White Light Coronagraph Data Research Articles

Estimating the early propagation direction of the coronal mass ejection with DIRECD during the severe event on May 8 and for the follow-up event on June 8, 2024

On May 8, 2024, the solar active region 13664 produced an X-class flare, several M-class flares, and multiple coronal mass ejections (CMEs) directed towards Earth. The initial CME resulted in coronal dimmings, which are characterized by localized reductions in extreme-ultraviolet (EUV) emissions and are indicative of mass loss and expansion during the eruption. On June 8, 2024, after one solar rotation, the same active region produced another eruptive M-class flare that was followed by coronal dimmings that were observed by the Solar Dynamics Observatory (SDO) and the Solar Terrestrial Relations Observatory (STEREO) spacecraft. We analyzed the early CME evolution and propagation direction from the expansion of the coronal dimming observed low in the corona using the method called dimming inferred estimation of the CME direction (DIRECD). DIRECD derived the key parameters of the early CME propagation from the expansion behavior of the associated coronal dimming at the end of its impulsive phase by generating a 3D CME cone model whose orthogonal projection on the solar sphere matches the dimming geometry. To validate the resulting 3D CME cone, we compared the CME properties derived in the low corona with white-light coronagraph data. Using DIRECD, we find that the CME on May 8, 2024 expands close to radially, with an inclination angle of 7.7$^ an angular width of $70^ and a cone height of $0.81 sun $, which was derived at the end of the impulsive dimming phase, and for which the CME showed connections to the dimming and still left footprints in the low corona. It was inclined 7.6$^ north in the meridional plane and 1.1$^ east in the equatorial plane. The CME on June 8, 2024, after one solar rotation, was inclined by 15.7$^ from the radial direction, had an angular width of $81^ and had a cone height of $0.89 sun $. The CME was inclined 6.9$^ south in the meridional plane and 14.9$^ west in the equatorial plane. A validation with white-light coronagraph data confirmed the accuracy of the 3D cone by matching the CME characteristics and projections with STEREO-A COR2 observations. Our study demonstrates that by tracking low coronal signatures such as the coronal dimming expansion in 2D for the May and June 2024 CMEs, we can estimate the 3D CME direction early in the CME evolution. This provides early lead times for mitigating adverse space weather impacts.

Three-part structure of a solar coronal mass ejection observed in low coronal signatures of Solar Orbiter

Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the Sun propagating through the heliosphere. Observations of the March 28, 2022, event provide unique images of a three-part solar CME in the low corona in active region 12975: a bright core or filament, a dark cavity, and a bright front edge. We investigated the relationship between coronal dimming, filament eruption, and early CME propagation in this rarely seen case. We employed 3D filament and CME shock reconstructions along with estimations of early CME evolution inferred from the associated expansion of the coronal dimming. We performed 3D reconstructions using data from Solar Orbiter, Solar TErrestrial RElations Observatory (STEREO-A), and Solar Dynamics Observatory (SDO) to analyse the path, height, and kinematics of the erupting filament. We developed the ATLAS-3D (Advanced Technique for single Line-of-sight Acquisition of Structures in 3D) method and validated it by comparing it to traditional approaches to reconstructing filament loops and the CME shock structure. ATLAS-3D uses Solar Orbiter data exclusively and integrates existing 3D filament reconstructions from the early stages of the event to establish spatial relationships between the filament and the CME frontal edge. Additionally, we employed the DIRECD method to estimate the characteristics of early CME propagation based on its coronal dimming evolution. The filament height increased from 28 to 616 Mm (0.04 to 0.89 $ R_ sun $) over 30 minutes, from 11:05 to 11:35 UT, with a peak velocity of $648 \ km s $ and a peak acceleration of $1624 \ m s $. At 11:45 UT, the filament deflected by about 12$^ reaching a height of 841 Mm (1.21 $ R_ sun $). Simultaneously, the quasi-spherical CME shock expanded from 383 to 837 Mm (0.55 to 1.2 $ R_ sun $) between 11:25 and 11:35 UT. Over 10 minutes, the distance between the filament apex and the CME leading edge more than doubled, from approximately 93 to 212 Mm (0.13 to 0.3 $ R_ sun $),demonstrating significant growth and increasing separation between them. Key parameters estimated from DIRECD and the 3D filament reconstructions include the CME direction (inclined by $6^ from radial expansion), a half-width of $21^ and a cone height of 1.12 $ R_ sun $, which was derived at the end of the dimming's impulsive phase. The reconstructed 3D CME cone, which represents the inner part of the CME,\ closely matches the observed filament shape at 11:45 UT in terms of both height and angular width. Validation with white-light coronagraph data confirmed the accuracy of the 3D cone, particularly in terms of filament and CME characteristics, including projections to STEREO-A COR2 times. The eruptive event on March 28, 2022, showed rapid filament development and its subsequent deflection from the primary propagation direction. This confirms that connections between dimming and CME expansion can be established by the end of the dimming's impulsive phase, preceding the filament’s deflection at 11:45 UT, illustrating further self-similar CME evolution. Our approach links the expanding dimming with the early CME development, highlighting dimmings as indicators and the DIRECD method's utility in correlating the 2D dimming with 3D CME structure. These findings provide valuable insights into early CME evolution and demonstrate the importance of using multi-viewpoint observations and novel reconstruction methods in space weather forecasting.

