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1.
1 INTRODUCTIONCoronal majss ejections (CMEs) are often seen as spectacular eruptions of matter fromthe Sun which propagate outward through the heliosphere and often interact with the Earth'smagnetosphere (Hundhausen, 1997; Gosling, 1997; and references herein). It is well known thatthese interactions can have substalltial consequences on the geomagnetic environment of theEarth, sometimes resulting in damage to satellites (e.g., McAllister et al., 1996; Berdichevskyet al., 1998). CMEs… 相似文献
2.
The speeds of coronal mass ejection events 总被引：2，自引：0，他引：2
J. T. Gosling E. Hildner R. M. MacQueen R. H. Munro A. I. Poland C. L. Ross 《Solar physics》1976,48(2):389-397
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. 相似文献
3.
We describe the radio signatures that led up to and concluded the solar eruptive event of 14 July 2000 (Bastille Day Event).
These radio signatures provide a means of remotely sensing the associated solar activity and transient phenomena. For many
days prior to the Bastille Day Event kilometric Type III radio storm emissions were observed that were presumably associated
with the active region NOAA 9077. These storm emissions continued until the X5.7 flare at ∼ 10 UT on 14 July 2000 that characterized
the Bastille Day Event, then ceased abruptly. The Bastille Day Event itself produced very intense, complex, long-duration
Type III-like radio emissions, which appear to have been associated with electrons generated (accelerated) deep in the solar
corona. The coronal mass ejection (CME) associated with the Bastille Day Event generated decametric to kilometric Type II
radio emissions as the CME propagated through the solar corona and interplanetary medium. The frequency drift of these Type II
radio emissions are related to the dynamics of the propagating CME and indicate that the CME experienced significant deceleration
as it propagated from the high corona into the interplanetary medium. 相似文献
4.
Lines of magnetic force, computed under the assumption that the solar corona is free of electric currents, have been compared with loop prominence systems associated with three flares in August, 1972. The computed fields closely match the observations of loops at a height of 40000 km at times 3–4 h after onset of the associated flares. Inferred magnetic field intensities in the loops range from 1300 G where the loops converge into a sunspot to 50–80 G at 40 000 km above the photosphere. The first-seen and lowest-lying loops are sheared with respect to the calculated fields. Higher loops conform more closely to the current-free fieldlines. A model of Barnes and Sturrock is used to relate the degree of shear to the excess magnetic energy available during the flare of August 7. On various lines of evidence, it is suggested that magnetic energy was available to accelerate particles not only during the impulsive phase of the flare, but also during the following 2–3 h. The particle acceleration region seems to be in the magnetic fields just above the visible loops. The bright outer edges of the flare ribbons are identified as particle impact regions. The dense knots of loop prominence material fall to the ribbons' inner edges.On leave from Tel Aviv University, Tel Aviv, Israel. 相似文献
5.
The relation between the ejected plasma cloud and the shock wave propagating ahead of it is examined for 27 pairs of such events. The flare sprays and the eruptive prominences observed in H line as well as the fast-moving sources of type-IV radio bursts have been considered as such ejected plasma clouds. Propagation of the shock wave in the solar corona has been examined from the observations of type-II radio bursts. Using the Parker model of the propagation of a shock wave, the shock wave velocity has been compared with the plasma cloud velocity. Energy interconnection between these two events has been studied. In the majority of the investigated cases there exists an energetic interconnection between the plasma cloud and the shock wave. 相似文献
6.
