Coronal Mass Ejections Speed Research Articles

Novel scaling laws to derive spatially resolved flare and CME parameters from sun-as-a-star observables

Coronal mass ejections (CMEs) are often associated with X-ray (SXR) flares powered by magnetic reconnection in the low corona, while the CME shocks in the upper corona and interplanetary (IP) space accelerate electrons often producing the type II radio bursts. The CME and the reconnection event are part of the same energy release process as highlighted by the correlation between reconnection flux ( that quantifies the strength of the released magnetic free energy during the SXR flare, and the CME kinetic energy that drives the IP shocks leading to type II bursts. Unlike the Sun, these physical parameters cannot be directly inferred in stellar observations. Hence, scaling laws between unresolved sun-as-a-star observables, namely SXR luminosity ( and type II luminosity ( and the physical properties of the associated dynamical events are crucial. Such scaling laws also provide insights into the interconnections between the particle acceleration processes across low-corona to IP space during solar-stellar "flare-CME-type II" events. Using long-term solar data in the SXR to radio waveband, we derived a scaling law between two novel power metrics for the flare and CME-associated processes. The metrics of "flare power" ( and "CME power" ( where is the CME speed, scale as propto pm0.04 $. In addition and show power-law trends with with indices of 1.12pm 0.05 and 0.61pm 0.05, respectively. These power laws help infer the spatially resolved physical parameters and from disk-averaged observables and during solar-stellar flare-CME-type II events.

Dependence of coronal mass ejections on the morphology and toroidal flux of their source magnetic flux ropes

Context. Coronal mass ejections (CMEs) stand as intense eruptions of magnetized plasma from the Sun, and they play a pivotal role in driving significant changes of the heliospheric environment. Deducing the properties of CMEs from their progenitors in solar source regions is crucial for space weather forecasting. Aims. The primary objective of this paper is to establish a connection between CMEs and their progenitors in solar source regions, enabling us to infer the magnetic structures of CMEs before their full development. Methods. We created a dataset comprising a magnetic flux rope series with varying projection shapes (S-, Z-, and toroid-shaped), sizes, and toroidal fluxes using the Regularized Biot-Savart Laws (RBSL). These flux ropes were inserted into solar quiet regions with the aim of imitating the eruptions of quiescent filaments. Thereafter, we simulated the propagation of these flux ropes from the solar surface to a distance of 25 R⊙ with our global coronal magnetohydrodynamic (MHD) model COCONUT. Results. Our parametric survey revealed significant impacts of source flux ropes on the consequent CMEs. Regarding the flux-rope morphology, we find that the projection shape (e.g., sigmoid or torus) can influence the magnetic structures of CMEs at 20 R⊙, albeit with minimal impacts on the propagation speed. However, these impacts diminish as source flux ropes become fat. In terms of toroidal flux, our simulation results demonstrate a pronounced correlation with the propagation speed of CMEs as well as the successfulness in erupting. Conclusions. This work builds the bridge between the CMEs in the outer corona and their progenitors in solar source regions. Our parametric survey suggests that the projection shape, cross-section radius, and toroidal flux of source flux ropes are crucial parameters in predicting magnetic structures and the propagation speed of CMEs, providing valuable insights for space weather prediction. On the one hand, the conclusion drawn here could be instructive in identifying the high-risk eruptions with the potential to induce stronger geomagnetic effects (Bz and propagation speed). On the other hand, our findings hold practical significance for refining the parameter settings of launched CMEs at 21.5 R⊙ in heliospheric simulations, such as with EUHFORIA, based on observations for their progenitors in solar source regions.

Revisiting empirical solar energetic particle scaling relations

Aims. The space radiation environment conditions and the maximum expected coronal mass ejection (CME) speed are assessed by investigating scaling laws between the peak proton flux and fluence of solar energetic particle (SEP) events with the speed of the CMEs. Methods. We used a complete catalog of SEP events, covering the last ∼25 years of CME observations (i.e., 1997–2017). We calculated the peak proton fluxes and integrated event fluences for events that reached an integral energy of up to E > 100 MeV. For a sample of 38 strong SEP events, we first investigated the statistical relations between the recorded peak proton fluxes (IP) and fluences (FP) at a set of integral energies of E > 10 MeV, E > 30 MeV, E > 60 MeV, and E > 100 MeV versus the projected CME speed near the Sun (VCME) obtained by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO). Based on the inferred relations, we further calculated the integrated energy dependence of both IP and FP, assuming that they follow an inverse power law with respect to energy. By making use of simple physical assumptions, we combined our derived scaling laws to estimate the upper limits for VCME, IP, and FP by focusing on two cases of known extreme SEP events that occurred on 23 February 1956, (GLE05) and in AD774/775, respectively. Based on the physical constraints and assumptions, several options for the upper limit VCME associated with these events were investigated. Results. A scaling law relating IP and FP to the CME speed as VCME5 for CMEs ranging between ∼3400–5400 km/s is consistent with values of FP inferred for the cosmogenic nuclide event of AD774/775. At the same time, the upper CME speed that the current Sun can provide possibly falls within an upper limit of VCME ≤ 5500 km/s.

