Coronal Mass Ejections Launch Research Articles

Unveiling the journey of a highly inclined CME

Context. A fast (∼2000 km s−1) and wide (> 110°) coronal mass ejection (CME) erupted from the Sun on March 13, 2012. Its interplanetary counterpart was detected in situ two days later by STEREO-A and near-Earth spacecraft, such as ACE, Wind, and Cluster. We suggest that at 1 au the CME extended at least 110° in longitude, with Earth crossing its east flank and STEREO-A crossing its west flank. Despite their separation, measurements from both positions showed very similar in situ CME signatures. The solar source region where the CME erupted was surrounded by three coronal holes (CHs). Their locations with respect to the CME launch site were east (negative polarity), southwest (positive polarity) and west (positive polarity). The solar magnetic field polarity of the area covered by each CH matches that observed at 1 au in situ. Suprathermal electrons at each location showed mixed signatures with only some intervals presenting clear counterstreaming flows as the CME transits both locations. The strahl population coming from the shortest magnetic connection of the structure to the Sun showed more intensity. Aims. The aim of this work is to understand the propagation and evolution of the CME and its interaction with the surrounding CHs, to explain the similarities and differences between the observations at each spacecraft, and report what one of the most longitudinal expanded CME structures measured in situ would be. Methods. Known properties of the large-scale structures from a variety of catalogues and previous studies were used to have a better overview of this particular event. In addition, multipoint observations were used to reconstruct the 3D geometry of the CME and determine the context of the solar and heliospheric conditions before the CME eruption and during its propagation. The graduated cylindrical shell model (GCS) was used to reproduce the orientation, size and speed of the structure with a simple geometry. Also, the Drag-Based Model (DBM) was utilised to understand the conditions of the interplanetary medium better in terms of the drag undergone by the structure while propagating in different directions. Finally, a comparative analysis of the different regions of the structure through the different observatories was carried out in order to directly compare the in situ plasma and magnetic field properties at each location. Results. The study presents important findings regarding the in situ measured CME on March 15, 2012, detected at a longitudinal separation of 110° in the ecliptic plane despite its initial inclination being around 45° when erupted (March 13). This suggests that the CME may have deformed and/or rotated, allowing it to be observed near its legs with spacecraft at a separation angle greater than 100°. The CME structure interacted with high-speed streams generated by the surrounding CHs. The piled-up plasma in the sheath region exhibited an unexpected correlation in magnetic field strength despite the large separation in longitude. In situ observations reveal that at both locations there was a flank encounter – where the spacecraft crossed the first part of the CME – then encountered ambient solar wind, and finally passed near the legs of the structure. Conclusions. A scenario covering all evidence is proposed for both locations with a general view of the whole structure and solar wind conditions. Also, the study shows the necessity of having multipoint observations of large-scale structures in the heliosphere.

Separating the effects of earthside and far side solar events. A case study

On 8 November 2013 a halo-type coronal mass ejection (CME) was observed, together with flares and type II radio bursts, but the association between the flares, radio bursts, and the CME was not clear. Our aim is to identify the origin of the CME and its direction of propagation, and to exclude features that were not connected to it. On the Earth-facing side, a GOES C5.7 class flare occurred close to the estimated CME launch time, followed by an X1.1 class flare. The latter flare was associated with an EUV wave and metric type II bursts. On the far side of the Sun, a filament eruption, EUV dimmings, and ejected CME loops were observed by imaging instruments onboard the Solar TErrestrial RElations Observatory (STEREO) spacecraft that were viewing the backside of the Sun. The STEREO radio instruments observed an interplanetary (IP) type II radio burst at decameter-hectometric wavelengths, which was not observed by the radio instrument onboard the Wind spacecraft located at L1 near Earth. We show that the halo CME originated from the eruption on the far side of the Sun, and that the IP type II burst was created by a shock wave ahead of the halo CME. The radio burst remained unobserved from the earthside, even at heliocentric source heights larger than 9 solar radii. During the CME propagation, the X-class flare eruption caused a small plasmoid ejection earthward, the material of which was superposed on the earlier CME structures observed in projection. The estimated heights of the metric type II burst match well with the EUV wave launched by the X-class flare. As this radio emission did not continue to lower frequencies, we conclude that the shock wave did not propagate any further. Either the shock driver died out, as a blast wave, or the driver speed no longer exceeded the local Alfven speed.

