flare-CME Events Research Articles

Solar flares associated coronal mass ejection accompanied with DH type II radio burst in relation with interplanetary magnetic field, geomagnetic storms and cosmic ray intensity

In this paper, we have selected 114 flare-CME events accompanied with Deca-hectometric (DH) type II radio burst chosen from 1996 to 2008 (i.e., solar cycle 23). Statistical analyses are performed to examine the relationship of flare-CME events accompanied with DH type II radio burst with Interplanetary Magnetic field (IMF), Geomagnetic storms (GSs) and Cosmic Ray Intensity (CRI). The collected sample events are divided into two groups. In the first group, we considered 43 events which lie under the CME span and the second group consists of 71 events which are outside the CME span. Our analysis indicates that flare-CME accompanied with DH type II radio burst is inconsistent with CSHKP flare-CME model. We apply the Chree analysis by the superposed epoch method to both set of data to find the geo-effectiveness. We observed different fluctuations in IMF for arising and decay phase of solar cycle in both the cases. Maximum decrease in Dst during arising and decay phase of solar cycle is different for both the cases. It is noted that when flare lie outside the CME span CRI shows comparatively more variation than the flare lie under the CME span. Furthermore, we found that flare lying under the CME span is more geo effective than the flare outside of CME span. We noticed that the time leg between IMF Peak value and GSs, IMF and CRI is on average one day for both the cases. Also, the time leg between CRI and GSs is on average 0 to 1 day for both the cases. In case flare lie under the CME span we observed high correlation (0.64) between CRI and Dst whereas when flare lie outside the CME span a weak correlation (0.47) exists. Thus, flare position with respect to CME span play a key role for geo-effectiveness of CME.

Understanding Problem Forecasts of ISEST Campaign Flare-CME Events

The goal of the International Study of Earth-affecting Solar Transients (ISEST) project as part of the Variability of the Sun and Its Terrestrial Impact (VarSITI) program is to understand the origin, evolution, and propagation of solar transients through the space between the Sun and Earth, and to improve our prediction capability for space weather. A goal of ISEST Working Group 4 (Campaign Events) is to study a set of well-observed Sun-to-Earth events to develop an understanding of why some events are successfully forecast (textbook cases), whereas others become problem or failed forecasts. In this article we study six cases during the rise of Solar Cycle 24 that highlight forecasting problems. Likely source coronal mass ejections (CMEs) were identified in all six cases, but the related solar surface activity ranged from uncertain or weak to X-class flares. The geoeffects ranged from none to severe as in the two Sun–Earth events in 2015 that caused severe storms. These events were chosen to illustrate some key problems in understanding the chain from cause to geoeffect.

RELATION BETWEEN THE CORONAL MASS EJECTION ACCELERATION AND THE NON-THERMAL FLARE CHARACTERISTICS

We investigate the relationship between the main acceleration phase of coronal mass ejections (CMEs) and the particle acceleration in the associated flares as evidenced in Reuven Ramaty High Energy Solar Spectroscopic Imager non-thermal X-rays for a set of 37 impulsive flare-CME events. Both the CME peak velocity and peak acceleration yield distinct correlations with various parameters characterizing the flare-accelerated electron spectra. The highest correlation coefficient is obtained for the relation of the CME peak velocity and the total energy in accelerated electrons (c = 0.85), supporting the idea that the acceleration of the CME and the particle acceleration in the associated flare draw their energy from a common source, probably magnetic reconnection in the current sheet behind the erupting structure. In general, the CME peak velocity shows somewhat higher correlations with the non-thermal flare parameters than the CME peak acceleration, except for the spectral index of the accelerated electron spectrum, which yields a higher correlation with the CME peak acceleration (c ?0.6), indicating that the hardness of the flare-accelerated electron spectrum is tightly coupled to the impulsive acceleration process of the rising CME structure. We also obtained high correlations between the CME initiation height h 0 and the non-thermal flare parameters, with the highest correlation of h 0 to the spectral index ? of flare-accelerated electrons (c 0.8). This means that CMEs erupting at low coronal heights, i.e., in regions of stronger magnetic fields, are accompanied by flares that are more efficient at accelerating electrons to high energies. In the majority of events (~80%), the non-thermal flare emission starts after the CME acceleration, on average delayed by 6 minutes, in line with the standard flare model where the rising flux rope stretches the field lines underneath until magnetic reconnection sets in. We find that the current sheet length at the onset of magnetic reconnection is 21 ? 7?Mm. The flare hard X-ray peaks are well synchronized with the peak of the CME acceleration profile, and in 75% of the cases they occur within ?5?minutes. Our findings provide strong evidence for the tight coupling between the CME dynamics and the particle acceleration in the associated flare in impulsive events, with the total energy in accelerated electrons being closely correlated with the peak velocity (and thus the kinetic energy) of the CME, whereas the number of electrons accelerated to high energies is decisively related to the CME peak acceleration and the height of the pre-eruptive structure.

