White-light Coronal Mass Ejections Research Articles

Prominence Eruptions and Coronal Mass Ejection: A Statistical Study Using Microwave Observations

We present the results of a statistical study of a large number of solar prominence events (PEs) observed by the Nobeyama Radioheliograph. We studied the association rate, relative timing, and spatial correspondence between PEs and coronal mass ejections (CMEs). We classified the PEs as radial and transverse, depending on whether the prominence moved predominantly in the radial or horizontal direction. The radial events were faster and attained a larger height above the solar surface than the transverse events. Out of the 186 events studied, 152 (82%) were radial events, while only 34 (18%) were transverse events. Comparison with white-light CME data revealed that 134 (72%) PEs were clearly associated with CMEs. We compare our results with those of other studies involving PEs and white-light CMEs in order to address the controversy in the rate of association between CMEs and prominence eruptions. We also studied the temporal and spatial relationship between prominence and CME events. The CMEs and PEs seem to start roughly at the same time. There was no solar cycle dependence of the temporal relationship. The spatial relationship was, however, solar cycle dependent. During the solar minimum, the central position angle of the CMEs had a tendency to be offset closer to the equator as compared to that of the PE, while no such effect was seen during solar maximum.

Coronal Mass Ejection of 2000 July 14 Flare Event: Imaging from Near‐Sun to Earth Environment

We report the results of our investigation of interplanetary effects caused by the large solar flare (X5.7/3B) that occurred on 2000 July 14. In association with this event a bright, fast, halo coronal mass ejection (CME) was observed. The analysis of multiwavelength, high-cadence images obtained from the Nancay Radioheliograph shows the on-disk signatures of the initiation of the CME at low-coronal heights, ≤2 R☉. The formation of the CME inferred from the radio data indicates a nearly developed halo at the low corona. The white-light images and CME follow-up measurements in the interplanetary medium also show, in agreement with the radio data, the propagation of the fully developed halo CME. The inference on the consequences of the CME in the inner heliosphere is from the interplanetary scintillation (IPS) observations obtained with the Ooty Radio Telescope and multiantenna system at the Solar-Terrestrial Environment Laboratory. Scintillation measurements at Ooty on a grid of a large number of radio sources provided an opportunity to image the disturbance associated with the CME at different distances from the Sun before its arrival at the near-Earth space. The scintillation data in particular also played a crucial role in understanding the radial evolution of the speed of the CME in the inner heliosphere. The speed-distance plot indicates a two-level deceleration: (1) a low decline in speed at distances within or about 100 solar radii and (2) a rapid decrease at larger distances from the Sun. The linear increase in the size of the CME with radial distance is also briefly discussed. The expansion of the CME, formation of the halo in the low corona, and its speed history in the interplanetary medium suggest a driving energy, which is likely supplied by the twisted magnetic flux rope system associated with the CME.

X-ray Ejecta, White-Light CMEs and a Coronal Shock Wave

We report on a coronal shock wave inferred from the metric type II burst of 13 January 1996. To identify the shock driver, we examined mass motions in the form of X-ray ejecta and white-light coronal mass ejections (CMEs). None of the ejections could be considered fast (> 400 km s−1) events. In white light, two CMEs occurred in quick succession, with the first one associated with X-ray ejecta near the solar surface. The second CME started at an unusually large height in the corona and carried a dark void in it. The first CME decelerated and stalled while the second one accelerated, both in the coronagraph field of view. We identify the X-ray ejecta to be the driver of the coronal shock inferred from metric type II burst. The shock speed reported in the Solar Geophysical Data (1000–2000 km s−1) seems to be extremely large compared to the speeds inferred from X-ray and white-light observations. We suggest that the MHD fast-mode speed in the inner corona could be low enough that the X-ray ejecta is supermagnetosonic and hence can drive a shock to produce the type II burst.

Origin of Helical Coronal Disturbances from the Sun

By combining data from the Nobeyama Radioheliograph and the LASCO coronagraph aboard the SoHO spacecraft, we report two helical coronal disturbances accompanying white-light coronal mass ejections (CMEs). These are activated prominences at the base, rotating around each vertical axis while moving on the solar surface with projected speeds of ≥50 km s-1. The activity continues in a CME core and in a neighboring streamer growing over 6 R☉. Neither flare activity nor radio bursts were observed during the two events. We suggest that the apparent presence or absence of a CME core depends on the density of the eruptive material associated with the CME.

