Multiple shocks generated by the 2024 May 14 coronal mass ejection

The newly revised sunspot number series allows for placing historical geoeffective storms in the context of several hundred years of solar activity. Using statistical analyses of the Geostationary Operational Environmental Satellites (GOES) X-ray observations from the past ~30 years and the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) Coronal Mass Ejection (CME) catalog (1996-present), we present sunspot-number-dependent flare and CME rates. In particular, we present X-ray flare rates as a function of sunspot number for the past three cycles. We also show that the 1-8 AA X-ray background flux is strongly correlated with sunspot number across solar cycles. Similarly, we show that the CME properties (e.g., proxies related to the CME linear speed and width) are also correlated with sunspot number for SC 23 and 24. These updated rates will enable future predictions for geoeffective events and place historical storms in the context of present solar activity.

The trajectories of coronal mass ejection (CME) are often observed to deviate from radial propagation from the source while within the coronagraph field of view (\(\mbox{R} <15\,\mbox{--}\,30~\mbox{R}_{\mathrm{sun}}\)). To better understand nonradial propagation within the corona, we first analyze the trajectories of five CMEs for which both the source and 3D trajectory (latitude, longitude, and velocity) can be well determined from solar imaging observations, primarily using observations from the twin Solar TErrestrial RElations Observatory (STEREO) spacecraft. Next we analyze the cause of any nonradial propagation using a potential field source surface (PFSS) model to determine the direction of the magnetic pressure forces exerted on the CME at various heights in the corona. In two cases, we find that the CME deviation from radial propagation primarily occurs before it reaches the coronagraph field of view (below 1.5 solar radii). Based on the observations and the magnetic pressure forces calculated from the PFSS model, we conclude that for these cases the deviation is the result of strong active-region fields causing an initial asymmetric expansion of the CME that gives rise to the apparent rapid deflection and nonradial propagation from the source. Within the limitations of the PFSS model, the magnetic fields for all five cases appear to guide the CMEs out of the corona through the weak-field region around the heliospheric current sheet even when the current sheet is inclined and warped.

Ray-like features observed by coronagraphs in the wake of Coronal Mass Ejections (CMEs) are sometimes interpreted as the white light counterparts of current sheets (CSs) produced by the eruption. The 3D geometry of these ray-like features is largely unknown and its knowledge should clarify their association to the CS and place constraints on CME physics and coronal conditions. With this study we test these important implications for the first time. An example of such a post-CME ray was observed by various coronagraphs, including these of the SECCHI instrument suite of the STEREO twin spacecraft and the Large Angle Spectrometric Coronagraph LASCO onboard the Solar and Heliospheric Observatory (SOHO). The ray was observed in the aftermath of a CME which occurred on 9 April 2008. The twin STEREO spacecraft were separated by about degrees on that day. This significant separation combined with a third "eye" view supplied by LASCO allow for a truly multi-viewpoint observation of the ray and of the CME. We applied 3D forward geometrical modeling to the CME and to the ray as simultaneously viewed by SECCHI-A and B and by SECCHI-A and LASCO, respectively. We found that the ray can be approximated by a rectangular slab, nearly aligned with the CME axis, and much smaller than the CME in both terms of thickness and depth (~ 0.05 and 0.15 Rsun respectively). We found that the ray and CME are significantly displaced from the associated post-CME flaring loops. The properties and location of the ray are fully consistent with the expectations of the standard CME theories for post-CME current sheets. Therefore, our multi-viewpoint observations supply strong evidence that the observed post-CME ray is indeed related to a post-CME current sheet.

Context.Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs.Aims.To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon.Methods.Thetype II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory(STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary.Results.The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular withθBn~ 70°. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3–1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4–1.6.

