Large Coronal Mass Ejections Research Articles

Solar Type II Radio Bursts and IP Type II Events

We have examined radio data from the WAVES experiment on the Wind spacecraft in conjunction with ground-based data in order to investigate the relationship between the shocks responsible for metric type II radio bursts and the shocks in front of coronal mass ejections (CMEs). The bow shocks of fast, large CMEs are strong interplanetary (IP) shocks, and the associated radio emissions often consist of single broad bands starting below approx. 4 MHz; such emissions were previously called IP type II events. In contrast, metric type II bursts are usually narrowbanded and display two harmonically related bands. In addition to displaying complete dynamic spectra for a number of events, we also analyze the 135 WAVES 1 - 14 MHz slow-drift time periods in 2001-2003. We find that most of the periods contain multiple phenomena, which we divide into three groups: metric type II extensions, IP type II events, and blobs and bands. About half of the WAVES listings include probable extensions of metric type II radio bursts, but in more than half of these events, there were also other slow-drift features. In the 3 yr study period, there were 31 IP type II events; these were associated with the very fastest CMEs. The most common form of activity in the WAVES events, blobs and bands in the frequency range between 1 and 8 MHz, fall below an envelope consistent with the early signatures of an IP type II event. However, most of this activity lasts only a few tens of minutes, whereas IP type II events last for many hours. In this study we find many examples in the radio data of two shock-like phenomena with different characteristics that occur simultaneously in the metric and decametric/hectometric bands, and no clear example of a metric type II burst that extends continuously down in frequency to become an IP type II event. The simplest interpretation is that metric type II bursts, unlike IP type II events, are not caused by shocks driven in front of CMEs.

The Interplanetary Responses to the Great Solar Activities in Late October 2003

Based on the observations of the Sun and the interplanetary medium, a series of solar activities in late October 2003 and their consequences are studied comprehensively. Thirteen X-ray flares with importance greater than M-class, six frontside halo coronal mass ejections (CMEs) with span angle larger than 100∘ and three associated eruptions of filament materials are identified by examining lots of solar observations from October 26 to 29. All these flares were associated with type III radio bursts, all the frontside halo CMEs were accompanied by type II or type II-like radio bursts. Particularly, among these activities, two major solar events caused two extraordinary enhancements (exceeding 1000 particles/(cm2s−1sterMev−1) of solar energetic particle (SEP) flux intensity near the Earth, two large ejecta with fast shocks preceding, and two great geomagnetic storms with Dst peak value of −363 and −401 nT, respectively. By using a cross correlation technique and a force-free cylindrical flux rope model, the October 29 magnetic cloud associated with the largest CME are analyzed, including its orientation and the sign of its helicity. It is found that the helicity of the cloud is negative, contrary to the regular statistical pattern that negative- and positive-helical interplanetary magnetic clouds would be expected to come from northern and southern solar hemisphere. Moreover, the relationship between the orientation of magnetic cloud and associated filament is discussed. In addition, some discussion concerning multiple-magnetic-cloud structures and SEP events is also given.

Study on the Radiation Mechanism of Plasmas Near L1 Point Affected by CMEs and the Associated Microwave Bursts

CME在产生和发展过程中与日冕和行星际介质相互作用并发出不同波长的射电辐射.在研究了无CME时空间等离子体的各种辐射机制基础上,统计分析了1999年2月至1999年8月期间有较大的CME发生情况下,在CME影响下L1拉格朗日点附近等离子体参数发生变化后的射电辐射机制.分析结果表明,其射电辐射机制主要是轫致辐射、微量的回旋辐射和更加微弱的复合辐射.此外,分析讨论了1999年2月至1999年8月期间与CME共生的太阳微波爆发.分析结果表明,与CME共生的是微波逐渐型爆发、尖峰爆发,其辐射机制主要是轫致辐射、回旋共振辐射、等离子体辐射及电子回旋脉泽辐射.

