Multi-wavelength observations of the onset phase of a coronal mass ejection

The structure and dynamics of the initial phases of a coronal mass ejection (CME) seen in soft X-ray, extreme ultraviolet and optical emission are described. The event occurred on the SW limb of the Sun in active region AR 8026 on 9 April 1997. Just prior to the CME there was a class C1.5 flare. Images taken with the Extreme Ultraviolet Imaging Telescope (EIT) reveal the emergence of a candle-flame shaped extreme ultraviolet (EUV) cavity at the time of the flare. Yohkoh images, taken about 15 min later, show that this cavity is filled with hot X-ray emitting gas. It is most likely that this is the site of the flare. Almost simultaneous to the flare, an H surge or small filament eruption occurs about 50 arc sec northwards along the limb from the EUV cavity. At both the site of the core of the hot, EUV cavity and the filament ejection are X-ray jets. These jets seem to be connected by hot loops near their bases. Both jets disappear within a few minutes of one another.Clear evidence of the CME first appeared in the Large Angle Spectrometric Coronagraph (LASCO) and EIT images 40 min after the flare and onset of the filament ejection. It seems to come from a region between the two X-ray jets. This leads to the speculation that magnetic field reconnection near one footpoint of a loop system triggers reconnection near its other footpoint. The loop system is destabilized and ultimately gives rise to the CME. This possibility is supported by magnetic field and H images taken when the active region was at disk center which show that the active region had a double bipole structure with dark H filaments between the bipoles.     

Giant Meterwave Radio Telescope observations of an M2.8 flare: Insights into the initiation of a flare–coronal mass ejection event

We present the first observations of a solar flare with the GMRT. An M2.8 flare observed at 1060 MHz with the GMRT on 17 November 2001 was associated with a prominence eruption observed at 17 GHz by the Nobeyama radioheliograph and the initiation of a fast partial halo CME observed with the LASCO C2 coronagraph. Towards the start of the eruption, we find evidence for reconnection above the prominence. Subsequently, we find evidence for rapid growth of a vertical current sheet below the erupting arcade, which is accompanied by the flare and prominence eruption.     

Yohkoh/SXT observations of a coronal mass ejection near the solar surface

We report the observations of a coronal mass ejection (CME) using the Soft X-ray Telescope on board the Yohkoh Mission. The CME had the familiar three part structure (frontal loop, prominence core and a cavity). The erupting prominence was observed by the Nobeyama radioheliograph. We were able to determine the mass of the CME (2.6 × 10¹⁴ g) from X-ray observations which seems to be at the lower end of the range of CME masses reported before from white light observations. This is the first time the mass of a CME has been determined from X-ray observations. The height of onset of the CME was 0.3R_⊙. The CME moved much faster than the erupting prominence while its acceleration was smaller than that of the erupting prominence.J. Leonard Culhane     

Multi-wavelength observations of the 1998 September 27 flare spray

We report on observations of a large eruptive event associated with a flare that occurred on 27 September 1998 made with the Richard B. Dunn Solar Telescope at Sacramento Peak Observatory (several wave bands including off-line-center H), in soft and hard X-rays (GOES and BATSE), and in several TRACE wave bands (including Feix/x 171 Å, Fexii 195 Å, and Civ 1550 Å). The flare initiation is signaled by two H foot-point brightenings which are closely followed by a hard X-ray burst and a subsequent gradual increase in other wavelengths. The flare light curves show a complicated, three-component structure which includes two minor maxima before the main GOES class C5.2 peak after which there is a characteristic exponential decline. During the initial stages, a large spray event is observed within seconds of the hard X-ray burst which can be directly associated with a two-ribbon flare in H. The emission returns to pre-flare levels after about 35 min, by which time a set of bright post-flare loops have begun to form at temperatures of about 1.0–1.5 MK. Part of the flare plasma also intrudes into the penumbra of a large sunspot, generally a characteristic of very powerful flares, but the flare importance in GOES soft X-rays is in fact relatively modest. Much of the energy appears to be in the form of a second ejection which is observed in optical and ultraviolet bands, traveling out via several magnetic flux tubes from the main flare site (about 60° from Sun center) to beyond the limb.     

