Onset Of Coronal Mass Ejections Research Articles

Photospheric signatures of CME onset

ABSTRACT Coronal mass ejections (CMEs) are solar eruptions that involve large-scale changes to the magnetic topology of an active region. There exists a range of models for CME onset which are based on twisted or sheared magnetic field above a polarity inversion line (PIL). We present observational evidence that topological changes at PILs, in the photosphere, form a key part of CME onset, as implied by many models. In particular, we study the onset of 30 CMEs and investigate topological changes in the photosphere by calculating the magnetic winding flux, using the artop code. By matching the times and locations of winding signatures with CME observations produced by the almanac code, we confirm that these signatures are indeed associated with CMEs. Therefore, as well as presenting evidence that changes in magnetic topology at the photosphere are a common signature of CME onset, our approach also allows for the finding of the source location of a CME within an active region.

Recent progress on understanding coronal mass ejection/flare onset by a NASA living with a star focused science team

We present a report of recent progress on the topic of understanding solar coronal mass ejection (CME) onset from both modeling and observational viewpoints, as carried out from 2019 to the present by the NASA Living with a Star Focused Science Topic team on “Understanding the Onset of Major Solar Eruptions.” Following the typical Focused Science Topic paradigm, a number of research groups were selected and joined together to tackle this problem. The work being carried out by this team explores the role of topology and of helicity transport in creating an environment favorable to CME eruption and in then providing the energy required for CME onset. The team investigated CME energization and initiation via photospheric shearing, via flux rope formation, and via magnetic flux emergence. This article will highlight recent progress made by six American research groups working in these areas. We do not intend to present an exhaustive review of these topics, but rather summarize the ideas from these research groups regarding ongoing and upcoming challenges to the questions of how, when, and why coronal mass ejections erupt from the sun.

Search for Solar Sources of Interplanetary Coronal Mass Ejections Using the Reverse Model of Magnetodynamic Interaction of the Solar Wind in the Heliosphere

In the development and testing of methods for predicting interplanetary coronal mass ejections (ICMEs), it is important to establish their relationship with sources on the Sun—coronal mass ejections (CMEs) observed by coronagraphs. The often used inverse ballistic calculation of the CME onset time does not consider variations in the CME speed when moving through the heliosphere and can give an uncertainty up to a day. With a good accuracy (on the order of ±10 h), the propagation of CMEs in the heliosphere from the Sun to the Earth is described by the model of the magnetodynamic interaction of CMEs with the background solar wind (drag-based model, DBM). In this paper, we propose to search for possible coronal sources of ICMEs, observed near the Earth, using the reverse model of magnetodynamic interaction (reverse DBM, RDBM), which reconstructs in the reverse course the probable propagation of CMEs in the heliosphere and determines their outflow parameters in the solar corona using the measured ICME parameters. The model uses the speed of the background solar wind, which is calculated from the area of coronal holes in the central part of the Sun and presented on the website of the Space Monitoring Data Center of the Skobeltsyn Institute of Nuclear Physics, Moscow State University (SINP MSU), with correction factors.

Coronal mass ejections and high-speed solar wind streams effect on HF ionospheric communication channel

This article analyzes the degree of solar coronal mass ejections and high-speed solar wind streams influence on the ionospheric communication channel in the short-wavelength range. Regularities in the coronal mass ejections influence on the parameters of the ionosphere are revealed. It is shown that there is a decrease in the values of the used differential parameter of critical frequency of the ionosphere F2 layer after the onset of coronal mass ejections of the loop type, while no significant changes are observed from other types of coronal mass ejections. The contribution of the high-speed solar wind flux to the features of the behavior of ionospheric parameters is demonstrated. Deviations of critical frequency and maximum observed frequency of the ionosphere F2 layer indicate a change in conditions in the ionosphere, leading to disruption of radio communication in the short-wavelength range. The results of ground-based measurements of the ionospheric plasma parameters were obtained by the methods of oblique and vertical sounding of the ionosphere. The use of the method of oblique sounding made it possible to obtain data on the state of the ionosphere where there are no vertical sounding stations.

