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1.
On 13 June 2010, an eruptive event occurred near the solar limb. It included a small filament eruption and the onset of a relatively narrow coronal mass ejection (CME) surrounded by an extreme ultraviolet (EUV) wave front recorded by the Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) at high cadence. The ejection was accompanied by a GOES M1.0 soft X-ray flare and a Type-II radio burst; high-resolution dynamic spectra of the latter were obtained by the Appareil de Routine pour le Traitement et l’Enregistrement Magnetique de l’Information Spectral (ARTEMIS IV) radio spectrograph. The combined observations enabled a study of the evolution of the ejecta and the EUV wave front and its relationship with the coronal shock manifesting itself as metric Type-II burst. By introducing a novel technique, which deduces a proxy of the EUV compression ratio from AIA imaging data and compares it with the compression ratio deduced from the band-split of the Type-II metric radio burst, we are able to infer the potential source locations of the radio emission of the shock on that AIA images. Our results indicate that the expansion of the CME ejecta is the source for both EUV and radio shock emissions. Early in the CME expansion phase, the Type-II burst seems to originate in the sheath region between the EUV bubble and the EUV shock front in both radial and lateral directions. This suggests that both the nose and the flanks of the expanding bubble could have driven the shock.  相似文献   

2.
The SOL2001-12-26 moderate solar eruptive event (GOES importance M7.1, microwaves up to 4000 sfu at 9.4 GHz, coronal mass ejection (CME) speed 1446 km?s?1) produced strong fluxes of solar energetic particles and ground-level enhancement (GLE) of cosmic-ray intensity (GLE63). To find a possible reason for the atypically high proton outcome of this event, we study multi-wavelength images and dynamic radio spectra and quantitatively reconcile the findings with each other. An additional eruption probably occurred in the same active region about half an hour before the main eruption. The latter produced two blast-wave-like shocks during the impulsive phase. The two shock waves eventually merged around the radial direction into a single shock traced up to \(25~\mathrm{R}_{\odot}\) as a halo ahead of the expanding CME body, in agreement with an interplanetary Type II event recorded by the Radio and Plasma Wave Investigation (WAVES) experiment on the Wind spacecraft. The shape and kinematics of the halo indicate an intermediate regime of the shock between the blast wave and bow shock at these distances. The results show that i) the shock wave appeared during the flare rise and could accelerate particles earlier than usually assumed; ii) the particle event could be amplified by the preceding eruption, which stretched closed structures above the developing CME, facilitated its lift-off and escape of flare-accelerated particles, enabled a higher CME speed and stronger shock ahead; iii) escape of flare-accelerated particles could be additionally facilitated by reconnection of the flux rope, where they were trapped, with a large coronal hole; and iv) the first eruption supplied a rich seed population accelerated by a trailing shock wave.  相似文献   

3.
We model the propagation of a coronal shock wave, using nonlinear geometrical acoustics. The method is based on the Wentzel–Kramers–Brillouin (WKB) approach and takes into account the main properties of nonlinear waves: i) dependence of the wave front velocity on the wave amplitude, ii) nonlinear dissipation of the wave energy, and iii) progressive increase in the duration of solitary shock waves. We address the method in detail and present results of the modeling of the propagation of shock-associated extreme-ultraviolet (EUV) waves as well as Moreton waves along the solar surface in the simplest solar corona model. The calculations reveal deceleration and lengthening of the waves. In contrast, waves considered in the linear approximation keep their length unchanged and slightly accelerate.  相似文献   

