We present a comprehensive multi-instrument analysis of a sequence of eruptive prominences observed on 21 September 2025, associated with clearly detected coronal mass ejections (CMEs). These events were simultaneously observed by PROBA-3/ASPIICS (in both He I D3 and Fe XIV), SDO/AIA, PROBA-2/SWAP 174 Å, Solar Orbiter/FSI 304 and 174 Å, and Metis in both visible light and UV Lyα, as well as from a separated viewpoint by STEREO-A/EUVI and COR1/COR2, and LASCO C2/C3 in the outer corona. The well-suited constellation of spacecraft, separated by approximately 45° each, together with the range of available instruments, provides unprecedented coverage of the eruptive structures from the solar surface through the low corona and into the outer corona, enabling the tracking of prominences across multiple temperature regimes and perspectives. The multi-wavelength and multi-viewpoint analysis of these eruptive prominences allows investigation of how prominence plasma evolves and interacts with the surrounding corona, and explores the contribution to the early CMEs development.

How to cite: Liberatore, A., Patel, B., Mierla, M., Susino, R., Frassati, F., Romoli, M., and Zhukov, A.: The Role of Eruptive Prominences in early CME Evolution: Investigation from Coordinated Multi-instrument Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13526, https://doi.org/10.5194/egusphere-egu26-13526, 2026.

Coronal dimmings are regions of transiently reduced extreme ultraviolet (EUV) and soft X-ray (SXR) emission caused by plasma evacuation during the liftoff of coronal mass ejections (CMEs). As such, they serve as powerful diagnostics of CME initiation and early evolution. In May 2024, active region (AR) 13664 was among the most flare productive regions in recent decades, producing 54 M-class and 12 X-class flares. The rapid sequence of Earth-directed CMEs from AR13664 triggered the most intense geomagnetic storm in two decades. We present a two-part analysis of the coronal dimmings from AR 13664 associated with the May 2024 storms.

First, we systematically identify and analyse 22 dimming events (16 on-disc and 6 off-limb) and their characteristic parameters using SDO/AIA observations. We find that the dimming area, growth rate, and magnetic flux strongly correlate with GOES flare peak flux, fluence, and flare reconnection flux. These correlations are stronger than those found in previous statistical studies, highlighting the tight coupling between flares and dimmings. However, we find no correlation between dimming properties and CME maximum speed derived from SOHO/LASCO coronagraph measurements, suggesting that dimmings are more closely linked to the early-stage CME evolution rather than their later propagation. 

Second, we investigate the morphology and spatial evolution of the 16 on-disc dimmings in relation to flare ribbon location and coronal magnetic field structures. We employ high resolution PFSS and NLFF extrapolations alongside the dimming morphology to identify which magnetic structures are involved in the eruptions and how they participate in them. By considering the dimming expansion direction and the flare ribbon location, we identify two distinct magnetic domains associated with different polarity inversion lines. We also relate the dimming expansion, together with the orientation of the flare ribbons along the PILs, to the different geoeffectiveness of the associated CMEs.

These results underscore the extensive potential of coronal dimmings to characterise solar eruptions and understand the physical processes behind them.

How to cite: Razquin, A., Veronig, A. M., Dissauer, K., Barnes, G., Podladchikova, T., and Jain, S.: Coronal dimmings as diagnostics of the May 2024 solar energetic events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5329, https://doi.org/10.5194/egusphere-egu26-5329, 2026.

How to cite: Hu, H., Chen, C., Jiao, Y., Zhu, B., Wang, R., Zhao, X., and Yang, L.: Lateral Deformation of Large-scale Coronal Mass Ejections during the Transition from Nonradial to Radial Propagation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5427, https://doi.org/10.5194/egusphere-egu26-5427, 2026.