An investigation of the causal relationship between sunspot groups and coronal mass ejections by determining source active regions

ABSTRACT Although the source active regions of some coronal mass ejections (CMEs) were identified in CME catalogues, vast majority of CMEs do not have an identified source active region. We propose a method that uses a filtration process and machine learning to identify the sunspot groups associated with a large fraction of CMEs and compare the physical parameters of these identified sunspot groups with properties of their corresponding CMEs to find mechanisms behind the initiation of CMEs. These CMEs were taken from the Coordinated Data Analysis Workshops (CDAW) data base hosted at NASA’s website. The Helioseismic and Magnetic Imager (HMI) Active Region Patches (HARPs) were taken from the Stanford University’s Joint Science Operations Center (JSOC) data base. The source active regions of the CMEs were identified by the help of a custom filtration procedure and then by training a long short-term memory network (LSTM) to identify the patterns in the physical magnetic parameters derived from vector and line-of-sight magnetograms. The neural network simultaneously considers the time series data of these magnetic parameters at once and learns the patterns at the onset of CMEs. This neural network was then used to identify the source HARPs for the CMEs recorded from 2011 till 2020. The neural network was able to reliably identify source HARPs for 4895 CMEs out of 14 604 listed in the CDAW data base during the aforementioned period.

Interrelationships between Halo-Type Coronal Mass Ejections and Solar Flares Based on Observations in the 23rd and 24th Cycles

Solar activity of an explosive character during the 23rd and 24th cycles is analyzed. X-ray observations from the GOES-15 satellite during flares and observations during coronal mass ejections (CME) with the SOHO/LASCO coronagraph are used. The delay intervals between the onset of a flare and the onset of a Halo-type CME associated the same active region were analyzed. It is shown that the time interval between the onset of the flare and the onset of the CME is an average of 2 times shorter for flares in classes ≥ X1 than for less powerful flares. All events accompanied by powerful flares in classes ≥ X1 were examined separately. The interrelationship between Halo-type CME and the geomagnetic indices Kp and Dst, used for space weather forecasting, was evaluated. It is shown that the probability of a dangerous magnetic storm on the earth with Kp ≥ 7 is more than 80% if two conditions are met simultaneously: VCME ≥ 1000 km/s and |Dst| ≥ 100 nT.

Radio-loud and radio-quiet CMEs: solar cycle dependency, influence on cosmic ray intensity, and geo-effectiveness

Coronal mass ejections (CMEs) largely influence the space weather and cause geomagnetic perturbations. Hence, the statistical studies pertaining to the occurrence of CMEs over the solar cycles and their consequence at the near-Earth region are extremely important. For an in-depth understanding, such studies need to be carried out considering various observational aspects of CMEs. With this motivation, here we present a statistical study of radio-loud (RL) and radio-quiet (RQ) CMEs during solar cycles 23 and 24. We also assess their geo-effectiveness and analyze their influence on cosmic ray intensity (CRI). The RL and RQ CMEs constitute 40% and 60% cases, respectively, of the total population of CMEs that arrive the near-Earth region at 1 AU. The mean speed of RL CMEs (≈1170 km s−1) was found to be significantly higher (almost twice) than the mean speed of RQ CMEs (≈519 km s−1) in the low corona while their speed became comparable (≈536 km s−1 for RL and ≈452 km s−1 for RQ CMEs) at near-Earth region. The yearly-averaged speeds of Earth-reaching CMEs follow solar cycle variations. The CRI and geomagnetic Dst index are found to have good negative correlation with speed of Earth-reaching CMEs. RL CMEs were found to be more effective in producing CRI depressions and geomagnetic storms (GSs) in comparison to RQ CMEs; in about 70% cases RL CMEs produced CRI depression and GSs earlier than the RQ CMEs. Superposed epoch analysis suggests strongest depression in CRI occurs 2-5 days and 4-9 days after the onset of RL and RQ CMEs, respectively. Further, GS events show a time-lag of 1-5 days and 3-8 days, respectively, with respect to RL and RQ CMEs.

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.

The High Helium Abundance and Charge States of the Interplanetary CME and Its Material Source on the Sun

Abstract Identifying the source of the material within coronal mass ejections (CMEs) and understanding CME onset mechanisms are fundamental issues in solar and space physics. Parameters relating to plasma composition, such as charge states and He abundance (A He), may be different for plasmas originating from differing processes or regions on the Sun. Thus, it is crucial to examine the relationship between in situ measurements of CME composition and activity on the Sun. We study the CME that erupted on 2014 September 10, in association with an X1.6 flare, by analyzing Atmospheric Imaging Assembly imaging and Interface Region Imaging Spectrograph (IRIS) spectroscopic observations and its in situ signatures detected by Wind and Advanced Composition Explorer. We find that during the slow expansion and intensity increase of the sigmoid, plasma temperatures of 9 MK, and higher, first appear at the footpoints of the sigmoid, associated with chromospheric brightening. Then the high-temperature region extends along the sigmoid. IRIS observations confirm that this extension is caused by transportation of hot plasma upflow. Our results show that chromospheric material can be heated to 9 MK, and above, by chromospheric evaporation at the sigmoid footpoints before flare onset. The heated chromospheric material can transport into the sigmoidal structure and supply mass to the CME. The aforementioned CME mass supply scenario provides a reasonable explanation for the detection of high charge states and elevated A He in the associated interplanetary CME. The observations also demonstrate that the quasi-steady evolution in the precursor phase is dominated by magnetic reconnection between the rising flux rope and the overlying magnetic field structure.

