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1.
We use Yohkoh soft X-ray telescope data and H full-disk observations to study the evolution of chromospheric filaments and coronal sigmoids in 6 active regions in association with coronal mass ejections (CMEs). In two cases, CMEs are directly observed by the SOHO/LASCO C2 coronagraph. In four cases, other observations (magnetic clouds, geomagnetic storms, sigmoid-arcade evolution) are used as CME indicators. Prior to eruption, each active region shows a bright coronal sigmoidal loop and underlying H filament. The sigmoid activates, erupts and gets replaced by a cusp, or an arcade. In contrast, the H filament shows no significant changes in association with sigmoid eruption and CME. We explain these observations in a framework of the classical two-ribbon flare model. 相似文献
2.
A time series of K3 spectroheliograms taken at the Coimbra Observatory exhibits an erupting loop on the east limb on July 9, 1982 in active region NOAA 3804. The Goddard SMM Hard X-Ray Burst Spectrometer (HXRBS) observations taken during this period reveal a hard X-ray flare occurring just before the loop eruption is observed, and SMS-GOES soft X-ray observations reveal a strong long-duration event (LDE) following the impulsive phase of the flare. A Solwind coronagram exhibits a powerful coronal mass ejection (CME) associated with the erupting loop. H flare and prominence observations as well as centimeter and decimeter radio observations of the event are also reviewed. A large, north–south-oriented quiescent prominence reported within the upper part of the CME expansion region may play a role in the eruption as well. The spatial and temporal correlations among these observations are examined in the light of two different current models for prominence eruption and CME activation: (1) The CME is triggered by the observed hard X-ray impulsive flare. (2) The CME is not triggered by a flare, and the observed soft X-ray flare is an LDE due to reconnection within the CME bubble. It is concluded that this event is probably of a mixed type that combines characteristics of models (1) and (2). The July 9 event is then compared to three other energetic CME and flare eruptions associated with the same active-region complex, all occurring in the period July 9 through September 4, 1982. It is noted that these four energetic events coincide with the final evolutionary phase of a long-lasting active-region complex, which is discussed in a companion paper (Bumba, Garcia, and Jordan, 1997). The paper concludes by addressing the solar flare myth controversy in the light of this work. 相似文献
3.
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
4.
We study the initiation and development of the limb coronal mass ejection (CME) of 15 May 2001, utilizing observations from Mauna Loa Solar Observatory (MLSO), the Solar and Heliospheric Observatory (SOHO), and Yohkoh. The pre-eruption images in various spectral channels show a quiescent prominence imbedded in the coronal void, being overlaid by the coronal arch. After the onset of rapid acceleration, this three-element structure preserved its integrity and appeared in the MLSO MK-IV coronagraph field of view as the three-part CME structure (the frontal rim, the cavity, and the prominence) and continued its motion through the field of view of the SOHO/LASCO coronagraphs up to 30 solar radii. Such observational coverage allows us to measure the relative kinematics of the three-part structure from the very beginning up to the late phases of the eruption. The leading edge and the prominence accelerated simultaneously: the rapid acceleration of the frontal rim and the prominence started at approximately the same time, the prominence perhaps being slightly delayed (4 – 6 min). The leading edge achieved the maximum acceleration amax 600 ± 150 m s–2 at a heliocentric distance 2.4 –2.5 solar radii, whereas the prominence reached amax 380± 50 m s–2, almost simultaneously with the leading edge. Such a distinct synchronization of different parts of the CME provides clear evidence that the entire magnetic arcade, including the prominence, erupts as an entity, showing a kind of self-similar expansion. The CME attained a maximum velocity of vmax 1200 km s–1 at approximately the same time as the peak of the associated soft X-ray flare. Beyond about 10 solar radii, the leading edge of the CME started to decelerate at a–20 m s–2, most likely due to the aerodynamic drag. The deceleration of the prominence was delayed for 10 –30 min, which is attributed to its larger inertia. 相似文献
5.