It is generally accepted that magnetic flux ropes (MFRs) are a critical component of many coronal mass ejections. However, the nature of the pre-eruptive magnetic configuration of CMEs is still under debate. A more crucial question is how the pre-eruptive magnetic configuration forms in the Sun and further evolves toward eruptions. In our previous statistical studies, we investigated pre-eruptive magnetic properties of 80 erupting MFRs whose feet are well identified by conjugate coronal dimmings. An interesting finding from our previous study is that 17 out of 80 MFRs carried significant non-neutralized electric currents prior to their eruption.  Here we investigate the entire evolution of these MFRs from birth to eruption. Impressively, the significant non-neutralized electric current appeared several hours ahead of the formation of coronal MFRs. The buildup of coronal MFRs were simultaneous with evolution of the non-neutralized electric current in the photosphere. The preflare brightening with two ribbon-like structures always observed among the coronal MFRs. Quantitative measurements indicate that the significant non-neutralized electric current also flows through the footpoints of the erupting MFRs. The asymmetric distributions of electric current and magnetic twist were found in these MFRs. The evolution of the photospheric non-neutralized electric current is demonstrated to signal the buildup of the pre-eruptive structure and the imminent eruption.

How to cite: Wang, W., Liu, R., Qiu, J., Guo, J., and Wang, Y.: Evolution of Solar Magnetic Flux Ropes with Significant Non-neutralized Electric Current toward Eruption, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9648, https://doi.org/10.5194/egusphere-egu26-9648, 2026.

Recent multi-spacecraft observations show the complex structure of Interplanetary Coronal Mass Ejections (ICMEs) as they propagate through interplanetary space. These observations allow us to monitor magnetic-field-related parameters systematically across vast spatial domains. Among the measurable quantities, magnetic helicity is of particular interest as it is quasi-conserved even in resistive MHD. It serves as a robust measure of the magnetic field complexity and, consequently, provides a physically grounded tracer for linking the magnetic topology of the ICME’s source region in the low solar atmosphere to the large-scale magnetic configuration in interplanetary space.

We present the analysis of a flare/CME event (SOL2024-03-23T X1.1) paired with a study of the ICME’s flux rope global structure that presumably impacted Solar Orbiter (at a heliocentric distance of 0.39 AU), BepiColombo (0.58 AU), STEREO-A (0.96 AU), as well as Wind (0.99 AU).

To model the three-dimensional coronal magnetic field of the solar source active region (NOAA 13614), we employ a non-linear force-free (NLFF) extrapolation based on the recently developed machine-learning approach. To infer the properties of the associated CME at the different locations in interplanetary space, we apply the semi-empirical 3DCORE model to the individual in-situ spacecraft data. Based on the modeling of the underlying magnetic field structure, we are able to compute the magnetic helicity in the solar source region (using a finite-volume method) as well as in interplanetary space, the latter using a linear force-free ("Lundquist") and a nonlinear force-free ("Gold-Hoyle") approach. This approach allows us to trace its evolution continuously from the low corona to near-Earth space. Our broader objective is to establish consistent and physically meaningful helicity estimates across coronal and Heliospheric domains.

How to cite: Moulin, A., Thalmann, J., Veronig, A., Dumbović, M., Rüdisser, H., Möstl, C., Amerstorfer, U., and Davies, E.: Tracing Magnetic Helicity from the Solar Source Region to Interplanetary Space: A Multi-Spacecraft Analysis of the March 23, 2024 ICME, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6837, https://doi.org/10.5194/egusphere-egu26-6837, 2026.

We investigate combined remote-sensing and in-situ data for a case study on a coronal mass ejection (CME) interacting with the nearby located heliospheric current sheet (HCS). The CME is related to the largest directly observed flare (X9.0) of solar cycle 25 on October 3, 2024. We find the CME source region to be a so-called nested active region, hence, persisting over several solar rotations. The active region and its evolution is therefore significantly linked to the structure of the global magnetic field. In-situ measurements indicate that a combined system of HCS and CME structures is propagating outward and generating a weak shock front ahead of it. The CME itself is highly interrupted by clear HCS-related structures, i.e., the heliospheric plasma sheet. The interaction process might have caused the CME-related shock-sheath region to be separated from the magnetic ejecta part by almost 40 hours. This event shows the intrinsic relation between solar surface structures, global magnetic field and the evolution of complex eruptive events.