Predicting the Geoeffectiveness of CMEs Using Machine Learning

Coronal mass ejections (CMEs) are the most geoeffective space weather phenomena, being associated with large geomagnetic storms, and having the potential to cause disturbances to telecommunications, satellite network disruptions, and power grid damage and failures. Thus, considering these storms’ potential effects on human activities, accurate forecasts of the geoeffectiveness of CMEs are paramount. This work focuses on experimenting with different machine-learning methods trained on white-light coronagraph data sets of close-to-Sun CMEs, to estimate whether such a newly erupting ejection has the potential to induce geomagnetic activity. We developed binary classification models using logistic regression, k-nearest neighbors, support vector machines, feed-forward artificial neural networks, and ensemble models. At this time, we limited our forecast to exclusively use solar onset parameters, to ensure extended warning times. We discuss the main challenges of this task, namely, the extreme imbalance between the number of geoeffective and ineffective events in our data set, along with their numerous similarities and the limited number of available variables. We show that even in such conditions adequate hit rates can be achieved with these models.

Origin of Radio Enhancements in Type II Bursts in the Outer Corona

We study interplanetary (IP) solar radio type II bursts from 2011 – 2014 in order to determine the cause of the intense enhancements in their radio emission. Type II bursts are known to be due to propagating shocks that are often associated with fast halo-type coronal mass ejections (CMEs). We analysed the radio spectral data and the white-light coronagraph data from 16 selected events to obtain directions and heights for the propagating CMEs and the type II bursts. CMEs preceding the selected events were included in the analysis to verify whether CME interaction was possible. As a result, we were able to classify the events into five different groups. 1) Events where the heights of the CMEs and type II bursts are consistent, indicating that the shock is located at the leading front of the CME. The radio enhancements are superposed on the type II lanes, and they are probably formed when the shock meets remnant material from earlier CMEs, but the shock continues to propagate at the same speed. 2) Events where the type II heights agree with the CME leading front and an earlier CME is located at a height that suggests interaction. The radio enhancements and frequency jumps could be due to the merging process of the CMEs. 3) Events where the type II heights are significantly lower than the CME heights almost from the start. Interaction with close-by streamers is probably the cause for the enhanced radio emission, which is located at the CME flank region. 4) Events where the radio enhancements are located within wide-band type II bursts and the causes for the radio enhancements are not clear. 5) Events where the radio enhancements are associated with later-accelerated particles (electron beams, observed as type III bursts) that stop at the type II burst emission lane, and no other obvious reason for the enhancement can be identified. Most of the events (38%) were due to shock–streamer interaction, while one quarter of the events was due to possible CME–CME interaction. The drift rates, bandwidth characteristics, or cross-correlations of various characteristics did not reveal any clear association with particular category types. The chosen atmospheric density model causes the largest uncertainties in the derived radio heights, although in some cases, the emission bandwidths also lead to relatively large error margins. Our conclusion is that the enhanced radio emission associated with CMEs and propagating shocks can have different origins, depending on their overall configuration and the associated processes.

