine the magnetic properties of the FR when it is intersected by the spacecraft at 1 AU.…”