Kinematics Of Coronal Mass Ejections Research Articles

Probing Velocity Dispersion Inside Coronal Mass Ejections: New Insights on Their Initiation

This work studies the kinematics of the leading edge and the core of six coronal mass ejections (CMEs) in the combined field of view of Sun Watcher using Active Pixel System detector and Image Processing (SWAP) on board PRoject for On-Board Autonomy (PROBA-2) and the ground-based K-Cor coronagraph of the Mauna Loa Solar Observatory. We report, for the first time, on the existence of a critical height hc , which marks the onset of velocity dispersion inside the CME. This height for the studied events lies between 1.4 and 1.8 R ⊙, in the inner corona. We find the critical heights to be relatively higher for gradual CMEs, as compared to impulsive ones, indicating that the early initiation of these two classes might be different physically. We find several interesting imprints of the velocity dispersion on CME kinematics. The critical height is strongly correlated with the flux-rope minor radius and the mass of the CME. Also, the magnitude of the velocity dispersion shows a reasonable positive correlation with the above two parameters. We believe these results will advance our understanding of CME initiation mechanisms and will help provide improved constraints on CME initiation models.

Multi-instrument observations and tracking of a coronal mass ejection front from low to middle corona

The shape and dynamics of coronal mass ejections (CMEs) vary significantly based on the instrument and wavelength used. This has led to significant debate about the proper definitions of CME/shock fronts, pile-up/compression regions, and core observations in projection in optically thin vs. optically thick emission. Here we present an observational analysis of the evolving shape and kinematics of a large-scale CME that occurred on May 7, 2021 on the eastern limb of the Sun as seen from 1 AU. The eruption was observed continuously, consecutively by the Atmospheric Imaging Assembly (AIA) telescope suite on the Solar Dynamics Observatory (SDO), the ground-based COronal Solar Magnetism Observatory (COSMO) K-coronagraph (K-Cor) on Mauna Loa, and the C2 and C3 telescopes of the Large Angle Solar Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SoHO). We apply the updated multi-instrument version of the recently developed Wavetrack Python suite for automated detection and tracking of coronal eruptive features to evaluate and compare the evolving shape of the CME front as it propagated from the solar surface out to 20 solar radii. Our tool allows tracking features beyond just the leading edge and is an important step towards semi-automatic manufacturing of training sets for training data-driven image segmentation models for solar imaging. Our findings confirm the expected strong connection between EUV waves and CMEs. Our novel, detailed analysis sheds observational light on the details of EUV wave-shock-CME relations that lacking for the gap region between the low and middle corona.

SoloHI observations of coronal mass ejections observed by multiple spacecraft

Context. The Solar Orbiter Heliospheric Imager (SoloHI) instrument of the Solar Orbiter mission is a next-generation heliospheric imager. New observations from SoloHI demonstrate the improved spatial and temporal resolution compared to previous observations of the heliosphere and corona. At perihelion, the field of view (FoV) of SoloHI covers the transition between the coronagraph (COR2) and heliospheric imager (HI1) Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite. In this paper, we focus on an active solar period following the first Solar Orbiter science perihelion that resulted in a number of well-observed large coronal mass ejections (CMEs) in SoloHI data in March and April 2022. Specifically, we highlight a series of events produced by AR12795 between 28 March and 2 April and show overlapping observations with SECCHI/COR2 and HI1 and LASCO/C3. Aims. We compare the performance of the SoloHI instrument against similar observations from 1 au imagers. We describe CME observations, highlighting the unique structural features captured within the SoloHI FoV. These observations demonstrate that SoloHI will provide new insights into CME morphology and evolution from a unique vantage point. Methods. To provide a direct and relevant comparison, images from all the telescopes we used in the paper are presented in FoVs common to each and with minimal processing applied. The J-maps we used to highlight outflowing features are also presented to show that the CME kinematics can be tracked through the SoloHI FoV, and also to report how the rest of the Heliophysics Systems Observatory (HSO) can be used to support the SoloHI data. Results. The high-resolution SoloHI images of these eruptions, taken from ∼0.3 au, reveal a number of detailed structural CME features, including internal cavities or cores of the CME flux rope(s). They also show the surrounding material and associated sheath region of the compressed upstream solar wind plasma. Many features that could not have been observed by other instruments are highlighted and discussed. Conclusions. The SoloHI instrument is performing well and has already provided detailed observations of CMEs that can help us understand the details of the internal structure and magnetic field of CMEs. These new observations in combination with synoptic observations from 1 au offer new opportunities for CME propagation from the corona to the heliosphere.

