CME interactions with coronal holes and their interplanetary consequences

Context. We explore the impact of interactions between coronal mass ejections (CMEs) – known as CME–CME interactions – on Earth using remote-sensing and in situ observations and estimate the amplification of the geo-effectiveness of the individual CMEs by a factor of ∼2 due to CME–CME interactions. Aims. We present 3D reconstructions of interacting CMEs, which provide essential information on the orientation and interaction of the events. Additionally, we analysed coronal evolution of CMEs and their in situ characteristics at 1 AU to explore the impact of interactions between CMEs on their geo-effectiveness. Methods. We analysed CME interaction using white light data from LASCO and STEREO COR-A. The reported CMEs were reconstructed using the gradual cylindrical shell (GCS) model and simulated self-consistently with the physics-based 3D MHD model EUHFORIA (EUropean Heliosphere FORecasting Information Asset). By running different simulations, we estimated the geo-effectiveness of both individual and interacting CMEs using an empirical relationship method for the disturbance storm index. Results. The SOHO/LASCO spacecraft observed three CMEs erupting from the Sun within an interval of 10 h during a very active period in early November 2021. There were two partial halo CMEs that occurred on 1 Nov. 2021 at 19:00 UT and 22:00 UT, respectively, from the active region 12887 (S28W58), and a third halo CME occurred from AR 12891 (N17E03) on 2 Nov. 2021 at 02:48 UT. By combining remote observations close to the Sun, in situ data at 1 AU, and further numerical analyses of each individual CME, we are able to identify the initial and interplanetary evolution of the CMEs. Conclusions. (i) White light observations and a 3D reconstruction of the CMEs show cannibalism by CME-2 on CME-1 and a flank interaction of CME-3 with the merged CME-1 and CME-2 at 45–50 Rs. (ii) Interacting CMEs exhibit an increase in geo-effectiveness compared to an individual CME.

Interplanetary coronal mass ejections (ICMEs) are the heliospheric counterparts of solar coronal mass ejections, and their comprehensive cataloging near Earth has enabled significant advances across space science disciplines. As a part of the Project Space Life by Eco Astronomy Inc, this review presents a synthesis of the Near-Earth ICME since 1996” dataset compiled by I. G. Richardson and H. V. Cane, highlighting its historical development, methodology, key findings, and broad applications. The dataset encompasses approximately 600 ICMEs observed at 1 AU from 1996 through early 2024, spanning solar cycles 23, 24, and the rise of 25. We discuss how ICMEs are identified using in-situ plasma, magnetic field, composition, and energetic particle signatures, and how this approach has evolved with improved data (e.g. ACE spacecraft measurements). The ICME catalogs reveals clear solar-cycle trends, ICME occurrence rises by an order of magnitude from solar minimum to maximum with the yearly counts peaking in 2000 (51 events) and dipping to only a few events at recent minima. It also captures intriguing temporal patterns such as a quasi-periodicity of ~150 days in ICME occurrence (Cane & Richardson, January 1, 2003). We synthesize the typical ICME properties (duration, speed, magnetic field strength) and how they vary between cycles: e.g. cycle 23 produced more frequent and faster ICMEs than the weaker cycle 24. The dataset’s extensive annotations (footnotes) link each ICME to associated phenomena like geomagnetic sudden commencements, storm indices, and cosmic ray depressions, allowing analysis of ICME impacts. We review how ~90% of major geomagnetic storms (Dst ≤ –100 nT) in 1996–2005 were caused by ICMEs or their driven shocks (Richardson & Cane, 2007), underlining their geo effectiveness. We summarize statistical correlations between ICME parameters (speed, magnetic field, size) and geomagnetic storm intensity and discuss notable events. Beyond geomagnetism, ICMEs are shown to modulate galactic cosmic rays, causing short-term intensity drops (Forbush decreases) in ~80% of cases (I & H, 2011) and contributing to long-term cosmic-ray modulation over the solar cycle. The rich Richardson-Cane ICME database has fostered multidisciplinary benefits: improving space weather forecasts (by providing empirical event data for CME arrival and storm predictions), informing heliospheric physics (e.g. ICME propagation and solar-cycle variability), elucidating cosmic ray transport (through ICME-caused particle decreases), and aiding studies of impacts on technological systems (satellites, power grids, GPS) and Earth’s atmosphere. We conclude by emphasizing the value of this continually updated ICME catalogs for future research and cross-disciplinary applications, and we include a comprehensive appendix of ICME analysis figures derived from the dataset.