We intend to provide a comprehensive answer to the question on whether all Coronal Mass Ejections (CMEs) have flux rope structure. To achieve this, we present a synthesis of the LASCO CME observations over the last 16 years, assisted by 3D MHD simulations of the breakout model, EUV and coronagraphic observations from STEREO and SDO, and statistics from a revised LASCO CME database. We argue that the bright loop often seen as the CME leading edge is the result of pileup at the boundary of the erupting flux rope irrespective of whether a cavity or, more generally, a three-part CME can be identified. Based on our previous work on white light shock detection and supported by the MHD simulations, we identify a new type of morphology, the ‘two-front’ morphology. It consists of a faint front followed by diffuse emission and the bright loop-like CME leading edge. We show that the faint front is caused by density compression at a wave (or possibly shock) front driven by the CME. We also present highly detailed multi-wavelength EUV observations that clarify the relative positioning of the prominence at the bottom of a coronal cavity with a clear flux rope structure. Finally, we visually check the full LASCO CME database for flux rope structures. In the process, we classify the events into two clear flux rope classes (‘three-part’, and ‘Loop’), jets and outflows (no clear structure). We find that at least 40 % of the observed CMEs have clear flux rope structures and that ～?29 % of the database entries are either misidentifications or inadequately measured and should be discarded from statistical analyses. We propose a new definition for flux rope CMEs (FR-CMEs) as a coherent magnetic, twist-carrying coronal structure with angular width of at least 40° and able to reach beyond 10 R⊙ which erupts on a time scale of a few minutes to several hours. We conclude that flux ropes are a common occurrence in CMEs and pose a challenge for future studies to identify CMEs that are clearly not FR-CMEs. 相似文献
6.
This paper deals with the influence of the distance of the apparent axes of coronal mass ejections (CMEs) from a neutral line (NL) on the source surface and of coronal hole (CH) boundaries upon apparent characteristics of CMEs: e.g., the structure, the velocity of individual features, and the width.(a) It is found that the chance of measuring a CME velocity of ascent appears to decrease with increasing distance from a neutral line or coronal hole.(b) The apparent velocity of a CME appears to depend on the distance of its core from a neutral line or coronal hole boundary. CME speeds for events within 15 deg of a surface neutral line are significantly higher than those apparently much farther from surface neutral lines.(c) CME spans tend to be wider when they are more closely associated with surface neutral lines. It is shown that the contribution of CMEs in the neighbourhood of the NL (the heliomagnetic latitude of the CME apparent axis L < 15 deg) decreases with increasing length of the chain of coronal streamers separating the CH of like polarity of the magnetic field and depends on the character of the relationship between CMEs and other forms of activity. The study revealed a concentration of the apparent axes of CMEs toward zero lines of the photospheric magnetic field from the J. M. Wilcox Solar Observatory at Stanford. 相似文献
7.
B. Vršnak 《Solar physics》1990,127(1):129-137
The kinematics and the development of the internal structure in the eruptive prominence of August 16, 1988 are described. The prominence exposed helical structure, and the pitch of the fine structure filaments was measured. The evolution of the pitch was measured in the legs of the prominence and at its summit from the pre-eruptive phase up to the late phases of the eruption. The pitch angle was decreasing in the legs as well as at the summit. However, the observations indicate that the integral twist remained constant. The prominence was twisted more at the summit where it was wider than in the legs. The effective twist at the prominence summit was approximately 20 and in the legs it amounted to about 8 . Such a ratio did not change during the eruption, i.e., no redistribution of the twist was observed within the accuracy of measurements. The nature of the instability causing the eruption is discussed and the energetics of the process is considered. 相似文献
8.
The distribution of times t between coronal mass ejections (CMEs) in the Large Angle and Spectrometric Coronagraph (LASCO) CME catalog for the years 1996–2001 is examined. The distribution exhibits a power-law tail (t) with an index –2.36±0.11 for large waiting times (t>10 hours). The power-law index of the waiting-time distribution varies with the solar cycle: for the years 1996–1998 (a period of low activity), the power-law index is –1.86±0.14, and for the years 1999–2001 (a period of higher activity), the index is –2.98±0.20. The observed CME waiting-time distribution, and its variation with the cycle, may be understood in terms of CMEs occurring as a time-dependent Poisson process. The CME waiting-time distribution is compared with that for greater than C1 class solar flares in the Geostationary Operational Environmental Satellite (GOES) catalog for the same years. The flare and CME waiting-time distributions exhibit power-law tails with very similar indices and time variation. 相似文献
9.
