Shock deceleration in interplanetary coronal mass ejections (ICMEs) beyond Mercury’s orbit until one AU

Abstract

The CDPP propagation tool is used to propagate interplanetary coronal mass ejections (ICMEs) observed at Mercury by MESSENGER to various targets in the inner solar system (VEX, ACE, STEREO-A and B). The deceleration of ICME shock fronts between the orbit of Mercury and 1 AU is studied on the basis of a large dataset. We focus on the interplanetary medium far from the solor corona, to avoid the region where ICME propagation modifications in velocity and direction are the most drastic. Starting with a catalog of 61 ICMEs recorded by MESSENGER, the propagation tool predicts 36 ICME impacts with targets. ICME in situ signatures are investigated close to predicted encounter times based on velocities estimated at MESSENGER and on the default propagation tool velocity (500 km s−1). ICMEs are observed at the targets in 26 cases and interplanetary shocks (not followed by magnetic ejecta) in two cases. Comparing transit velocities between the Sun and MESSENGER ($ {\bar{v}}_{\mathrm{SunMess}}$) and between MESSENGER and the targets ($ {\bar{v}}_{\mathrm{MessTar}}$), we find an average deceleration of 170 km s−1 (28 cases). Comparing $ {\bar{v}}_{\mathrm{MessTar}}$ to the velocities at the targets (v Tar), average ICME deceleration is about 160 km s−1 (13 cases). Our results show that the ICME shock deceleration is significant beyond Mercury’s orbit. ICME shock arrival times are predicted with an average accuracy of about six hours with a standard deviation of eleven hours. Focusing on two ICMEs detected first at MESSENGER and later on by two targets illustrates our results and the variability in ICME propagations. The shock velocity of an ICME observed at MESSENGER, then at VEX and finally at STEREO-B decreases all the way. Predicting arrivals of potentially effective ICMEs is an important space weather issue. The CDPP propagation tool, in association with in situ measurements between the Sun and the Earth, can permit to update alert status of such arrivals.

Over-expansion of a coronal mass ejection generates sub-Alfvénic plasma conditions in the solar wind at Earth

“…As expected, the transit velocities are lower than the initial velocities observed by LASCO, but larger than the velocities measured at 1 au by ACE. Deceleration in the interplanetary medium is expected for fast ICMEs (Gopalswamy et al 2001a), as confirmed with several cases of ICMEs observed at different distances between the solar corona and 1 au (Grison et al 2018). The aforementioned velocities also suggest that CME2 experienced a higher deceleration than CME1 during its travel between the Sun and the Earth.…”

Low Geo‐Effectiveness of Fast Halo CMEs Related to the 12 X‐Class Flares in 2002

“…We now test the association between the discontinuities and the halo CMEs based on velocity comparisons. As fast ICME shocks are progressively slowing down in the interplanetary medium at least up to 1 AU (Gopalswamy et al, 2000;Grison et al, 2018), we expect v bal to be lower than the CME velocity v estimated from coronagraph observations and to be larger than the velocity observed at L1 (v L1 ). This is the case for the discontinuity observed the 25 July 13:00 UT (flare-related CME #6) (v L1 = 520; v bal = 625; v = 2285 km·s −1 ).…”

Solar Wind Velocities at Comets C/2011 L4 Pan‐STARRS and C/2013 R1 Lovejoy Derived Using a New Image Analysis Technique

“…In addition, the ICMEs could simply have decelerated, e.g. Grison et al (2018), to the ambient slow v sw of ∼250 kms −1 . The possible merging of the two ICMEs would have resulted in a complex ICME-solar wind outflow at the comet, which may have compressed the fast solar wind ahead.…”

“…It is far more likely that this turbulent period is associated with an ICME-on-ICME interaction from the last two ICMEs reported in Table 3 and Figure 28. In addition, the ICMEs could simply have decelerated, for example, Grison et al (2018), to the ambient slow v sw of ∼250 km s −1 . The possible merging of the two ICMEs would have resulted in a complex ICME-SW outflow at the comet, which may have compressed the fast SW ahead.…”