Coronal flux ropes and their interplanetary counterparts

We report on a study comparing coronal flux ropes inferred from eruption data with their interplanetary counterparts constructed from in situ data. The eruption data include the source-region magnetic field, post-eruption arcades, and coronal mass ejections (CMEs). Flux ropes were fit to the interplanetary CMEs (ICMEs) considered for the 2011 and 2012 Coordinated Data Analysis Workshops (CDAWs). We computed the total reconnected flux involved in each of the associated solar eruptions and found it to be closely related to flare properties, CME kinematics, and ICME properties. By fitting flux ropes to the white-light coronagraph data, we obtained the geometric properties of the flux ropes and added magnetic properties derived from the reconnected flux. We found that the CME magnetic field in the corona is significantly higher than the ambient magnetic field at a given heliocentric distance. The radial dependence of the flux-rope magnetic field strength is faster than that of the ambient magnetic field. The magnetic field strength of the coronal flux ropes is also correlated with that in interplanetary flux ropes constructed from in situ data, and with the observed peak magnetic field strength in ICMEs. The physical reason for the observed correlation between the peak field strength in ICMEs is the higher magnetic field content in faster coronal flux ropes and ultimately the higher reconnected flux in the eruption region. The magnetic flux ropes constructed from the eruption data and coronagraph observations provide a realistic input that can be used by various models to predict the magnetic properties of ICMEs at Earth and other destination in the heliosphere.

INTERCHANGE RECONNECTION FORCED BY THE FILAMENT ERUPTION INSIDE A PSEUDO-STREAMER

We present rare observational signatures of interchange reconnection (IR) forced by the filament eruption inside a pseudo-streamer (PS). The PS was centered above a positive-polarity region bounded by two negative-polarity coronal holes (CHs), and thus its base contained two polarity inversion lines and a pair of loop arcades where two filaments were harbored. In white-light coronagraph data from two different views, it showed up as a fan-shaped structure consisting of fine rays and a coronal streamer. Followed by a two-ribbon flare and a coronal mass ejection, one of the filaments and its overlying arcade erupted away from the nearby CH and flew over the other arcade to interact with the PS's remote CH. As a result, distinct ribbon-like remote brightenings formed along the remote CH boundary and were. connected to the positive-polarity flare ribbon by a loop system, but the nearby open-field region largely remained. unchanged. except that compact brightenings and a following small coronal dimming appeared close to one end of the erupted filament. In combination with the coronal magnetic configuration that derived from the potential-field source-surface model, these observations can be interpreted as follows: the erupting field was first deflected and guided by the nearby CH's open field. and then reconnected with the oppositely oriented open field of the remote CH, during which both the closed field bridging the erupted filament and the remoter CH's open field were transported in the opposite direction. The observations thus supported the idea that PSs provide favorable environments for IR to take place and remote brightenings along their CH boundaries represent a credible IR signature on the solar surface.

STREAMER WAVES DRIVEN BY CORONAL MASS EJECTIONS

Between July 5th and July 7th 2004, two intriguing fast coronal mass ejection(CME)-streamer interaction events were recorded by the Large Angle and Spectrometric Coronagraph (LASCO). At the beginning of the events, the streamer was pushed aside from their equilibrium position upon the impact of the rapidly outgoing and expanding ejecta; then, the streamer structure, mainly the bright streamer belt, exhibited elegant large scale sinusoidal wavelike motions. The motions were apparently driven by the restoring magnetic forces resulting from the CME impingement, suggestive of magnetohydrodynamic kink mode propagating outwards along the plasma sheet of the streamer. The mode is supported collectively by the streamer-plasma sheet structure and is therefore named "streamer wave" in the present study. With the white light coronagraph data, we show that the streamer wave has a period of about 1 hour, a wavelength varying from 2 to 4 solar radii, an amplitude of about a few tens of solar radii, and a propagating phase speed in the range 300 to 500 km s$^{-1}$. We also find that there is a tendancy for the phase speed to decline with increasing heliocentric distance. These observations provide good examples of large scale wave phenomena carried by coronal structures, and have significance in developing seismological techniques for diagnosing plasma and magnetic parameters in the outer corona.

Automatic Detection and Extraction of Coronal Dimmings from SDO/AIA Data

The volume of data anticipated from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) highlights the necessity for the development of automatic-detection methods for various types of solar activity. Initially recognized in the 1970s, it is now well established that coronal dimmings are closely associated with coronal mass ejections (CMEs), and they are particularly noted as a reliable indicator of front-side (halo) CMEs, which can be difficult to detect in white-light coronagraph data.