The understanding of the causes that produce the deflection of coronal mass ejections (CMEs) is essential for the space weather forecast. We study the effects on CME trajectories produced by the different properties of a coronal hole (CH), close to the ejection area. We perform ideal magnetohydrodynamics simulations emulating the early rising of the CME in the presence of a CH. We find that, the stronger the magnetic field and the wider the CH area, the larger the CME deflection. The deflection reduces as the CH moves away from the ejection region. To quantify the deflection we propose a dimensionless parameter that depends on the CH properties. We show that a minimum magnetic energy region, responsible for the deflection, is associated with the presence of the CH near the CME. We establish a relationship between the CH properties, the location of the minimum magnetic region, and the CME deflection.

To investigate the relations between coronal mass ejection (CME) speed and magnetic field properties measured in the photospheric surface of CME source regions, we selected 22 disk CMEs in the rising and early maximum phases of the current Solar Cycle 24. For the CME speed, we used two-dimensional (2D) projected speed observed by the Large Angle and Spectroscopic Coronagraph onboard the Solar and Heliospheric Observatory (SOHO/LASCO), as well as a 3D speed calculated from the triangulation method using multi-point observations. Two magnetic parameters of CME source regions were considered: the average of magnetic helicity injection rate and the total unsigned magnetic flux. We then classified the selected CMEs into two groups, showing: i) a monotonically increasing pattern with one sign of helicity (group A: 16 CMEs) and ii) a pattern of significant helicity injection followed by its sign reversal (group B: 6 CMEs). We found that: 1) 3D speed generally shows better correlations with the magnetic parameters than the 2D speed for 22 CME events in Solar Cycle 24; 2) 2D speed and the magnetic parameters of 22 CME events in this solar cycle have lower values than those of 47 CME events in Solar Cycle 23; 3) all events of group B in Solar Cycle 24 occur only after the beginning of the maximum phase, a trend well consistent with that shown in Solar Cycle 23; 4) the 2D speed and the helicity parameter of group B events continue to increase in the declining phase of Solar Cycle 23, while those of group A events abruptly decrease in the same period. Our results indicate that the two CME groups have a different tendency in the solar cycle variations of CME speed and the helicity parameters. Active regions that show a complex helicity evolution pattern tend to appear in the maximum and declining phases, while active regions with a relatively simple helicity evolution pattern appear throughout the whole solar cycle.

The properties and the spatial distribution of the large-scale structures of the Solar Corona (SC) determine the observed solar wind structure at 1 AU. Coronal Holes (CHs) are the primary source of the fast solar wind, which is the most geoeffective component of solar wind, and they appear as large dark patches in the Extreme Ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory (SDO) and the Extreme Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SoHO). These observatories provide images of the SC at different wavelengths, which enables the identification of CH morphology and other large-scale structures along a given line of sight. It is crucial to understand the CH regions and their properties for effective space weather forecasting. This work is part of the WindTRUST project, with the primary goal of improving the reliability of solar wind models for space weather forecasting. Here, we aim to develop an automatic threshold-based CH detection tool for predictions across solar cycles 23, 24, and 25. We also plan to integrate this CH detection tool into a solar wind model validation pipeline, creating a fully automated validation system that provides a quantitative assessment of predictions. We categorized the large-scale features of the SC, such as active regions, solar flares, coronal mass ejections (CMEs), and filaments, based on their spatial distribution, phase of the solar cycle, and additional properties, including the GOES solar flare class. A Sequential Neural Network (NN) model was then trained by optimizing the architecture of the hidden layers to achieve higher predictive accuracy. The resulting model estimates the threshold required for integration into the Coronal Hole (CH) detection scheme, thereby enabling automated, consistent identification of CH boundaries in EUV images across solar cycles 23, 24, and 25. To interpret the performance of our NN model, we divided the predicted CH results into solar minimum and maximum cases across the solar cycles 23, 24, and 25. We also provide a comparison of our CH detection results with those obtained from other detection tools. Once we identify CH contours from our model, we validate them using a diagnostic test against CH contours from the Potential Field Source Surface (PFSS) model (non-MHD) and the WindPredict (WP) model (Polytropic and Alfven Wave) (MHD). Finally, we couple the CH detection tool with the validation pipeline to develop an automation tool for solar wind predictions.