Optical instrumentation for chromospheric monitoring during solar cycle 25 at Paris and Côte d’Azur observatories

We present the observing program proposed by Paris and Côte d’Azur Observatories for monitoring solar activity during the upcoming cycle 25 and providing near real time images and movies of the chromosphere for space-weather research and applications. Two optical instruments are fully dedicated to this task and we summarize their capabilities. Short-term and fast-cadence observations of the chromosphere will be performed automatically at Calern observatory (Côte d’Azur), where dynamic events, as flare development, Moreton waves, filament instabilities and Coronal Mass Ejections onset, will be tracked. This new set of telescopes will operate in 2021 with narrow bandpass filters selecting Hα and CaII K lines. We present the instrumental design and a simulation of future images. At Meudon, the Spectroheliograph is well adapted to the long-term and low-cadence survey of chromospheric activity by recently improved and optimized spectroscopic means. Surface scans deliver daily (x, y, λ) datacubes of Hα, CaII K and CaII H line profiles. We describe the nature of available data and emphasize the new calibration method of spectra.

Relationship Between Rising Phase of Solar Cycle 23rd and 24th with Respect to Geoeffectiveness

The current article demonstrates the geoeffectiveness of solar flare associated Coronal mass ejection (CME) accompanied with Deca-hectometric (DH) type II radio bursts by comparing the set of events in the rising phase of solar cycle 23rd (1996–2001) and 24th (2009–2014). Our observations are: (i) Solar cycle 23rd have high Dst index than the solar cycle 24th except for the year 1999. (ii) Dst has its peak between 3rd to 5th day after the CME onset for both the solar cycles. (iii) The correlation coefficient between Interplanetary magnetic fields (IMF) and Dst is good for both the solar cycles. (iv) Solar cycle 23rd have very strong correlation between CRI and Dst as compare to solar cycle 24th. Thus, our predictions show that solar cycle 23rd is more geoeffective than solar cycle 24th.

A Prospective New Diagnostic Technique for Distinguishing Eruptive and Noneruptive Active Regions

Abstract Active regions are the source of the majority of magnetic flux rope ejections that become coronal mass ejections (CMEs). To identify in advance which active regions will produce an ejection is key for both space weather prediction tools and future science missions such as Solar Orbiter. The aim of this study is to develop a new technique to identify which active regions are more likely to generate magnetic flux rope ejections. The new technique will aim to (i) produce timely space weather warnings and (ii) open the way to a qualified selection of observational targets for space-borne instruments. We use a data-driven nonlinear force-free field (NLFFF) model to describe the 3D evolution of the magnetic field of a set of active regions. We determine a metric to distinguish eruptive from noneruptive active regions based on the Lorentz force. Furthermore, using a subset of the observed magnetograms, we run a series of simulations to test whether the time evolution of the metric can be predicted. The identified metric successfully differentiates active regions observed to produce eruptions from the noneruptive ones in our data sample. A meaningful prediction of the metric can be made between 6 and 16 hr in advance. This initial study presents an interesting first step in the prediction of CME onset using only line-of-sight magnetogram observations combined with NLFFF modeling. Future studies will address how to generalize the model such that it can be used in a more operational sense and for a variety of simulation approaches.

Stealth Coronal Mass Ejections from Active Regions

Abstract Stealth coronal mass ejections (CMEs) are eruptions from the Sun that have no obvious low coronal signature. These CMEs are characteristically slower events but can still be geoeffective and affect space weather at Earth. Therefore, understanding the science underpinning these eruptions will greatly improve our ability to detect and, eventually, forecast them. We present a study of two stealth CMEs analyzed using advanced image processing techniques that reveal their faint signatures in observations from the extreme-ultraviolet (EUV) imagers on board the Solar and Heliospheric Observatory, Solar Dynamics Observatory, and Solar Terrestrial Relations Observatory spacecraft. The different viewpoints given by these spacecraft provide the opportunity to study each eruption from above and the side contemporaneously. For each event, EUV and magnetogram observations were combined to reveal the coronal structure that erupted. For one event, the observations indicate the presence of a magnetic flux rope before the CME’s fast-rise phase. We found that both events originated in active regions and are likely to be sympathetic CMEs triggered by a nearby eruption. We discuss the physical processes that occurred in the time leading up to the onset of each stealth CME and conclude that these eruptions are part of the low-energy and velocity tail of a distribution of CME events and are not a distinct phenomenon.