Probabilistic hazard assessment: Application to geomagnetic activity

Probabilistic Hazard Assessment (PHA) provides an appropriate methodology for assessing space weather hazards and their impact on technology. PHA is widely used in geosciences to determine the probability of exceedance of critical thresholds, caused by one or more hazard sources. PHA has proved useful with limited historical data to estimate the likelihood of specific impacts. PHA has also driven the development of empirical and physical models, or ensembles of models, to replace measured data. Here we aim to highlight the PHA method to the space weather community and provide an example of how it could be used. In terms of space weather impact, the critical hazard thresholds might include the Geomagnetically Induced Current in a specific high voltage power transformer neutral, or the local pipe-to-soil potential in a particular metal pipe. We illustrate PHA in the space weather context by applying it to a twelve-year dataset of Earth-directed solar Coronal Mass Ejections (CME), which we relate to the probability that the global three-hourly geomagnetic activity index Kp exceeds specific thresholds. We call this a “Probabilistic Geomagnetic Hazard Assessment”, or PGHA. This provides a simple but concrete example of the method. We find that the cumulative probability of Kp > 6−, > 7−, > 8− and Kp = 9o is 0.359, 0.227, 0.090, 0.011, respectively, following observation of an Earth-directed CME, summed over all CME launch speeds and solar source locations. According to the historical Kp distribution, this represents an order of magnitude increase in the a priori probability of exceeding these thresholds. For the lower Kp thresholds, the results are somewhat distorted by our exclusion of coronal hole high-speed stream effects. The PHGA also reveals useful probabilistic associations between solar source location and subsequent maximum Kp for operational forecasters.

Probabilistic Drag-Based Ensemble Model (DBEM) Evaluation for Heliospheric Propagation of CMEs

The Drag-based Model (DBM) is a 2D analytical model for heliospheric propagation of Coronal Mass Ejections (CMEs) in ecliptic plane predicting the CME arrival time and speed at Earth or any other given target in the solar system. It is based on the equation of motion and depends on initial CME parameters, background solar wind speed, \(w\) and the drag parameter \(\gamma \). A very short computational time of DBM (< 0.01 s) allowed us to develop the Drag-Based Ensemble Model (DBEM) that takes into account the variability of model input parameters by making an ensemble of n different input parameters to calculate the distribution and significance of the DBM results. Thus the DBEM is able to calculate the most likely CME arrival times and speeds, quantify the prediction uncertainties and determine the confidence intervals. A new DBEMv3 version is described in detail and evaluated for the first time determining the DBEMv3 performance and errors by using various CME–ICME lists and it is compared with previous DBEM versions, ICME being a short-hand for interplanetary CME. The analysis to find the optimal drag parameter \(\gamma \) and ambient solar wind speed \(w\) showed that somewhat higher values (\(\gamma \approx 0.3 \times 10^{-7}\) km−1, \(w \approx \) 425 km s−1) for both of these DBEM input parameters should be used for the evaluation than the previously employed ones. Based on the evaluation performed for 146 CME–ICME pairs, the DBEMv3 performance with mean error (ME) of −11.3 h, mean absolute error (MAE) of 17.3 h was obtained. There is a clear bias towards the negative prediction errors where the fast CMEs are predicted to arrive too early, probably due to the model physical limitations and input errors (e.g. CME launch speed). This can be partially reduced by using larger values for \(\gamma \) resulting in smaller prediction errors (\(\mathrm{ME} =-3.9\) h, MAE = 14.5 h) but at the cost of larger prediction errors for single fast CMEs as well as larger CME arrival speed prediction errors. DBEMv3 showed also slight improvement in the performance for all calculated output parameters compared to the previous DBEM versions.