Earth's magnetosphere is a magnetic shield that protects the Earth from the energetic emissions of the high-speed Solar Wind (HSSW). We perform a statistical analysis of the response of Earth's magnetosphere inner part under the impact of HSSW over 40 years of data encompassing solar cycles 20-23. With misidentified events or events interacting with interplanetary coronal mass ejections (ICMEs) removed, only 23552 events were identified. The results we obtained show that more than 85% of the events recorded from 1964 to 2009 are generated by coronal holes (CHs). Almost all observations were confined between 250-800 km/s and show a unimodal distribution per solar cycle: (1) 93% of the solar wind (SW) velocities are on the order of 567.77 ± 2.46 km/s for solar cycle 20, (2) 81% of the SW velocities are worth 524.30 ± 2.69 km/s for cycle 21, (3) 92% of the SW velocities progress to 565.15 ± 2.72 km/s for cycle 22, and (4) 75% of the SW velocities show a value on the order of 530.38 ± 2.22 km/s for cycle 23. Furthermore, our analysis shows a lower electron density at the beginning of the cycle (48%) than at the end of the solar cycle (52%). Thus HSSWs are more frequent at the end of solar cycles, while the magnetospheric electric field (EM) instead shows dominant features during the upward phase of odd cycles and the downward phase of even cycles. Therefore, the stability of the inner magnetosphere is more significant during the decline of solar cycles. Key words: High-speed solar winds, magnetospheric electric field, interplanetary coronal mass ejections.

Context. Meter-wavelength type II solar radio bursts are thought to be the signatures of shock-accelerated electrons in the corona. Studying these bursts can give information about the initial kinematics, dynamics, and energetics of coronal mass ejections (CMEs) in the absence of white-light observations. Aims. We investigate the occurrence of type II bursts in solar cycles 23 and 24 and their association with CMEs. We also explore whether type II bursts might occur in the absence of a CME. Methods. We performed a statistical analysis of type II bursts that occurred between 200 and 25 MHz in solar cycles 23 and 24 and determined the temporal association of these radio bursts with CMEs. We categorized the CMEs based on their linear speed and angular width and studied the distribution of type II bursts with fast (≥500 km s−1), slow (< 500 km s−1), wide (≥60°), and narrow (< 60°) CMEs. We explored the dependence of type II bursts occurrence on the phases of the solar cycle. Results. Our analysis shows that during solar cycles 23 and 24, 768 and 435 type II bursts occurred, respectively. Of these, 79% were associated with CMEs in solar cycle 23, and 95% were associated with CMEs in solar cycle 24. However, only 4% and 3% of the total number of CMEs were accompanied by type II bursts in solar cycle 23 and 24, respectively. Most of the type II bursts in both cycles were related to fast and wide CMEs (48%). We also determined the typical drift rate and duration for type II bursts, which is 0.06 MHz s−1 and 9 min. Our results suggest that type II bursts dominate at heights ≈1.7 − 2.3 ± 0.3 R⊙. A clear majority have an onset height around 1.7 ± 0.3 R⊙ assuming the four-fold Newkirk model. Conclusions. The results indicate that most of the type II bursts had a white-light CME counterpart, but a few type II bursts lacked a clear CME association. There were more CMEs in cycle 24 than in cycle 23. However, cycle 24 contained fewer type II radio bursts than cycle 23. The onset heights of type II bursts and their association with wide CMEs reported in this study indicate that the early lateral expansion of CMEs may play a key role in the generation of these radio bursts.