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 (< 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.

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.

Forecasting the transit times of earth-directed halo CMEs using artificial neural network: A case study application with GCS forward-modeling technique

Mitigating the lethal threats caused by coronal mass ejections (CMEs) on human and space operations can be accomplished with a fast and accurate forecast of Earth-directed CME transit times. The current paper presents a robust Cascade Forward Neural Network (CFNN) framework to predict the transit times of Earth-directed halo CMEs using a total of 290 CME/Interplanetary coronal mass ejections (ICME) pairs of datasets for the past two and half decades (solar cycle; SC 23, 24, 25). It is the first time incorporating deprojected speeds into a machine learning framework to mitigate uncertainties due to projection effects during CME transit time prediction. The CFNN model forecasted the transit times of 87 Earth-directed CMEs and recorded a mean absolute error (MAE) of 7.3 h. In addition, 5 selected fast-moving (energetic) halo CME episodes during the deep phases (solar minima) of SC 25 were reconstructed using the Graduated Cylindrical Shell (GCS) forward-modeling technique. The events were predicted using the CFNN model (MAE = 4.5 h) in comparison with the Drag-Based model (DBM; MAE = 6.2 h) and Empirical Shock Arrival model (ESA; MAE = 13.5 h) to evaluate the robustness and the flexibility of the CFNN framework as well as the reliability of the CME 3D speed as a proxy for the space speed. The CFNN framework demonstrated satisfactory performance in contrast to previously used models by minimizing CME arrival time prediction errors due to projection effects. Hence, the study validated the efficiency of the GCS model for studying the 3D kinematics of CMEs and emphasized the essence of utilizing deprojected speeds in machine learning frameworks as better alternatives for fast, reliable, and accurate CME arrival (transit) time predictions.

Evolution of Solar Eruptive Events: Investigating the Relationships among Magnetic Reconnection, Flare Energy Release, and Coronal Mass Ejections

We study the evolution of solar eruptive events by investigating the temporal relationships among magnetic reconnection, flare energy release, and the acceleration of coronal mass ejections (CMEs). Leveraging the optimal viewing geometry of the Solar TErrestrial RElations Observatory (STEREO) relative to the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) during 2010–2013, we identify 12 events with sufficient spatial and temporal coverage for a detailed examination. STEREO and SDO data are used to measure the CME kinematics and the reconnection rate, respectively, and hard X-ray (HXR) measurements from RHESSI provide a signature of the flare energy release. This analysis expands upon previous solar eruptive event timing studies by examining the fast-varying features, or “bursts,” in the HXR and reconnection rate profiles, which represent episodes of energy release. Through a time lag correlation analysis, we find that HXR bursts occur throughout the main CME acceleration phase for most events, with the HXR bursts lagging the acceleration by 2 ± 9 minutes for fast CMEs. Additionally, we identify a nearly one-to-one correspondence between bursts in the HXR and reconnection rate profiles, with HXRs lagging the reconnection rate by 1.4 ± 2.8 minutes. The studied events fall into two categories: events with a single dominant HXR burst and events with a train of multiple HXR bursts. Events with multiple HXR bursts, indicative of intermittent reconnection and/or particle acceleration, are found to correspond with faster CMEs.