Direct observations of a flare related coronal and solar wind disturbance

Numerous mass ejections from the Sun have been detected with orbiting coronagraphs. Here for the first time we document and discuss the direct association of a coronagraph observed mass ejection, which followed a 2B flare, with a large interplanetary shock wave disturbance observed at 1 AU. Estimates of the mass (2.4 × 10¹⁶ g) and energy content (1.1 × 10³² erg) of the coronal disturbance are in reasonably good agreement with estimates of the mass and energy content of the solar wind disturbance at 1 AU. The energy estimates as well as the transit time of the disturbance are also in good agreement with numerical models of shock wave propagation in the solar wind.     

Space weather effects of coronal mass ejection

This paper describes the space weather effects of a major CME which was accompanied by extremely violent events on the Sun. The signatures of the event in the interplanetary medium (IPM) sensed by Ooty Radio Telescope, the solar observations by LASCO coronagraph onboard SOHO, GOES X-ray measurements, satellite measurements of the interplanetary parameters, GPS based ionospheric measurements, the geomagnetic storm parameter Dst and ground based ionosonde data are used in the study to understand the space weather effects in the different regions of the solar-terrestrial environment. The effects of this event are compared and possible explanations attempted.     

Thermal and nonthermal emissions during a coronal mass ejection

We report on the thermal and nonthermal radio emissions from a coronal mass ejection (CME) observed at meter-decameter wavelengths using the Clark Lake multifrequency radioheliograph. From white-light observations of the Solar Maximum Mission Coronagraph/Polarimeter instrument the CME was found to have a speed of 450 km s^–1. Since there was no nonthermal radio emission in the beginning of the event and the one which occurred later was quite weak, we were able to observe the thermal structure of the CME in radio. Type III bursts and a nonthermal continuum started several minutes after the CME onset. We use the radio and optical observations to show that the CME was not driven by the flare. We investigate the thermal structure and geometry of the mass ejection in radio and compare it with the optical evidence. Finally we develop a schematic model of the event and point out that particle acceleration high in the corona is possible.     

The speeds of coronal mass ejection events

The outward speeds of mass ejection events observed with the white light coronagraph experiment on Skylab varied over a range extending from less than 100 km s^–1 to greater than 1200 km s^–1. For all events the average speed within the field of view of the experiment (1.75 to 6 solar radii) was 470 km s^–1. Typically, flare associated events (Importance 1 or greater) traveled faster (775 km s^–1) than events associated with eruptive prominences (330 km s^–1); no flare associated event had a speed less than 360 km s^–1, and only one eruptive prominence associated event had a speed greater than 600 km s^–1. Speeds versus height profiles for a limited number of events indicate that the leading edges of the ejecta move outward with constant or increasing speeds.Metric wavelength type II and IV radio bursts are associated only with events moving faster than about 400 km s^–1; all but two events moving faster than 500 km ^–1 produced either a type II or IV radio burst or both. This suggests that the characteristic speed with which MHD signals propagate in the lower (1.1 to 3 solar radii) corona, where metric wavelength bursts are generated, is about 400 to 500 km s^–1. The fact that the fastest mass ejection events are almost always associated with flares and with metric wavelength type II and IV radio bursts explains why major shock wave disturbances in the solar wind at 1 AU are most often associated with these forms of solar activity rather than with eruptive prominences.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The sources of material comprising a mass ejection coronal transient

The origin of the material which is ejected during a white light coronal transient has not been determined heretofore. Study of a disturbance on 26 and 27 August 1973, during which a slowly ascending prominence and a more rapid accompanying coronal transient were simultaneously observed, helps to resolve this question. Prominence images obtained in Hα 6563 Å and in He II 304 Å are nearly identical. The mass ejection transient observed in white light (3700–7000 Å) appeared to be a loop about 1 R_⊙ higher than the top of the ascending prominence; it accelerated away from the prominence below it. These observations imply: (1) the bulk of the ejected material did not originate in the ascending prominence; (2) therefore, most of the material must have come from the low corona above the prominence, (and was at coronal temperatures during its outward passage); and (3) the total event - ascending prominence accompanied by coronal mass ejection - was far larger, more energetic, and longer lasting than would be inferred from the prominence observations alone. The transient of 26–27 August was slow and of atypical shape compared to other mass ejection transients, but we believe that these three conclusions apply to most, if not all, of the more than 60 loop-shaped coronal transients observed by the High Altitude Observatory's coronagraph during the nine-month flight of Skylab.     