A treatment of the all-clear problem for solar energetic particle events and subsequent decision making

We discuss the relatively overlooked problem of All Clear in Solar Energetic Particle (SEP) event prediction. These proton and heavier ion events are injected in major solar eruptions, propagate directionally into the heliosphere at relativistic speeds and threaten equipment and personnel at low-Earth orbit and beyond. SEPs are rare to extreme events associated with solar flares and coronal mass ejections (CMEs), with one SEP event detected in-situ every several hundreds of flares and CMEs observed remotely. This abysmal overall association improves drastically to below 1:2 for fast (i.e., shock-fronted) and halo (i.e., propagating mainly along the Sun–Earth line) CMEs. All Clear implies an assessment of tolerable conditions within a preset prediction window. Relying on one of the most comprehensive data sets for SEP events, we implement a methodology that provides an All Clear for events of NOAA severity S1 and above (S1+) and identify the minimal eruption attributes (flare size and CME speed) that could give rise to such SEP events from source locations in the Sun. The results correspond to and reflect settings of minimum complexity, giving rise to different attributes for different longitudinal zones in the earthward solar hemisphere. This work presents proof of concept; complexity can be increased at will for more demanding All Clear definitions, subject only to sufficient statistics due to the scarcity of the phenomenon. At this point, feedback is desired from stakeholders on what fits their definition of All Clear (we expect different definitions from different operators), so that to define the precise settings on which to run this and similar exercises.

Characterizing High-Energy Solar Proton Events with Energies Below and Above 100 MeV

We analyzed 58 high-energy proton events that occurred during the years 1996 – 2022. In 32 out of the 58 (55%) events, the proton energies extended up to ∼68\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\sim 68$\\end{document} MeV but did not reach 100 MeV. In the remaining 26 events, the proton energies exceeded 100 MeV. We studied the differences in the characteristics of these proton events and their associations with solar and interplanetary phenomena to improve understanding proton sources and acceleration processes.The coronal mass ejections (CMEs) associated with >100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$>100$\\end{document} MeV proton events appeared to be, on average, more energetic than those associated with <100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$< 100$\\end{document} MeV proton events. The peak and integrated fluxes (fluence) of the soft X-ray (SXR) flares were higher in > 100 MeV proton events, but there was almost no difference in the rise times of the flares. In a major part of the >100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$> 100$\\end{document} MeV proton events, protons were released over the rise phase of the SXR flares, whereas in most of the <100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$<100$\\end{document} MeV events the proton releases occurred after the peak of the SXR flares. We established limits for the CME speed VCME and SXR peak flux Fpk or total fluence Fi, which helped us to distinguish the events in the two groups. Solar eruptions with VCME>1000\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$> 1000$\\end{document} km s−1 and F>pk5⋅10−5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$_{\\mathrm{pk}} > 5 \\cdot 10^{-5} $\\end{document} W m−2 had a high probability to produce proton events of >100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$> 100$\\end{document} MeV. On the other hand, eruptions with V>CME900\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$_{\\mathrm{CME}} > 900$\\end{document} km s−1 and F<i5⋅10−4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$_{i} <5 \\cdot 10^{-4} $\\end{document} J m−2 and eruptions with V<CME900\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$_{ \\mathrm{CME}} < 900$\\end{document} km s−1 irrespective of the SXR total fluence were very likely to produce proton events of <100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$< 100$\\end{document} MeV.All proton events were associated with decametric Type III radio bursts, and most of them had Type II bursts associations either in metric or decametric–hectometric (DH) wavelengths or both. Both metric- and DH-Type II emissions were observed in 50% of <100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$<100$\\end{document} MeV proton events while they were observed in 88% of >100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$>100$\\end{document} MeV events. Our analysis showed that protons in most of the >100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$>100$\\end{document} MeV events were released low in the corona (≤3.0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\leq 3.0$\\end{document} R⊙) before the onsets of the DH-Type II radio bursts. Conversely, protons in most of the <100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$<100$\\end{document} MeV events were released higher in the corona (>3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$>3$\\end{document} R⊙) and after the DH-Type II onsets.We conclude that protons in most of the >100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$> 100$\\end{document} MeV events are accelerated either by the flare reconnection processes or by shocks low in the corona and could undergo reacceleration higher in the corona in CME shocks manifested in DH-Type II radio emission. In the <100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$<100$\\end{document} MeV events, protons are mainly accelerated in CME shocks at coronal heights >3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$>3$\\end{document} R⊙.