We report results from the combined analysis of UV and radio observations of a CME-driven shock observed on 7 May 2004 above the southeast limb of the Sun at 1.86 R ⊙ with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO). The coronal mass ejection (CME) was first detected in white-light by the SOHO’s Large Angle and Spectrometric Coronagraph (LASCO) C2 telescope and shock-associated type II metric emission was recorded simultaneously by ground-based radio spectrographs. The shock speed (∼ 690 km s−1), as deduced from the analysis of the type II emission drift in the radio spectra and the pre-shock local electron density estimated with the diagnostics provided by UVCS observations of the O vi λλ 1031.9, 1037.6 doublet line intensities, is just a factor ∼ 0.1 higher than the CME speed inferred by means of the white-light (and EUV) data in the middle corona. The local magnetosonic speed, computed from a standard magnetic field model, was estimated as high as ∼ 600 km s−1, implying that the CME speed was probably just sufficient to drive a weak fast-mode MHD shock ahead of the front. Simultaneously with the type II radio emission, significant changes in the O vi doublet line intensities and profiles were recorded in the UVCS spectra and found compatible with abrupt post-shock plasma acceleration and modest ion heating. This work provides further evidence for the CME-driven origin of the shocks observed in the middle corona.

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.

We describe an empirical model to predict the 1‐AU arrival of coronal mass ejections (CMEs). This model is based on an effective interplanetary (IP) acceleration described by Gopalswamy et al. [2000b] that the CMEs are subject to, as they propagate from the Sun to 1 AU. We have improved this model (1) by minimizing the projection effects (using data from spacecraft in quadrature) in determining the initial speed of CMEs, and (2) by allowing for the cessation of the interplanetary acceleration before 1 AU. The resulting effective IP acceleration was higher in magnitude than what was obtained from CME measurements from spacecraft along the Sun‐Earth line. We evaluated the predictive capability of the CME arrival model using recent two‐point measurements from the Solar and Heliospheric Observatory (SOHO), Wind, and ACE spacecraft. We found that an acceleration cessation distance of 0.76 AU is in reasonable agreement with the observations. The new prediction model reduces the average prediction error from 15.4 to 10.7 hours. The model is in good agreement with the observations for high‐speed CMEs. For slow CMEs the model as well as observations show a flat arrival time of ∼4.3 days. Use of quadrature observations minimized the projection effects naturally without the need to assume the width of the CMEs. However, there is no simple way of estimating the projection effects based on the surface location of the Earth‐directed CMEs observed by a spacecraft (such as SOHO) located along the Sun‐Earth line because it is impossible to measure the width of these CMEs. The standard assumption that the CME is a rigid cone may not be correct. In fact, the predicted arrival times have a better agreement with the observed arrival times when no projection correction is applied to the SOHO CME measurements. The results presented in this work suggest that CMEs expand and accelerate near the Sun (inside 0.7 AU) more than our model supposes; these aspects will have to be included in future models.

To predict whether a coronal mass ejection (CME) will impact Earth, the\neffects of the background on the CME's trajectory must be taken into account.\nWe develop a model, ForeCAT (Forecasting a CME's Altered Trajectory), of CME\ndeflection due to magnetic forces. ForeCAT includes CME expansion, a three-part\npropagation model, and the effects of drag on the CME's deflection. Given the\nbackground solar wind conditions, the launch site of the CME, and the\nproperties of the CME (mass, final propagation speed, initial radius, and\ninitial magnetic strength), ForeCAT predicts the deflection of the CME. Two\ndifferent magnetic backgrounds are considered: a scaled background based on\ntype II radio burst profiles and a Potential Field Source Surface (PFSS)\nbackground. For a scaled background where the CME is launched from an active\nregion located between a CH and streamer region the strong magnetic gradients\ncause a deflection of 8.1 degrees in latitude and 26.4 degrees in longitude for\na 1e15 g CME propagating out to 1 AU. Using the PFSS background, which captures\nthe variation of the streamer belt position with height, leads to a deflection\nof 1.6 degrees in latitude and 4.1 degrees in longitude for the control case.\nVarying the CME's input parameters within observed ranges leads to the majority\nof CMEs reaching the streamer belt within the first few solar radii. For these\nspecific backgrounds, the streamer belt acts like a potential well that forces\nthe CME into an equilibrium angular position.\n