Narrowband dm-spikes as indication of flare mass ejection

The paper presents the radio spectra of seven solar flares (May 16, 1981; August 19, 1981; January 31, 1982; February 1, 1982; June 3, 1982; June 7, 1982; and July 12, 1982), whose common feature is the presence of narrowband dm-spikes. A close relationship was found among dm-spikes, dm-pulsations and type II radio bursts. Moreover, all flares under study showed indications of a mass ejection process. Based both on these facts and on the theory of dm-spikes (Kuijpers et al., 1981), our observations can be explained by runaway processes in several small regions within the ejected and tearing magnetic structure of the flare.     

Simultaneous radio and white light observations of the 1984 June 27 coronal mass ejection event

We present the two-dimensional imaging observations of radio bursts in the frequency range 25–50 MHz made with the Clark Lake multifrequency radioheliograph during a coronal mass ejection event (CME) observed on 1984, June 27 by the SMM Coronagraph/Polarimeter and Mauna Loa K-coronameter. The event was spatially and temporally associated with precursors in the form of meter-decameter type III bursts, soft X-ray emission and a H flare spray. The observed type IV emission in association with the CME (and the H spray) could be interpreted as gyrosynchrotron emission from a plasmoid containing a magnetic field of 2.5 G and nonthermal electrons with a number density of 10⁵ cm^–3 and energy 350 keV.On leave from Indian Institute of Astrophysics, Kodaikanal, India.     

X-ray observations of limb flare loops and post-flare coronal arch

We present observations of another post-flare arch following an eruptive flare, detected in X-ray lines above the western solar limb on 2 May 1985.     

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 cycle variation of interplanetary coronal mass ejection latitudes

With the use of interplanetary coronal mass ejections (ICMEs) compiled by Richardson and Cane from 1996 to 2007 and the associated coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO), we investigate the solar cycle variation of real ICME-associated CME latitudes during solar cycle 23 using Song et al.’s method. The results show the following:

Deflection of coronal mass ejection in the interplanetary medium

A solar coronal mass ejection (CME) is a large-scale eruption of plasma and magnetic fields from the Sun. It is believed to be the main source of strong interplanetary disturbances that may cause intense geomagnetic storms. However, not all front-side halo CMEs can encounter the Earth and produce geomagnetic storms. The longitude distribution of the Earth-encountered front-side halo CMEs (EFHCMEs) has not only an east–west (E–W) asymmetry  (Wang et al., 2002), but also depends on the EFHCMEs' transit speeds from the Sun to 1 AU. The faster the EFHCMEs are, the more westward does their distribution shift, and as a whole, the distribution shifts to the west. Combining the observational results and a simple kinetic analysis, we believe that such E–W asymmetry appearing in the source longitude distribution is due to the deflection of CMEs' propagation in the interplanetary medium. Under the effect of the Parker spiral magnetic field, a fast CME will be blocked by the background solar wind ahead and deflected to the east, whereas a slow CME will be pushed by the following background solar wind and deflected to the west. The deflection angle may be estimated according to the CMEs' transit speed by using a kinetic model. It is shown that slow CMEs can be deflected more easily than fast ones. This is consistent with the observational results obtained by Zhang et al. (2003), that all four Earth-encountered limb CMEs originated from the east. On the other hand, since the most of the EFHCMEs are fast events, the range of the longitude distribution given by the theoretical model is E40°,W70°, which is well consistent with the observational results (E40°,W75°).     

The eruption of a prominence and coronal mass ejection which drive reconnection

Two possible limiting scenarios are proposed for the production of a coronal mass ejection. In the first the magnetic field around a prominence evolves until it loses equilibrium and erupts, which drives reconnection below the prominence and an eruption of the overlying magnetic arcade. In the second a large-scale magnetic arcade evolves until it loses equilibrium and erupts, thereby causing a prominence to erupt. In general it is likely to be the non-equilibrium of the coupled system which creates the eruption. Furthermore, large quiescent prominences are expected to be centred within the magnetic bubble of a coronal mass ejection whereas when active-region prominences erupt they are likely to be located initially to one side of the bubble.A model is set up for the eruption of a magnetically coupled prominence and coronal mass ejection. This represents a development of the Anzer and Pneuman (1982) model by overcoming two limitations of it, namely that: it is not globally stable initially and so one wonders how it can be set up in a stable way before the eruption; it has reconnection driving the CME whereas recent observations suggest that the reverse may be happening. In our model we assume that magnetic reconnection below the prominence is driven by the eruption and the driver is magnetic non-equilibrium in the coupled prominence-mass ejection system. The prominence is modelled as a twisted flux tube and the mass ejection as an overlying void and magnetic bubble. Two different models of the prominence are considered. In one a globally stable equilibrium becomes unstable when a threshold magnetic flux below the prominence is exceeded and, in the other, equilibrium ceases to exist. In both cases, the prominence and mass-ejection accelerate upwards before reaching constant velocities in a manner that is consistent with observations. It is found that the greater the reconnection that is driven by the eruption, the higher is the final speed.     