Observations of a prominence eruption and loop contraction

Context.Prominence eruptions provide key observations to understand the launch of coronal mass ejections as their cold plasma traces a part of the unstable magnetic configuration.Aims.We select a well observed case to derive observational constraints for eruption models.Methods.We analyze the prominence eruption and loop expansion and contraction observed on 02 March 2015 associated with a GOES M3.7 class flare (SOL2015-03-02T15:27) using the data from Atmospheric Imaging Assembly (AIA) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We study the prominence eruption and the evolution of loops using the time-distance techniques.Results.The source region is a decaying bipolar active region where magnetic flux cancellation is present for several days before the eruption. AIA observations locate the erupting prominence within a flux rope viewed along its local axis direction. We identify and quantify the motion of loops in contraction and expansion located on the side of the erupting flux rope. Finally, RHESSI hard X-ray observations identify the loop top and two foot-point sources.Conclusions.Both AIA and RHESSI observations support the standard model of eruptive flares. The contraction occurs 19 min after the start of the prominence eruption indicating that this contraction is not associated with the eruption driver. Rather, this prominence eruption is compatible with an unstable flux rope where the contraction and expansion of the lateral loop is the consequence of a side vortex developing after the flux rope is launched.

CMEs in the Heliosphere: I. A Statistical Analysis of the Observational Properties of CMEs Detected in the Heliosphere from 2007 to 2017 by STEREO/HI-1

We present a statistical analysis of coronal mass ejections (CMEs) imaged by the Heliospheric Imager (HI) instruments on board NASA’s twin-spacecraft STEREO mission between April 2007 and August 2017 for STEREO-A and between April 2007 and September 2014 for STEREO-B. The analysis exploits a catalogue that was generated within the FP7 HELCATS project. Here, we focus on the observational characteristics of CMEs imaged in the heliosphere by the inner (HI-1) cameras, while following papers will present analyses of CME propagation through the entire HI fields of view. More specifically, in this paper we present distributions of the basic observational parameters – namely occurrence frequency, central position angle (PA) and PA span – derived from nearly 2000 detections of CMEs in the heliosphere by HI-1 on STEREO-A or STEREO-B from the minimum between Solar Cycles 23 and 24 to the maximum of Cycle 24; STEREO-A analysis includes a further 158 CME detections from the descending phase of Cycle 24, by which time communication with STEREO-B had been lost. We compare heliospheric CME characteristics with properties of CMEs observed at coronal altitudes, and with sunspot number. As expected, heliospheric CME rates correlate with sunspot number, and are not inconsistent with coronal rates once instrumental factors/differences in cataloguing philosophy are considered. As well as being more abundant, heliospheric CMEs, like their coronal counterparts, tend to be wider during solar maximum. Our results confirm previous coronagraph analyses suggesting that CME launch sites do not simply migrate to higher latitudes with increasing solar activity. At solar minimum, CMEs tend to be launched from equatorial latitudes, while at maximum, CMEs appear to be launched over a much wider latitude range; this has implications for understanding the CME/solar source association. Our analysis provides some supporting evidence for the systematic dragging of CMEs to lower latitude as they propagate outwards.

Investigating the Origins of Two Extreme Solar Particle Events: Proton Source Profile and Associated Electromagnetic Emissions

Abstract We analyze the high-energy particle emission from the Sun in two extreme solar particle events in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth’s magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 1998 May 2 event is associated with a flare and a coronal mass ejection (CME), which were well observed by the Nançay Radioheliograph, thus the images of the radio sources are available. For the 2003 November 2 event, the low corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory are available. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images, and other data available for both events. We find a common scenario for both eruptions, including the flare’s dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME.