Interplanetary Type IV Solar Radio Bursts: A Comprehensive Catalog and Statistical Results

Decameter hectometric (DH; 1–14 MHz) type IV radio bursts are produced by flare-accelerated electrons trapped in postflare loops or the moving magnetic structures associated with the coronal mass ejections (CMEs). From a space weather perspective, it is important to systematically compile these bursts, explore their spectrotemporal characteristics, and study the associated CMEs. We present a comprehensive catalog of DH type IV bursts observed by the Radio and Plasma Wave Investigation instruments on board the Wind and Solar TErrestrial RElations Observatory spacecraft covering the period of white-light CME observations by the Large Angle and Spectrometric Coronagraph on board the Solar and Heliospheric Observatory mission between 1996 November and 2023 May. The catalog has 139 bursts, of which 73% are associated with a fast (>900 km s−1) and wide (>60°) CME, with a mean CME speed of 1301 km s−1. All DH type IV bursts are white-light CME-associated, with 78% of the events associated with halo CMEs. The CME source latitudes are within ±45°. Seventy-seven events had multiple-vantage-point observations from different spacecraft, letting us explore the impact of the line of sight on the dynamic spectra. For 48 of the 77 events, there were good data from at least two spacecraft. We find that, unless occulted by nearby plasma structures, a type IV burst is best viewed when observed within a ±60° line of sight. Also, bursts with a duration above 120 minutes have source longitudes within ±60°. Our inferences confirm the inherent directivity in the type IV emission. Additionally, the catalog forms a Sun-as-a-star DH type IV burst database.

Solar Eruptive Phenomena Associated with Solar Energetic Electron Spectral Types

The energy spectral shape of solar energetic electron events carries important information on the energetic electron source/acceleration at the Sun. We investigate the association of six newly identified solar energetic electron spectral types with solar eruptive phenomena, including the downward double-power-law (DDPL) spectrum with break energy E B above 20 keV (DDPL EB≥20keV ), DDPL with E B below 20 keV (DDPL EB<20keV ), upward double-power law (UDPL), single-power-law (SPL), Ellision–Ramaty–like (ER), and logarithmic-parabola (LP). We find that the SPL type shows (the other five types show) an association with hard X-ray flares of ∼38% (∼55%–82%) and an association with west-limb coronal mass ejections (CMEs) of ∼76% (∼85%–93%). Among the other five types, the DDPL EB<20keV and ER (LP and DDPL EB≥20keV ) types only have an association with type II radio bursts of ∼7%–8% (∼16%–20%) and an association with halo CMEs of ∼5%–9% (∼11%–21%); however, the UDPL type exhibits a significant (∼47% and ∼50%) association with type II bursts and halo CMEs, with a significantly faster median CME speed of 1000−120+550 km s−1. For DDPL EB≥20keV (DDPL EB<20keV ) with a positive (no) correlation between spectral indexes and no (a positive) correlation between the spectral index and break energy, the spectrum appears to be flatter as the associated CME (flare) becomes faster (stronger). These results suggest that the SPL type can result from the initial acceleration process that likely occurs high in the corona, and then provide seed populations for further acceleration processes to form the other five types: the DDPL EB<20keV and ER types via flare-related processes, the LP and DDPL EB≥20keV types via CME-related processes, and the UDPL type via CME-driven shocks.