We investigate how a weak coronal mass ejection (CME) launched on 2016 October 8 without obvious signatures in the low corona produced a relatively intense geomagnetic storm. Remote sensing observations from SDO, STEREO, and SOHO and in situ measurements from Wind are employed to track the CME from the Sun to the Earth. Using a graduated cylindrical shell model, we estimate the propagation direction and the morphology of the CME near the Sun. CME kinematics are determined from the wide-angle imaging observations of STEREO A and are used to predict the CME arrival time and speed at the Earth. We compare ENLIL MHD simulation results with in situ measurements to illustrate the background solar wind where the CME was propagating. We also apply a Grad–Shafranov technique to reconstruct the flux-rope structure from in situ measurements in order to understand the geoeffectiveness associated with the CME magnetic field structure. Key results are obtained concerning how a weak CME can generate a relatively intense geomagnetic storm: (1) there were coronal holes at low latitudes, which could produce high speed streams (HSSs) to interact with the CME in interplanetary space; (2) the CME was bracketed between a slow wind ahead and an HSS behind, which enhanced the southward magnetic field inside the CME and gave rise to the unexpected geomagnetic storm.

Large non-radial propagation of a coronal mass ejection on 2011 January 24

We analyse the characteristics of interplanetary coronal mass ejections (ICMEs) during Solar Cycles 23 and 24. The present analysis is primarily based on the near-Earth ICME catalogue (Richardson and Cane, 2010). An important aspect of this study is to understand the near-Earth and geoeffective aspects of ICMEs in terms of their association (type II ICMEs) versus absence (non-type II ICMEs) of decameter-hectometer (DH) type II radio bursts, detected by Wind/WAVES and STEREOS/WAVES. Notably, DH type II radio bursts driven by a CME indicate powerful MHD shocks leaving the inner corona and entering the interplanetary medium. We find a drastic reduction in the occurrence of ICMEs by 56% in Solar Cycle 24 compared to the previous cycle (64 versus 147 events). Interestingly, despite a significant decrease in ICME/CME counts, both cycles contain almost the same fraction of type II ICMEs (~47%). Our analysis reveals that, even at a large distance of 1 AU, type II CMEs maintain significantly higher speeds compared to non-type II events (523 km/s versus 440 km/s). While there is an obvious trend of decrease in ICME transit times with increase in the CME initial speed, there also exists a noticeable wide range of transit times for a given CME speed. Contextually, Cycle 23 exhibits 10 events with shorter transit times ranging between 20-40 hours of predominantly type II categories while, interestingly, Cycle 24 almost completely lacks such "fast" events. We find a significant reduction in the parameter $V_{ICME} \times B_{z}$, the dawn to dusk electric field, by 39% during Solar Cycle 24 in comparison with the previous cycle. Further, $V_{ICME} \times B_{z}$ shows a strong correlation with Dst index, which even surpasses the consideration of $B_{z}$ and $V_{ICME}$ alone. The above results imply the crucial role of $V_{ICME} \times B_{z}$ toward effectively modulating the geoeffectiveness of ICMEs.

Coronal mass ejections (CMEs) initiation: models and observations

Propagation of coronal mass ejections (CMEs) from the Sun far into interplanetary space is not well understood, due to limited observations. In this study we examine the propagation characteristics of two geo-effective CMEs, which occurred on 2005 May 6 and 13, respectively. Significant heliospheric consequences associated with the two CMEs are observed, including interplanetary CMEs (ICMEs) at the Earth and Ulysses, interplanetary shocks, a long-duration type II radio burst, and intense geomagnetic storms. We use coronagraph observations from SOHO/LASCO, frequency drift of the long-duration type II burst, in situ measurements at the Earth and Ulysses, and magnetohydrodynamic propagation of the observed solar wind disturbances at 1 au to track the CMEs from the Sun far into interplanetary space. We find that both of the CMEs underwent a major deceleration within 1 au and thereafter a gradual deceleration when they propagated from the Earth to deep interplanetary space, due to interactions with the ambient solar wind. The results also reveal that the two CMEs interacted with each other in the distant interplanetary space even though their launch times on the Sun were well separated. The intense geomagnetic storm for each case was caused by the southward magnetic fields ahead of the CME, stressing the critical role of the sheath region in geomagnetic storm generation, although for the first case there is a corotating interaction region involved.