J. B. Smith Jr. D. M. Speich R. M. Wilson E. Tandberg-Hanssen S. T. Wu 《Solar physics》1977,52(2):379-391
Skylab soft X-ray observations of two lower coronal limb events and corresponding H observations (Skylab and ground-based) are analyzed. We discuss the morphology and evolution of an eruptive prominence occurring on 21 August 1973, beginning (in H) at about 1300 UT and of a surge on 4 December 1973, beginning at about 1758 UT. For the eruptive prominence, measured X-ray flux is used in the determination of line-of-sight temperatures, emission measures, and electron densities. A peak temperature of 8.5 × l06 K and densities to 3.5 × l09 cm-3 are derived. A time-dependent, two-dimensional, single-fluid magnetohydrodynamic computer code has been used to simulate the coronal response to these prominences. We find that the coronal response to the observed eruptive prominence may be simulated with a density-dominated pressure pulse at the base of the corona ( 30000 km above photosphere), while a temperature pulse of short duration will simulate the coronal response to the surge. Approximately 1031 ergs and 1040 particles (or 1016 g) were deposited into the corona during the eruptive prominence event, while about 1029 ergs and 1038 particles (or 1014 g) were injected during the surge event. A shock wave formed ahead of the ejected material at about 70000 km above the photosphere in the eruptive prominence event and had a velocity of 275 km s-1 at 1.5 r
above the limb.Presently at NASA / Marshall Space Flight Center. 相似文献
7.
An H solar prominence with the characteristics of a spray was ejected in association with a bright limb flare. Knots of material were observed to a distance of more than one solar radius above the west limb of the Sun. The optical event was followed by 80 MHz emission from a type IV source which was observed moving out through several solar radii.Coronagraph observations have been used to determine the trajectories and velocities of the knots in directions perpendicular to the line of sight. After some early deceleration velocities increase to 300–500 km/sec and slowly decline with variations depending on the initial direction of outflow. We suggest that the magnetic field over the spot group is deformed by the energy of the mass motions of material fragments, some of which then continue to move outward from the Sun. 相似文献
8.
Based on a topological model for the magnetic field of a solar active region (AR), we suggest a criterion for the existence of magnetic null points on the separators in the corona. With the problem of predicting solar flares in mind, we have revealed a model parameter whose decrease means that the AR evolves toward a major eruptive flare. We analyze the magnetic field evolution for AR 9077 within two days before the Bastille Day flare on July 14, 2000. The coronal conditions are shown to have become more favorable for magnetic reconnection, which led to a 3B/X5.7 eruptive flare. 相似文献
9.
On 10 March 2001 the active region NOAA 9368 produced an unusually impulsive solar flare in close proximity to the solar limb. This flare has previously been studied in great detail, with observations classifying it as a type 1 white-light flare with a very hard spectrum in hard X-rays. The flare was also associated with a type II radio burst and coronal mass ejection. The flare emission characteristics appeared to closely correspond to previous instances of seismic emission from acoustically active flares. Using standard local helioseismic methods, we identified the seismic signatures produced by the flare that, to date, is the least energetic (in soft X-rays) of the flares known to have generated a detectable acoustic transient. Holographic analysis of the flare shows a compact acoustic source strongly correlated with the impulsive hard X-rays, visible continuum, and radio emission. Time?–?distance diagrams of the seismic waves emanating from the flare region also show faint signatures, mainly in the eastern sector of the active region. The strong spatial coincidence between the seismic source and the impulsive visible continuum emission reinforces the theory that a substantial component of the seismic emission seen is a result of sudden heating of the low photosphere associated with the observed visible continuum emission. Furthermore, the low-altitude magnetic loop structure inferred from potential-field extrapolations in the flaring region suggests that there is a significant anti-correlation between the seismicity of a flare and the height of the magnetic loops that conduct the particle beams from the corona. 相似文献
10.
By use of the H observations of the Astrophysical Observatory in Catania, Italy and the Purple Mountain Observatory in Nanking, China as well as hard X-ray and gamma-ray burst data from the Solar Maximum Mission (SMM) Gamma-Ray Spectrometer (GRS), a major eruptive loop prominence was studied during the limb solar flare event of 1981 April 27.Our preliminary analysis shows that there seems to exist a second abrupt energy release for this event, almost 20 min after the end of the impulsive phase of the flare. This energy release is probably associated with the rapidity in upward motion or activation of the loop prominence.A possible candidate for such a process could be the reconnection of the old magnetic field with a newly emerging magnetic field.A theoretical gross estimate for the energy release and particle acceleration has also been made in this work. It appears that the proposed model for charged particle acceleration is very efficient. 相似文献
11.