53 impulsive (38–315 keV) near‐relativistic solar electron events with beam‐like pitch‐angle distributions were observed by the ACE/EPAM experiment while the SOHO/LASCO coronographs were observing coronal mass ejections (CME) between 2.5 and 30 R⊙. Simnett, Roelof and Haggerty [in companion papers to be published in Ap. J., 2002] report a close association among the impulsive electron beams, solar electromagnetic emissions, and western hemisphere CMEs, jets, etc. They find that the electron injections are delayed ∼10 minutes after the electromagnetic emissions and ∼20 minutes after the CME launches, so that the electron release occurs when the CME has travelled 1–2 R⊙ beyond the CME launch altitude. The median exciter speed of the associated solar type III radio bursts (deduced from WIND/WAVES decametric spectrograms) is 0.08c, implying that the characteristic electron energies in the exciter front are only a few keV. Since no prompt near‐relativistic electrons are injected until ∼10 minutes after the type III burst, the energy spectrum of the type III associated electrons must be steep at these energies. Therefore the near‐relativistic electrons that must be present to produce the microwave and hard X‐ray bursts also do not escape promptly with intensities measurable by ACE/EPAM. Inverse correlation between the finite delays of near‐relativistic electrons after the CME launch confirms that the electrons are injected when the CMEs are ∼1–2 R⊙ above the photosphere. The positive correlation between CME speed and electron intensity (as well as spectral hardness) is consistent with the process of shock acceleration. Therefore we conclude that the simplest explanation of the observational associations is that the electrons are accelerated by CME‐driven shocks in the corona at altitudes ∼1–2 R⊙ above the photosphere. We see no reason why ions should not also be accelerated concurrently in the corona by this same process, although the final velocity of the ions may be less than that of the electrons.

Ground level events (GLEs) occupy the high-energy end of gradual solar energetic particle (SEP) events. They are associated with coronal mass ejections (CMEs) and solar flares, but we still do not clearly understand the special conditions that produce these rare events. During Solar Cycle 23, a total of 16 GLEs were registered, using ground-based neutron monitor data. We first ask if these GLEs are clearly distinguishable from other SEP events observed from space. Setting aside possible difficulties in identifying all GLEs consistently, we then try to find observables which may unmistakably isolate these GLEs by studying the basic properties of the associated eruptions and the active regions (ARs) that produced them. It is found that neither the magnitudes of the CMEs and flares nor the complexities of the ARs give sufficient conditions for GLEs. It is possible to find CMEs, flares or ARs that are not associated with GLEs but that have more extreme properties than those associated with GLEs. We also try to evaluate the importance of magnetic field connection of the AR with Earth on the detection of GLEs and their onset times. Using the potential field source surface (PFSS) model, a half of the GLEs are found to be well-connected. However, the GLE onset time with respect to the onset of the associated flare and CME does not strongly depend on how well-connected the AR is. The GLE onset behavior may be largely determined by when and where the CME-driven shock develops. We could not relate the shocks responsible for the onsets of past GLEs with features in solar images, but the combined data from the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) have the potential to change this for GLEs that may occur in the rising phase of Solar Cycle 24.

It is well known that coronal mass ejections (CMEs) are often associated with flares and filament eruptions. Previous studies of CMEs, however, have not established any association between CMEs and surges. In this paper, we present a detailed analysis of a large emerging flux region (EFR) surge and a jetlike CME, both observed on 1998 April 16. Our analysis shows a close temporal and spatial relationship between the two. Using observations from the Large Angle and Spectrometric Coronagraph (LASCO) and Hida Flare Monitoring Telescope (Hα, Hα ± 0.8 A), we found that the CME's onset time and central position angle were coincident with the surge features. Magnetograms and Hα filtergrams showed that the surge resulted from the successive emergence of a bipolar sunspot group, NOAA Active Region 8203, which was the only active region in the northern hemisphere. The surge was impulsively accelerated at around the peak time of the GOES SXR flux. The associated CME appeared in the field of view of LASCO C2 16 minutes after the surge disappeared. Importantly, observations from the EUV Imaging Telescope at λ195 A clearly demonstrate topological changes in the coronal field due to its interaction with the EFR. An initially closed EFR-loop system opened up during the surge. There was no filament involved in this surge-CME event. We propose that the onset of the CME resulted from the significant restructuring of the large-scale coronal magnetic field as a result of flux emergence in the active region. This surge-CME event strongly suggests that emerging flux may not only trigger a surge but also simultaneously trigger a CME by means of small-scale reconnection in the lower atmosphere.