We analyze five events of the interaction of coronal mass ejections (CMEs) with the remote coronal rays located up to 90°
away from the CME as observed by the SOHO/LASCO C2 coronagraph. Using sequences of SOHO/LASCO C2 images, we estimate the kink
propagation in the coronal rays during their interaction with the corresponding CMEs ranging from 180 to 920 km s−1 within the interval of radial distances from 3 R
⊙ to 6 R
⊙. We conclude that all studied events do not correspond to the expected pattern of shock wave propagation in the corona. Coronal
ray deflection can be interpreted as the influence of the magnetic field of a moving flux rope within the CME. The motion
of a large-scale flux rope away from the Sun creates changes in the structure of surrounding field lines, which are similar
to the kink propagation along coronal rays. The retardation of the potential should be taken into account since the flux rope
moves at a high speed, comparable with the Alfvén speed. 相似文献
10.
Observations are reported of two multiple CME events which were detected on 2–3 June 1997 and 9–10 June 1998, using the LASCO instrument on board SOHO. Each event consists of a group of four related CMEs which emerge from progressively higher latitudes over a time period of approximately 16 hours. In both cases there is on-disk activity visible in EIT EUV images which involves bright emission along the south polar crown filament and there is also ejection of mass from other regions of the corona during the time period of each event. We present a multi-wavelength view of these events (i.e. white-light, H, EUV and, in the case of the 2–3 June 1997 event, soft X-ray), which suggest that ejection of mass from one point in the corona can lead to a destabilization of a previously stable structure and the further ejection of mass from different regions of the corona, in a systematic way. The observations also show that the CME phenomenon is not always a localised event but can occur on a global level; and that complex CME activity can arise at relatively quiet-Sun periods as evidenced by the lack of significant X-ray flares or radio signatures. 相似文献
11.
Large Doppler velocities with unique, almost regular elliptical features were observed in the H spectra of the May 15, 2000 eruptive prominence. These features were interpreted in the frame of axially symmetric models of the eruptive prominence. The rotational (7–60 km s–1), expansion (30–44 km s–1), axial (3–19 km s–1), and global (66–160 km s–1) prominence plasma velocities were derived. The plasma velocity patterns were compared with the observed helical structures of the H prominence. The velocities of selected H blobs in the image plane were determined. The axially symmetric detwisting process of the magnetic flux rope of the eruptive prominence was recognized. 相似文献
12.
Observations of internal structure and development of four helical prominences are presented. We assume that the helically twisted fine structure threads are outlining magnetic field lines and we found that it is possible to describe the magnetic fields by the uniform twist configuration, with the twists ranging between 2 and 7. The estimated lower limits for the magnetic fields were about 20 G which give lower limits for the currents flowing along the prominences in the range between 2 × 1010 A and 2 × 1011 A and current densities at the axis of the prominences about 10-4 A m-2. The upper limit of electron drift velocity could be estimated as 1 m s-1, which is far below the critical velocities for the onset of plasma microinstabilities.The stability of the studied prominences is discussed and the criteria for the onset of eruptive instability are established for a prominence modelled as a twisted and elliptically curved magnetic flux tube which is anchored in the photosphere and affected by its mirror-current. The eruption starts when the prominence attains a critical height which must be larger than half of the footpoint separation and depends on the values of twist, radius, and footpoint distance of the magnetic flux tube. The observed examples of eruptive prominences agree very well with the predictions. Possible applications to the two-ribbon flare process are outlined.Properties of stable cylindrical prominences in equilibrium are analyzed and a criterion for the distinction between the Kuperus-Raadu and Kippenhahn-Schlüter types of prominences is proposed. According to established criteria, two of the studied prominences were of the Kuperus-Raadu type, while the other two were of the Kippenhahn-Schlüter type. 相似文献
13.