How to cite: Temmer, M., Heinemann, S., Dresing, N., Dumbovic, M., and Asvestari, E.: Disruption of the October 3, 2024 CME by the Heliospheric Current Sheet – A Sun-to-Earth Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3021, https://doi.org/10.5194/egusphere-egu26-3021, 2026.

Coronal mass ejections (CME)-driven shocks are the most efficient accelerators of gradual solar energetic particles (SEPs), which pose risks to technological infrastructure and human activity in space. Knowing the physical properties of expanding shocks is critical in order to prevent SEPs hazard and to understand their impact to the near-Earth environment. However, a thorough picture on how the properties of shocks evolve from the corona to the heliosphere remains poorly constrained.  We present a study of a unique event, a shock driven by a circumsolar CME on 2023 March 13, observed from multiple spacecraft, using both remote sensing observations from STEREO-A/COR2 and in-situ data from Parker Solar Probe (PSP), Solar Orbiter (SolO), and Wind. We focused on the determination of some key parameters, such as the density compression ratio and the Alfvénic Mach number. The analysis of remote-sensing data has required advanced modelling of the 3D geometry of the observed shock complemented by raytracing simulation of the Thomson scattered emission, which was compared with the brightness measured from STEREO-A/COR2.
Following the evolution of the parameters, we have found that closer to the Sun, both the density compression ratio and the Alfvénic Mach number remain almost constant, while they increase at larger radial distances. These results highlight a non-trivial evolution of the properties of the shock during its journey throughout the interplanetary medium, with implications for SEP acceleration and space-weather forecasting.

This study was carried out within the "Data-based predictions of solar energetic particle arrival to the Earth: ensuring space data and technology integrity from hazardous solar activity events" (CUP H53D23011020001) funded by Next Generation EU’ PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR), and the Space It Up! project, funded by the Italian Space Agency (ASI) and the Ministry of University and Research (MUR), under Contract Grant Nos. 2024-5-E.0-CUP n.I53D24000060005.

How to cite: Nisticò, G., Chiappetta, F., Chimenti, M., Larosa, A., Malara, F., Pucci, F., Sorriso-Valvo, L., Zimbardo, G., and Perri, S.: Evolution of interplanetary CME-driven shocks from remote-sensing and in-situ observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20092, https://doi.org/10.5194/egusphere-egu26-20092, 2026.

Interaction of Coronal Mass Ejection (CMEs) with Solar High-Speed Streams (HSSs) could alter their plasma and magnetic field properties. The properties of such an interaction should be encoded in the in-situ plasma and magnetic field observations. To characterise the properties of such interaction, we analyse the in-situ signatures of 28 interplanetary coronal mass ejections (ICMEs)b interacting with high-speed streams (HSS) at 1AU between 2010 and 2018. We analyse the ICME velocity profiles, duration of the sheath and magnetic obstacle (MO), and distortion of the MO, as well as search for the signatures of the reconnection exhausts. We find 20 events where ICME is in front of the HSS and 8 events where it is behind the HSS. Statistical analysis is performed for these two classes of interaction separately. We find that ICMEs interacting with HSS generally show distinct speed profiles for cases where HSS is in front or behind. We find that HSS catching up to ICMEs tends to accelerate them from the back, whereas HSS in front of ICMEs do not significantly alter the typical speed expansion profiles but tends to inhibit the formation of sheath. We find that 70 precent of such events does not show discernible sheath region. We find that the average magnetic field magnitude tends to be higher for cases where the ICME is in front of the HSS compared to when it is behind. Although we find reconnection exhaust signatures in about 30% events, we do not find significant evidence of the distortion of the internal magnetic structure. Our results indicate that interaction with HSS does not significantly influence the ICME internal magnetic structure, however, it may significantly influence its kinematics.