F. Nagai 《Solar physics》1980,68(2):351-379
A dynamical model is proposed for the formation of soft X-ray emitting hot loops in solar flares. It is examined by numerical simulations how a solar model atmosphere in a magnetic loop changes its state and forms a hot loop when the flare energy is released in the form of heat liberation either at the top part or around the transition region in the loop.When the heat liberation takes place at the top part of the loop which arches in the corona, the plasma temperature around the loop apex rises rapidly and, as the result, the downward thermal conductive flux is increased along the magnetic tube of force. Soon after the thermal conduction front rushes into the upper chromosphere, a local peak of pressure is produced near the conduction front and the chromospheric material begins to expand into the corona to form a high-temperature (107 K-3 × 107 K at the loop apex) and high-density (1010 cm–3-1011 cm–3 at the loop apex) loop. The velocity of the expanding material can reach a few hundred kilometres per second in the coronal part. The thermal conduction front also plays a role of piston pushing the chromospheric material downward and gives birth to a shock wave which propagates through the minimum temperature region into the photosphere. If, on the other hand, the heat source is placed around the transition region in the loop, the expansion of the material into the corona occurs from the beginning of the flare and the formation process of the hot loop differs somewhat from the case with the heat source at the top part of the loop.Thermal components of radiations emitted from flare regions, ranging from soft X-rays to radio wavelengths, are interpreted in a unified way by using physical quantities obtained as functions of time and position in our flare loop model as will be discussed in detail in a following paper. 相似文献
12.
On 11 January 2002, using the Multi-channel Infrared Solar Spectrograph (MISS) at the Purple Mountain Observatory (PMO), we obtained Hα, Ca ii 8542 Å and He i 10?830 Å spectra and slit-jaw Hα images of a peculiar solar limb event. A close resemblance of its intensity to that of a small flare and the GOES X-ray flux indicates that it was an active prominence. However, its morphological evolution and velocity variation were different from general typical active prominences, such as limb flares, post-flare loops, surges and sprays. It started with the ejection of material from the flare site. In the early phase, the ejecta was as bright as a limb flare and kept rising until reaching the height of (8????10)×104 km at an almost constant velocity of 91.7 km? s ?1 with its lower part always connected to the solar surface. EUV images in 195 Å show similar structure as in the Hα line, indicating the coexistence of plasmas with temperatures differing by more than two orders of magnitude. Later some material started to fall back to another bright area on the solar surface. The falling material did not show the collimated structure of surges or the arc structure of flaring arches. A red-shift velocity of more than 200 km? s ?1 was detected in a bright point close to the outer edge of the closed loop system formed later, which dispersed in a few minutes and became a part of the newly formed large loop. The ejected material did not leave the sun, indicating that the magnetic reconnection was not sufficient to remove the overlying field lines during the process. The spectral line profiles showed large widths and variable velocities, and therefore the line-pair method is not applicable to this event for the estimation of physical parameters. 相似文献
13.
H. Xie O. C. St. Cyr N. Gopalswamy S. Yashiro J. Krall M. Kramar J. Davila 《Solar physics》2009,259(1-2):143-161
We have conducted a statistical study 27 coronal mass ejections (CMEs) from January 2007 – June 2008, using the stereoscopic views of STEREO SECCHI A and B combined with SOHO LASCO observations. A flux-rope model, in conjunction with 3D triangulations, has been used to reconstruct the 3D structures and determine the actual speeds of CMEs. The origin and the dynamic evolution of the CMEs are investigated using COR1, COR2 and EUVI images. We have identified four types of solar surface activities associated with CMEs: i) total eruptive prominence (totEP), ii) partially eruptive prominence (PEP), iii) X-ray flare, and iv) X-type magnetic structure (X-line). Among the 27 CMEs, 18.5% (5 of 27) are associated with totEPs, 29.6% (8 of 27) are associated with PEPs, 26% (7 of 27) are flare related, and 26% (7 of 27) are associated with X-line structures, and 43% (3 of 7) are associated with both X-line structures and PEPs. Three (11%) could not be associated with any detectable activity. The mean actual speeds for totEP-CMEs, PEP-CMEs, flare-CMEs, and X-line-CMEs are 404 km?s?1,247 km?s?1,909 km?s?1, and 276 km?s?1, respectively; the average mean values of edge-on and broadside widths for the 27 CMEs are 52 and 85 degrees, respectively. We found that slow CMEs (V≤400 km?s?1) tend to deflect towards and propagate along the streamer belts due to the deflections by the strong polar magnetic fields of corona holes, while some faster CMEs show opposite deflections away from the streamer belts. 相似文献
14.