4.
Wei Liu  Leon Ofman 《Solar physics》2014,289(9):3233-3277
Global extreme-ultraviolet (EUV) waves are spectacular traveling disturbances in the solar corona associated with energetic eruptions such as coronal mass ejections (CMEs) and flares. Over the past 15 years, observations from three generations of space-borne EUV telescopes have shaped our understanding of this phenomenon and at the same time led to controversy about its physical nature. Since its launch in 2010, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) has observed more than 210 global EUV waves in exquisite detail, thanks to its high spatio–temporal resolution and full-disk, wide-temperature coverage. A combination of statistical analysis of this large sample, more than 30 detailed case studies, and data-driven MHD modeling, has been leading their physical interpretations to a convergence, favoring a bimodal composition of an outer, fast-mode magnetosonic wave component and an inner, non-wave CME component. Adding to this multifaceted picture, AIA has also discovered new EUV wave and wave-like phenomena associated with various eruptions, including quasi-periodic fast propagating (QFP) wave trains, magnetic Kelvin–Helmholtz instabilities (KHI) in the corona and associated nonlinear waves, and a variety of mini-EUV waves. Seismological applications using such waves are now being actively pursued, especially for the global corona. We review such advances in EUV wave research focusing on recent SDO/AIA observations, their seismological applications, related data-analysis techniques, and numerical and analytical models.  相似文献   

5.
We statistically analyzed the kinematical evolution and wave pulse characteristics of 60 strong large-scale EUV wave events that occurred during January 2007 to February 2011 with the STEREO twin spacecraft. For the start velocity, the arithmetic mean is 312±115 km?s?1 (within a range of 100?–?630 km?s?1). For the mean (linear) velocity, the arithmetic mean is 254±76 km?s?1 (within a range of 130?–?470 km?s?1). 52 % of all waves under study show a distinct deceleration during their propagation (a≤?50 m?s?2), the other 48 % are consistent with a constant speed within the uncertainties (?50≤a≤50 m?s?2). The start velocity and the acceleration are strongly anticorrelated with c≈?0.8, i.e. initially faster events undergo stronger deceleration than slower events. The (smooth) transition between constant propagation for slow events and deceleration in faster events occurs at an EUV wave start-velocity of v≈230 km?s?1, which corresponds well to the fast-mode speed in the quiet corona. These findings provide strong evidence that the EUV waves under study are indeed large-amplitude fast-mode MHD waves. This interpretation is also supported by the correlations obtained between the peak velocity and the peak amplitude, impulsiveness, and build-up time of the disturbance. We obtained the following association rates of EUV wave events with other solar phenomena: 95 % are associated with a coronal mass ejection (CME), 74 % to a solar flare, 15 % to interplanetary type II bursts, and 22 % to coronal type II bursts. These findings are consistent with the interpretation that the associated CMEs are the driving agents of the EUV waves.  相似文献   

6.
We study the effect of projection and line-of-sight integration on the interpretation of the morphology and kinematics of EUV waves. We have performed a three-dimensional magnetohydrodynamic simulation of a coronal mass ejection (CME) erupting in an environment that mimics the low solar corona and calculated the resulting emission measure of the event from five different viewing angles. Our study provides more quantitative information about the impact of the viewing angle and projection effect on the properties of EUV waves than previous studies on the subject. Analyzing the emission measure of the lower corona reveals wave-like increases that move away from the eruption site, which we interpret as EUV waves. Behind the EUV wave front we can recognize coronal dimming regions. A comparison of the emission measure and calculated density supports the view that EUV waves are true waves. Our results show that the origin of the observed EUV wave is height-dependent, which means that the measured speed and the morphology depend on the viewing direction. Consequently, care should be taken when EUV observations are used to infer the true propagation speeds of EUV wave fronts.  相似文献   