We report on the occurrence of Hα dimming associated with a sigmoid eruption in a quiet-sun region on 14 August 2001. The
coronal sigmoid in soft X-ray images from the Yohkoh Soft X-ray Telescope was located over an Hα filament channel. Its eruption was accompanied by a flare of GOES X-ray class
C2.3 and possibly associated with a halo coronal mass ejection (CME) observed with the Large Angle and Spectroscopic Coronagraphs (LASCO) on board the Solar and Heliospheric Observatory (SOHO). During the eruption, coronal bipolar double dimming took place at the regions with opposite magnetic polarities around
the two sigmoid ends, but the underlying chromospheric channel did not show observable changes corresponding to the coronal
eruption. Different from the erupting coronal sigmoid itself, however, the coronal dimming had a detectable chromosphere counterpart,
i.e., Hα dimming. By regarding the sigmoid as a coronal sign for a flux rope, these observations are explained in the framework
of the flux rope model of CMEs. The flux rope is possibly deeply rooted in the chromosphere, and the coronal and Hα dimming
regions mark its evacuated feet, through which the material is possibly fed to the halo CME. 相似文献
14.
We re-examine observations bearing on the origin of metric type II bursts for six impulsive solar events in November 1997. Previous analyses of these events indicated that the metric type IIs were due to flares (either blast waves or ejecta). Our point of departure was the study of Zhang et al. (2001) based on the Large Angle and Spectrometric Coronagraphs C1 instrument (occulting disk at 1.1 R0) that identified the rapid acceleration phase of coronal mass ejections (CMEs) with the rise phase of soft X-ray light curves of associated flares. We find that the inferred onset of rapid CME acceleration in each of the six cases occurred 1–3 min before the onset of metric type II emission, in contrast to the results of previous studies for certain of these events that obtained CME launch times 25–45 min earlier than type II onset. The removal of the CME-metric type II timing discrepancy in these events and, more generally, the identification of the onset of the rapid acceleration phase of CMEs with the flare impulsive phase undercuts a significant argument against CMEs as metric type II shock drivers. In general, the six events exhibited: (1) ample evidence of dynamic behavior [soft X-ray ejecta, extreme ultra-violet imaging telescope (EIT) dimming onsets, and wave initiation (observed variously in H, EUV, and soft X-rays)] during the inferred fast acceleration phases of the CMEs, consistent with the cataclysmic disruption of the low solar atmosphere one would expect to be associated with a CME; and (2) an organic relationship between EIT dimmings (generally taken to be source regions of CMEs) and EIT waves (which are highly associated with metric type II bursts) indicative of a CME-driver scenario. Our analysis indicates that the broad (90 to halo) CMEs observed in the outer LASCO coronagraphs for these impulsive events began life as relatively small-scale structures, with angular spans of 15 in the low corona. A review of on-going work bearing on other aspects (than timing) of the question of the origin of metric type II bursts (CME association; connectivity of metric and decametric-hectometric type II shocks; spatial relationship between CMEs and metric shocks) leads to the conclusion that CMEs remain a strong candidate to be the principal/sole driver of metric type II shocks vis-à-vis flare blast waves/ejecta. 相似文献
15.
The characteristics of the magnetic field ubiquitously permeating the coronal plasma are still largely unknown. In this paper we analyze some aspects of coronal physics, related to the magnetic field behavior, which forthcoming SOHO UVCS observations can help better understand. To this end, three coronal structures will be examined: streamers, coronal mass ejections (CMEs), and coronal holes.As to streamers and CMEs, we show, via simulations of the Ly- and white-light emission from these objects, calculated on the basis of recent theoretical models (Wang et al., 1995), how new data from SOHO can help in advancing our knowledge of the streamer/CME magnetic configuration. Our discussion highlights also those observational signatures which might offer clues on reconnection processes in streamers' current sheets.Coronal holes (CHs) are discussed in the last section of the paper. Little is known about CH flux tube geometry, which is closely related to the behavior of the solar wind at small heliocentric distances.Indirect evidence for the flux tube spreading factors, within a few solar radii, is here examined. 相似文献
16.