Propagation of coronal mass ejections from the Sun to the Earth

Coronal Mass Ejections (CMEs), as they can inject a large amounts of mass and magnetic flux into the interplanetary space, are the primary source of space weather phenomena on the Earth. The present review first briefly introduces the solar surface signatures of the origins of CMEs and then focuses on the attempts to understand the kinematic evolution of CMEs from the Sun to the Earth. CMEs have been observed in the solar corona in white-light from a series of space missions over the last five decades. In particular, LASCO/SOHO has provided almost continuous coverage of CMEs for more than two solar cycles until today. However, the observations from LASCO suffered from projection effects and limited field of view (within 30 Rs from the Sun). The launch in 2006 of the twin STEREO spacecraft made possible multiple viewpoints imaging observations, which enabled us to assess the projection effects on CMEs. Moreover, heliospheric imagers (HIs) onboard STEREO continuously observed the large and unexplored distance gap between the Sun and Earth. Finally, the Earth-directed CMEs that before have been routinely identified only near the Earth at 1 AU in in situ observations from ACE and WIND, could also be identified at longitudes away from the Sun-Earth line using the in situ instruments onboard STEREO. Our review presents the frequently used methods for estimation of the kinematics of CMEs and their arrival time at 1 AU using primarily SOHO and STEREO observations. We emphasize the need of deriving the three-dimensional (3D) properties of Earth-directed CMEs from the locations away from the Sun-Earth line. The results improving the CME arrival time prediction at Earth and the open issues holding back progress are also discussed. Finally, we summarize the importance of heliospheric imaging and discuss the path forward to achieve improved space weather forecasting.

Influence of the drag force on the leading edge of a coronal mass ejection

Context. The drag based model (DBM) is frequently used to analyse the kinematics of coronal mass ejections (CMEs) in interplanetary space. The DBM incorporates a 2D solution with the leading edge of the CME. Aims. Certain aspects of the evolution of the CME leading edge in the DBM have not been fully and accurately described previously. The main goal of this paper is to clarify these issues. Methods. We analysed the behaviour of the leading edge according to the DBM equations by studying the dependence of the radial distance of each segment of the leading edge on the angular coordinate, ϕ, and observed the limits as time goes to infinity. We also analysed the behaviour of the velocity profile, v(ϕ). Results. We showed that for isotropic solar wind conditions, the distance between the apex and the flank is a monotonically increasing function of time that converges at infinity to a constant value. The leading edge never becomes fully circular. The analysis of the v(ϕ) profile shows that the speed of all CME leading-edge segments converges towards the solar wind speed, w, but the speed of the CME flank never exceeds that of the apex. Conclusions. The drag force alone cannot flatten the leading edge of a CME in isotropic solar wind conditions. This also holds for any model that uses the drag as a description of the CME kinematics if the typical initial assumption that the flank is slower and farther behind than the apex is used. On the other hand, non-isotropic solar wind conditions can change this conclusion and even introduce a deformation of the leading edge. A similar effect can be obtained with temporal variations in solar wind conditions along the path of the CME, or by introducing other forces.

Quantifying the Uncertainty in CME Kinematics Derived From Geometric Modeling of Heliospheric Imager Data

AbstractGeometric modeling of Coronal Mass Ejections (CMEs) is a widely used tool for assessing their kinematic evolution. Furthermore, techniques based on geometric modeling, such as ELEvoHI, are being developed into forecast tools for space weather prediction. These models assume that solar wind structure does not affect the evolution of the CME, which is an unquantified source of uncertainty. We use a large number of Cone CME simulations with the HUXt solar wind model to quantify the scale of uncertainty introduced into geometric modeling and the ELEvoHI CME arrival times by solar wind structure. We produce a database of simulations, representing an average, a fast, and an extreme CME scenario, each independently propagating through 100 different ambient solar wind environments. Synthetic heliospheric imager observations of these simulations are then used with a range of geometric models to estimate the CME kinematics. The errors of geometric modeling depend on the location of the observer, but do not seem to depend on the CME scenario. In general, geometric models are biased towards predicting CME apex distances that are larger than the true value. For these CME scenarios, geometric modeling errors are minimised for an observer in the L5 region. Furthermore, geometric modeling errors increase with the level of solar wind structure in the path of the CME. The ELEvoHI arrival time errors are minimised for an observer in the L5 region, with mean absolute arrival time errors of 8.2 ± 1.2 h, 8.3 ± 1.0 h, and 5.8 ± 0.9 h for the average, fast, and extreme CME scenarios.