Numerical simulations of solar energetic particle event timescales associated with ICMEs

Recently, S. W. Kahler studied the timescales of solar energetic particle (SEP) events associated with coronal mass ejections (CMEs) from analysis of spacecraft data. They obtained different timescales for SEP events, such as TO, the onset time from CME launch to SEP onset, TR, the rise time from onset to half the peak intensity (0.5 I p ), and TD, the duration of the SEP intensity above 0.5 I p . In this work, we solve the transport equation for SEPs considering interplanetary coronal mass ejection (ICME) shocks as energetic particle sources. With our modeling assumptions, our simulations show similar results to Kahler’s analysis of spacecraft data, that the weighted average of TD increases with both CME speed and width. Moreover, from our simulation results, we suggest TD is directly dependent on CME speed, but not dependent on CME width, which were not found in the analysis of observational data.

Numerical simulations of solar energetic particle event timescales associated with ICMEs

Recently, S. W. Kahler studied the timescales of solar energetic particle (SEP) events associated with coronal mass ejections (CMEs) from analysis of spacecraft data. They obtained different timescales for SEP events, such as TO, the onset time from CME launch to SEP onset, TR, the rise time from onset to half the peak intensity (), and TD, the duration of the SEP intensity above . In this work, we solve the transport equation for SEPs considering interplanetary coronal mass ejection (ICME) shocks as energetic particle sources. With our modeling assumptions, our simulations show similar results to Kahler’s analysis of spacecraft data, that the weighted average of TD increases with both CME speed and width. Moreover, from our simulation results, we suggest TD is directly dependent on CME speed, but not dependent on CME width, which were not found in the analysis of observational data.

Numerical study of the propagation characteristics of coronal mass ejections in a structured ambient solar wind

AbstractUsing a three‐dimensional (3‐D) magnetohydrodynamics (MHD) model, we analyze and study the propagation characteristics of coronal mass ejections (CMEs) launched at different positions in a realistic structured ambient solar wind. Here the ambient solar wind structure during the Carrington rotation 2095 is selected, which is the characteristics of activity rising phase. CMEs with a simple spherical plasmoid structure are initiated at different solar latitudes with respect to the heliospheric current sheet (HCS) and the Earth in the same ambient solar wind. Then, we numerically obtained the evolution process of the CMEs from the Sun to the interplanetary space. When the Earth and the CME launch position are located on the same side of the HCS, the arrival time of the shock at the Earth is faster than that when the Earth and the CME launch position are located on the opposite side of the HCS. The disturbance amplitudes for the same side event are also larger than those for the opposite side event. This may be due to the fact that the HCS between the CME and the Earth for the opposite side event hinders its propagation and weaken it. The CMEs tend to deflect toward the HCS in the latitudinal direction near the corona and then propagate almost parallel to the HCS in the interplanetary space. This deflecting tendency may be caused by the dynamic action of near‐Sun magnetic pressure gradient force on the ejected coronal plasma.

GLOBAL ENERGETICS OF SOLAR FLARES. IV. CORONAL MASS EJECTION ENERGETICS

ABSTRACT This study entails the fourth part of a global flare energetics project, in which the mass m cme, kinetic energy E kin, and the gravitational potential energy E grav of coronal mass ejections (CMEs) is measured in 399 M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission, using a new method based on the EUV dimming effect. EUV dimming is modeled in terms of a radial adiabatic expansion process, which is fitted to the observed evolution of the total emission measure of the CME source region. The model derives the evolution of the mean electron density, the emission measure, the bulk plasma expansion velocity, the mass, and the energy in the CME source region. The EUV dimming method is truly complementary to the Thomson scattering method in white light, which probes the CME evolution in the heliosphere at r ≳ 2 R ⊙, while the EUV dimming method tracks the CME launch in the corona. We compare the CME parameters obtained in white light with the LASCO/C2 coronagraph with those obtained from EUV dimming with the Atmospheric Imaging Assembly onboard the SDO for all identical events in both data sets. We investigate correlations between CME parameters, the relative timing with flare parameters, frequency occurrence distributions, and the energy partition between magnetic, thermal, nonthermal, and CME energies. CME energies are found to be systematically lower than the dissipated magnetic energies, which is consistent with a magnetic origin of CMEs.