Using TRACE 171 Å image observations and H spectra and images observed at the Ondejov Observatory, the October 1, 2001, eruptive prominence is studied. The evolution of this prominence is described and velocities of specific parts of the prominence are determined. It was found that, after the rising phase of the cold loop-like prominence, its upper part expanded and below this expanding part, around one of its legs a `ring' structure, visible in the TRACE images, was formed. Then, at the same place, a tearing of the prominence leg was recognized. Simultaneous spectral observations of this structure reveal a very broad H line, which indicates strong turbulent motion at these positions. These processes were accompanied by an expanding H envelope. Due to the similarity of the observed `ring' and tearing structures with those modeled by Lau and Finn (1996), the prominence leg tearing is interpreted as a reconnection process between two parallel magnetic ropes having parallel electric currents, but anti-parallel axial magnetic fields. 相似文献
17.
The semiannual mean CME velocities for the time interval of 1979–1989 have been analyzed to reveal a complex cyclic variation with a peak at the solar cycle maximum and a secondary peak at the minimum of the cycle. The growth of the mean CME width is accompanied by a growth of the mean CME velocity. It is shown that the cyclic variations of the mean CME velocity and the mean CME width are associated with the cyclic variations of the large-scale magnetic field structure and that the secondary peak of the semiannual mean CME velocity in 1985–1986 is due to a significant contribution of fast CMEs with a width of 100° at the minimum of the cycle. This peak is supposed to be due to the increasing role of the global large-scale magnetic field system with a characteristic size of cells of 70°–100° at the minimum of the cycle and the respective particularities of the large-scale magnetic field configuration in the corona. 相似文献
18.
A spectroscopic investigation of a quiescent prominence has been performed: the line profiles of the H and K lines have been carefully determined in all regions of the prominence where these emissions are likely to originate in optically thin layers. Therefore we have been able to study the electron temperature T
e and the microturbulent velocity in the outer parts of the prominence. We find that on the average, T
e = 5700 K (Figure 1) and = 6.7 km s-1 (Figure 2) which are in very good agreement with classical data. Figure 3 represents the radial velocity measurements and Figure 4 the ratio of the total intensity of H to K lines. Thus the prominence we have observed does not show for T
e and the regular increase outward which has been described by Hirayama (1971). On the other hand increases towards the Equator, in the dynamically active part of the prominence, which could indicate that represents the effect of macroturbulence rather than microturbulence (Kawaguchi, 1966). In this part of the prominence only the K line is in emission and the average value of the microturbulence is 9.4 km s-1, the radial velocity is also generally increasing. At last, according to the absolute intensities of the H and K lines, the electron density in the outer layers of the prominence is no more than 1 × 1010 cm-3. 相似文献
19.
Kâmuran Avcioglu M. Türker Özkan H. Hüseyin Mentese 《Astrophysics and Space Science》1990,164(2):263-276
We investigate the near-ultraviolet high-resolution LWR spectra of the stars Cas, And, Tau, Gem, Cru, Boo, and Peg, obtained with the aid of the International Ultraviolet Explorer Satellite. We have given here a list of the strongest and most prevalent emission lines in the near-ultraviolet spectra of Boo, KlIIIp, and Peg, M2.5II-III which have the same luminosity class and different spectral type. The near-ultraviolet continuum flux measurements and integrated emission line fluxes of these stars for the 2500–3200 Å region are presented in order to compare the variations in the appearance of the near-ultraviolet flux distribution with the temperature structure of their chromospheres for K and M giant stars. We also discuss differences between observed and calculated fluxes found from the Planck function. 相似文献
20.
The eruptive prominence observed on 27 May 1999 in H at Ondejov Observatory is analyzed using image-processing techniques. To understand the physical processes behind the prominence eruption, heated structures inside the cold H prominence material are sought. Two local minima of intensity (holes), the first above and the second below the erupting H prominence, have been found in the processed H images. A comparison of H images with the SOHO/EIT and Yohkoh/SXT images showed: (a) the cold H prominence is visible as a dark feature in the EIT images, (b) the upper local minimum of intensity in the H image corresponds to a hot structure seen in EIT, (c) the lower minimum corresponds to a hot loop observed by SXT. The physical significance of the H intensity minima and their relation to the hot structures observed by EIT and SXT is discussed. The time sequence of observed processes is in favor of the prominence eruption model with the destabilization of the loop spanning the prominence. For comparison with other events the velocities of selected parts of the eruptive prominence are determined. 相似文献