Coronal mass ejections (CMEs) are massive solar eruptions, which have a significant impact on Earth. In this paper, we propose a new method, called DeepCME, to estimate two properties of CMEs, namely, CME mass and kinetic energy. Being able to estimate these properties helps better understand CME dynamics. Our study is based on the CME catalog maintained at the Coordinated Data Analysis Workshops Data Center, which contains all CMEs manually identified since 1996 using the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory. We use LASCO C2 data in the period between 1996 January and 2020 December to train, validate, and test DeepCME through 10-fold cross validation. The DeepCME method is a fusion of three deep-learning models, namely ResNet, InceptionNet, and InceptionResNet. Our fusion model extracts features from LASCO C2 images, effectively combining the learning capabilities of the three component models to jointly estimate the mass and kinetic energy of CMEs. Experimental results show that the fusion model yields a mean relative error (MRE) of 0.013 (0.009, respectively) compared to the MRE of 0.019 (0.017, respectively) of the best component model InceptionResNet (InceptionNet, respectively) in estimating the CME mass (kinetic energy, respectively). To our knowledge, this is the first time that deep learning has been used for CME mass and kinetic energy estimations.

A solar radio type II/type IV event with exceptionally low frequency flare continuum radiation was observed on May 2, 1998 with the Wind spacecraft. This flare continuum, associated with the type II burst (FCII), descended to 7.5 MHz (2.5–3 solar radii), the lowest frequency ever observed for this type of emission. It lasted for &gt;2 hours at 13.8 MHz. Simultaneous observations were made with ground‐based radiospectrographs, and with the Extreme Ultraviolet Imaging Telescope (EIT) and Large Angle and Spectrometric Coronagraph (LASCO) telescopes. The radio event consists of a group of intense type III bursts observed from 1000 MHz down to 0.03 MHz, the plasma frequency at 1 AU. The type II burst was recorded from 45 MHz down to 0.4 MHz, and an interplanetary shock was observed at 1 AU on May 4 at 0500 UT. The type II shock commenced within a few minutes of the flash phase of the flare and of the liftoff time of a coronal mass ejection (CME) observed by EIT and LASCO. The derived speeds of the type II shock, the CME in the plane of the sky, and the shock from the Sun to 1 AU are all ≈ 1000 km s−1. After estimating the liftoff time and radial speed of the CME front, we find that the type II shock and flare continuum were in the wake of the CME. This event shows evidence of acceleration of electrons in the corona out to 3 AS for ≳2 hours. Theoretical implications on the generation of the flare continuum radiation and its relation to the observed brightness temperature are considered. The source model of type II‐flare continuum of Robinson [1985], in which electrons are accelerated by the shock wave traversing CME expanding loops, is discussed in view of these observations.

In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre-Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO).

A large set of coronal mass ejections (CMEs, 3463) has been selected to study their periodic oscillations in speed in the Solar and Heliospheric Observatory (SOHO) mission’s Large Angle and Spectrometric Coronagraph (LASCO) field of view. These events, reported in the SOHO/LASCO catalog in the period of time 1996 – 2004, were selected based on having at least 11 height–time measurements. This selection criterion allows us to construct at least ten-point speed–distance profiles and evaluate kinematic properties of CMEs with a reasonable accuracy. To identify quasi-periodic oscillations in the speed of the CMEs a sinusoidal function was fitted to speed–distance profiles and the speed–time profiles. Of the considered events 22 % revealed periodic velocity fluctuations. These speed oscillations have on average amplitude equal to $87~\mbox{km}\,\mbox{s}^{-1}$ and period $7.8 R _{\odot}/241~\mbox{min}$ (in distance/time). The study shows that speed oscillations are a common phenomenon associated with CME propagation implying that all the CMEs have a similar magnetic flux-rope structure. The nature of oscillations can be explained in terms of magnetohydrodynamic (MHD) waves excited during the eruption process. More accurate detection of these modes could, in the future, enable us to characterize magnetic structures in space (space seismology).