DO INTERACTING CORONAL MASS EJECTIONS PLAY A ROLE IN SOLAR ENERGETIC PARTICLE EVENTS?

Gradual solar energetic (E > 10 MeV) particle (SEP) events are produced in shocks driven by fast and wide coronal mass ejections (CMEs). With a set of western hemisphere 20 MeV SEP events, we test the possibility that SEP peak intensities, Ip, are enhanced by interactions of their associated CMEs with preceding CMEs (preCMEs) launched during the previous 12 hr. Among SEP events with no, 1, or 2 or more (2+) preCMEs, we find enhanced Ip for the groups with preCMEs, but no differences in TO+TR, the time from CME launch to SEP onset and the time from onset to SEP half-peak Ip. Neither the timings of the preCMEs relative to their associated CMEs nor the preCME widths W {sub pre}, speeds V {sub pre}, or numbers correlate with the SEP Ip values. The 20 MeV Ip of all the preCME groups correlate with the 2 MeV proton background intensities, consistent with a general correlation with possible seed particle populations. Furthermore, the fraction of CMEs with preCMEs also increases with the 2 MeV proton background intensities. This implies that the higher SEP Ip values with preCMEs may not be due primarily to CME interactions, such as the 'twin-CME' scenario, butmore » are explained by a general increase of both background seed particles and more frequent CMEs during times of higher solar activity. This explanation is not supported by our analysis of 2 MeV proton backgrounds in two earlier preCME studies of SEP events, so the relevance of CME interactions for larger SEP event intensities remains unclear.« less

A COMPARISON OF SOLAR ENERGETIC PARTICLE EVENT TIMESCALES WITH PROPERTIES OF ASSOCIATED CORONAL MASS EJECTIONS

The dependence of solar energetic proton (SEP) event peak intensities Ip on properties of associated coronal mass ejections (CMEs) has been extensively examined, but the dependence of SEP event timescales is not well known. We define three timescales of 20?MeV SEP events and ask how they are related to speeds v CME or widths W of their associated CMEs observed by LASCO/SOHO. The timescales of the EPACT/Wind 20?MeV events are TO, the onset time from CME launch to SEP onset; TR, the rise time from onset to half the peak intensity (0.5Ip); and TD, the duration of the SEP intensity above 0.5Ip. This is a statistical study based on 217 SEP-CME events observed during 1996-2008. The large number of SEP events allows us to examine the SEP-CME relationship in five solar-source longitude ranges. In general, we statistically find that TO declines slightly with v CME, and TR and TD increase with both v CME and W. TO is inversely correlated with log Ip, as expected from a particle background effect. We discuss the implications of this result and find that a background-independent parameter TO+TR also increases with v CME and W. The correlations generally fall below the 98% significance level, but there is a significant correlation between v CME and W which renders interpretation of the timescale results uncertain. We suggest that faster (and wider) CMEs drive shocks and accelerate SEPs over longer times to produce the longer TR and TD SEP timescales.

Stealth Coronal Mass Ejections: A Perspective

“Stealth CME” has become a commonly used term in recent studies of solar activity. It refers to a coronal mass ejection (CME) with no apparent solar surface association, and therefore has no easily identifiable signature to locate the region on the Sun from which the CME erupted. We review the literature and express caution in categorising CMEs in this way. CMEs were discovered some 40 years ago and there have been numerous statistical studies of associations with phenomena in the solar atmosphere which clearly identify a range of associations, from bright flares and large prominence eruptions to small flares, and even a lack of flares or any identifiable surface activity at all. In this sense the stealth CME concept is not new. One major question relates to whether the range of associations reveal different CME classes, i.e. different CME launch processes, or are indicative of a spectrum of coronal responses to one common process. We favour the latter and stress that this spectrum must be considered in the description of the CME launch, meaning that the physics of a so-called stealth CME must not be fundamentally different from a CME associated with major surface events. On the other hand we also stress that the use of a stealth CME category implies that all surface activity could indeed be detected using modern instrumentation. We argue that this may not be the case, and that even in the SDO era of full-Sun, high resolution imaging, we are restricted by instrument sensitivity and bandwidth issues. Thus, having reviewed the case for stealth CMEs as a distinct category, we stress the need to keep the concept in perspective.