The first coronal mass ejection observed in both visible-light and UV H I Ly-αchannels of the Metis coronagraph on board Solar Orbiter

Context.The Metis coronagraph on board Solar Orbiter offers a new view of coronal mass ejections (CMEs), observing them for the first time with simultaneous images acquired with a broad-band filter in the visible-light interval and with a narrow-band filter around the H ILy-αline at 121.567 nm, the so-called Metis UV channel.Aims.We show the first Metis observations of a CME, obtained on 16 and 17 January 2021. The event was also observed by the EUI/FSI imager on board Solar Orbiter, as well as by other space-based coronagraphs, such as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here with Metis data.Methods.Different images are analysed here to reconstruct the 3D orientation of the expanding CME flux rope using the graduated cylindrical shell model. This also allows us to identify the possible location of the source region. Measurements of the CME kinematics allow us to quantify the expected Doppler dimming in the Ly-αchannel.Results.Observations show that most CME features seen in the visible-light images are also seen in the Ly-αimages, although some features in the latter channel appear more structured than their visible-light counterparts. We estimated the expansion velocity of this event to be below 140 km s−1. Hence, these observations can be understood by assuming that Doppler dimming effects do not strongly reduce the Ly-αemission from the CME. These velocities are comparable with or smaller than the radial velocities inferred from the same data in a similar coronal structure on the east side of the Sun.Conclusions.The first observations by Metis of a CME demonstrate the capability of the instrument to provide valuable and novel information on the structure and dynamics of these coronal events. Considering also its diagnostics capabilities regarding the conditions of the ambient corona, Metis promises to significantly advance our knowledge of such phenomena.

An Insight into the Coupling of CME Kinematics in Inner and Outer Corona and the Imprint of Source Regions

Abstract Despite studying coronal mass ejections (CMEs) for several years, we do not yet have a complete understanding of their kinematics. To this end, it is essential to understand the change in kinematics of the CMEs as they travel from the inner corona (<3 R ⊙) up to the higher heights of the outer corona. We conduct a follow-up statistical study of several 3D kinematic parameters of 59 CMEs previously studied by Majumdar et al. (2020). The source regions of these CMEs are identified and classified as active regions (ARs), active prominences (APs), or prominence eruptions (PEs). We study several statistical correlations between different kinematic parameters of the CMEs. We show that the CMEs’ average kinematic parameters change as they propagate from the inner to the outer corona, indicating the importance of a region where the common practice is to perform averaging. We also find that the CME parameters in the outer corona are highly influenced by those in the inner corona, indicating the importance of the inner corona in the understanding of the kinematics. Furthermore, we find that the source regions of the CMEs tend to have a distinct imprint on the statistical correlations between different kinematic parameters, and that an overall correlation tends to wash away this crucial information. The results of this work supports the possibility of different dynamical classes for the CMEs from ARs and prominences, which gets manifested in their kinematics.

