Halo Coronal Mass Ejection Event Research Articles

Implementation and validation of the FRi3D flux rope model in EUHFORIA

The “Flux Rope in 3D” (FRi3D, Isavnin, 2016), a coronal mass ejection (CME) model with global three-dimensional (3D) geometry, has been implemented in the space weather forecasting tool EUHFORIA (Pomoell and Poedts, 2018). By incorporating this advanced flux rope model in EUHFORIA, we aim to improve the modelling of CME flank encounters and, most importantly, the magnetic field predictions at Earth. After using synthetic events to showcase FRi3D’s capabilities of modelling CME flanks, we optimize the model to run robust simulations of real events and test its predictive capabilities. We perform observation-based modelling of the halo CME event that erupted on 12 July 2012. The geometrical input parameters are constrained using the forward modelling tool included in FRi3D with additional flux rope geometry flexibilities as compared to the pre-existing models. The magnetic field input parameters are derived using the differential evolution algorithm to fit FRi3D parameters to the in situ data at 1 AU. An observation-based approach to constrain the density of CMEs is adopted, in order to achieve a better estimation of mass corresponding to the FRi3D geometry. The CME is evolved in EUHFORIA’s heliospheric domain and a comparison of FRi3D’s predictive performance with the previously implemented spheromak CME in EUHFORIA is presented. For this event, FRi3D improves the modelling of the total magnetic field magnitude and Bz at Earth by ∼30% and ∼70%, respectively. Moreover, we compute the expected geoeffectiveness of the storm at Earth using an empirical Dst model and find that the FRi3D model improves the predictions of minimum Dst by ∼20% as compared to the spheromak CME model. Finally, we discuss the limitations of the current implementation of FRi3D in EUHFORIA and propose possible improvements.

On the Origin of Solar Halo Coronal Mass Ejections

We present an investigation of halo coronal mass ejections (HCMEs) to understand the origin of HCMEs which is very important because HCMEs are regarded as main causes of heliospheric and geomagnetic disturbances. In this study, we have investigated 313 HCMEs observed during 1996–2012 by LASCO, coronal holes (CHs) and solar flares phenomena. On investigation of 313 HCMEs and related solar flares and coronal holes data, we find that all 313 HCMEs were observed when there were CHs and solar flares within 10° to 60°. We also find that the 128 (40.8%) and 74 (23.6%) HCMEs events were observed when there were CHs and solar flares within 10° and 20°, respectively. The speed of HCMEs does not increase with the increase of the area of CHs while the solar winds speed increases with increase of CHs area. We are of the view that the HCMEs may have been produced by some mechanism, in which the mass ejected by solar flares or active prominences, gets connected with the open magnetic lines of CHs (source of high speed solar wind streams) and moves along them to appear as a HCMEs, earlier suggested by Verma and Pande (1989) and Verma (1998, 2002). The various results obtained in the present analysis are discussed in the light of existing scenario of heliospheric physics.

Auto-detection of Halo CME Parameters as the Initial Condition of Solar Wind Propagation

Halo coronal mass ejections (CMEs) originating from solar activities give rise to geomagnetic storms when they reach the Earth. Variations in the geomagnetic field during a geomagnetic storm can damage satellites, communication systems, electrical power grids, and power systems, and induce currents. Therefore, automated techniques for detecting and analyzing halo CMEs have been eliciting increasing attention for the monitoring and prediction of the space weather environment. In this study, we developed an algorithm to sense and detect halo CMEs using large angle and spectrometric coronagraph (LASCO) C3 coronagraph images from the solar and heliospheric observatory (SOHO) satellite. In addition, we developed an image processing technique to derive the morphological and dynamical characteristics of halo CMEs, namely, the source location, width, actual CME speed, and arrival time at a 21.5 solar radius. The proposed halo CME automatic analysis model was validated using a model of the past three halo CME events. As a result, a solar event that occurred at 03:38 UT on Mar. 23, 2014 was predicted to arrive at Earth at 23:00 UT on Mar. 25, whereas the actual arrival time was at 04:30 UT on Mar. 26, which is a difference of 5 hr and 30 min. In addition, a solar event that occurred at 12:55 UT on Apr. 18, 2014 was estimated to arrive at Earth at 16:00 UT on Apr. 20, which is 4 hr ahead of the actual arrival time of 20:00 UT on the same day. However, the estimation error was reduced significantly compared to the ENLIL model. As a further study, the model will be applied to many more events for validation and testing, and after such tests are completed, on-line service will be provided at the Korean Space Weather Center to detect halo CMEs and derive the model parameters.