7.
Multi-spacecraft observations are used to study the in-situ effects of a large coronal mass ejection (CME) erupting from the farside of the Sun on 3 November 2011, with particular emphasis on the associated solar energetic particle (SEP) event. At that time both Solar Terrestrial Relations Observatory (STEREO) spacecraft were located more than 90 degrees from Earth and could observe the CME eruption directly, with the CME visible on-disk from STEREO-B and off the limb from STEREO-A. Signatures of pressure variations in the corona such as deflected streamers were seen, indicating the presence of a coronal shock associated with this CME eruption. The evolution of the CME and an associated extreme-ultraviolet (EUV) wave were studied using EUV and coronagraph images. It was found that the lateral expansion of the CME low in the corona closely tracked the propagation of the EUV wave, with measured velocities of 240±19 km?s?1 and 221±15 km?s?1 for the CME and wave, respectively. Solar energetic particles were observed to arrive first at STEREO-A, followed by electrons at the Wind spacecraft at L1, then STEREO-B, and finally protons arrived simultaneously at Wind and STEREO-B. By carrying out a velocity-dispersion analysis on the particles arriving at each location, it was found that energetic particles arriving at STEREO-A were released first and that the release of particles arriving at STEREO-B was delayed by about 50 minutes. Analysis of the expansion of the CME to a wider longitude range indicates that this delay is a result of the time taken for the CME edge to reach the footpoints of the magnetic-field lines connected to STEREO-B. The CME expansion is not seen to reach the magnetic footpoint of Wind at the time of solar-particle release for the particles detected here, suggesting that these particles may not be associated with this CME.  相似文献   

8.
Combining the observations of STEREO satellites with the method of three-dimensional magnetohydrodynamic (MHD) numerical simulation, adopt- ing the magnetic ?eld data of the Wilcox Solar Observatory (WSO) and the model of potential ?eld source surface to build up the initial magnetic ?eld in solar corona, and adding a time-varying disturbance of pressure to the active re- gion on the solar surface, the study on the event of coronal mass ejection (CME) and extreme-ultraviolet (EUV) wave happened at 05:35 UT of 2009 February 13 has been performed. It is judged from the images of COR1/STEREO-A that the front speed of this CME is about 350 km·s−1, and the angular width is about 60°. By analyzing the running difference images of EUVI/STEREO-B at 195 ?A, it is found that the bright toroidal wavefront is spreading toward all directions around the active region, and behind the bright toroidal wavefront is a coronal dimming area. The positions of the wavefront in four directions are taken to perform linear ?ttings, it is known that the EUV wave speed is 247 km·s−1, and the EUV wave speed obtained from the numerical simulation is 245 km·s−1. After the IDL visualization program has been carried out for the calculated result, the structures of the bright loop and dimming area can be seen clearly. The numerical simulation is consistent with the satellite observation, which shows that the observed EUV wave may belong to the fast magnetosonic wave.  相似文献   

9.
Studies of the onset of Earth-directed coronal mass ejections (CMEs) rely on solar disk observations where CME structures are difficult to disentangle because of the diversity and transient character of the phenomena involved. Dimmings and coronal waves are among the best evidence of the large-scale reorganization of coronal magnetic fields associated with the onset of CMEs. The physical mechanism behind EIT waves is still unclear: they are considered as MHD waves and/or as a consequence of plasma compression on the extending border of a dimming. In this paper, we address the problem of automatically detecting and analyzing EIT waves and dimmings in EUV images. This paper presents a “proof of principle” that automated detection of EIT wave and dimmings is indeed possible. At the current stage of work, the method can unambiguously detect dimmings and EIT waves when applied on a typical test-case event. Moreover, we propose a way to extract these events from the data, and determine such parameters as life time, depth, area and volume of dimmings for future catalogs. For EIT waves we unambiguously define, in near solar minimum conditions, the eruption center, the front of EIT wave and its propagation velocity. In addition, we show that the presented methods yield new insights about the geometrical shape of dimmings and the connection with the EIT wave front properties, and the apparent angular rotation of the EIT wave under study.  相似文献   

10.
By using the multi-wavelength observations from the Solar Terrestrial Relations Observatory (STEREO), the Solar and Heliospheric Observatory (SOHO), the Transition Region and Coronal Explorer (TRACE) and the HINODE, we study a coronal mass ejection (CME) and associated coronal dimming occurred on 2009 December 13, as a consequence of the expansion and eruption of EUV loops. The activities were probably triggered by the new flux emergence and the convergence motions, which were evident in the magnetograms from Michelson Doppler Imager (MDI) on the SOHO. The emergence led to the destabilization and eruption of the preexistent flux rope, which was highly-sheared over the polarity inversion line. Driven by the ejection of the flux rope, the overlying loops initially slowly rose and then erupted. As a result, two coronal dimming regions formed at the footprints of the loops and a B1.9 flare, about half an hour later, occurred in the eruptive region near one foot of the eruptive loops. The CME had a very close temporal and spatial relationship to the expanding loops, and it is very likely that the CME directly developed from the eruptive loops. The CME mass calculated from the EUV dimming was of the same order of the typical CME mass, suggesting that the dimming region supplied major of the mass for the CME. The kinematic evolution of the CME was basically consistent with the three-phases scenario: the initiation phase, impulsive acceleration phase, and propagation phase. The onset of the CME could be well explained by the emerging flux trigger mechanism.  相似文献   