Filament eruption, flare, coronal dimming and associated partial halo CME on 2001 September 17

Using Hα, EUV, photospheric magnetic field and white-light coronagraph data, we study the eruption of an active-region Hα filament and associated partial-halo type coronal mass ejection (CME) occurring in NOAA AR 9616 on 2001 September 17. Accompanied by an M1.5 flare, the small active-region filament quickly erupted, a quiet-sun region outside the active region intensively darkened so a remote coronal dimming region was formed, and then a long Hα surge developed from the eruption site. During the eruption, remote EUV brightening appeared along the dimming boundary, leaving behind huge EUV loops connecting the eruption source region and the remote EUV brightening. Finally, as a definite indication of the start of CME, a large-scale dark rim appeared to span the eruption region. These observations indicate that a much larger-scale rearrangement of the coronal magnetic fields, eventually represented by the occurrence of the CME, was involved in the eruption of the filament with small spatial scale. The relationship between the filament eruption, flare and coronal dimming is also discussed.

Source Region of High and Low Speed Wind during the Spartan 201-05 Flight

The large-scale coronal magnetic fields of the Sun are believed to play an important role in organizing the coronal plasma and channeling the high and low speed solar wind along the open magnetic field lines of the polar coronal holes and the rapidly diverging field lines close to the current sheet regions, as has been observed by the instruments aboard the Ulysses spacecraft from March 1992 to March 1997. We have performed a study of this phenomena within the framework of a semi-empirical model of the coronal expansion and solar wind using Spartan, SOHO, and Ulysses observations during the quiescent phase of the solar cycle. Key to this understanding is the demonstration that the white light coronagraph data can be used to trace out the topology of the coronal magnetic field and then using the Ulysses data to fix the strength of the surface magnetic field of the Sun. As a consequence, it is possible to utilize this semi-empirical model with remote sensing observation of the shape and density of the solar corona and in situ data of magnetic field and mass flux to predict values of the solar wind at all latitudes through out the solar system. We have applied this technique to the observations of Spartan 201–05 on 1–2 November, 1998, SOHO and Ulysses during the rising phase of this solar cycle and speculate on what solar wind velocities Ulysses will observe during its polar passes over the south and the north poles during September of 2000 and 2001. In order to do this the model has been generalized to include multiple streamer belts and co-located current sheets. The model shows some interesting new results.

Semiempirical Two‐dimensional MagnetoHydrodynamic Model of the Solar Corona and Interplanetary Medium

We have developed a two-dimensional semiempirical MHD model of the solar corona and solar wind. The model uses empirically derived electron density profiles from white-light coronagraph data measured during the Skylub period and an empirically derived model of the magnetic field which is fitted to observed streamer topologies, which also come from the white-light coronagraph data The electron density model comes from that developed by Guhathakurta and coworkers. The electron density model is extended into interplanetary space by using electron densities derived from the Ulysses plasma instrument. The model also requires an estimate of the solar wind velocity as a function of heliographic latitude and radial component of the magnetic field at 1 AU, both of which can be provided by the Ulysses spacecraft. The model makes estimates as a function of radial distance and latitude of various fluid parameters of the plasma such as flow velocity V, effective temperature T(sub eff), and effective heat flux q(sub eff), which are derived from the equations of conservation of mass, momentum, and energy, respectively. The term effective indicates that wave contributions could be present. The model naturally provides the spiral pattern of the magnetic field far from the Sun and an estimate of the large-scale surface magnetic field at the Sun, which we estimate to be approx. 12 - 15 G. The magnetic field model shows that the large-scale surface magnetic field is dominated by an octupole term. The model is a steady state calculation which makes the assumption of azimuthal symmetry and solves the various conservation equations in the rotating frame of the Sun. The conservation equations are integrated along the magnetic field direction in the rotating frame of the Sun, thus providing a nearly self-consistent calculation of the fluid parameters. The model makes a minimum number of assumptions about the physics of the solar corona and solar wind and should provide a very accurate empirical description of the solar corona and solar wind Once estimates of mass density rho, flow velocity V, effective temperature T(sub eff), effective heat flux q(sub eff), and magnetic field B are computed from the model and waves are assumed unimportant, all other plasma parameters such as Mach number, Alfven speed, gyrofrequency, etc. can be derived as a function of radial distance and latitude from the Sun. The model can be used as a planning tool for such missions as Slar Probe and provide an empirical framework for theoretical models of the solar corona and solar wind The model will be used to construct a semiempirical MHD description of the steady state solar corona and solar wind using the SOHO Large Angle Spectrometric Coronagraph (LASCO) polarized brightness white-light coronagraph data, SOHO Extreme Ultraviolet Imaging Telescope data, and Ulysses plasma data.