Solar flares, coronal mass ejections (CMEs), solar energetic particles (SEPs), and fast solar wind represent the energetic phenomena on the Sun. Flares and CMEs originate from closed magnetic field structures on the Sun typically found in active regions and quiescent filament regions. On the other hand, fast solar wind originates from open field regions on the Sun, identified as coronal holes. Energetic particles are associated with flares, CMEs, and fast solar wind, but the ones associated with CMEs are the most intense. The energetic phenomena have important consequences in the heliosphere and contribute significantly to adverse space weather. This paper provides an over view of the energetic phenomena on the Sun including their origin interplanetary propagation and space weather consequences.

<p>Previous studies of Coronal Mass Ejections (CMEs) have shown the importance of understanding their geometrical structure and internal magnetic field configuration for improving forecasting at Earth. The precise prediction of the CME shock and the magnetic cloud arrival time, their magnetic field strength and the orientation upon impact at Earth is still challenging and relies on solar wind and CME evolution models and precise input parameters. In order to understand the propagation of CMEs in the interplanetary medium, we need to understand their interaction with the complex features in the magnetized background solar wind which deforms, deflects and erodes the CMEs and determines their geo-effectiveness. Hence, it is important to model the internal magnetic flux-rope structure in the CMEs as they interact with CIRs/SIRs, other CMEs and solar transients in the heliosphere. The spheromak model (Verbeke et al. 2019) in the heliospheric wind and CME evolution simulation EUHFORIA (Pomoell and Poedts, 2018), fits well with the data near the CME nose close to its axis but fails to predict the magnetic field in CME legs when these impact Earth (Scolini et al. 2019). Therefore, we implemented the FRi3D stretched flux-rope CME model (Isavnin, 2016) in EUHFORIA to model a more realistic CME geometry. Fri3D captures the three-dimensional magnetic field structure with parameters like skewing, pancaking and flattening that quantify deformations experienced by an interplanetary CME. We perform test runs of real CME events and validate the ability of FRi3D coupled with EUHFORIA in predicting the CME geo-effectiveness. We have modeled two real events with FRi3D. First, a CME event on 12 July 2012 which was a head-on encounter at Earth. Second, the flank CME encounter of 14 June 2012 which did not leave any magnetic field signature at Earth when modeled with Spheromak. We compare our results with the results from non-magnetized cone simulations and magnetized simulations employing the spheromak flux-rope model. We further discuss how constraining observational parameters using the stretched flux rope CME geometry in FRi3D affects the prediction of the magnetic field strength in our simulations, highlighting improvements and discussing future perspective.</p><p><em>This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405 (EUHFORIA 2.0)</em></p>

Studying the behavior of coronal mass ejections (CMEs) is important for both solar physics and space weather. The correlations of smoothed monthly mean daily integrated CME acceleration [ $a$ ], mass [ $M$ ], and the force [ $Ma$ ] to drive CMEs with sunspot activity [ $R_{\mathrm{I}}$ ] are analyzed for both slow and fast CMEs and for both Solar Cycles 23 and 24 separately. It is found that $a$ is inversely related to both $R_{\mathrm{I}}$ and $M$ . The correlation between $Ma$ and $R_{\mathrm{I}}$ for both slow and fast CMEs is negative at the rising phase of Solar Cycle 23 and positive otherwise. There is a sharp peak in $\gamma =Ma/R_{\mathrm{I}}$ near the solar minimum (December 2008) for both slow and fast CMEs. However, for fast CMEs, there is a sharp negative peak near the previous solar minimum (August 1996) and another positive peak near the current solar minimum (2019). The positive (negative) peak tends to be related to the solar minimum from a stronger (weaker) to a weaker (stronger) solar cycle. These results suggest that the CME acceleration depends more on the strength of solar activity than on the CME’s speed. Stronger magnetic activity may slow down the CMEs that are too massive or too fast and weaker activity may speed up the CMEs that are less massive or too slow. During a few years’ period of magnetic-field polarity reversal around the solar minimum, the force provided by large-scale magnetic-field structures may not be strong enough to constrain CME motions, leading to the “escape” of CMEs with large $|\gamma |$ .