Factors Related to the Origin of a Gradual Coronal Mass Ejection Associated with an Eruptive Prominence on 1998 June 21–22

We present observations of a coronal mass ejection (CME) associated with an eruptive prominence during 1998 June 21-22 by LASCO (Large Angle Spectroscopic Coronagraph) aboard SOHO (Solar and Heliospheric Observatory). Various features in the three-part structured, white-light CME as observed by LASCO-C2 and C3 coronagraphs were compared with features in the other wavelengths, for example, in Fe XIV and Fe X emission lines obtained from LASCO C1, in Hα from Helio-Research and at 17 GHz obtained from Nobeyama Radioheliograph. We have investigated conditions in several data sets to understand the eruptive and the pre-eruptive scenario of the CME. The CME and the eruptive prominence accelerate up to ~20 R☉ and then decelerate to the velocity of the ambient slow solar wind. The analysis clearly shows that this particular CME is a typical case of a very slow or gradual CME for which it is difficult to define an exact onset time. The CME could be tracked for about 30 hours until it crossed a distance of 30 R☉ and disappeared from the field of view of the LASCO-C3 coronagraph. The height-time profiles of various features of this CME suggest that the leading edge of the CME and the top of the prominence or the core follow similar pattern, implying a common driver for both the CME and the eruptive prominence. The observations provide strong evidence that the CME and the prominence eruption resulted from a common cause which is the global restructuring of the magnetic field in the corona in an extensive volume of space near and including the CME. The restructuring in turn was a consequence of newly emerging flux regions near and within the neighboring active regions close to the base of the CME.

Radio Tracking of a White-Light Coronal Mass Ejection from Solar Corona to Interplanetary Medium.

For a solar flare/coronal mass ejection (CME) event on 1999 May 3, type II radio emissions were observed from the metric through the hectometric wavelength regimes. By comparing the dynamics of the CME with that implied by the frequency range and frequency drift rates of the type II radio emissions, it is concluded that the decametric-hectometric type II radio emissions were associated with the CME. The dynamics implied by the metric type II radio burst suggest a distinct coronal shock, associated with the flare, which only produced radio emissions in the low corona.

A comparison of ground‐based and spacecraft observations of coronal mass ejections from 1980–1989

We report here an analysis of observations of solar coronal mass ejections (CMEs) acquired in white light by the Mark III (MK3) K coronameter at Mauna Loa Solar Observatory between 1980 and 1989. Statistical properties of the locations, sizes, and speeds of these events are described. These properties are compared to those in the two other white light CME catalogs from the 1980s, the CMEs observed by the Solwind and SMM spaceborne coronagraphs, and relatively good statistical agreement is found between the three data sets taken over the entire period of observation. A detailed examination was performed for the 141 MK3 CMEs that were also observed by SMM. Virtually all (93%) of the CMEs detected low in the corona by the MK3 instrument were observed to travel out of the SMM field of view, into interplanetary space. The average width of CMEs in the MK3 field of view was 12° smaller than that measured in SMM, and we interpret this statistic as an indication of some increase in size as CMEs move outward through the corona. For a subset of 55 of those mass ejections we were able to combine detailed observations from both MK3 and SMM. Using the combined measurements, we were able to detect and to quantify the initial period of acceleration in a much larger fraction (61%) of the features than was possible from either MK3 alone (9%) or SMM alone (21%). The acceleration was positive for 87% of those features, with an average (median) value of +0.264 km s−2 (+0.044 km s−2). A distinction in terms of association with other forms of solar activity was also evident in this analysis: 55% of the CMEs associated with active regions moved with constant speed, but 82% of the features associated with the eruption of solitary prominences moved with constant acceleration. Also, the average speed for CMEs associated with active regions was significantly faster than those with prominence association (955 versus 411 km s−1). The detection of positive acceleration demonstrates that the forces propelling the CME continue to dominate these events, at least through the altitudes covered by the MK3 and SMM fields of view.

Large‐scale structures and multiple neutral lines associated with coronal mass ejections

We use Yohkoh soft X‐ray telescope (SXT) images of eruptive events visible against the solar disk to examine the coronal structures and the boundaries of the large‐scale magnetic fields considered to be involved in coronal mass ejections (CMEs). From an initial list of about 100 large‐scale events we selected five for detailed study. The transient X‐ray structures in these events spanned distances across the solar surface ranging from 35 to >100 heliographic degrees, comparable to the spans of white light CMEs observed at the limb. The widths of the coronal loop arcades spanned two or three neutral lines, or a single, highly convoluted neutral line. Our interpretation of these results is that multipolar magnetic systems are a common configuration of the source fields of many CMEs, contrary to the first‐order approximation that CMEs involve the eruption of simple, bipolar structures.