Solar Filament Eruptions as Precursors to Flare–CME Events: Establishing the Temporal Connection

Abstract Elongated structures on the Sun’s surface known as filaments are known to have a connection with energetic events of space weather consequence (flares and coronal mass ejections (CMEs)). In this work, we explore the connection between the eruptive dynamics of filaments and the initiation of solar flares and CMEs. We estimate the filament eruption start time by tracking the filament throughout its eruption phase. We define the filament eruption start time as the time from which the filament area starts to decrease as observed in Hα images. A total of 33 eruptive filament events are reported in this study, out of which 73% are CME associated and 76% are related to solar flares. We find a good correlation between area decay rate of the quiescent filaments and the speed of the associated CMEs with a correlation coefficient of 0.75. By analyzing the time delay of the extreme ultraviolet brightening of solar flares relative to the start time of associated filament eruption, we show that in 83% of cases, filament eruption precedes the flare brightening, which indicates that eruptive filaments can be considered as one of the precursors for the occurrence of a solar flare. Finally, we study the time delay of the CME onset from the time of initiation of the filament eruption process and show that for most of the cases, CMEs occur within 2 hr from the start time of the filament eruptions. This study would be useful for space weather assessment and characterization based on automated trackers of solar filament dynamics.

Early-stage Solar Energetic Particle Acceleration by Coronal Mass Ejection-driven Shocks with Realistic Seed Spectra. I. Low Corona

Abstract An outstanding problem in heliospheric physics is understanding the acceleration of solar energetic particles (SEPs) in coronal mass ejections (CMEs) and flares. A fundamental question is whether the acceleration occurs in interplanetary space or near the Sun. Recent work has shown that CME-driven shocks may produce SEPs while still below five solar radii. In this work we explore SEP acceleration during the onset of CMEs and shocks even lower in the corona, using realistic suprathermal spectra, for a selection of events. We have calculated quiet-time, pre-event suprathermal particle spectra from 1 au observations, and scaled them back to the low corona to serve as seed spectra. For each event, AIA observations and the CASHeW framework were used to model the compressive/shock wave kinematics and its interaction with the corona. The proton acceleration was then modeled using an analytic diffusive shock acceleration model as the shock waves propagate between ∼1.05 and ∼1.3 solar radii. We demonstrate the capability of low coronal shock-related extreme ultraviolet waves to accelerate protons to multi-MeV energies in a matter of minutes, in the very early stages of the associated solar eruptions. We find that strong proton energization occurs for high values of the density jump, Alfvén Mach number, and shock speed. In future work the results of this early-stage shock acceleration will be used to model the continued acceleration higher in the corona.

Characteristics of Late-phase >100 MeV Gamma-Ray Emission in Solar Eruptive Events

Abstract We characterize and catalog 30 solar eruptive events observed by the Fermi Large Area Telescope (LAT) having late-phase >100 MeV γ-ray emission (LPGRE), identified 30 yr ago in what were called long-duration gamma-ray flares. We show that LPGRE is temporally and spectrally distinct from impulsive phase emission in these events. The spectra are consistent with the decay of pions produced by >300 MeV protons and are not consistent with primary electron bremsstrahlung. Impulsive >100 keV X-ray emission was observed in all 27 LPGRE events where observations were made. All but two of the LPGRE events were accompanied by a fast and broad coronal mass ejection (CME). The LPGRE start times range from CME onset to 2 hr later. Their durations range from ∼0.1 to 20 hr and appear to be correlated with durations of >100 MeV solar energetic particle (SEP) proton events. The power-law spectral indices of the >300 MeV protons producing LPGRE range from ∼2.5 to 6.5 and vary during some events. Combined γ-ray line and LAT measurements indicate that LPGRE proton spectra are steeper above 300 MeV than they are below 300 MeV. The number of LPGRE protons >500 MeV is typically about 10× the number in the impulsive phase of the solar eruptive event and ranges in nine events from ∼0.01× to 0.5× the number in the accompanying SEP event, with large systematic uncertainty. What appears to be late-phase electron bremsstrahlung with energies up to ∼10 MeV was observed in one LPGRE event. We discuss how current models of LPGRE may explain these characteristics.