Large solar flares and coronal mass ejections: Their manifestations in the chromosphere

A phenomenological model of a united (solar flare-coronal mass ejection (CME)) event is briefly described. The model is based on the analysis of the images of the development of some events in various spectral ranges. A modified classification of the chomospheric manifestations of the event is proposed. A phenomenological model describing phenomena in the process of the development of intense solar flare-CME events in the activity complexes on the Sun is briefly presented. The model is based on the analysis of the observation data for some major flares (May 16, 1981, October 19, 2001, July 23, 2002).

Coronal Magnetic Connectivity and EUV Dimmings

Coronal dimming can be considered to be a disk signature of front-side coronal mass ejections (CMEs) (Thompson et al.: 2000, Geophys. Res. Lett.27, 1431). The study of the magnetic connectivity associated with coronal dimming can shed new light on the magnetic nature of CMEs. In this study, four major flare-CME events on 14 July 2000, 28 October 2003, 7 November 2004, and 15 January 2005 are analyzed. They were all halo CMEs associated with major flare activity in complex active regions (ARs) and produced severe space weather consequences. To explore the magnetic connectivity of these CMEs, global potential-field extrapolations based on the composite synoptic magnetograms from the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory are constructed, and their association with coronal dimming is revealed by the Extreme ultraviolet Imaging Telescope. It is found that each flare-CME event involved interaction of more than ten sets of magnetic-loop systems. These loop systems occupied over 50% of all identified loop systems in the visible hemisphere and covered a wide range of solar longitudes and latitudes. We categorize the loop systems as active-region loops (ARLs), AR-interconnecting loops (ARILs) including transequatorial loops (TLs), and long arcades (LAs) straddling filament channels. A recurring pattern, the saddle-field configuration (SFC), consisting of ARILs, is found to be present in all four major flare-CME events. The magnetic connectivity revealed by this work implies that intercoupling and interaction of multiple flux-loop systems are required for a major CME. For comparison, a simple flare-CME event of 12 May 1997 with a relatively simple magnetic configuration is chosen. Even for this simple flare-CME event, we find that multiple flux-loop systems are also present.

MHD Numerical Simulation of Interdependent Flares and CMEs

Using time-dependent resistive magnetohydrodynamic simulations, we study a flux rope eruption caused by magnetic reconnection with implication in coexistent flare-CME events. Without the resistance the flux rope system presents a double catastrophe. We use the first catastrophic state as the initial condition, in which an isolated flux rope coexists with two current sheets: a vertical one below and a transverse one above the flux rope. The flux rope erupts when reconnection starts in the current sheets, and the flux rope dynamics depends on the reconnection sequence in the two current sheets. We obtain three cases: reconnection occurs (1) simultaneously in the two current sheets, (2) first in the transverse one and then in the vertical, and (3) in an order opposite to case 2. Such a model exhibits characteristics of both magnetic breakout model for CME initiation and standard flare model. We argue that both breakout-like and tether-cutting reconnections may be important for CME eruptions.