11.
This work investigates a typical coronal mass ejection (CME) observed on 2003 February 18, by various space and ground instruments, in white light, Ha, EUV and X-ray. The Ha and EUV images indicate that the CME started with the eruption of a long filament located near the solar northwest limb. The white light coronal images show that the CME initiated with the rarefaction of a region above the solar limb and followed by the formation of a bright arcade at the boundary of the rarefying region at height 0.46 R(?) above the solar surface. The rarefying process synchronized with the slow rising phase of the eruptive filament, and the CME leading edge was observed to form as the latter started to accelerate. The lower part of the filament brightened in Ha as the filament rose to a certain height and parts of the filament was visible in the GOES X-ray images during the rise. These brightenings imply that the filament may be heated by the magnetic reconnection below the filament in the early stage of the eruption. We suggest that a possible mechanism which leads to the formation of the CME leading edge and cavity is the magnetic reconnection which takes place below the filament after the filament has reached a certain height.  相似文献   

12.
We analyze multiwavelength observations of an M2.9/1N flare that occurred in AR NOAA 11112 on 16 October 2010. AIA 211 Å EUV images reveal the presence of a faster coronal wave (decelerating from ≈?1390 to ≈?830 km?s?1) propagating ahead of a slower wave (decelerating from ≈?416 to ≈?166 km?s?1) towards the western limb. The dynamic radio spectrum from Sagamore Hill radio telescope shows the presence of a metric type II radio burst, which reveals the presence of a coronal shock wave (speed ≈?800 km?s?1). The speed of the faster coronal wave, derived from AIA 211 Å images, is found to be comparable to the coronal shock speed. AIA 171 Å high-cadence observations showed that a coronal loop, which was located at a distance of ≈?0.32R ⊙ to the west of the flaring region, started to oscillate by the end of the impulsive phase of the flare. The results indicate that the faster coronal wave may be the first driver of the transversal oscillations of coronal loop. As the slower wave passed through the coronal loop, the oscillations became even stronger. There was a plasmoid eruption observed in EUV and a white-light CME was recorded, having velocity of ≈?340?–?350 km?s?1. STEREO 195 Å images show an EIT wave, propagating in the same direction as the lower-speed coronal wave observed in AIA, but decelerating from ≈?320 to ≈?254 km?s?1. These observations reveal the co-existence of both waves (i.e. coronal Moreton and EIT waves), and the type II radio burst seems to be associated with the coronal Moreton wave.  相似文献   

13.
We study the kinematical characteristics and 3D geometry of a large-scale coronal wave that occurred in association with the 26 April 2008 flare-CME event. The wave was observed with the EUVI instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B) with a mean speed of ∼ 240 km s−1. The wave is more pronounced in the eastern propagation direction, and is thus, better observable in STEREO-B images. From STEREO-B observations we derive two separate initiation centers for the wave, and their locations fit with the coronal dimming regions. Assuming a simple geometry of the wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B observations. We find that the wave structure is asymmetric with an inclination toward East. The associated CME has a deprojected speed of ∼ 750±50 km s−1, and it shows a non-radial outward motion toward the East with respect to the underlying source region location. Applying the forward fitting model developed by Thernisien, Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the CME flux rope position on the solar surface to be close to the dimming regions. We conclude that the expanding flanks of the CME most likely drive and shape the coronal wave.  相似文献   