X‐Ray and Radio Studies of a Coronal Eruption: Shock Wave, Plasmoid, and Coronal Mass Ejection

On 1994 July 31, a fast (900 km s-1) eruptive structure was observed in X-rays, followed by a slower plasmoid (180 km s-1). They were associated with a coronal mass ejection, prominence eruption, and a host of metric radio bursts. The X-ray structure seems to be a part of a white light coronal mass ejections (CME), as inferred from the white light images of July 30 and 31. A type II burst was observed at the leading edge of the X-ray eruption, while a type IV burst was spatially associated with the detached plasmoid. The type III radio bursts occurred on thin overdense structures associated with the eruption. We detected the rise of plasma levels because of mass addition to the type III burst sources as a result of the eruption. This event further clarifies the manifestation of a CME in X-rays. We identify the X-ray eruption as the driver of the coronal shock wave. This provides answer to the long-standing question regarding the origin of coronal and interplanetary shock waves. We have also found evidence to support the idea that herringbone bursts are produced when the coronal shock wave crosses open magnetic field lines.

Comparison of CMEs, magnetic clouds, and bidirectionally streaming proton events in the heliosphere using helios data

Coronal Mass Ejections (CMEs) are large, energetic expulsions of mass and magnetic fields from the Sun; they can significantly affect large volumes of the heliosphere and appear to be a key cause of geomagnetic storms. We have compiled a list of all significant CMEs detected by the HELIOS white light photometers from 1975–1982. We are studying the characteristics of these CMEs, and present preliminary results of their associations with in-situ features, especially magnetic “clouds” and periods of bidirectionally streaming ions, two classes of structures considered indicative of interplanetary loops. Advantages of this data set include reliable association in the interplanetary medium of the white light CME plasma with the in-situ features, and observations of a large number of events over a long time base.

Clark Lake Radio Observations of Coronal Mass Ejections

We review some recent studies of mass ejections from the Sun using 2-D imaging observations of the Clark Lake multifrequency radioheliograph. Radio signatures of both fast and slow coronal mass ejections (CMEs) have been observed using the Clark Lake radioheliograph. Using temporal and positional analysis of moving type IV and type II bursts, and white light CMEs we find that the type II's and CMEs need not have a direct cause and effect relationship. Instead, the type II seems to be generated by a “decoupled shock”, probably due to an associated flare. The moving type IV burst requires nonthermal particles trapped in magnetic structures associated with the CME. Since nonthermal particles can be generated independent of the speed of CMEs, moving type IV bursts need not be associated only with fast CMEs. Specific examples are presented to support these views.

Large-scale propagation properties of interplanetary disturbances revealed from IPS and spacecraft observations

Interplanetary scintillation (IPS) observations may be used to study large-scale propagation properties of transient interplanetary disturbances in a three-dimensional manner, although current IPS observations have several limitations, e.g., poor time resolution and line-of-sight integration. Comparative studies with spacecraft solar wind and white-light coronal mass ejection (CME) observations are quite helpful in interpretation of IPS observations. An interplanetary disturbance apparently in association with a disappearing solar filament, which took place near the central meridian of the Sun on late 22 April, 1979, is discussed to examine previous deductions from IPS observations. Three-station IPS observations of the flow speed and spacecraft observations suggest that a quasi-spherical interplanetary disturbance was formed around the Sun-Earth line, whereas the center of the disturbance derived from the distribution of enhanced IPS across the sky (g-maps) is located to the east of the Sun-Earth line.

The X-ray signature of solar coronal mass ejections

The coronal response to six solar X-ray flares has been investigated. At a time coincident with the projected onset of the white-light coronal mass ejection associated with each flare, there is a small, discrete soft X-ray enhancement. These enhancements (precursors) precede by typically ∼20 m the impulsive phase of the solar flare which is dominant by the time the coronal mass ejection has reached an altitude above 0.5 R⊙. We identify motions of hot X-ray emitting plasma, during the precursors, which may well be a signature of the mass ejection onsets. Further investigations have also revealed a second class of X-ray coronal transient, during the main phase of the flare. These appear to be associated with magnetic reconnection above post-flare loop systems.

Associations between coronal mass ejections and soft X-ray events

The association between white light coronal mass ejections (CMEs) and full-disk X ray events have been examined as a function of X ray duration during the recent years of high sunspot activity (1979-1981). On a time scale of hours, no duration interval has been found that separates X ray events into two distinct classes depending on whether or not they have associated CMEs. Rather, the tendency for long-duration X ray events to have associated CMEs reflects the fact that, as X ray duration increases, the differential distribution of events without CMEs falls off faster than the distriution of X ray events with CMEs.