How to cite: Remeshan, A. K., Dumbović, M., Fargette, N., and Temmer, M.: Characterisation of in situ signatures of coronal mass ejections interacting with high-speed streams, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17902, https://doi.org/10.5194/egusphere-egu26-17902, 2026.

There is current renewed interest in using distant retrograde orbits (DRO) for a space weather forecasting mission, which would temporarily place spacecraft at a position near the Sun--Earth line, but closer to the Sun than the L1 point. For a continuous coverage, several spacecraft would be needed at such sub-L1 distances. With in situ observations of the magnetic field, the southward Bz < 0 field of solar coronal mass ejections (CMEs), which is not accessible remotely, could be measured hours in advance. This Bz < 0 field is a decisive factor for forecasting geomagnetic storm intensity. Here, we analyse DROs at different distances for their efficacy for a space weather forecasting mission. First, we present a simple open-source numerical framework to generate DRO trajectories, based on equations for the constrained three-body problem. This makes them easily accessible for their introduction into numerical or empirical simulations of the solar wind or CMEs. Secondly, we analyze their general characteristics, such as relationships between their minimum distance to the Sun along the Sun-Earth line and their widest longitudinal extent. Third, we combine recent progress on our understanding of the magnetic structure of CMEs with the DRO characteristics and the possible number of spacecraft, to find clues on an optimal mission configuration, at distances between 0.8 and 0.9 au from the Sun. We also identify knowledge gaps and open challenges. ESA HENON (launch 2026) and ESA SHIELD (planned for the 2030s) are bound to be the first missions to realize space weather forecasts with sub-L1 data on DROs. We here provide a baseline for future studies by combining DRO calculations with the current state of knowledge on CMEs, for space weather forecasts with strongly enhanced lead times. 

How to cite: Möstl, C., Weiler, E., Davies, E. E., Rüdisser, H. T., Amerstorfer, U. V., Camattari, F., Lugaz, N., and Palmerio, E.: Calculation of distant retrograde orbits and their use for space weather forecasting, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4993, https://doi.org/10.5194/egusphere-egu26-4993, 2026.

Being one of the major drivers of space weather, coronal mass ejections (CMEs) have been in the spotlight of space physics research for many years. As a result, we now have a larger variety of analytical and numerical models at our disposal to describe CMEs as magnetised as well as non-magnetised structures. By applying these models to reconstruct past CME events, we can assess their performance and accuracy and whether they can be used for improving our forecasting capabilities. Such studies also help to identify all physical processes that are relevant to adequately describe CME evolution in the interplanetary space and avoid oversimplified model assumptions. But CME model applications do not stop there. Sculpting the interplanetary space, CMEs play a crucial role in particle transport both of solar and galactic origin. And current CME models can help not only to study the transport of solar energetic particles from a fundamental point of view but also offer the possibility to explain specific particle events observed by spaceborne instruments or ground-based detectors.

Despite such advancements, CME models suffer both from numerical and observational limitations. From artifacts introduced by numerical implementation schemes to difficulties in constraining observationally the numerous parameters involved in CME modelling, these issues introduce an element of uncertainty in our reconstructions. Of particular interest is the understanding of how observed parameters translate into model input. Especially when considering that the CME configurations we use have smooth, uniform, and often symmetric shapes during insertion which do not reflect the complex structures observed in remote sensing observations.

In this presentation, we will explore the state-of-the-art in CME modelling including current advancements in flux rope numerical implementation that has great potential in boosting CME studies. We will revisit how CME modelling contributed to a better understanding of the physical process that impact flux rope evolution and discuss some of the many applications of CME modelling in particle research. Finally, we address the limitations we are facing and the future needs and aspects of CME modelling.

How to cite: Asvestari, E.: Exploring current advancements, applications, limitations, and future aspects of modelling coronal mass ejections, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14598, https://doi.org/10.5194/egusphere-egu26-14598, 2026.