Decimetric Emission 500″ Away from a Flaring Site: Possible Scenarios from GMRT Solar Radio Observations

We present a study of decimetric radio activity, using the first high time cadence (0.5 s) images from the ${\textit{Giant Meterwave Radio Telescope}}$ (${\textit{GMRT}}$) at 610 MHz, associated with ${\textit{GOES}}$ C1.4 and M1.0 class solar flares, and a coronal mass ejection (CME) onset that occurred on 20 June 2015. The high spatial resolution images from ${\textit{GMRT}}$ show a strong radio source during the C1.4 flare, located ~500$''$ away from the flaring site with no corresponding bright footpoints or coronal features nearby. In contrast, however, strong radio sources are found near the flaring site during the M1.0 flare and around the CME onset time. Weak radio sources, located near the flaring site, are also found during the maximum of the C1.4 flare activity, which show a temporal association with metric type III bursts identified by the Solar Broadband Radio Spectrometer at Yunnan Astronomical Observatory. Based on a multi-wavelength analysis and magnetic potential field source surface extrapolations, we suggest that the source electrons of ${\textit{GMRT}}$ radio sources and metric type III bursts were originated from a common electron acceleration site. We also show that the strong ${\textit{GMRT}}$ radio source is generated by a coherent emission process and its apparent location far from the flaring site is possibly due to the wave-ducting effect.

Flares before and after coronal mass ejections

Flare characteristics such as the flare occurrence number density and the distribution of peak flux as well as duration of flares occurring on either side of a coronal mass ejection (CME) onset time are studied. While the flares are rather evenly distributed statistically on either side of the CME onset time, the flare peak flux and duration tend to decrease depending upon their occurrence either before or after the CME onset. This is consistent with the earlier findings that flares emit higher energy before a CME whereas the energy is less in flares occurring after a CME.

Automatic Near‐Real‐Time Detection of CMEs in Mauna Loa K‐Cor Coronagraph Images

AbstractA simple algorithm has been developed to detect the onset of coronal mass ejections (CMEs), together with speed estimates, in near‐real time using linearly polarized white‐light solar coronal images from the Mauna Loa Solar Observatory K‐Cor telescope. Ground observations in the low corona can warn of CMEs well before they appear in space coronagraphs. The algorithm used is a variation on the Solar Eruptive Event Detection System developed at George Mason University. It was tested against K‐Cor data taken between 29 April 2014 and 20 February 2017, on days identified as containing CMEs. This resulted in testing of 139 days' worth of data containing 171 CMEs. The detection rate varied from close to 80% when solar activity was high down to as low as 20–30% when activity was low. The difference in effectiveness with solar cycle is attributed to the relative prevalence of strong CMEs between active and quiet periods. There were also 12 false detections, leading to an average false detection rate of 8.6%. The K‐Cor data were also compared with major solar energetic particle (SEP) storms during this time period. There were three SEP events detected either at Earth or at one of the two STEREO spacecraft when K‐Cor was observing during the relevant time period. The algorithm successfully generated alerts for two of these events, with lead times of 1–3 h before the SEP onset at 1 AU. The third event was not detected by the automatic algorithm because of the unusually broad width in position angle.

DERIVING THE PROPERTIES OF CORONAL PRESSURE FRONTS IN 3D: APPLICATION TO THE 2012 MAY 17 GROUND LEVEL ENHANCEMENT

ABSTRACT We study the link between an expanding coronal shock and the energetic particles measured near Earth during the ground level enhancement of 2012 May 17. We developed a new technique based on multipoint imaging to triangulate the three-dimensional (3D) expansion of the shock forming in the corona. It uses images from three vantage points by mapping the outermost extent of the coronal region perturbed by the pressure front. We derive for the first time the 3D velocity vector and the distribution of Mach numbers, M FM, of the entire front as a function of time. Our approach uses magnetic field reconstructions of the coronal field, full magnetohydrodynamic simulations and imaging inversion techniques. We find that the highest M FM values appear near the coronal neutral line within a few minutes of the coronal mass ejection onset; this neutral line is usually associated with the source of the heliospheric current and plasma sheet. We illustrate the variability of the shock speed, shock geometry, and Mach number along different modeled magnetic field lines. Despite the level of uncertainty in deriving the shock Mach numbers, all employed reconstruction techniques show that the release time of GeV particles occurs when the coronal shock becomes super-critical (M FM > 3). Combining in situ measurements with heliospheric imagery, we also demonstrate that magnetic connectivity between the accelerator (the coronal shock of 2012 May 17) and the near-Earth environment is established via a magnetic cloud that erupted from the same active region roughly five days earlier.