Coronal dimming parameters and their variations in the 24th solar cycle

We analyzed coronal dimming parameters and their relation to coronal mass ejections to determine the location of possible ejections sources on the solar disk in the 24th solar cycle. We used Solar Demon database that contains flares and dimmings parameters obtained from SDO/AIA image. Coronal mass ejections from the CACTus database were associated with 16% of all the dimmings for the period 2010–2018. On average, dimmings associated with coronal mass ejections are events with large absolute parameter values. Correlation coefficient between dimming position angle and associated coronal mass ejection position angle is 0.96. Correlation coefficients between the coronal mass ejection speed and dimming parameters are close to 0.5 for dimmings in the central region of the solar disk. Obtained results can be used to model coronal mass ejections propagation and to define the probability of their arrival in near-Earth space.

Correcting Projection Effects in CMEs Using GCS‐Based Large Statistics of Multi‐Viewpoint Observations

AbstractThis study addresses the limitations of single‐viewpoint observations of Coronal Mass Ejections (CMEs) by presenting results from a 3D catalog of 360 CMEs during solar cycle 24, fitted using the Graduated Cylindrical Shell (GCS) model. The data set combines 326 previously analyzed CMEs and 34 newly examined events, categorized by their source regions into active region (AR) eruptions, active prominence (AP) eruptions, and prominence eruptions (PE). Estimates of errors are made using a bootstrapping approach. The findings highlight that the average 3D speed of CMEs is ∼1.3 times greater than the 2D speed. PE CMEs tend to be slow, with an average speed of 432 km s−1. AR and AP speeds are higher, at 723 and 813 km s−1, respectively, with the latter having fewer slow CMEs. The distinctive behavior of AP CMEs is attributed to factors like overlying magnetic field distribution or geometric complexities leading to less accurate GCS fits. A linear fit of projected speed to width gives a gradient of ∼2 km s−1 deg−1, which increases to 5 km s−1 deg−1 when the GCS‐fitted ‘true’ parameters are used. Notably, AR CMEs exhibit a high gradient of 7 km s−1 deg−1, while AP CMEs show a gradient of 4 km s−1 deg−1. PE CMEs, however, lack a significant speed‐width relationship. We show that fitting multi‐viewpoint CME images to a geometrical model such as GCS is important to study the statistical properties of CMEs, and can lead to a deeper insight into CME behavior that is essential for improving future space weather forecasting.

A Comparative Study of Ground-level Enhancement Events of Solar Energetic Particles

Major solar eruptions can accelerate protons up to relativistic energies. Solar relativistic ions arriving at 1 au may cause a solar particle event detectable by the worldwide network of neutron monitors (NMs), a ground-level enhancement (GLE) event. Using the newly computed NM yield function, we have fitted the 15 historic GLEs. Moments of the fitted proton distributions are used for the analysis. Profiles of the proton net flux are very diverse, while some profiles are similar. For this study, we select two events with similar time profiles, GLE 60 (2001 April 15) and GLE 65 (2003 October 28), and ask what makes these GLEs similar. We compare the GLEs with their progenitor solar flares and coronal mass ejections (CMEs). We find a close relationship between the rise and peak of the GLE, on the one hand, and the solar flare and the metric radio emissions from extended coronal sources at the base of the CME, on the other hand. The GLE decay time, the rate of the proton spectrum evolution, and the CME speed are proportional to the duration of the soft X-ray flare. We compare the two GLEs with GLE 59 (2000 July 14) analyzed by Klein et al. and with the deka-MeV nucleon−1 proton and helium data from the ERNE instrument on the Solar and Heliospheric Observatory spacecraft. The comparison indicates that a single solar eruption can produce more than one component of solar energetic particles, differently contributing at different energies and locations.

Eruption of prominence initiated by loss of equilibrium: multipoint observations

ABSTRACT Using the SDO/AIA, SOHO/LASCO, STEREO/SECCHI, and ground-based H α, radio observations, we studied a prominence eruption (PE) from the western limb that occurred on 2013 December 4. PE is associated with a moderate coronal mass ejection (CME) and GOES class C4.7 flare. Before a couple of days, the prominence pre-existed as an inverse-S shaped filament lying above fragmented opposite polarities between two active regions. Initially, the prominence appears as kinked or writhed as observed from different vantage points. From a careful study of magnetic field observations, we infer that the flux emergence at one leg of the prominence causes the loss of equilibrium which then initiates the slow upward motion of the prominence followed by onset of the eruption at a projected height of 35 Mm. The fast rise motion is also in synchronization with the flare impulsive phase but the average acceleration is quite small (150 ms−2) compared to strong flare cases. In the LASCO field of view (FOV), the CME continues to accelerate at 3 ms−2 attaining a speed of 450 km s−1 at 16 R⊙. In the extended STEREO-A FOV upto 38 R⊙, the CME decelerates 0.82 m s−2. The PE launched type III bursts delayed by 14 min with respect to the flare peak time (04:58 UT). Since the prominence is lying in the fragmented polarities, it is likely that the sheared arcade has little contribution to the poloidal flux of the rising magnetic flux rope and subsequently weak flare is recorded. This study of PE emphasizes the influence of the magnetic reconnection on the CME speed, launch of type II, III burst, and the CME propagation distance farther away from the Sun.