Can a halo CME from the limb be geoeffective?

The probability for a halo coronal mass ejection (CME) to be geoeffective is assumed to be higher the closer the CME launch site is located to the solar central meridian. However, events far from the central meridian may produce severe geomagnetic storms, like the case in April 2000. In this work, we study the possible geoeffectiveness of full halo CMEs with the source region situated at solar limb. For this task, we select all limb full halo (LFH) CMEs that occurred during solar cycle 23, and we search for signatures of geoeffectiveness between 1 and 5 days after the first appearance of each CME in the LASCO C2 field of view. When signatures of geomagnetic activity are observed in the selected time window, interplanetary data are carefully analyzed in order to look for the cause of the geomagnetic disturbance. Finally, a possible association between geoeffective interplanetary signatures and every LFH CME in solar cycle 23 is checked in order to decide on the CME's geoeffectiveness. After a detailed analysis of solar, interplanetary, and geomagnetic data, we conclude that of the 25 investigated events, there are only four geoeffective LFH CMEs, all coming from the west limb. The geoeffectiveness of these events seems to be moderate, turning to intense in two of them as a result of cumulative effects from previous mass ejections. We conclude that ejections from solar locations close to the west limb should be considered in space weather, at least as sources of moderate disturbances.

Initial Fe/O Enhancements in Large, Gradual, Solar Energetic Particle Events: Observations from Wind and Ulysses

Shocks driven by fast coronal mass ejections (CMEs) are the dominant particle accelerators in large, “gradual” solar energetic particle (SEP) events. In these events, the event-integrated value of the iron-to-oxygen ratio (Fe/O) is typically ∼ 0.1, at least at energies of a few MeV/nucleon. However, at the start of some gradual events, when intensities are low and growing, initially Fe/O is ∼ 1. This value is also characteristic of small, “impulsive” SEP events, in which particle acceleration is due to magnetic reconnection. These observations suggested that SEPs in gradual events also include a direct contribution from the flare that accompanied the CME launch. If correct, this interpretation is of critical importance: it indicates a clear path to interplanetary space for particles from the reconnection region beneath the CME. A key issue for the flare origin is “magnetic connectedness”, i.e., proximity of the flare site to the solar footpoint of the observer’s magnetic field line.

INNER HELIOSPHERIC FLUX ROPE EVOLUTION VIA IMAGING OF CORONAL MASS EJECTIONS

Understanding the evolution of flux ropes in coronal mass ejections (CMEs) is of importance both to the scientific and technological communities. Scientifically their presence is critical to models describing CME launch and they likely play a role in CME evolution. Technologically they are the major contributor to severe geomagnetic storms. Using a new processing technique on the STEREO/SECCHI heliospheric imaging data, we have tracked a magnetic flux rope observed by the Wind spacecraft in December 2008 to its origins observed by coronagraphs. We thereby establish that the cavity in the classic three-part coronagraph CME is the feature that becomes the magnetic cloud. This implies that the bright material ahead of the cavity is piled-up coronal or solar wind material. We track the evolution of the cavity en-route and find that its structure transforms from concave inward (curving away from the Sun) to concave outward (toward the Sun) around 0.065 AU from the Sun. The pileup was tracked and its leading edge remained concave inward throughout its journey. Two other CMEs in January 2009 are also inspected and a similar cavity is observed in each, suggesting that they too each contained a flux rope. The results presented here are the first direct observation, through continuous tracking, associating a particular flux rope observed in situ with the same flux rope before ejection from the corona. We speculate that detailed heliospheric imagery of CMEs may lead to a means by which flux ropes can be identified remotely in the heliosphere.

