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

Abstract

Using in situ measurements and remote-sensing observations, we study a coronal mass ejection (CME) that left the Sun on 9 July 2013 and impacted both Mercury and Earth while the planets were in radial alignment (within 3 • ). The CME had an initial speed as measured by coronagraphs of 580 ± 20 km/s, an inferred speed at Mercury of 580 ± 30 km/s, and a measured maximum speed at Earth of 530 km/s, indicating that it did not decelerate substantially in the inner heliosphere. The magnetic field measurements made by MESSENGER and Wind reveal a very similar magnetic ejecta at both planets. We consider the CME expansion as measured by the ejecta duration and the decrease of the magnetic field strength between Mercury and Earth and the velocity profile measured in situ by Wind. The long-duration magnetic ejecta (20 and 42 hr at Mercury and Earth, respectively) is found to be associated with a relatively slowly expanding ejecta at 1 AU, revealing that the large size of the ejecta is due to the CME itself or its expansion in the corona or innermost heliosphere and not due to a rapid expansion between Mercury at 0.45 AU and Earth at 1 AU. We also find evidence that the CME sheath is composed of compressed material accumulated before the shock formed, as well as more recently shocked material.

Cross Helicity of the 2018 November Magnetic Cloud Observed by the Parker Solar Probe

“…Sheaths and their magnetic cloud or ICME drivers are a major cause of geomagnetic activity (Gosling et al 1991;Kilpua et al 2019). Like the solar wind, the properties of magnetic clouds (e.g., Bothmer & Schwenn 1998;Liu et al 2005;Wang et al 2005;Leitner et al 2007;Good et al 2019;Vršnak et al 2019) and their sheaths (Good et al 2020;Lugaz et al 2020) evolve with heliocentric distance.…”

Spatial Coherence of Interplanetary Coronal Mass Ejection Sheaths at 1 AU

“…Previous studies have often used either single‐point observations (Owens et al., 2005) or compared observations within the sheath at different heliocentric distances (Good et al., 2020; Lugaz et al., 2020; Salman et al., 2020). There is not, however, an understanding of the extent to which different structures and their generation mechanisms are localized in the sheath.…”

Spatial coherence of interplanetary coronal mass ejection sheaths at 1 AU

“…Previous studies have often used either single-point observations (Owens et al, 2005) or compared observations within the sheath at different heliocentric distances (Good et al, 2020;Lugaz et al, 2020;Salman et al, 2020). There is not, however, an understanding of the extent to which different structures and their generation mechanisms are localized in the sheath.…”