On March 15, 2015 a Coronal Mass Ejection (CME) associated with a C9.1 class flare caused the biggest geomagnetic storm of solar cycle 24. We present a numerical modeling study of the pre-eruption energetic phase, onset and evolution of this CME in the solar corona and the inner heliosphere. The CME initiation is modeled using the STITCH (STatisTical Injection of Condensed Helicity) methodology with the extended 3D global magnetohydrodynamic (MHD) model of the solar corona, Alfven Wave Solar atmosphere Model (AWSoM). STITCH is a statistical approximation of the hard to capture (numerically) small scale photospheric motions, by injecting a net helicity and forming sheared filament channels over polarity inversion lines (PILs). This emulates the energy build-up due to the small-scale convective motions and magnetic reconnection on the solar surface. In comparison to analytical flux-rope models, this method provides a realistic way to investigate the onset and eruption of a CME from the solar surface utilizing observations of the photospheric magnetic field. The shearing of the PIL of the erupting active region energizes the filament channel leading to flare reconnection and eruption of the CME flux-rope structure. We describe the magnetic and plasma properties of the pre-eruption and post eruption phase of the CME and its evolution characteristics.

How to cite: Sachdeva, N., Antiochos, S., and van der Holst, B.: Data-Driven Numerical Modeling of CME Onset and Eruption, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15438, https://doi.org/10.5194/egusphere-egu26-15438, 2026.

Coronal mass ejections (CMEs), powerful solar eruptions with massive plasma ejected into the interplanetary space, are caused by the release of the magnetic free enengy stored in coronal electric currents. Photospheric current helicity, defined as the integral of the product of vertical electric current density and vertical magnetic field ($H_c=\int j_zB_z\ dS$), serves as a key parameter in understanding the eruptions. Using a 3D magnetohydrodynamic model, we identify a current helicity reversal pattern associated with the eruption: a pre-eruption decrease and a post-eruption increase. This helicity reversal is attributed to the redistribution of electric currents: before the eruption, currents concentrate toward the polarity inversion line (PIL); after the eruption they move away from the PIL, consistent with the flare ribbon separation, which is caused by the upward progression reconnection site. To validate this pattern, we conducted an observational analysis of 50 $\geq$M5.0 eruptive flares. The results reveal that 58\% of cases exhibited a pre-eruption decrease and 92\% showed the post-eruption increase in current helicity. Detailed analysis of two cases with this reversal suggests that they share the same current redistribution pattern, consistent with the mechanism identified in the simulations. Moreover, the pre-eruption decrease could be observed clearly even in the long-term evolution of the two cases. Current helicity can serve as an indicator of when electric currents are built up for the subsequent eruption, and it has the potential to predict CMEs to some extent.

How to cite: Sun, Z., Li, T., Tian, H., Bian, X., and Kontogiannis, I.: Current Helicity Reversal during Coronal Mass Ejections, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1903, https://doi.org/10.5194/egusphere-egu26-1903, 2026.

Studying the structure of solar active regions through magnetic field modelling and observations strengthens our understanding of eruptive phenomena in the solar atmosphere. AR12975 featured an interesting event, where a significant restructuring of a pre-existing filament occurs approximately 1.5 hours before fully erupting. This event also shows clear signatures of coronal dimmings, which refer to a decrease in brightness in EUV and SXR observations of the Sun. They are interpreted as the density depletion caused by a coronal mass ejetion (CME) liftoff. As such, they are one of the most prominent low-corona signatures of CMEs and serve as important diagnostics for CME initiation and magnetic field reconfiguration after an eruption. Core dimmings, also known as flux rope dimmings, mark the footpoints of the erupting CME flux rope. To study them more in-depth we perform a time-dependent data-driven magnetofrictional simulation of AR12975. In particular, we focus on its magnetic structure and how the footpoints of the magnetic flux rope relate to the core dimming signatures observed in different EUV wavelenghts. To identify the magnetic flux rope from the model we use the Graphical User Interface for Tracking and Analysing flux Ropes (GUITAR). GUITAR uses a set of MFR proxies (here: combined maps of the twist parameter as well as the logarithm of the squashing factor) in combination with mathematical morphology operations to locate the MFR cross-section in a 2D plane. We also use GUITAR to disentangle the two flux systems that take part in the eruption. 