Coronal mass ejections observed by heliospheric imagers at 0.2 and 1 au

Context. We study two coronal mass ejections (CMEs) observed between April 1 to 2, 2019 by both the inner Wide-Field Imager for Parker Solar Probe (WISPR-I) onboard the Parker Solar Probe (PSP) spacecraft (located between about 46 and 38 solar radii during this period) and the inner heliospheric imager (HI-1) onboard the Solar Terrestrial Relations Observatory Ahead (STEREO-A) spacecraft, orbiting the Sun at about 0.96 au. This is the first study of CME observations from two viewpoints in similar directions but at considerably different solar distances. Aims. Our objective is to derive CME kinematics from WISPR-I observations and to compare them with results from HI-1. This allows us to understand how the PSP observations affect the CME kinematics, especially due to its proximity to the Sun. Methods. We estimated the CME positions, speeds, accelerations, propagation directions, and longitudinal deflections using imaging observations from two spacecrafts and a set of analytical expressions that consider the CME as a point structure and take the rapid change in spacecraft position into account. We derived the kinematics using each viewpoint independently and both viewpoints as a constraint. Results. We found that both CMEs are slow (<400 km s−1), propagating eastward of the Sun-Earth line (westward of PSP and STEREO-A). The second CME seems to accelerate between ~0.1 and ~0.2 au and deflect westward with an angular speed consistent with the solar rotation speed. We found some discrepancies in the CME solar distance (up to 0.05 au, particularly for CME #1), latitude (up to ~10°), and longitude (up to 24°) when comparing results from different fit cases (different observations or set of free parameters). Conclusions. Discrepancies in longitude are likely due to the feature that is tracked visually, rather than instrumental biases or fit assumptions. For similar reasons, the CME #1 solar distance, as derived from WISPR-I observations, is larger than the HI-1 result, regardless of the fit parameters considered. Error estimates for CME kinematics do not show any clear trend associated with the observing instrument. The source region location and the lack of any clear in situ counterparts (both at near-Earth and at PSP) support our estimate of the propagation direction for both events.

Assessing the Projection Correction of Coronal Mass Ejection Speeds on Time‐of‐Arrival Prediction Performance Using the Effective Acceleration Model

AbstractWhite light images of coronal mass ejections (CMEs) are projections on the plane‐of‐sky (POS). As a result, CME kinematics are subject to projection effects. The error in the true (deprojected) speed of CMEs is one of the main causes of uncertainty to Space Weather forecasts, since all estimates of the CME time‐of‐arrival (ToA) at a certain location within the heliosphere require, as input, the CME speed. We use single viewpoint observations for 1,037 flare‐CME events between 1996 and 2017 and propose a new approach for the correction of the CME speed assuming radial propagation from the flare site. Our method is uniquely capable to produce physically reasonable deprojected speeds across the full range of source longitudes. We bound the uncertainty in the deprojected speed estimates via limits in the true angular width of a CME based on multiview‐point observations. Our corrections range up to 1.37–2.86 for CMEs originating from the center of the disk. On average, the deprojected speeds are 12.8% greater than their POS speeds. For slow CMEs (VPOS < 400 km/s) the full ice‐cream cone model performs better while for fast and very fast CMEs (VPOS > 700 km/s) the shallow ice‐cream model gives much better results. CMEs with 691–878 km/s POS speeds have a minimum ToA mean absolute error (MAE) of 11.6 h. This method, is robust, easy to use, and has immediate applicability to Space Weather forecasting applications. Moreover, regarding the speed of CMEs, our work suggests that single viewpoint observations are generally reliable.

Relationship between solar energetic particle intensities and coronal mass ejection kinematics using STEREO/SECCHI field of view

Solar energetic particles (SEPs) accelerated from shocks driven by coronal mass ejections (CMEs) are one of the major causes of geomagnetic storms on Earth. Therefore, it is necessary to predict the occurrence and intensity of such disturbances. For this purpose we analyzed in detail 38 non-interacting halo and partial halo CMEs, as seen by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph, generating SEPs (in > 10 MeV, > 50 MeV, and > 100 MeV energy channels) during the quadrature configuration of the Solar TErrestrial RElations Observatory (STEREO) twin spacecrafts with respect to the Earth, which marks the ascending phase of solar cycle 24 (i.e., 2009–2013). The main criteria for this selection period is to obtain height–time measurements of the CMEs without significant projection effects and in a very large field of view. Using the data from STEREO/Sun Earth Connection Coronal and Heliospheric Investigation (STEREO/SECCHI) images we determined several kinematic parameters and instantaneous speeds of the CMEs. First, we compare instantaneous CME speed and Mach number versus SEP fluxes for events originating at the western and eastern limb; we observe high correlation for the western events and anticorrelation for the eastern events. Of the two parameters, the Mach number offers higher correlation. Next we investigated instantaneous CME kinematic parameters such as maximum speed, maximum Mach number, and the CME speed and Mach number at SEP peak flux versus SEP peak fluxes. Highly positive correlation is observed for Mach number at SEP peak flux for all events. The obtained instantaneous Mach number parameters from the emperical models was verified with the start and end time of type II radio bursts, which are signatures of CME-driven shock in the interplanetary medium. Furthermore, we conducted estimates of delay in time and distance between CME, SEP, and shock parameters. We observe an increase in the delay in time and distance when SEPs reach peak flux with respect to CME onset as we move from the western to the eastern limb. Western limb events (longitude 60°) have the best connectivity and this decreases as we move towards the eastern limb. This variation is due to the magnetic connectivity from the Sun to the Earth, called the Parker spiral interplanetary magnetic field. Comparative studies of the considered energy channels of the SEPs also throw light on the reacceleration of suprathermal seed ions by CME-driven shocks that are pre-accelerated in the magnetic reconnection.