14.
Using data from the Transition Region and Coronal Explorer (TRACE), Solar and Heliospheric Observatory (SOHO), Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and Hida Observatory (HO), we present a detailed study of an EUV jet and the associated Hα filament eruption in a major flare in the active region NOAA 10044 on 29 July 2002. In the Hα line wings, a small filament was found to erupt out from the magnetic neutral line of the active region during the flare. Two bright EUV loops were observed rising and expanding with the filament eruption, and both hot and cool EUV plasma ejections were observed to form the EUV jet. The two thermal components spatially separated from each other and lasted for about 25 minutes. In the white-light corona data, a narrow coronal mass ejection (CME) was found to respond to this EUV jet. We cannot find obvious emerging flux in the photosphere accounting for the filament eruption and the EUV jet. However, significant sunspot decay and magnetic-flux cancelation owing to collision of opposite flux before the events were noticed. Based on the hard X-ray data from RHESSI, which showed evidence of magnetic reconnection along the main magnetic neutral line, we think that all of the observed dynamical phenomena, including the EUV jet, filament eruption, flare, and CME, should have a close relation to the flux cancelation in the low atmosphere.  相似文献   

15.
A major, albeit serendipitous, discovery of the SOlar and Heliospheric Observatory mission was the observation by the Extreme Ultraviolet Telescope (EIT) of large-scale extreme ultraviolet (EUV) intensity fronts propagating over a significant fraction of the Sun??s surface. These so-called EIT or EUV waves are associated with eruptive phenomena and have been studied intensely. However, their wave nature has been challenged by non-wave (or pseudo-wave) interpretations and the subject remains under debate. A string of recent solar missions has provided a wealth of detailed EUV observations of these waves bringing us closer to resolving the question of their nature. With this review, we gather the current state-of-the-art knowledge in the field and synthesize it into a picture of an EUV wave driven by the lateral expansion of the CME. This picture can account for both wave and pseudo-wave interpretations of the observations, thus resolving the controversy over the nature of EUV waves to a large degree but not completely. We close with a discussion on several remaining open questions in the field of EUV waves research.  相似文献   

16.
Magnetosonic wave formation driven by an expanding cylindrical piston is numerically simulated to obtain better physical insight into the initiation and evolution of large-scale coronal waves caused by coronal eruptions. Several very basic initial configurations are employed to analyze intrinsic characteristics of MHD wave formation that do not depend on specific properties of the environment. It turns out that these simple initial configurations result in piston/wave morphologies and kinematics that reproduce common characteristics of coronal waves. In the initial stage, the wave and the expanding source region cannot be clearly resolved; i.e. a certain time is needed before the wave detaches from the piston. Thereafter, it continues to travel as what is called a “simple wave.” During the acceleration stage of the source region inflation, the wave is driven by the piston expansion, so its amplitude and phase-speed increase, whereas the wavefront profile steepens. At a given point, a discontinuity forms in the wavefront profile; i.e. the leading edge of the wave becomes shocked. The time/distance required for the shock formation is shorter for a more impulsive source-region expansion. After the piston stops, the wave amplitude and phase speed start to decrease. During the expansion, most of the source region becomes strongly rarefied, which reproduces the coronal dimming left behind the eruption. However, the density increases at the source-region boundary, and stays enhanced even after the expansion stops, which might explain stationary brightenings that are sometimes observed at the edges of the erupted coronal structure. Also, in the rear of the wave a weak density depletion develops, trailing the wave, which is sometimes observed as weak transient coronal dimming. Finally, we find a well-defined relationship between the impulsiveness of the source-region expansion and the wave amplitude and phase speed. The results for the cylindrical piston are also compared with the outcome for a planar wave that is formed by a one-dimensional piston, to find out how different geometries affect the evolution of the wave.  相似文献   