Extremely high speed solar wind: 29–30 October 2003

On 29–30 October 2003 the Solar Wind Electron Proton Alpha Monitor (SWEPAM) instrument on the Advanced Composition Explorer (ACE) spacecraft measured solar wind speeds in excess of 1850 km/s, some of the highest speeds ever directly measured in the solar wind. These speeds were observed following two large coronal mass ejection (CME) driven shocks. Surprisingly, despite the unusually high speeds, many of the other solar wind parameters were not particularly unusual in comparison with other large transient events. The magnetic field reached −68 nT, a large but not unprecedented value. The proton temperatures were significantly higher than typical for a CME in the solar wind at 1 AU (>107 K), but the proton densities were moderate, leading to low to moderate proton beta. The solar wind dynamic pressure was not unusual for large events but, when coupled with the large negative Bz, was sufficient to cause intense geomagnetic disturbances.

The Solar Mass Ejection Imager (Smei)

We describe an instrument (SMEI) which has been specifically designed to detect and forecast the arrival of solar mass ejections and other heliospheric structures which are moving towards the Earth. Such events may cause geomagnetic storms, with resulting radiation hazards and disruption to military and commercial communications; damage to Earth-orbiting spacecraft; and also terrestrial effects such as surges in transcontinental power transmission lines. The detectors are sensitive over the optical wave-band, which is measured using CCD cameras. SMEI was launched on 6 January 2003 on the Coriolis spacecraft into a Sun-synchronous polar orbit as part of the US DoD Space Test Programme. The instrument contains three cameras, each with a field of view of 60°×3°, which are mounted onto the spacecraft such that they scan most of the sky every 102-min orbit. The sensitivity is such that changes in sky brightness equivalent to a tenth magnitude star in one square degree of sky may be detected. Each camera takes an image every 4 s. The normal telemetry rate is 128 kbits s−1. In order to extract the emission from a typical large coronal mass ejection, stellar images and the signal from the zodiacal dust cloud must be subtracted. This requires accurate relative photometry to 0.1%. One consequence is that images of stars and the zodiacal cloud will be measured to this photometric accuracy once per orbit. This will enable studies of transient zodiacal cloud phenomena, flare stars, supernovae, comets, and other varying point-like objects.

Ulysses COSPIN observations of cosmic rays and solar energetic particles from the South Pole to the North Pole of the Sun during solar maximum

Abstract. In 2000–2001 Ulysses passed from the south to the north polar regions of the Sun in the inner heliosphere, providing a snapshot of the latitudinal structure of cosmic ray modulation and solar energetic particle populations during a period near solar maximum. Observations from the COSPIN suite of energetic charged particle telescopes show that latitude variations in the cosmic ray intensity in the inner heliosphere are nearly non-existent near solar maximum, whereas small but clear latitude gradients were observed during the similar phase of Ulysses’ orbit near the 1994–95 solar minimum. At proton energies above ~10 MeV and extending up to >70 MeV, the intensities are often dominated by Solar Energetic Particles (SEPs) accelerated near the Sun in association with intense solar flares and large Coronal Mass Ejections (CMEs). At lower energies the particle intensities are almost constantly enhanced above background, most likely as a result of a mix of SEPs and particles accelerated by interplanetary shocks. Simultaneous high-latitude Ulysses and near-Earth observations show that most events that produce large flux increases near Earth also produce flux increases at Ulysses, even at the highest latitudes attained. Particle anisotropies during particle onsets at Ulysses are typically directed outwards from the Sun, suggesting either acceleration extending to high latitudes or efficient cross-field propagation somewhere inside the orbit of Ulysses. Both cosmic ray and SEP observations are consistent with highly efficient transport of energetic charged particles between the equatorial and polar regions and across the mean interplanetary magnetic fields in the inner heliosphere.Key words. Interplanetary physics (cosmic rays) – Solar physics, astrophysics and astronomy (energetic particles; flares and mass ejections)

Flare- and Shock-accelerated Energetic Particles in the Solar Events of 2001 April 14 and 15