Forerunners: Early coronal manifestations of solar mass ejection events

Coronal ejection transients viewed with the white light coronagraph on Skylab are studied from the times of their very earliest manifestations for clues to their origin. Excess coronal mass with a configuration like that of the eventual transient is seen in twelve events prior to the transient's associated near-surface H eruption or flare. In seven of the events, data are adequate to observe the rates of outward mass motion of coronal material prior to their surface manifestations. The observations place severe constraints on different solar mass ejection mechanisms because they spread the process responsible for the ejection over a larger region of the corona and over a longer period of time than normally considered. The observations suggest the corona is an active participant in the ejection that begins with the acceleration of the outer portion of a preexisting structure and ends with the obvious surface manifestation.Skylab Solar Workshop Postdoctoral Appointee 1975–78. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

EUV and coronagraphic observations of coronal mass ejections

The Large Angle Spectrometric Coronagraph (LASCO) and Extreme-ultraviolet Imaging Telescope (EIT) onboard Solar and Heliospheric Observatory (SOHO) provide us with unprecedented multi-wavelength observations helping us to understand different dynamic phenomena on the Sun and in the corona. In this paper we discuss the association between post-eruptive arcades (PEAs) detected by EIT and white-light coronal mass ejections (CMEs) detected by LASCO/C2 telescope.     

Multi-wavelength observations of the 2014 June 11 M3.9 flare: temporal and spatial characteristics

We present multi-wavelength observations of an M-class flare(M3.9) that occurred on 2014 June 11. Our observations were conducted with the Dunn Solar Telescope(DST), employing adaptive optics, the multi-camera system Rapid Oscillations in Solar Atmosphere(ROSA), the new Hydrogen-Alpha Rapid Dynamics camera(HARDcam) in various wavelengths, such as Ca II K, Mg I b_2(at 5172.7 ?A), and Hα narrow band and G-band continuum filters. Images were re-constructed using the Kiepenheuer-Institut Speckle Interferometry Package(KISIP) code, to improve our image resolution. We observed intensity increases of ≈120%–150% in the Mg, Ca K and Hα narrow band filters during the flare. Intensity increases for the flare observed in the SDO EUV channels were several times larger, and the X-rays, as recorded by GOES, increased over a factor of 30 for the harder band. Only a modest delay was found between the onset of flare ribbons of a nearby sympathetic flare and the main flare ribbons observed in these narrow band filters. The peak flare emission occurred within a few seconds for the Ca K, Mg and Hα bands. Timedistance techniques indicate propagation velocities of ≈60 km s~(-1) for the main flare ribbon and as high as300 km s~(-1) for smaller regions, which we attribute to filament eruptions. This result and delays and velocities observed with SDO(≈100 km s~(-1)) for different coronal heights agree well with the simple model of energy propagation versus height, although a more detailed model for the flaring solar atmosphere is needed. Finally, we detected marginal quasi-periodic pulsations(QPPs) in the 40–60 s range for the Ca K,Mg and Hα bands, and such measurements are important for disentangling the detailed flare-physics.     

Influence of coronal mass ejection on geomagnetic activity during 1988–1993

The most rapid and dramatic evolution in the solar corona occurs in events now known as Coronal Mass Ejections (CMEs). There have considerable importance for our understanding of the evolution of the mass and energy injected into the interplanetary medium. In this work, we have studied the relation of CMEs with geomagnetic activity for the period of 1988 to 1993. Not all CMEs are capable of producing geomagnetic disturbances. Our study indicates that the maximum chance of a geomagnetic disturbance occurs two to three days after a CME in association with B-type solar flares.