Three-dimensional relation between coronal dimming, filament eruption, and CME

Context.Coronal dimmings are localized regions of reduced emission in the extreme-ultraviolet (EUV) and soft X-rays formed as a result of the expansion and mass loss by coronal mass ejections (CMEs) low in the corona. Distinct relations have been established between coronal dimmings (intensity, area, magnetic flux) and key characteristics of the associated CMEs (mass and speed) by combining coronal and coronagraphic observations from different viewpoints in the heliosphere.Aims.We investigate the relation between the spatiotemporal evolution of the dimming region and both the dominant direction of the filament eruption and CME propagation for the 28 October 2021 X1.0 flare/CME event observed from multiple viewpoints in the heliosphere by Solar Orbiter, STEREO-A, SDO, and SOHO.Methods.We present a method for estimating the dominant direction of the dimming development based on the evolution of the dimming area, taking into account the importance of correcting the dimming area estimation by calculating the surface area of a sphere for each pixel. To determine the propagation direction of the flux rope during early CME evolution, we performed 3D reconstructions of the white-light CME by graduated cylindrical shell modeling (GCS) and 3D tie-pointing of the eruptive filament.Results.The dimming evolution starts with a radial expansion and later propagates more to the southeast. The orthogonal projections of the reconstructed height evolution of the prominent leg of the erupting filament onto the solar surface are located in the sector of the dominant dimming growth, while the orthogonal projections of the inner part of the GCS reconstruction align with the total dimming area. The filament reaches a maximum speed of ≈250 km s−1at a height of about ≈180 Mm before it can no longer be reliably followed in the EUV images. Its direction of motion is strongly inclined from the radial direction (64° to the east, 32° to the south). The 3D direction of the CME and the motion of the filament leg differ by 50°. This angle roughly aligns with the CME half-width obtained from the CME reconstruction, suggesting a relation between the reconstructed filament and the associated leg of the CME body.Conclusions.The dominant propagation of the dimming growth reflects the direction of the erupting magnetic structure (filament) low in the solar atmosphere, though the filament evolution is not directly related to the direction of the global CME expansion. At the same time, the overall dimming morphology closely resembles the inner part of the CME reconstruction, validating the use of dimming observations to obtain insight into the CME direction.

Exploring the impact of imaging cadence on inferring CME kinematics

The kinematics of coronal mass ejections (CMEs) are crucial for understanding their initiation mechanism and predicting their impact on Earth and other planets. With most of the acceleration and deceleration occurring below 4 R⊙, capturing this phase is vital to better understand their initiation mechanism. Furthermore, the kinematics of CMEs in the inner corona (&lt; 3 R⊙) are closely related to their propagation in the outer corona and their eventual impact on Earth. Since the kinematics of CMEs are mainly probed using coronagraph data, it is crucial to investigate the impact of imaging cadence on the precision of data analysis and the conclusions drawn from it and also for determining the flexibility of designing observational campaigns with upcoming coronagraphs. This study investigates the impact of imaging cadence on the kinematics of ten CMEs observed by the K-Coronagraph of the Mauna Loa Solar Observatory. We manually track the CMEs using high cadence (15 s) white-light observations of K-Cor and vary the cadence as 30 s, 1, 2, and 5 min to study the impact of cadence on the kinematics. We also employed the bootstrapping method to estimate the confidence interval of the fitting parameters. Our results indicate that the average velocity of the CMEs does not have a high dependence on the imaging cadence, while the average acceleration shows significant dependence on the same, with the confidence interval showing significant shifts for the average acceleration for different cadences. The impact of degraded cadence is also seen in the estimation of the time of onset of acceleration. We further find that it is difficult to find an optimum cadence to study all CMEs, as it is also influenced by the pixel resolution of the instrument and the speed of the CME. However, except for very slow CMEs (speeds less than 300 km−1), our results indicate a cadence of 1 min to be reasonable for the study of their kinematics. The results of this work will be important in the planning of observational campaigns for the existing and upcoming missions that will observe the inner corona.