We report heavy-ion composition and spectra for the solar energetic particle (SEP) events of 2001 April 14 and 15, using the combined capabilities of the Advanced Composition Explorer (ACE), Wind, and the Interplanetary Monitoring Platform 8 (IMP-8) to cover the energy range from ∼30 keV nucleon^(-1) to ∼400 MeV nucleon^(-1). These two events are, respectively, the largest impulsive event and the largest ground-level event observed so far in solar cycle 23. These events arose from the same active region and launched into similar interplanetary conditions. Both were associated with large western flares and fast coronal mass ejections (CMEs). However, the two events are distinctly different, thereby providing useful reminders of the fundamental differences between flare- and shock-accelerated SEPs. The detailed observations present challenges for our theoretical understanding of SEP production. Of particular note is the fact that iron has a harder power-law energy spectrum than oxygen above ∼3 MeV nucleon^(-1) in the shock-dominated April 15 event. This spectral difference, which is seen in many other gradual events of various sizes and heliolongitudes, leads to enhanced Fe/O at high energies. Simple shock acceleration models predict the same power-law index for all species. Thus, understanding the origin of this spectral difference will significantly contribute to the resolution of the ongoing debate about the relative roles of CME-driven shocks and flares in producing high-energy solar heavy ions.

Origin of the May 1998 suprathermal particles: Solar and Heliospheric Observatory/Charge, Element, and Isotope Analysis System/(Highly) Suprathermal Time of Flight results

The Solar and Heliospheric Observatory/Charge, Element, and Isotope Analysis System/(Highly) Suprathermal Time of Flight ((H)STOF) mass spectrometer measures the elemental composition and the charge state distribution of ions with suprathermal energies in the range 10–4000 keV amu−1 from above the solar wind particle distribution up to low‐energy flare particle energies. We analyze the time period around the large coronal mass ejection event on 2–3 May 1998. Using data from (H)STOF, we study the charge state distribution of He, the CNO group, and Fe. In addition, we investigate the energy dependence of the mean ionic charge state of Fe in the energy‐per‐nucleon range 12–100 keV amu−1. Furthermore, we also report energy spectra of H+, He++, and He+ and the variations in the elemental abundance ratios He/H, He/CNO, and Fe/CNO. These observations greatly extend the energy range in which particles associated with this time period have been measured. Because of their elevated energies, suprathermal particles are the prime seed population for further acceleration in gradual events. We identify interstellar pickup ions as an important nonsolar seed population. The observed low mean ionic charge states of Fe and the small Fe/CNO ratio are typical for large gradual events. The energy dependence of the Fe charge states may be a result of the presence of different iron populations or of the thermal history of the accelerated material. The temporal variations of Fe/CNO and He/CNO indicate a stronger confinement of low‐rigidity particles at the acceleration site.

The Large‐Scale Coronal Field Structure and Source Region Features for a Halo Coronal Mass Ejection

On 1998 May 2 a class X1/3B flare occurred at 13:42 UT in NOAA Active Region 8210 near disk center, which was followed by a halo coronal mass ejection (CME) at 15:03 UT observed by SOHO/LASCO. Using the boundary element method (BEM) on a global potential model, we reconstruct the large-scale coronal field structure from a composite boundary by SOHO/MDI and Kitt Peak magnetograms. The extrapolated large field lines well model a transequatorial interconnecting loop (TIL) seen in the soft X-ray (SXR) between AR 8210 and AR 8214, which disappeared after the CME. The EUV Imaging Telescope (EIT) observed the widely extending dimmings, which noticeably deviate from the SXR TIL in position. We find that the major dimmings are magnetically linked to the flaring active region but some dimmings are not. The spatial relationships of these features suggest that the CME may be led by a global restructuring of multipolar magnetic systems due to flare disturbances. Mass, magnetic energy, and flux of the ejected material estimated from the dimming regions are comparable to the output of large CMEs, derived from the limb events. At the CME source region, Huairou vector magnetograms show that a strong shear was rapidly developed in a newly emerging flux region (EFR) near the main spot before the flare. Magnetic field extrapolations reveal the presence of a bald patch (defined as the locations where the magnetic field is tangent to the photosphere) at the edge of the EFR. The preflare features such as EUV loop brightenings and SXR jets appearing at the bald patch suggest a slow reconnection between the TIL field system and a preexisting overlying field above the sheared EFR flux system. High-cadence Yohkoh/SXT images reveal a fast expanding motion of loops above a bright core just several minutes before the hard X-ray onset. This may be a precursor for the eruption of the sheared EFR flux to produce the flare. We propose a scenario, similar to the breakout model in principle, that can interpret many observed features.