S. T. Wu Y. Q. Hu S. Wang M. Dryer E. Tandberg-Hanssen 《Astrophysics and Space Science》1982,83(1-2):189-194
In this paper, a new ideal magnetohydrodynamic (MHD) model is used to examine the dynamical response of the upper solar atmosphere to injection of cold mass from the photosphere akin to a surge. A significant new physical phenomenon is revealed: the formation of an almost stationary loop prominence in the atmosphere as a consequence of the ejected material. Simultaneously with the formation of this new loop, the simulation exhibits MHD waves that propagate outward (i.e., away from the loop) to excite coronal material. It is conjectured that these waves may trigger a class of coronal disturbances. 相似文献
15.
On 27 June 2012, an eruptive solar prominence was observed in the extreme ultraviolet (EUV) and radio wavebands. At the Aalto University Metsähovi Radio Observatory (MRO) it was observed at 37 GHz. It was the first time that the MRO followed a radio prominence with dense sampling in the millimetre wavelengths. This prompted us to study the connection of the 37 GHz event with other wavelength domains. At 37 GHz, the prominence was tracked to a height of around \(1.6~\mathrm{R}_{\odot}\), at which the loop structure collapsed. The average velocity of the radio prominence was \(55 \pm 6~\mbox{km}\,\mbox{s}^{-1}\). The brightness temperature of the prominence varied between \(800 \pm 100\) K and \(3200 \pm 100\) K. We compared our data with the Solar Dynamic Observatory (SDO)/Atmospheric Imaging Assembly (AIA) instrument’s 304 Å EUV data, and found that the prominence behaves very similarly in both wavelengths. The EUV data also reveal flaring activity nearby the prominence. We present a scenario in which this flare works as a trigger that causes the prominence to move from a stable stage to an acceleration stage. 相似文献
16.
We report on a prominence eruption as seen in H with the Crimean Lyot coronagraph, the global H network, and coronal images from the LASCO C2 instrument on board SOHO. We observed an H eruption at the northwest solar limb between 07:38:50 UT and 07:58:29 UT on 11 August 2000. The eruption originated in a quiet-Sun region and was not associated with an H filament. No flare was associated with the eruption, which may indicate that, in this case, a flux rope was formed prior to the eruption of the magnetic field. The H images and an H Dopplergram show a helical structure present in the erupted magnetic field. We suggest that the driving mechanism of the eruption may be magnetic flux emergence or magnetic flux injection. The limb H observations provide missing data on CME speed and acceleration in the lower corona. Our data show that the prominence accelerated impulsively at 5.5 km s–2 and reached a speed slightly greater than 800 km s–1 in a narrow region (h<0.14 R
) above the solar surface. The observations presented here also imply that, based only on a CME's speed and acceleration, it cannot be determined whether a CME is the result of a flare or an eruptive prominence. 相似文献
17.