17.
Thompson  B.J.  Reynolds  B.  Aurass  H.  Gopalswamy  N.  Gurman  J.B.  Hudson  H.S.  Martin  S.F.  St. Cyr  O.C. 《Solar physics》2000,193(1-2):161-180
We report coincident observations of coronal and chromospheric flare wave transients in association with a flare, large-scale coronal dimming, metric radio activity and a coronal mass ejection. The two separate eruptions occurring on 24 September 1997 originate in the same active region and display similar morphological features. The first wave transient was observed in EUV and H data, corresponding to a wave disturbance in both the chromosphere and the solar corona, ranging from 250 to approaching 1000 km s–1 at different times and locations along the wavefront. The sharp wavefront had a similar extent and location in both the EUV and H data. The data did not show clear evidence of a driver, however. Both events display a coronal EUV dimming which is typically used as an indicator of a coronal mass ejection in the inner corona. White-light coronagraph observations indicate that the first event was accompanied by an observable coronal mass ejection while the second event did not have clear evidence of a CME. Both eruptions were accompanied by metric type II radio bursts propagating at speeds in the range of 500–750 km s–1, and neither had accompanying interplanetary type II activity. The timing and location of the flare waves appear to indicate an origin with the flaring region, but several signatures associated with coronal mass ejections indicate that the development of the CME may occur in concert with the development of the flare wave.  相似文献   

18.
We investigate the early phase of the 13 February 2009 coronal mass ejection (CME). Observations with the twin STEREO spacecraft in quadrature allow us to compare for the first time in one and the same event the temporal evolution of coronal EUV dimmings, observed simultaneously on-disk and above-the-limb. We find that these dimmings are synchronized and appear during the impulsive acceleration phase of the CME, with the highest EUV intensity drop occurring a few minutes after the maximum CME acceleration. During the propagation phase two confined, bipolar dimming regions, appearing near the footpoints of a pre-flare sigmoid structure, show an apparent migration away from the site of the CME-associated flare. Additionally, they rotate around the ‘center’ of the flare site, i.e., the configuration of the dimmings exhibits the same ‘sheared-to-potential’ evolution as the postflare loops. We conclude that the motion pattern of the twin dimmings reflects not only the eruption of the flux rope, but also the ensuing stretching of the overlying arcade. Finally, we find that: i) the global-scale dimmings, expanding from the source region of the eruption, propagate with a speed similar to that of the leaving CME front; ii) the mass loss occurs mainly during the period of strongest CME acceleration. Two hours after the eruption Hinode/EIS observations show no substantial plasma outflow, originating from the ‘open’ field twin dimming regions.  相似文献   

19.
Willson  Robert F. 《Solar physics》2000,197(2):399-419
Very Large Array (VLA) observations of the Sun at 91 and 400 cm wavelength have been used to investigate the radio signatures of EUV heating events and coronal mass ejections (CMEs) detected by SOHO and TRACE. Our 91 cm observations show the onset of Type I noise storm emission about an hour after an EUV ejection event was detected by EIT and TRACE. The EUV event also coincided with the estimated start time of a CME detected by the LASCO C2 coronagraph, suggesting an association between the production of nonthermal particles and evolving plasma-magnetic field structures at different heights in the corona. On another day, our VLA 400 cm observations reveal weak, impulsive microbursts that occurred sporadically throughout the middle corona. These low-brightness-temperature (T b=0.7–22×106 K) events may be weak Type III bursts produced by beams of nonthermal electrons which excite plasma emission at a height where the local plasma frequency or its first harmonic equals the observing frequency of 74 MHz. For one microburst, the emission was contained in two sources separated by 0.7 R 0, indicating that the electron beams had access to widely-divergent magnetic field lines originating at a common site of particle acceleration. Another 400 cm microburst occurred in an arc-like source lying at the edge of EUV loops that appeared to open outward into the corona, possibly signaling the start of a CME. In most instances the 400 cm microbursts were not accompanied by detectable EUV activity, suggesting that particles that produce the microbursts were independently accelerated in the middle corona, perhaps as the result of some quasi-continuous, large-scale process of energy release.  相似文献   

20.
Gopalswamy  N.  Cyr  O.C. St.  Kaiser  M.L.  Yashiro  S. 《Solar physics》2001,203(1):149-163
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.  相似文献   

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