Ensemble Modeling of Successive Halo CMEs: A Case Study

The Wang–Sheeley–Arge (WSA)–Enlil cone modeling system is used for making routine arrival-time forecasts of Earth-directed halo coronal mass ejections (CMEs), since they typically produce the most geoeffective events. A major objective of this work is to better understand the sensitivity of the WSA–Enlil modeling results to input model parameters and how these parameters contribute to the overall model uncertainty and performance. In this study, ensemble-modeling results for a succession of three halo CME events that occurred on 2 – 4 August 2011 are presented. We investigate the sensitivity of the modeled CME arrival times to small variations in the input-cone properties by creating ensemble sets of numerical simulations for each CME event, based on multiple sets of cone parameters. We find that the accuracy of the modeled CME arrival times not only depends on the small variations to the initial input geometry, but also on the reliable specification of the background solar wind, which is driven by the input maps of the photospheric magnetic field. The accuracy in the arrival-time predictions also depends on whether the cone parameters for all three CMEs are specified in a single WSA–Enlil simulation. The inclusion or exclusion of one or two of the preceding CMEs affects the solar-wind conditions through which the succeeding CME propagates. Although the accuracy of the modeled arrival times is sensitive to the input maps that are used to drive the background solar wind, the spread in the modeling ensemble remains mostly unchanged when different input maps are used.

MHD numerical study of the latitudinal deflection of coronal mass ejection

In this paper, we analyze and quantitatively study the deflection of coronal mass ejection (CME) in the latitudinal direction during its propagation from the Corona to interplanetary (IP) space using a three‐dimensional (3‐D) numerical magnetohydrodynamics (MHD) simulation. To this end, 12 May 1997 CME event during the Carrington rotation 1922 is selected. First, we try to reproduce the physical properties for this halo CME event observed by the WIND spacecraft. Then, we study the deflection of CME, and quantify the effect of the background magnetic field and the initiation parameters (such as the initial magnetic polarity and the parameters of the CME model) on the latitudinal deflection of CMEs. The simulations show that the initial magnetic polarity substantially affects the evolution of CMEs. The “parallel” CMEs (with the CME's initial magnetic field parallel to that of the ambient field) originating from high latitude show a clear Equatorward deflection at the beginning and then propagate almost parallel to heliospheric current sheet and the “antiparallel” CMEs (with the CME's initial magnetic field opposite to that of the ambient field) deflect toward the pole. Our results demonstrate that the latitudinal deflection extent of the “parallel” CMEs is mainly controlled not only by the background magnetic field strength but also by the initial magnetic field strength of the CMEs. There is an anticorrelation between the latitudinal deflection extent and the CME average transit speed and the energy ratio Ecme/Esw.

Quadrupolar Dimmings During a Partial Halo Coronal Mass Ejection Event

We present detailed observations of the formations of four distinct coronal dimmings during a flare of 17 September 2002, which was followed by an eruption of a huge coronal loop system, and then an over-and-out partial halo coronal mass ejection (CME), with the same direction as the loop system eruption but laterally far offset from the flare site. Among the four dimmings, two compact ones were symmetrically located in the opposite polarity regions immediately adjacent to the highly sheared magnetic polarity inversion line in the flare region, and hence were probably composed of bipolar double dimmings due to a flux-rope eruption and represented its evacuated footpoints. However, another nearby compact dimming and a remote diffuse one were formed in the opposite polarity footpoint regions of the eruptive loop system, and thus probably consisted of a pair of dimmings magnetically linked by the erupting loop system and also indicated its evacuated footpoints. The loop system might have played a role in guiding the erupting flare field and producing the over-and-out CME, but its eruption might simply have been pushed out by the erupting flare field, because there was no reconnection signature between them. From comparison with a derived potential-field source-surface (PFSS) magnetic configuration, our observations consistently suggest that the dimmings were formed in pairs and originated from the eruptions of the two different magnetic systems. We thus define them as “quadrupolar dimmings.”

Cone model-based SEP event calculations for applications to multipoint observations

The problem of modeling solar energetic particle (SEP) events is important to both space weather research and forecasting, and yet it has seen relatively little progress. Most important SEP events are associated with coronal mass ejections (CMEs) that drive coronal and interplanetary shocks. These shocks can continuously produce accelerated particles from the ambient medium to well beyond 1 AU. This paper describes an effort to model real SEP events using a Center for Integrated Space weather Modeling (CISM) MHD solar wind simulation including a cone model of CMEs to initiate the related shocks. In addition to providing observation-inspired shock geometry and characteristics, this MHD simulation describes the time-dependent observer field line connections to the shock source. As a first approximation, we assume a shock jump-parameterized source strength and spectrum, and that scatter-free transport occurs outside of the shock source, thus emphasizing the role the shock evolution plays in determining the modeled SEP event profile. Three halo CME events on May 12, 1997, November 4, 1997 and December 13, 2006 are used to test the modeling approach. While challenges arise in the identification and characterization of the shocks in the MHD model results, this approach illustrates the importance to SEP event modeling of globally simulating the underlying heliospheric event. The results also suggest the potential utility of such a model for forcasting and for interpretation of separated multipoint measurements such as those expected from the STEREO mission. Published by Elsevier Ltd. on behalf of COSPAR.