Two–Current‐Sheet Reconnection Model of Interdependent Flare and Coronal Mass Ejection

Time-dependent resistive magnetohydrodynamic simulations are carried out to study a flux rope eruption caused by magnetic reconnection with implication in coexistent flare-CME (coronal mass ejection) events. An early result obtained in a recent analysis of double catastrophe of a flux rope system is used as the initial condition, in which an isolated flux rope coexists with two current sheets: a vertical one below and a transverse one above the flux rope. The flux rope erupts when reconnection takes place in the current sheets, and the flux rope dynamics depends on the reconnection sequence in the two current sheets. Three cases are discussed: reconnection occurs (1) simultaneously in the two current sheets, (2) first in the transverse one and then in the vertical, and (3) in an order opposite to case 2. Such a two-current-sheet reconnection exhibits characteristics of both magnetic breakout for CME initiation and standard flare model. We argue that both breakout-like and tether-cutting reconnections may be important for CME eruptions and associated surface activities.

Radio and EUV signatures of a solar flare-CME event on November 28, 1998

Using the observational data of the solar radio spectrometer with a broad bandwidth of the Chinese National Astronomical Observatories (CNAO), the Nobeyama Radio Heliograph (NoRH) and Polarimeters (NoRP), YOHKOH and SOHO satellites, it is found that there are two characteristics in an X3.3 flare event associated with coronal mass ejection (CME). (i) X-ray and EUV loop interaction and evolution appeared evidently in corona, followed by the formation of a twisted loop structure, which is consistent with the theoretical calculations of Amari et al. (1999a,b) for the origin of flare-CME events. (ii) The slow frequency drift was shown in the radio observations, corresponding to the relevant movement of the radio source observed by NoRH, at a speed of several tens kilometers per second, which may be associated with the speed of the shock waves resulting from the CME.

Are Homologous Flare–Coronal Mass Ejection Events Triggered by Moving Magnetic Features?

Coronal mass ejections (CMEs) often present destabilization and eruption of a global (or large-scale) magnetic structure in the solar atmosphere. Furthermore, the Earth-directed CMEs are the primary driver of the disastrous space weather. Here we report on five homologous CMEs. They initiated in the early phase of five homologous X-class flares seen in NOAA Active Region 9236 on 2000 November 24-26. The flares appeared between the main sunspot with positive magnetic field and the moat of the active region. We examined the magnetic evolution in the source active region for the first three of the five flare-CME events and found that the main magnetic changes are magnetic flux emergence in the form of moving magnetic features (MMFs) in the vicinity of the main positive magnetic field. There are three peaks in the flux (number) distribution of the emerging MMFs. If each peak corresponds to an X-class flare and associated halo CME, there is a time lag of 10 hr between flux emergence and flaring. The flux appearing in the form of MMFs is 1.1 × 1022 Mx, with a net flux of -2.1 × 1021 Mx. Around the main spot region, about 9.1 × 1021 Mx of flux disappeared in the 2 day interval. This is indicative that the repeated flare-CME activities are triggered by the continuous emergence of MMFs.

Flare-CME Events Associated With a Superactive Region

In a few recent studies, 8 coronal mass ejections (CMEs) were identified to associate with a superactive region, AR 8100. They were all flare-CME events, It is found that the region is characterized by vigorous flux emergence and an imbalance of magnetic flux in two polarities. With the continuous flux emergence and its driven flux cancellation, the EUV dimming associated with flare activity increased in area. Whenever the dimming extended to an area of more than 50×50 square degrees on the solar surface, a flare in the region became CME-associated.

Coronal mass ejections and large scale structure of the corona

A comparative study of two events accompanied by both a flare and a CME has been performed. The data analysis has been made by comparing the observations of the LASCO/SOHO coronagraphs with those of the Nancay radioheliograph. The observations show a clear connection between coronal green and red line transient activity, burst radio emission and the CME development which is due to successive loop interactions. Signatures of these interactions are given by the radio emission. One can identify successive sequences in the evolution of the coronal restructuring leading to the full development of the CME. Identification and timing of these sequences result from the radio emission analysis. For flare-CME events, the evolution takes place in the low corona and is extremely fast of the order, on a few minutes.