Automated Detection of Accelerating Solar Eruptions Using Parabolic Hough Transform

Solar eruptions such as Coronal Mass Ejections (CMEs) observed in the inner solar corona (up to 4 R$_{\odot}$) show acceleration profiles which appear as parabolic ridges in height-time plots. Inspired by the white-light automated detection algorithms, Computer Aided CME Tracking System (CACTus) and Solar Eruptive Events Detection System (SEEDS), we employ the parabolic Hough Transform for the first time to automatically detect off-disk solar eruptions {from height-time plots. Due to the limited availability of white-light observations in the inner corona, we use Extreme UltraViolet (EUV) images of the Sun. In this paper we present a new algorithm, CME Identification in Inner Solar Corona (CIISCO), which is based on Fourier motion filtering and the parabolic Hough transform, and demonstrate its implementation using EUV observations taken from {\it Atmospheric Imaging Assembly} (AIA) on-board the Solar Dynamics Observatory (SDO), {\it Extreme Ultra Violet Imager} (EUVI) on-board the STEREO-A and B satellites, and {\it Sun Watcher using Active Pixel System detector and Image Processing} (SWAP) Imager on-board PROBA2. We show that CIISCO is able to identify any {off-disk} outward moving feature in EUV images. The use of automated detection algorithms, like CIISCO, can potentially be used to provide early warnings of CMEs if an EUV telescope is located at $\pm$ 90$^{\circ}$ from the Sun-Earth line, providing CME characteristics and kinematics close to the Sun. This paper also presents the limitations of this algorithm and the prospects for future improvement.

Cause and Kinematics of a Jetlike CME

Abstract In this article, we present the multiviewpoint and multiwavelength analysis of an atypical solar jet based on data from Solar Dynamics Observatory, SOlar and Heliospheric Observatory, and Solar TErrestrial RElations Observatory. It is generally believed that coronal mass ejections (CMEs) develop from the large-scale solar eruptions in the lower atmosphere. However, the kinematical and spatial evolution of the jet on 2013 April 28 suggests that the jet was clearly associated with a narrow CME with a width of ≈25° and speed of ≈450 km s−1. To better understand the link between the jet and the CME, we performed a coronal potential field extrapolation from the line-of-sight magnetogram of the active region. The extrapolations suggest that the jet eruption follows the same path of the open magnetic field lines from the source region, which provides a route for the jet material to escape from the solar surface toward the outer corona.

Multiwavelength Analysis of the Kinematics of a Long Duration Flare-CME Event on 27 January 2012

We present a detailed analysis of a long-duration flare associated with a coronal mass ejection (CME) event that occurred on 27 January 2012 in the active region (AR) 11402. We analyze the kinematics of the CME and the close relationship between the flare, radio burst, and CME. We used STEREO (Solar Terrestrial Relations Observatory)/EUVI A (Extreme Ultraviolet Imager) and white light data from STEREO (COR1 A and COR2 A) and LASCO (Large Angle and Spectrometric COronagraph) (C2/C3) coronagraphs, and X-ray data from the GOES (Geostationary Operational Environmental Satellite) spacecraft. The height of the CME is measured using the Graduated Cylindrical Shell (GCS) model. Our results show that: i) the speed of the CME (1460 km/s at $2.54~\mbox{R}_{\odot}$ ) is comparable to the speed of the type II radio burst (1581 km/s), ii) the height of the type II radio burst is lower than that of the CME leading edge, iii) the CME acceleration phase is found to be related to the rise time of the flare and its propagation phase is related to the decay phase of the flare, iv) the type II radio burst origin is likely to be near the CME region where a CME-streamer interaction takes place around $1.6~\mbox{R}_{\odot}$ , and v) the sequence of events and the CME kinematics show a close association between the CME and type II radio emissions.