Early signatures of large-scale field line opening

A fast halo-type coronal mass ejection (CME) associated with a two-ribbon flare, GOES class M 1.3, was observed on February 8, 2000. Soft X-ray and EUV images revealed several loop ejections and one wave-like moving front that started from a remote location, away from the flare core region. A radio type-II burst was observed near the trajectory of the moving soft X-ray front, although association with the CME itself cannot be ruled out. Large-scale dimmings were observed in EUV and soft X-rays, both in the form of disappearing transequatorial loops. We can pinpoint the time and the location of the first large-scale field-line opening by tracing the electron propagation paths above the active region and along the transequatorial loop system, in which large-scale mass depletion later took place. The immediate start of a type-IV burst (interpreted as an upward moving structure) which was located over a soft X-ray dimming region, confirms that the CME had lifted off .W e compare these signatures with those of another halo CME event observed on May 2, 1998, and discuss the possible connections with the magnetic breakout model.

Toroidal‐shaped interplanetary disturbance associated with the halo coronal mass ejection event on 14 July 2000

Interplanetary scintillation (IPS) measurements made with the 327 MHz radio telescopes of the Solar–Terrestrial Environment Laboratory, Nagoya University, have been used to study a three‐dimensional structure of the interplanetary (IP) disturbance associated with the halo coronal mass ejection (CME) event on 14 July 2000 (the so‐called “Bastille Day event”). The IPS observations indicated that the Bastille Day IP disturbance was between 0.3 and 0.7 AU at 17 ± 3 hours after the flare occurrence. A model fitting analysis has been applied here to the IPS observations to reconstruct a global structure of the Bastille Day IP disturbance. As a result, the IP disturbance is found to form a loop‐shaped structure that is significantly longer in the longitudinal (east–west) direction than in latitude. This toroidal‐shaped IP disturbance is found to cross the large‐scale magnetic neutral line almost perpendicularly at its center. Our IPS data also show a nonuniform expansion of the IP disturbance, and the fastest direction is found to lie near above the flare site. Using the best‐fit model determined here and information on the ambient solar wind density from in situ measurements, the mass contained by the IP disturbance has been estimated to be ∼ 5.3 × 1016 g. The result obtained from the present analysis is consistent with independent observations that suggest the Bastille Day interplanetary CME has decelerated significantly in the solar wind. The radial evolution of the apparent feature of the IP disturbance has been revealed from a model calculation using the best‐fit parameters, and this evolution is consistent with IPS measurements made at Ooty, India, slightly later in time. While an origin of the toroidal‐shaped disturbance is an open question, the compressed plasma between the coronal ejecta and the ambient solar wind or the ejecta itself are considered as a possible one.

Solar large-scale channeled dimmings produced by coronal mass ejections

A new type of dimmings, or transient coronal holes (i.e., regions of reduced soft-X-ray and EUV emission), is revealed in analyses of difference solar images obtained with the SOHO EIT ultraviolet telescope at 195 A. Such features can be observed on the solar disk after halo-type coronal mass ejections (CMEs). If several active regions, filaments, and other structures are present on the disk during a major eruptive event, then strongly anisotropic, channel-shaped (“channeled”) dimmings coexist with relatively compact dimmings adjacent to the eruption center. The channeled dimmings are comparable to the compact dimmings in terms of their contrast; stretch along several narrow, extended features (channels); and can span nearly the entire visible disk. Coronal waves, which appear as fronts of enhanced brightness traveling ahead of the dimmings in some halo CME events, are also anisotropic. We argue that such transient phenomena are closely related to the strong disturbance and restructuring of large-scale magnetic fields involved in CMEs, and the channeled character of the dimmings reflects the complexity of the global solar magnetosphere, in particular, near the solar-activity maximum.

Propagation of the Bastille Day 2000 CME Shock in the Outer Heliosphere

The Bastille Day (14 July) 2000 CME is a fast, halo coronal mass ejection event headed earthward. The ejection reached Earth on 15 July 2000 and produced a very significant magnetic storm and widespread aurora. At 1 AU the Wind spacecraft recorded a strong forward shock with a speed jump from ∼ 600 to over 1000 km s−1. About 6 months later, this CME-driven shock arrived at Voyager 2 (∼ 63 AU) on 12 January 2001 with a speed jump of ∼ 60 km s−1. This provides a good opportunity to study the shock propagation in the outer heliosphere. In this study, we employ a 2.5-D MHD numerical model, which takes the interaction of solar wind protons and interstellar neutrals into account, to investigate the shock propagation in detail and compare the model predictions with the Voyager 2 observations. The Bastille Day CME shock undergoes a dramatic change in character from the inner to outer heliosphere. Its strength and propagation speed decay significantly with distance. The model results at the location of Voyager 2 are in good agreement with in-situ observations.