The life of a CME and the development of a MIR: From the Sun to 58 AU

Large coronal mass ejections (CMEs) have major effects on the structure of the solar wind in the heliosphere. The plasma and magnetic field can be compressed ahead of CMEs to form merged interaction regions (MIRs). One signature of some CMEs that can be used to track them through the heliosphere is an enhanced alpha abundance. We use this signature and a one‐dimensional MHD model to track a CME from an active region on the Sun to Wind (1 AU), then to Ulysses (5.3 AU) and finally to Voyager 2 (58 AU). The arrival times of the CME ejecta at the three spacecraft are identified primarily by the increased alpha abundance. The observed plasma profiles and timing are close to those predicted by propagating data outward (from Earth to Ulysses and from Ulysses to Voyager 2) using the MHD model and give us confidence we are observing the same events at all three spacecraft. This event and a subsequent CME bracket a developing MIR and thus allow us to track the development of this structure.

Multi-scale temporal features of the 14 July 2000 meter- wavelength dynamic radio spectrum compared with TRACE data

The 14 July 2000 (`Bastille Day') eruptive and geoeffective flare event was observed by the digital IZMIRAN radio spectrograph in the frequency range of 25–270 MHz. This instrument allowed the analysis of various features of the dynamic radio spectrum and their comparison with other observational data, in particular with development of a spectacular EUV post-eruption arcade recorded aboard the Transition Region and Coronal Explorer (TRACE). (1) A compressed multi-hour radio spectrum shows that the event caused a conspicuous weakening of the pre-existing noise storm. This phenomenon was perhaps caused by interaction of a large halo coronal mass ejection (CME), recorded by the the Large Angle and Spectroscopic Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO), with emitting coronal structures. (2) Several type II bands are present at the initial and maximum phases of the flare event. The frequency drifts of the clearest bands correspond to the estimated shock wave speed of 1100–2300 km s−1 that is comparable with the CME speed observed in the sky plane. (3) Significant broadband enhancements of the metric radio emission took place around of 10:24–10:27 UT coinciding with sharp development of the EUV arcade in the northeast direction. It appears to correspond to the intensification of the electron acceleration in a process of post-eruption loop formation. (4) The high-resolution radio spectrum revealed a superposition of numerous type III-like bursts and/or pulsations with a time scale ranging from a few seconds to several tens of seconds. These features can be attributed particularly to successive formation of new loops of the arcade and corresponding temporal fragmentation of the electron acceleration in the course of the post-eruption reconnection. In summary, the analysis demonstrates the correspondence between the multi-scale temporal features of the metric radio emission and such phenomena as the CME and post-eruption EUV arcade. Some spectra, images, and movies illustrating the event are presented also on the accompanying CD-ROM.

CME's, filament eruptions, and sheared low-lying magnetic loops in multipolar magnetic configuration

The finite element method was used to solve a partial differential equation (magnetostatic equation) for multipolar magnetic regions. It is found that the height of magnetic field lines above the magnetic neutral line of a central strong bipolar magnetic field decreases as the field lines' footpoints approach the neutral line and also with increased magnetic shear. Both the electric current density and plasma pressure in the sheared low-lying loops are high. We suggest that the sheared low-lying loops may store the energies of large coronal mass ejections (CMEs) and filament eruptions. In addition, it is found that a lower pressure area exists above the low-lying loops and that it is similar in morphology to a coronal cavity. Above the lower pressure area there is a higher pressure area, which may be the source of CMEs. In this area magnetic shear leads to magnetic reconnection, which may be the cause of high coronal temperature.

Unusual composition of the solar wind in the 2–3 May 1998 CME observed with SWICS on ACE

Elemental, isotopic and charge state abundances provide valuable information about the source and acceleration mechanism of Coronal Mass Ejections (CMEs). Even though the kinetic properties of the plasma might be subject to changes because of dynamic effects occurring during the expansion of the CME, the composition of the solar wind remains unchanged after it leaves the low corona. Data from the Solar Wind Ion Composition Spectrometer (SWICS) on ACE are used to study the elemental and charge state composition of He, O, C, N, and Fe as well as the isotopic ratio of He during the very large CME of May 2–3, 1998. We find in this CME anomalously large enrichment of ³He++/4He++, He/O and Fe/O. During the 28 hour long cloud portion of the CME unusually cold material (4He+ and very low charge state heavy ions) was observed together with hot (high charge state ions) and normal solar wind plasma.