On the Expansion Speed of Coronal Mass Ejections: Implications for Self-Similar Evolution

A proper characterization of the kinematics of coronal mass ejections (CMEs) is important not only for practical purposes, i.e. space weather forecasting, but also to improve our current understanding of the physics behind their evolution in the middle corona and into the heliosphere. The first and core step toward this goal is the estimation of the three main components of the CME speeds, namely the expansion speed relative to the center of motion in both, the radial and lateral directions, and the propagation speed (i.e. $V_{\mathrm{front}}$ , $V_{\mathrm{lat}}$ , $V_{\mathrm{bulk}}$ , respectively). To this aim, we exploit the observations obtained with COR2 onboard the Solar Terrestrial Relations Observatory (STEREO) from 2007 to 2014 to investigate the relationships among the different components as a function of the heliocentric distance of the CME events. Here, we analyze a sample of 475 CMEs. The selected events exhibit clear flux rope signatures as seen either edge on (i.e. F-CMEs: three-part structure, presence of a cavity) or face on (i.e. L- or loop CMEs) in white light images. Our main findings are: i) L-CMEs show almost twice as large expansion speeds compared to F-CMEs ( $V_{\mathrm {front},\mathrm{L}}=367~\mbox{km}\,\mbox{s}^{-1}$ , $V_{\mathrm{lat},\mathrm{L}}=365~\mbox{km}\,\mbox{s}^{-1}$ vs. $V_{\mathrm{front},\mathrm{F}}=215~\mbox{km}\,\mbox{s}^{-1}$ , $V_{\mathrm{lat},\mathrm{F}}= 182~\mbox{km}\,\mbox{s}^{-1}$ ); ii) the relationship between the two components of the expansion speeds is linear and does not change with height; iii) the ratio of the propagation speed to the lateral expansion speed is a function of the angular width that describes the self-similarity evolution of a CME; and iv) 65% of the CMEs exhibit a self-similar evolution at 10 solar radii, reaching 70% at 15 solar radii.

Kinematics of coronal mass ejections in the LASCO field of view

In this paper we present a statistical study of the kinematics of 28894 coronal mass ejections (CMEs) recorded by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory spacecraft from 1996 until mid-2017. The initial acceleration phase is characterized by a rapid increase in CME velocity just after eruption in the inner corona. This phase is followed by a non-significant residual acceleration (deceleration) characterized by an almost constant speed of CMEs. We demonstrate that the initial acceleration is in the range 0.24–2616 m s−2 with median (average) value of 57 m s−2 (34 m s−2) and it takes place up to a distance of about 28 RSUN with median (average) value of 7.8 RSUN (6 RSUN). Additionally, the initial acceleration is significant in the case of fast CMEs (V > 900 km s−1), where the median (average) values are about 295 m s−2 (251 m s−2), respectively, and much weaker in the case of slow CMEs (V < 250 km s−1), where the median (average) values are about 18 m s−2 (17 m s−2), respectively. We note that the significant driving force (Lorentz force) can operate up to a distance of 6 RSUN from the Sun during the first 2 hours of propagation. We found a significant anti-correlation between the initial acceleration magnitude and the acceleration duration, whereas the residual acceleration covers a range from −1224 to 0 m s−2 with a median (average) value of −34 m s−2 (−17 m s−2). One intriguing finding is that the residual acceleration is much smaller during the 24th cycle in comparison to the 23rd cycle of solar activity. Our study has also revealed that the considered parameters, initial acceleration (ACCINI), residual acceleration (ACCRES), maximum velocity (VMAX), and time at maximum velocity (TimeMAX) mostly follow solar cycles and the intensities of the individual cycle.