Speed and Acceleration of Coronal Mass Ejections Associated with Sustained Gamma-Ray Emission Events Observed by Fermi/LAT

The sustained gamma-ray emission (SGRE) from the Sun is a prolonged enhancement of >100 MeV gamma-ray emission that extends beyond the flare impulsive phase. The origin of the >300 MeV protons resulting in SGRE is debated, with both flares and shocks driven by coronal mass ejections (CMEs) being the suggested sites of proton acceleration. We compared the near-Sun acceleration and space speed of CMEs with “Prompt” and “Delayed” (SGRE) gamma-ray components. We found that “Delayed”-component-associated CMEs have higher initial accelerations and space speeds than “Prompt Only”-component-associated CMEs. We selected halo CMEs (HCMEs) associated with type II radio bursts (shock-driving HCMEs) and compared the average acceleration and space speed between HCME populations with or without SGRE events, major solar energetic particle (SEP) events, metric, or decameter-hectometric (DH) type II radio bursts. We found that the SGRE-producing HCMEs associated with a DH type II radio burst and/or a major SEP event have higher space speeds and especially initial accelerations than those without an SGRE event. We estimated the radial distances and speeds of the CME-driven shocks at the end time of the 2012 January 23 and March 7 SGRE events using white-light images of STEREO Heliospheric Imagers and radio dynamic spectra of Wind WAVES. The shocks were at the radial distances of 0.6–0.8 au and their speeds were high enough (≈975 km s−1 and ≈750 km s−1, respectively) for high-energy particle acceleration. Therefore, we conclude that our findings support the CME-driven shock as the source of >300 MeV protons.

Response of the Ionospheric Total Electron Content During St. Patrick's Day Geomagnetic Storm in 2015 over the Philippine-Taiwan Region

The ionospheric total electron content (TEC) response during the St. Patrick's Day geomagnetic storm of 2015 (max Kp = 8) is an interest of study in the field of space weather since it is the strongest geomagnetic storm of Solar Cycle 24. The cause of this storm is a coronal mass ejection (CME) from the Sun on 15 Mar 2015 recorded by SOHO/LASCO and arrived at ~ 05:00 UT 17 Mar 2015. The CME speed is estimated at ~ 668 km/s. At the initial phase of the storm, the disturbance storm time (Dst) index rose from 15 nanoteslas nT at 03:21–56 nT at 05:31 UT. The main phase of the storm caused the Dst index to drop to the minimum value of –223 nT from 05:31–22:33 UT on 17 Mar 2015. In the Philippine-Taiwan sector, TEC during the main phase was enhanced by ~ 25 TECU on 10 GNSS receiver stations and was depleted afterward with a maximum depletion of ~ 33 TECU on PBAS. The recovery phase showed a TEC depletion on all stations for the whole day. The minimum dTEC (differential TEC) is observed at PBAS (Basco, Batanes, Philippines), and the maximum percent depletion is observed at TWTF (Taoyuan, Taiwan) during the early hours of photoionization. Results from this study verified that GNSS TEC measurements along Asian sectors dropped significantly during St. Patrick's geomagnetic storm.

Solar active region magnetic parameters and their relationship with the properties of halo coronal mass ejections

The coronal mass ejections (CMEs) from the sun consist of the plasma and strong magnetic fields (∼4–5 G at 1.3 R⊙) and generally, the fast CMEs are often associated with energetic particles of energy few hundreds of MeV. When the fast CMEs are ejected towards the Earth, they can disrupt the flow of solar wind in the heliosphere and impact the Earth's magnetosphere causing known space weather phenomena such as, geomagnetic storms, auroras, communication blackouts, satellite drag and failures. In this work, we have investigated a set of 60 halo coronal mass ejections (CMEs) associated with X-ray flares (≥C1.0) observed in 49 active regions during the period 2010–2016 in solar cycle 24. The X-ray flares and white light CMEs were observed by Geostationary Operational Environmental Satellite (GOES) and the Large Angle Spectrometric Coronagraph (LASCO) coronagraph on the Solar and Heliospheric Observatory (SOHO) satellite, respectively. The active region magnetic properties are obtained from Space - weather HMI Active Region Patch (SHARP) parameters for this set of events. For each active region (AR), the mean value is calculated from a 1-day time series for each of the 16 photospheric magnetic parameters extracted from the vector magnetogram products at a 12-min cadence. The dependency of flare flux and CME kinematics properties on the active region magnetic properties is further confirmed through correlation studies. As a result, we found a moderate to strong correlation value for flare flux and halo CME kinematic properties (like linear speed, space speed and kinetic energy) among the seven (USFLUX, TOTUSJZ, TOTUSJH, ABSNJZH, SAVNCPP, TOTPOT and MEANJZH) SHARP parameters. Most of the events (≥73%) were produced by βγδ, βγ and βδ Hale - type sunspot groups and Ekc/Dkc/Fkc McIntosh sunspot classes. It reveals that the most complex active regions are feasible sources of strong flare-associated halo CME productivity. The front side halo CME kinematic properties depend more on the vertical current helicity and polarity magnetic parameters than the other magnetic parameters. In addition, the flare intensity and speed of CME, calculated using an empirical model with the active region magnetic parameters, are found nearly equal to the observed values. This result will be useful to identify the important magnetic parameters for modelling the occurrence of flare-associated halo CMEs and to understand the physical relationship between them.