We study the magnetic field evolution and topology of the active region NOAA 10486 before the 3B/X1.2 flare of October 26, 2003, using observational data from the French–Italian THEMIS telescope, the Michelson Doppler Imager (MDI) onboard Solar and Heliospheric Observatory (SOHO), the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observation Station (HSOS), and the Transition Region and Coronal Explorer (TRACE). Three dimensional (3D) extrapolation of photospheric magnetic field, assuming a potential field configuration, reveals the existence of two magnetic null points in the corona above the active region. We look at their role in the triggering of the main flare, by using the bright patches observed in TRACE 1600 Å images as tracers at the solar surface of energy release associated with magnetic reconnection at the null points. All the bright patches observed before the flare correspond to the low-altitude null point. They have no direct relationship with the X1.2 flare because the related separatrix is located far from the eruptive site. No bright patch corresponds to the high-altitude null point before the flare. We conclude that eruptions can be triggered without pre-eruptive coronal null point reconnection, and the presence of null points is not a sufficient condition for the occurrence of flares. We propose that this eruptive flare results from the loss of equilibrium due to persistent flux emergence, continuous photospheric motion and strong shear along the magnetic neutral line. The opening of the coronal field lines above the active region should be a byproduct of the large 3B/X1.2 flare rather than its trigger. 相似文献
18.
Agalakov B. V. Ledenev V. G. Lubyshev B. I. Nefedyev V. P. Yazev S. A. Zubkova G. N. Kerdraon A. Urbarz H. W. 《Solar physics》1997,173(2):305-318
Based on observations from the Siberian solar radio telescope, and invoking data from other observatories, we investigate preflare changes in the sunspot and floccular sources of radio emission and the development of an importance 2N flare in the chromosphere and corona in the active region on August 23, 1988.It has been ascertained that preflare changes became observable six hours prior to the flare onset and manifested themselves in intense flux fluctuations above the sunspot and in an enhancement of the source emission flux above the flocculus.It is shown that the flare onset is associated with a newly emerged magnetic flux in the form of a pore near the filament and with the appearance of radio sources above the filament. The flare was accompanied by type III radio bursts and a noise storm at meter wavelengths. Coronal mass ejection parameters are estimated from type III burst observations. 相似文献
19.
Every two-ribbon flare observed during the Skylab period produced an observable coronal transient, provided the flare occurred close enough to the limb. The model presented here treats these two events as a combined process. Transients that occur without flares are believed to involve magnetic fields that are too weak to produce significant chromospheric emission. Adopting the hypothesis that the rising flare loop systems observed during two-ribbon flares are exhibiting magnetic reconnection, a model of a coronal transient is proposed which incorporates this reconnection process as the driving force. When two oppositely directed field lines reconnect a lower loop is created rooted to the solar surface (the flare loop) and an upper disconnected loop is produced which is free to rise. The magnetic flux of these upper loops is proposed as the driver for the transient. The force is produced by the increase in magnetic pressure under the filament and transient.A quantitative model is developed which treats the transient configuration in terms of four distinct parts- the transient itself with its magnetic field and material, the region just below the transient but above the filament, the filament with its magnetic field, and the reconnected flux beneath the filament. Two cases are considered - one in which all the prominence material rises with the transient and one in which the material is allowed to fall out of the transient. The rate of rise of the neutral line during the reconnection process is taken from the observations of the rising X-ray flare loop system during the 29 July, 1973 flare. The MHD equations for the system are reduced to four non-linear ordinary coupled differential equations which are solved using parameters believed to be realistic for solar conditions. The calculated velocity profiles, widths, etc., agree quite well with the observed properties of coronal transients as seen in white light. Since major flares are usually associated with a filament eruption about 10–15 min before the flare and since this model associates the transient with the filament eruption, we suspect that the transient is actually initiated some time before the actual flare itself.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
20.
A solar flare that occurred on the west limb at 1981, March 25, 2038 UT generated a massive, rapidly-expanding optical coronal transient, which moved outward with an approximately constant velocity of 800 km s–1. An associated magnetohydrodynamic shock travelled out ahead of the transient with a velocity estimated to be approximately 1000 km s–1. The optical and radio data on the transient and shock fit well with general theories concerning piston-driven shocks and with current MHD models for propagation of such shocks through the solar corona. 相似文献