Interplanetary Lyman α remote sensing with the Ulysses Interstellar Neutral Gas Experiment

The Ulysses neutral gas instrument obtained celestial sphere maps of interplanetary Lyman α emission from neutral hydrogen in 1991–1996. These maps are unique because the spacecraft was located at a wide range of heliocentric ecliptic latitudes. Eleven of these maps are compared with the predictions of an interstellar wind hydrogen model previously used to study Galileo and Pioneer Venus Lyman α data obtained near the ecliptic plane. The model provides reasonable agreement with the Ulysses maps. The lifetime of the interstellar hydrogen atoms against charge exchange with solar wind protons is shown to be more latitudinally isotropic at solar maximum in 1991 than at solar minimum in 1994 and 1995. This result agrees with white light coronagraph data that generally show a more isotropic coronal brightness pattern at solar maximum. The transition from a more symmetric to a more asymmetric solar wind charge exchange rate also explains differences between published Galileo data from solar maximum and Solar and Heliospheric Observatory (SOHO) Solar Wind Anisotropy Experiment (SWAN) data from solar minimum.

Radioheliograph and white-light coronagraph studies of a coronal mass ejection event

We analyze the radioheliograph and SMM-C/P observations of 1986 November 3 mass ejection event. The metric radio emissions are the only detected activity associated with the mass ejection, but are adequate to study the evolution of the event. The start time of the ejection seems to precede a possible flare behind the limb indicated by the early type III bursts. We discuss the physical relation between various types of bursts and the CME. We interpret moving type IV bursts as a plasma emission process. It is also shown using white-light coronagraph data that the density in the source region of the moving type IV is sufficient to support second harmonic plasma emission at the observed frequency of 50 MHz.

Solar gradual hard X-ray bursts and associated phenomena

White-light coronagraph, H-alpha and radio data are presented as well as hard X-ray data for a sample of 10 gradual hard X-ray bursts (GHBs) in an attempt to better understand the nature of these events. It is found that: (1) the hard X-ray photon energy spectrum began to harden near the onset of the GHBs and continued in this fashion during the decay phase; (2) a coronal mass ejection (CME) occurred in association with at least nine of the GHBs; (3) the GHBs occurred in the late phase of major flares; (4) the centimeter wavelength bursts associated with the GHBs had relatively low frequency spectral maxima, and in relation to the observed hard X-ray emission, they were microwave-rich; (5) the associated decimetric bursts showed significant intensity variations on time scales ranging from 0.1 to approximately greater than 1 minute; and (6) the GHBs were most strongly associated with type IV events. It is concluded that the acceleration and trapping of radiating electrons occurs in the postflare loop systems following CMEs.

A study of the background corona near solar minimum

The white light coronagraph data from Skylab is used to investigate the equatorial and polarK andF coronal components during the declining phase of the solar cycle near solar minimum. Measurements of coronal brightness and polarization brightness product between 2.5 and 5.5R⊙ during the period of observation (May 1973 to February 1974) lead to the conclusions that: (1) the equatorial corona is dominated by either streamers or coronal holes seen in projections on the limb approximately 50% and 30% of the time, respectively; (2) despite the domination by streamers and holes, two periods of time were found which were free from the influences of streamers or holes (neither streamers nor holes were within 30° in longitude of the limb); (3) the derived equatorial background density model is less than 15% below the minimum equatorial models of Newkirk (1967) and Saito (1970); (4) a spherically symmetric density model for equatorial coronal holes yields densities one half those of the background density model; and (5) the inferred brightness of theF-corona is constant to within ±10% and ±5% for the equatorial and polar values, respectively, over the observation period. While theF-corona is symmetric at 2R⊙ it begins to show increasing asymmetry beyond this radius such that at 5R⊙ the equatorialF-coronal brightness is 25% greater than the polar brightness.