How to cite: Wagner, A., Razquin, A., Veronig, A., Dissauer, K., Pomoell, J., and Kilpua, E.: Studying the connection between coronal dimmings and flux rope footpoints using data-driven modelling and observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5621, https://doi.org/10.5194/egusphere-egu26-5621, 2026.

How to cite: Liu, X., Antiochos, S., Sokolov, I., Gombosi, T., Sachdeva, N., and Zhao, L.: MHD Simulations of CMEs with Energy Conservation: Reconnection Thermodynamics as a Critical Aspect of CME Dynamics , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14296, https://doi.org/10.5194/egusphere-egu26-14296, 2026.

To enable timely action in mitigating damage from severe space weather events, there is an urgent need for advanced Sun-to-Earth MHD models capable of delivering timely, high-fidelity, and comprehensive space weather forecasts. Recently, the numerical stability of the time-evolving coronal MHD models COCONUT and SIP-IFVM have been significantly improved by the energy decomposition strategy and the extended magnetic field decomposition methods, respectively. The implicit temporal integrations, with Newton iterations or pseudo–time marching method performed within each time step, enables high computational efficiency with desired temporal accuracy. Several observation-based coronal evolution and CME propagation simulations further demonstrate that these methods collaboratively achieve an effective balance between high computational efficiency, numerical stability, and modeling accuracy. Currently, we further go to the planetary space by directly extending our coronal models to 1 AU or coupling the coronal model with an inner heliosphere model. Based on the faster-than-real-time time-evolving solar-terrestrial MHD model, we are performing CME propagation simulations in the time-evolving solar-terrestrial plasma background, rather than the usually adopted quasi-static background. We will report on the algorithm innovations we recently made for improving the performance of MHD coronal models and CME simulations. We will also discuss the impact of temporal variations in the coronal and solar wind background on CME propagation, as well as the effects of the interface introduced by coupling separately run coronal and inner heliosphere models, a common practice adopted to simplify parameter adjustment and reduce computational cost. These algorithmic innovations and resulting findings provide an opportunity to develop more reliable Sun-to-Earth MHD models suitable for practical CME simulations.

How to cite: Wang, H., Stefaan Poedts, S., Lani, A., Linan, L., Baratashvili, T., Zhou, Y., Guo, J., Dhib, R., Jeong, H.-J., Noraz, Q., Wu, H., Zhuo, R., Liu, J., Dong, L., Najafi-Ziyazi, M., Zhukov, J. M., and Schmieder, B.: HERMES: Highly Efficient and quasi-Realistic Modeling of coronal mass Ejections in a time-evolving Solar-terrestrial background, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19280, https://doi.org/10.5194/egusphere-egu26-19280, 2026.

One of the major challenges in space weather forecasting is the reliable prediction of the magnetic structure of interplanetary coronal mass ejections (ICMEs) in near-Earth space. This challenge becomes even more pronounced when a CME interacts with high-speed streams (HSSs) or other CMEs during its interplanetary evolution. Within the framework of global MHD modeling, several efforts have been made to simulate the CME magnetic field from the Sun to Earth. However, it remains difficult to deduce a flux-rope solution that can robustly reproduce the magnetic structure of CMEs. Moreover, a comprehensive understanding of how CME–HSS interactions lead to enhanced space weather impacts of CMEs and their associated sheath regions is still lacking.

In this work, we implement a new flux-rope model in the European Heliospheric Forecast Information Asset (EUHFORIA), featuring an initially force-free toroidal flux rope embedded in the low-coronal magnetic field. The novel embedding technique self-consistently generates a draping field around the flux rope, preserving the normal component of the magnetic field at the flux-rope boundary. The flux-rope dynamics in the low and middle corona are solved using a non-uniform advection constrained by the observed kinematics of the CME. This produces a global, non-toroidal, stretched loop-like magnetic structure, in which the lower half of the torus remains below the inner boundary of the heliospheric model. At heliospheric distances, the subsequent evolution is modeled as an MHD process using EUHFORIA, yielding a classical flux-rope geometry consistent with observations of bi-directional electrons.