Solar Wind Models from the Sun to 1 AU: Constraints by in situ and Remote Sensing Measurements

There are three major types of solar wind: The steady fast wind originating on open magnetic field lines in coronal holes, the unsteady slow wind coming probably from the temporarily open streamer belt and the transient wind in the form of large coronal mass ejections. The majority of the models is concerned with the fast wind, which is, at least during solar minimum, the normal mode of the wind and most easily modeled by multi-fluid equations involving waves. The in-situ constraints imposed on the models, mainly by the Helios (in ecliptic) and Ulysses (high-latitude) interplanetary measurements, are extensively discussed with respect to fluid and kinetic properties of the wind. The recent SOHO observations have brought a wealth of new information about the boundary conditions for the wind in the inner solar corona and about the plasma conditions prevailing in the transition region and chromospheric sources of the wind plasma. These results are presented, and then some key questions and scientific issues are identified.

Magnetic noise bursts near the interplanetary shock associated with the coronal mass ejection event on February 21, 1994: The Geotail observations

A large coronal mass ejection (CME) event was detected by both the Geotail and IMP 8 satellites on February 21, 1994. Magnetic noise bursts (MNB) associated with the CME event are studied with the Geotail observations. An interplanetary shock associated with the CME reached the Geotail satellite, which was in the solar wind, around 0903 UT with a speed of about 1000 km/s. Before the arrival of the shock, the MNB with frequencies above 10 Hz are found to be produced by the whistler mode waves. These whistler mode waves propagate in a direction quasi‐parallel to the ambient magnetic field (B0). After the arrival of the shock, the MNB are produced by two different kinds of waves. The first kind are whistler mode waves with frequencies from 10 Hz to about 200 Hz. The whistler mode waves‐propagate in a single direction nearly parallel to the ambient magnetic field. A stable ambient magnetic field is a necessary condition but not a sufficient condition for the detection of the whistler mode waves. These facts suggest that the sources of the whistler mode waves are in the nonlocal plasmas (such as the shock). The second are lower hybrid waves with frequencies around or less than the lower hybrid frequency. The lower hybrid waves mainly propagate in a direction nearly perpendicular to the ambient magnetic field. They are associated with a rapid change of B0. The large gradients in both the ambient magnetic field and the plasma density may trigger the lower hybrid drifting instability thus exciting the lower hybrid waves.

LASCO/EIT Observations of Coronal Mass Ejections from Large-Scale Filament Channels

AbstractSolar activity in the latter half of 1996 was dominated by the presence of an extended filament channel in the southern hemisphere, forming a switchback configuration where it merged with the polar crown. Several large coronal mass ejections (CMEs) were observed to originate on or near this magnetic neutral line by the LASCO and EIT instruments on SOHO. As this channel gradually disappeared, a new, extended channel formed to the west of the old one, and this new channel also produced a number of large CMEs. We report here on observations of two events (December 23, 1996 and February 7,1997), and discuss the global nature of these events.

LASCO and EIT Observations of the Dynamic Corona

The combined operations of the Large Angle Spectrometric Coronagraph (LASCO) and the Extreme Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO), launched in December 1995, have provided an unprecedented opportunity for observing essentially all coronal phenomena that are not hidden behind the disk of the Sun. Consequently, observations with these instrument are providing information on coronal mass ejections (CMEs) from their initiation through their development over 30 ⊙. They reveal a coronal that never reaches a steady state. The corona is the site of continuous, time-dependent outflows, both within the coronal holes and the high speed streams and in the streamer belts and their mid-latitude sources. The spatial scales of these outflows range from 10s of arc-seconds through about a solar radius in large CMEs.