Solar activity relations in energetic electron events measured by the MESSENGER mission

Aims. We perform a statistical study of the relations between the properties of solar energetic electron (SEE) events measured by the MESSENGER mission from 2010 to 2015 and the parameters of the respective parent solar activity phenomena in order to identify the potential correlations between them. During the time of analysis, the MESSENGER heliocentric distance varied between 0.31 and 0.47 au. Methods. We used a published list of 61 SEE events measured by MESSENGER, which includes information on the near-relativistic electron peak intensities, the peak-intensity energy spectral indices, and the measured X-ray peak intensity of the flares related to the SEE events. Taking advantage of multi-viewpoint remote-sensing observations, we reconstructed, whenever possible, the associated coronal mass ejections (CMEs) and shock waves; and we determined the three-dimensional (3D) properties (location, speed, and width) of the CMEs and the maximum speed of the 3D CME-driven shocks in the corona. We used different methods (Spearman, Pearson, and a Bayesian approach, namely the Kelly method to linear regression) to estimate the correlation coefficients between the flare intensity, maximum speed at the apex of the CME-driven shock, CME speed at the apex, and CME width with the electron peak intensities and with the energy spectral indices. In this statistical study, we considered and addressed the limitations of the particle instrument on board MESSENGER (elevated background intensity level, anti-Sun pointing). Results. There is an asymmetry to the east in the range of connection angles (CAs) for which the SEE events present the highest peak intensities, where the CA is the longitudinal separation between the footpoint of the magnetic field connecting to the spacecraft and the flare location. Based on this asymmetry, we define a subsample of well-connected events as when −65° ≤ CA ≤ +33°. For the well-connected sample, we find moderate to strong correlations between the near-relativistic electron peak intensity and the 3D CME-driven shock maximum speed at the apex (Spearman: cc = 0.53 ± 0.05; Pearson: cc = 0.65 ± 0.04; Kelly: cc = 0.87 ± 0.20), the flare peak intensity (Spearman: cc = 0.63 ± 0.03; Pearson: cc = 0.59 ± 0.03; Kelly: cc = 0.74 ± 0.30), and the 3D CME speed at the apex (Spearman: cc = 0.50 ± 0.04; Pearson: cc = 0.46 ± 0.03; Kelly: cc = 0.60 ± 0.39). When including poorly connected events (full sample), the relations between the peak intensities and the solar-activity phenomena are blurred, showing lower correlation coefficients. Conclusions. Based on the comparison of the correlation coefficients presented in this study using near 0.4 au data, (1) both flare and shock-related processes may contribute to the acceleration of near relativistic electrons in large SEE events, in agreement with previous studies based on near 1 au data; and (2) the maximum speed of the CME-driven shock is a better parameter to investigate particle-acceleration-related mechanisms than the average CME speed, as suggested by the stronger correlation with the SEE peak intensities.