We further investigate CME–HSS interactions using this modeling framework by constructing synthetic high-speed streams and studying their interaction with CMEs of varying kinematics. Our results show that CME–HSS interactions lead to significant deformation of the CME magnetic structure. We find that the relative speed between the CME and the HSS plays a decisive role in determining the degree of ICME compression and the resulting enhancement of its space weather impact.

How to cite: Sarkar, R., Pomoell, J., Kilpua, E., and Asvestari, E.: Modelling CME–High-Speed Stream Interactions Using a Novel Flux-Rope Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21712, https://doi.org/10.5194/egusphere-egu26-21712, 2026.

Coronal mass ejections are the main drivers of extreme space weather events, so it is essential to model these transients accurately and with enough lead time to be able to forecast severe geomagnetic storms. Many different analytic and numerical models are currently employed with different structures, from analytic flux ropes with drag based propagation and hydrodynamic pulses in 3D MHD, to magnetised flux ropes and spheromaks. Tools such as the CCMC CME scoreboard are currently used to compare space weather forecasts, however this only compares a few parameters and a more detailed evaluation of when different models replicate CME structures accurately is important to further our understanding. We compare the structure and in-situ signatures of 3 different magnetised CME models: the 3DCORE analytic flux rope, Spheromak and Gibson-Low flux rope models. There is a large amount of uncertainty when extrapolating from single point measurements to infer 3D structure, so we also explore whether galactic cosmic ray (GCR) particles could be used as another in situ measurement for determining the structure of a CME. GCRs show transient decreases in flux due to the passage of CMEs, and we model this using test particle simulations in conjunction with the CME models, reproducing GCR modulations known as a Forbush decreases, and explore how the Forbush decrease signature varies with CME model and parameters. Through these simulations, we aim to gain a greater understanding of what a CME `looks like’ and how to more accurately reproduce geoeffective CME structure using magnetised models.

How to cite: Norman, H., Desai, R., Arber, T., Bennet, K., Rüdisser, H., and Davies, E.: Comparing CME models to increase our understanding of 3D CME structure, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1156, https://doi.org/10.5194/egusphere-egu26-1156, 2026.

Interplanetary coronal mass ejections (ICMEs) carry magnetic clouds, multi-scale structures which span a considerable fraction of an astronomical unit and display a rich dynamics at many spatial scales, including turbulence. Spacecraft that encounter an ICME can measure smoothly rotating "magnetic cloud" (MC) intervals or less organised "magnetic obstacle" (MO) ones.

We aim to understand to what extent the interplay of expansion, turbulence, and internal cloud dynamics affects the magnetic cloud properties, which then translate to signatures measured by spacecraft. We perform 2.5D MHD simulations of a magnetic flux rope embedded in the turbulent expanding solar wind, using the expanding box model, which decouples large and small scales and provides high resolution. We employ virtual spacecraft to probe the local plasma properties.

The flux rope exhibits a coherent large-scale expansion, and clear and stable MC signatures are always found by spacecraft intercepting the flux rope core. Disordered MO signatures appear at the flux rope edges, due to both expansion and turbulent transport. The strength of the expanding flow controls the angular extent of coherent signatures, whereas the intensity of turbulence controls the variability between different spacecraft encounters and the amount of distortion and deflection that the cloud experiences. Our results support the idea that the MC/MO dualism is a consequence of the impact geometry. The presence of MO signatures at the edges is instead controlled by the initial confinement of the axial flux rope field by magnetic tension: disordered signatures disappear for narrow flux ropes.

How to cite: Sangalli, M., Kilpua, E., Good, S., Landi, S., Pomoell, J., and Verdini, A.: Evolution of magnetic cloud signatures in the turbulent solar wind: virtual spacecraft analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19705, https://doi.org/10.5194/egusphere-egu26-19705, 2026.