Spatial and Temporal Invariance in the Spectra of Energetic Particles in Gradual Solar Events

We show evidence of spatial and temporal invariance in the energy spectra of ~1-100 MeV protons from large gradual solar energetic particle (SEP) events. Nearly identical spectra are seen over longitude intervals of up to 160°, and the intensities at all energies decline with e-folding time constants of 6-18 hr for periods of ~3 days. The region of the invariant spectra is associated with acceleration on the eastern flank of the shock wave driven out from the Sun by a coronal-mass ejection (CME). The quasi-parallel shock in this region changes only slowly with time, and a quasi equilibrium is established for particles stored on field lines in the expanding volume between the shock and the Sun. On the western flank of the shock, the SEP event is more dynamic. Here, the nearly quasi-perpendicular shock produces harder spectra that change more rapidly with time as regions of the shock with varying speed and angle sweep across the observer's field line. Gradual SEP events arise from large CMEs with sufficient speeds to generate shocks that are fast enough to accelerate particles. In our study, shocks with transit speed >750 km s-1 always accelerate particles, while those with speeds of 500-750 km s-1 sometimes do. However, invariant spectra seem to occur in all gradual SEP events as a consequence of the structure and topology of the CME and shock.

A large polar crown coronal mass ejection and a “problem” goemagnetic storm: April 14–23, 1994

In the 1960s and 1970s, systematic programs to associate geomagnetic storms with solar flares gave rise to a category of “problem storms” for which there were no clear associations or for which the associations were with solar activity that seemed too insignificant to properly account for the magnitude of the geomagnetic events. In the last 2 decades the role of filament eruptions and coronal mass ejections (CMEs) in driving geomagnetic activity has received increasing attention, and an answer to the problem storm question has been pieced together. Until recently the inability to view CMEs on the solar disk has impeded a precise demonstration of the inferred relationships. The data from the Yohkoh Soft X ray Telescope (SXT), however, allow the association of soft X ray coronal structures with the aftermath of CMEs. Since CMEs are now believed to be the main cause of aperiodic severe disturbances of Earth's magnetosphere, the ability to distinguish the aftermath of a CME on the disk improves our ability to predict geomagnetic storms. On April 14, 1994, a large scale coronal arcade formation was observed by SXT after the eruption of a long section of the southern polar crown neutral line. Data from the Mauna Loa coronagraph are consistent with this event being the result of a CME that formed in the helmet streamer underlying the heliospheric current sheet. The CME was followed by a severe geomagnetic storm, starting 68 hr later, and was also observed at 3.2 AU and high heliographic latitude by the Ulysses satellite. Since there was no significant flare associated with the eruption, and no significant filament disappearance, the subsequent geomagnetic events are an extreme example of a problem storm and of the great utility of soft X ray imagers for the prediction of space weather. In this paper we have assembled a wide range of data relating to the solar event, the evolution of the region that generated it, and the various observed consequences at Earth and in the interplanetary medium. The global magnetic field changes leading to the CME are outlined, a brief description of the coronal arcade formation is given, and the arcade's association with subsequent events at Earth and the interplanetary disturbance observed at Ulysses is described. We present this case as an example of the advantages to be derived from a comprehensive multidisciplinary approach to studying these potentially disruptive phenomena.

The CME Event of February 21, 1994: Response of the Magnetic Field at the Earth's Surface.

On February 21, 1994, a large coronal mass ejection (CME) passed by the Earth. In the solar wind, the CME front was noted by very large changes in the solar wind dynamic pressure, flow direction, and magnetic field, as measured by several spacecraft. At the Earth's surface, many ground stations also recorded the passage of this CME, as a storm sudden commencement onset. We examine here several interesting features of the surface magnetic field response to this sudden commencement onset. In particular, we use the magnetometer records to examine the propagation time of the initial impulse along the Earth's surface. We also study in detail the initial amplitude change at several stations, and note the variation in the response as a function of magnetic latitude. In addition, we crudely estimate the relative contributions of the Chapman-Ferraro and the ionospheric current system to the surface response. Also of interest is the polarization and period of Psc oscillations superposed on the main impulse at several stations, including polarization reversals as a function of magnetic latitude. Corresponding ionospheric currents at stations along the 210° MM chain are also computed, and very large and sudden changes in the ionospheric current flow patterns are reported during the initial minutes of the sudden commencement onset. These and other results are interpreted in terms of previous models, paradigms, and statistical results.