SIR‐HUXt—A Particle Filter Data Assimilation Scheme for CME Time‐Elongation Profiles

AbstractWe present SIR‐HUXt, the integration of a sequential importance resampling data assimilation scheme with the HUXt solar wind model. SIR‐HUXt assimilates the time‐elongation profiles of Coronal Mass Ejection (CME) fronts in the low heliosphere, like those extracted from heliospheric imager (HI) data. Observing System Simulation Experiments are used to explore SIR‐HUXt's performance for a simple synthetic CME scenario of an Earth directed CME in a uniform solar wind, where the CME is initialized with the average CME speed and width. These experiments are performed for a range of observer locations, from 20° to 90° behind Earth, spanning the L5 point where ESA's Vigil mission will return HI data for operational space weather forecasting. For this idealized scenario, SIR‐HUXt performs well at constraining the CME speed, and has some success at constraining the CME longitude while the CME width is largely unconstrained by SIR‐HUXt. Rank‐histograms suggest the SIR‐HUXt ensembles are well calibrated, with no indications of bias or under/over dispersion. Improved constraints on the initial CME speed lead to improvements in the CME transit time and arrival speed. For an L5 observer, SIR‐HUXt reduced the transit time and arrival speed uncertainties by 69% and 63%. Therefore, SIR‐HUXt could improve the real‐world representivity of HUXt simulations and reduce the uncertainty of CME arrival time forecasts. The idealized scenario studied here likely enhances SIR‐HUXt's performance relative to the challenge of simulating real‐world CMEs and solar wind conditions. Future work should validate SIR‐HUXt with case studies of real CMEs in structured solar wind.

Parameter Study of Geomagnetic Storms and Associated Phenomena: CME Speed De-Projection vs. In Situ Data

In this study, we give correlations between the geomagnetic storm (GS) intensity and parameters of solar and interplanetary (IP) phenomena. We also perform 3D geometry reconstructions of geo-effective coronal mass ejections (CMEs) using the recently developed PyThea framework and compare on-sky and de-projected parameter values, focusing on the reliability of the de-projection capabilities. We utilize spheroid, ellipsoid and graduated cylindrical shell models. In addition, we collected a number of parameters of the GS-associated phenomena. A large variation in 3D de-projections is obtained for the CME speeds depending on the selected model for CME reconstruction and observer subjectivity. A combination of fast speed and frontal orientation of the magnetic structure upon its arrival at the terrestrial magnetosphere proves to be the best indicator for the GS strength. More reliable estimations of geometry and directivity, in addition to de-projected speeds, are important for GS forecasting in operational space weather schemes.

Parametric study of the kinematic evolution of coronal mass ejection shock waves and their relation to flaring activity

Context.Coronal and interplanetary shock waves produced by coronal mass ejections (CMEs) are major drivers of space-weather phenomena, inducing major changes in the heliospheric radiation environment and directly perturbing the near-Earth environment, including its magnetosphere. A better understanding of how these shock waves evolve from the corona to the interplanetary medium can therefore contribute to improving nowcasting and forecasting of space weather. Early warnings from these shock waves can come from radio measurements as well as coronagraphic observations that can be exploited to characterise the dynamical evolution of these structures.Aims.Our aim is to analyse the geometrical and kinematic properties of 32 CME shock waves derived from multi-point white-light and ultraviolet imagery taken by the Solar Dynamics Observatory (SDO), Solar and Heliospheric Observatory (SoHO), and Solar-Terrestrial Relations Observatory (STEREO) to improve our understanding of how shock waves evolve in 3D during the eruption of a CME. We use our catalogue to search for relations between the shock wave’s kinematic properties and the flaring activity associated with the underlying genesis of the CME piston.Methods.Past studies have shown that shock waves observed from multiple vantage points can be aptly reproduced geometrically by simple ellipsoids. The catalogue of reconstructed shock waves provides the time-dependent evolution of these ellipsoidal parameters. From these parameters, we deduced the lateral and radial expansion speeds of the shocks evolving over time. We compared these kinematic properties with those obtained from a single viewpoint by SoHO in order to evaluate projection effects. Finally, we examined the relationships between the shock wave and the associated flare when the latter was observed on the disc by considering the measurements of soft and hard X-rays.Results.We find that at around 25 solar radii (R⊙), the shape of a shock wave is very spherical, with a ratio between the lateral and radial dimensions (minor radii) remaining at aroundb/a ≈ 1.03 and a radial to lateral speed ratio (VR/VL)≈1.44. The CME starts to slow down a few tens of minutes after the first acceleration and then propagates at a nearly constant speed. We revisit past studies that show a relation between the CME speed and the soft X-ray emission of the flare measured by the Geostationary Operational Environmental Satellite (GOES) and extend them to higher flare intensities and shock speeds. The time lag between the peak of the flare and of the CME speed is up to a few tens of minutes. We find that for several well-observed shock onsets, a clear correlation is visible between the derivative of the soft X-ray flux and the acceleration of the shock wave.