Generic Magnetic Field Intensity Profiles of Interplanetary Coronal Mass Ejections at Mercury, Venus, and Earth From Superposed Epoch Analyses

Abstract

We study interplanetary coronal mass ejections (ICMEs) measured by probes at different heliocentric distances (0.3–1 AU) to investigate the propagation of ICMEs in the inner heliosphere and determine how the generic features of ICMEs change with heliospheric distance. Using data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER), Venus Express and ACE spacecraft, we analyze with the superposed epoch technique the profiles of ICME substructures, namely, the sheath and the magnetic ejecta. We determine that the median magnetic field magnitude in the sheath correlates well with ICME speeds at 1 AU, and we use this proxy to order the ICMEs at all spacecraft. We then investigate the typical ICME profiles for three categories equivalent to slow, intermediate, and fast ICMEs. Contrary to fast ICMEs, slow ICMEs have a weaker solar wind field at the front and a more symmetric magnetic field profile. We find the asymmetry to be less pronounced at Earth than at Mercury, indicating a relaxation taking place as ICMEs propagate. We also find that the magnetic field intensities in the wake region of the ICMEs do not go back to the pre‐ICME solar wind intensities, suggesting that the effects of ICMEs on the ambient solar wind last longer than the duration of the transient event. Such results provide an indication of physical processes that need to be reproduced by numerical simulations of ICME propagation. The samples studied here will be greatly improved by future missions dedicated to the exploration of the inner heliosphere, such as Parker Solar Probe and Solar Orbiter.

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

“…However, the ratio of the maximum magnetic field intensity measured in the sheath to that of the ejecta remained relatively constant throughout, which is consistent with Janvier et al (2019). We observed on average the maximum magnetic field strength in the ejecta to decrease by a factor of ∼3.4 from MESSENGER to Venus Express and ∼2 from Venus Express to near 1 AU.…”

“…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). 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).…”

“…Although present models based on numerical simulations (Jin et al, 2017;Lugaz et al, 2007;Odstrčil et al, 2002, 10.1029/2019JA027084 2004 or empirical methods (Gopalswamy et al, 2001;Kay et al, 2017;Kim et al, 2007;Vršnak et al, 2013) can forecast the basic characteristics of CMEs (speed and arrival time), it cannot predict the exact magnetic structure of the CME and the development of the sheath region. Recently, Janvier et al (2019) used data from MESSENGER, Venus Express, and ACE to determine statistically how CME magnetic field, of both ejecta and sheath evolve with radial distance (see also Gulisano et al, 2010;Winslow et al, 2015). That prompted us to search for conjunction events between radially aligned spacecraft in the inner heliosphere.…”

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

“…This finding supports the case for an upstream space weather monitor sitting on or near the Sun‐Earth line: The first‐order flux rope structure observed at such a monitor (and the normalized B z component of that structure) is likely to be the same as that arriving subsequently at the Earth, even in cases where the radial separation distance between the monitor and Earth is large (e.g., Event 8). With an estimation of how the field magnitude profile also evolves (as recently considered by Janvier et al, ), simple and accurate B z forecasting with a near‐Sun upstream monitor may be possible. However, differences due, for example, to a change in rope orientation may be difficult to predict without global modeling.…”

Evolution of a Long‐Duration Coronal Mass Ejection and Its Sheath Region Between Mercury and Earth on 9–14 July 2013

“…Janvier et al (2019) studied the average sheath duration increase from Mercury to Venus and Earth's orbits and found that the typical sheath duration increases by a factor of 5 from Mercury to Earth and the ratio of sheath to ME durations doubles between these two locations. Janvier et al (2019) studied the average sheath duration increase from Mercury to Venus and Earth's orbits and found that the typical sheath duration increases by a factor of 5 from Mercury to Earth and the ratio of sheath to ME durations doubles between these two locations.…”