In this work we have, for the first time, applied the interpretation of multiple “ghost-fronts” to two synthetic coronal mass ejections (CMEs) propagating within a structured solar wind using the Heliospheric Upwind eXtrapolation time (HUXt) solar wind model. The two CMEs occurred on 2012 June 13–14 showing multiple fronts in images from Solar Terrestrial Relations Observatory Heliospheric Imagers (HIs). The HUXt model is used to simulate the evolution of these CMEs across the inner heliosphere as they interacted with structured ambient solar wind. The simulations reveal that the evolution of CME shape is consistent with observations across a wide range of solar latitudes and that the manifestation of multiple “ghost-fronts” within HIs’ field of view is consistent with the positions of the nose and flank of the same CME structure. This provides further confirmation that the angular separation of these features provides information on the longitudinal extent of a CME. For one of the CMEs considered in this study, both simulations and observations show that a concave shape develops within the outer CME front. We conclude that this distortion results from a latitudinal structure in the ambient solar wind speed. The work emphasizes that the shape of the CME cannot be assumed to remain a coherent geometrical shape during its propagation in the heliosphere. Our analysis demonstrates that the presence of “ghost” CME fronts can be used to infer the distortion of CMEs by ambient solar wind structure as a function of both latitude and longitude. This information has the potential to improve the forecasting of space weather events at Earth.

We present two multipoint interplanetary coronal mass ejections (ICMEs) detected by the Tianwen-1 and Mars Atmosphere and Volatile Evolution spacecraft at Mars and the BepiColombo (0.56 au ∼0.67 au) upstream of Mars from 2021 December 5 to 31. This is the first time that BepiColombo is used as an upstream solar wind monitor ahead of Mars and that Tianwen-1 is used to investigate the magnetic field characteristics of ICMEs at Mars. The Heliospheric Upwind Extrapolation time model was used to connect the multiple in situ observations and the coronagraph observations from STEREO/SECCHI and SOHO/LASCO. The first fast coronal mass ejection event (∼761.2 km s⁻¹), which erupted on December 4, impacted Mars centrally and grazed BepiColombo by its western flank. The ambient slow solar wind decelerated the west flank of the ICME, implying that the ICME event was significantly distorted by the solar wind structure. The second slow ICME event (∼390.7 km s⁻¹) underwent an acceleration from its eruption to a distance within 0.69 au and then traveled with the constant velocity of the ambient solar wind. These findings highlight the importance of background solar wind in determining the interplanetary evolution and global morphology of ICMEs up to Mars distance. Observations from multiple locations are invaluable for space weather studies at Mars and merit more exploration in the future.

The Tianwen-1 spacecraft is China's first Mars exploration mission. The Mars Orbiter Magnetometer (MOMAG) is a scientific instrument on board the Tianwen-1 mission that is designed to study magnetic fields at Mars, including the solar wind to the magnetosheath and the ionosphere. Using the first Tianwen-1/MOMAG data that is publicly available, we present an interplanetary coronal mass ejection (ICME) and stream interaction region (SIR) list based on in situ observations at Mars between 2021 November 16 and 2021 December 31. We compared the magnetic field intensity and vector magnetic field measurements from Tianwen-1/MOMAG and Mars Atmospheric Volatile EvolutioN (MAVEN)/Magnetometer (MAG) during the ICME and SIR interval and found a generally good consistency between them. Due to MAVEN's orbital adjustment since 2019, the Tianwen-1/MOMAG instrument is almost unique in its status as an interplanetary magnetic field monitor currently at Mars. The observations indicate that the MOMAG instrument on Tianwen-1 is performing well and can provide accurate measurements of the vector magnetic field in the near-Mars solar wind space. The multipoint observations combining MOMAG, MINPA, and MEPA on board Tianwen-1 with MAG, SWIA, and STATIC on board MAVEN will help develop systematic studies of the characteristics of ICMEs and SIRs at Mars, and their influences on the Martian atmosphere and ionosphere.

Using the Stream Interaction Regions list from the Tianwen-1/Mars Orbiter Magnetometer (MOMAG) data between 2021 November and 2021 December and from Wind observations, we present an accurate prediction for the arrival time and in situ parameters of corotating interaction regions (CIRs) when the Earth and Mars have large longitudinal separations. Since CIRs were detected earlier at Earth than at Mars during the period examined, we employ Earth-based CIR detections for predicting CIR observations at Mars. The arrival time is calculated by the Parker spiral model under the assumption of steady corotation of the Sun and coronal holes, while the in situ parameters are derived from Wind data through radial dependent scaling laws. The CIR prediction results are compared to the actual observations obtained from the MOMAG and Mars Ion and Neutral Particle Analyzer instruments onboard Tianwen-1, as well as the Magnetometer and Solar Wind Ion Analyzer instruments onboard MAVEN. The predicted arrival time is close to the observed values with relative errors less than 10%, and the expected in situ data show a good consistency with the Martian measurements. The comparison results indicate that the prediction method has good performance and will be helpful for comparative analysis with Tianwen-1 observations at Mars in the future.

This work reports on the interaction between a fast forward shock and an interplanetary coronal-mass-ejection-like structure (ICMELS) as observed by in situ observations of radially aligned spacecraft. Around 2011 March 22, the Venus EXpress (VEX) and Solar TErrestrial RElations Observatory-A (STEREO-A) were nearly at the same longitude, providing us with an excellent opportunity to study the formation and evolution of the complex structures. The shock and ICMELS investigated in this paper are isolated near Venus, but when they approach STEREO-A, the shock nearly approaches the front edge of the ICMELS and forms a shock–ICMELS complex structure. The maximal magnetic field in the ICMELS increased 2.3 times due to shock compression, according to the observation. The recovery model, which restores the shocked portion of the shock–ICMELS to its uncompressed condition, likewise confirms this improvement. The interaction with the ICMELS, on the other hand, weakens shock 2. The magnetic compression ratio falls from 2.4 at Venus to 2.0 at STEREO-A. This research enables us to have a better physical knowledge of the impacts of the interaction between a shock and an ICME (or ICMELS), which will aid future space weather predictions.

The three successive coronal mass ejections (CMEs) that erupted from 2023 November 27–28, provide the first opportunity to shed light on the entire process of a shock propagating through, sequentially compressing, and modifying two preceding CMEs using in situ data from Solar Orbiter, Wind, and STEREO-A. We describe the interaction of the three CMEs as follows: CME-1 and CME-2 interacted with each other at distances close to the Sun. Subsequently, the shock (S3) driven by CME-3 caught up with and compressed ICME-2 before 0.83 au, forming a typical shock–ICME interaction event observed by the Solar Orbiter. The S3 continued to propagate, crossing ICME-2 and propagating into ICME-1 as observed by Wind, and completely overtaking both ICME-1 and ICME-2 at STEREO-A. The interaction between S3 and the preceding two ICMEs leads to a clear compression of preceding ICMEs including an increase in magnetic field (∼150%) and a reduction in the interval of ICMEs. It presents direct and compelling evidence that a shock can completely traverse two preceding CMEs, accompanied by a significant decrease in shock strength (magnetic compression ratio decrease from 1.74 to 1.49). Even though the three ICMEs interact significantly in the heliosphere, their magnetic field configurations exhibit coherence at different observation points, especially for ICME-3. Those results highlight the significant implications of shock–CME interactions for CME propagation and space weather forecasting.