INITIATION AND EARLY DEVELOPMENT OF THE 2008 APRIL 26 CORONAL MASS EJECTION

We present a detailed study of a coronal mass ejection (CME) with high temporal cadence observations in radio and extreme-ultraviolet (EUV). The radio observations combine imaging of the low corona with radio spectra in the outer corona and interplanetary space. The EUV observations combine the three points of view of the STEREO and SOHO spacecraft. The beginning of the CME initiation phase is characterized by emissions that are signatures of the reconnection of the outer part of the erupting configuration with surrounding magnetic fields. Later on, a main source of emission is located in the core of the active region. It is an indirect signature of the magnetic reconnection occurring behind the erupting flux rope. Energetic particles are also injected in the flux rope and the corresponding radio sources are detected. Other radio sources, located in front of the EUV bright front, trace the interaction of the flux rope with the surrounding fields. Hence, the observed radio sources enable us to detect the main physical steps of the CME launch. We find that imaging radio emissions in the metric range permits us to trace the extent and orientation of the flux rope which is later detected in interplanetary space. Moreover, combining the radio images at various frequencies with fast EUV imaging permits us to characterize in space and time the processes involved in the CME launch.

EVOLUTION OF SOLAR MAGNETIC FIELD AND ASSOCIATED MULTIWAVELENGTH PHENOMENA: FLARE EVENTS ON 2003 NOVEMBER 20

We analyze H-alpha images, soft X-ray profiles, magnetograms, extreme ultra-violet images and radio observations of two homologous flare events (M1.4/1N and M9.6/2B) on 20 November 2003 in the active region NOAA 10501 and study properties of reconnection between twisted filament systems, energy release and associated launch of coronal mass ejections (CMEs). During both events twisted filaments observed in H-alpha approached each other and initiated the flare processes. However, the second event showed the formation of cusp as the filaments interacted. The rotation of sunspots of opposite polarities, inferred from magnetograms likely powered the twisted filaments and injection of helicity. Along the current sheet between these two opposite polarity sunspots, the shear was maximum, which could have caused the twist in the filament. At the time of interaction between filaments, the reconnection took place and flare emission in thermal and non-thermal energy ranges attained the maximum. The radio signatures revealed the opening of field lines resulting from reconnection. The H-alpha images and radio data provide the inflow speed leading to reconnection and the scale size of particle acceleration region. The first event produced a narrow and slow CME, whereas the later one was associated with a fast full halo CME. The halo CME signatures observed between Sun and Earth using white-light and scintillation images and in-situ measurements indicated the magnetic energy utilized in the expansion and propagation. The magnetic cloud signature at the Earth confirmed the flux rope ejected at the time of filament interaction and reconnection.

Pre-CME Onset Fuses – Do the STEREO Heliospheric Imagers Hold the Clues to the CME Onset Process?

Understanding the onset of coronal mass ejections (CMEs) is surely one of the holy grails of solar physics today. Inspection of data from the Heliospheric Imagers (HI), which are part of the SECCHI instrument suite aboard the two NASA STEREO spacecraft, appears to have revealed pre-eruption signatures which may provide valuable evidence for identifying the CME onset mechanism. Specifically, an examination of the HI images has revealed narrow rays comprised of a series of outward-propagating plasma blobs apparently forming near the edge of the streamer belt prior to many CME eruptions. In this pilot study, we inspect a limited dataset to explore the significance of this phenomenon, which we have termed a pre-CME ‘fuse’. Although, the enhanced expulsion of blobs may be consistent with an increase in the release of outward-propagating blobs from the streamers themselves, it could also be interpreted as evidence for interchange reconnection in the period leading to a CME onset. Indeed, it is argued that the latter could even have implications for the end-of-life of CMEs. Thus, the presence of these pre-CME fuses provides evidence that the CME onset mechanism is either related to streamer reconnection processes or the reconnection between closed field lines in the streamer belt and adjacent, open field lines. We investigate the nature of these fuses, including their timing and location with respect to CME launch sites, as well as their speed and topology.