The Astrophysical Journal, 595:1251–1258, 2003 October 1
# 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A.
THE DYNAMICAL MORPHOLOGIES OF FLARES ASSOCIATED WITH THE TWO TYPES OF
SOLAR CORONAL MASS EJECTIONS
Mei Zhang
High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307;
and National Astronomical Observatory, Chinese Academy of Sciences, China; [email protected]
and
Leon Golub
Smithsonian Astrophysical Observatory; [email protected]
Received 2002 July 25; accepted 2003 June 11
ABSTRACT
In this paper we study the high-cadence TRACE observations of a sample of 28 X- and M-class flares, with
particular focus on the relation between flare morphology and the two types (fast and slow) of solar coronal
mass ejections (CMEs). Among the 28 flares studied, 10 are associated with fast CMEs, 10 are associated with
slow CMEs, and 8 are loosely associated with a CME. We find that flares associated with fast and slow CMEs
show different morphologies as groups. While all flares associated with fast CMEs show clear footpointseparating, two-ribbon brightenings during the flare, this feature is less often seen in flares associated with
slow CMEs or flares without CMEs. Meanwhile, while flares associated with slow CMEs sometimes show
tubular emission structures during the flare, this feature is not found in our sample of flares associated with
fast CMEs. This observational result suggests that the morphologies of flares, and hence possibly the
magnetic field topologies, are different for events associated with fast and with slow CMEs.
Subject headings: Sun: corona — Sun: coronal mass ejections (CMEs) — Sun: flares
The Low & Zhang theory is observationally testable.
One prediction of the theory is that the magnetic reconnection, which is usually observed as flares, is crucial to the
early development of fast CMEs. Thus, we expect to see
flares during the onset of fast CMEs. On the other hand,
the theory predicts that reconnection is not crucial for the
onset of slow CMEs, although it may actually happen during their development. In our previous paper (Zhang et al.
2002, hereafter Paper I), we considered a sample of flareassociated CMEs and studied the timing behavior of the
flares associated with fast and slow CMEs, respectively.
We found that flares associated with fast CMEs tend to
happen within half an hour of the CME onsets, while the
timing of flares associated with slow CMEs is only loosely
related to the CME onsets. This suggests that the occurrence of a flare does closely relate to the onset of a fast
CME, while it is only loosely associated with the onset of a
slow CME, a picture consistent with the Low & Zhang
theory.
Magnetic topologies determine the behaviors of both
types of CME and therefore their associated flares. Accordingly, the morphologies of flares may be distinct for those
flares associated with fast or slow CMEs in the picture of
Low & Zhang (2002). In this paper, we address this possibility with a morphological study of flares from the sample
treated in Paper I. The sample and the result will be presented in x 2. Interpretation and discussion will be addressed
in x 3. A brief summary will be given in x 4.
1. INTRODUCTION
Coronal mass ejections (CMEs), flares, and eruptive
prominences are three major forms of solar activity in the
corona. It has long been known that these three activities
are closely related, with CMEs having associations with
flares and eruptive prominences at the 50% and 75% levels,
respectively (Munro et al. 1979; Webb & Hundhausen
1987). It has also long been known that there are two types
of solar prominences, namely, normal and inverse prominences, detected by Leroy and his colleagues in the late
1970s (Leroy 1989; Tandberg-Hanssen 1995). Observations
indicate that the magnetic fields in prominences are principally horizontal, with a strong component along the long
prominence axis. Normal and inverse prominence configurations are distinguished by whether the measured prominence magnetic fields are in the same or opposite directions,
respectively, relative to the underlying photospheric magnetic field. Recently, Sheeley et al. (1999) did a systematic
study using SOHO LASCO data and confirmed that there
are two dynamical types of solar coronal mass ejections, an
idea first suggested by MacQueen & Fisher (1983) from Skylab observations. These observations provide the observational basis for the Low & Zhang (2002) theory of the two
types of solar coronal mass ejections.
Low & Zhang (2002) proposed that the two observed
types of coronal mass ejections, described as fast or slow
CMEs as characterized by their different speed versus height
profiles, relate to initial states represented, respectively, by
normal or inverse prominences. The topologically different
magnetic environments of these two prominence states will
produce distinct interplays between flux-rope expulsion
(CME) and magnetic reconnection (flare) and hence link the
three major coronal activities under one uniform MHD
theory.
2. THE SAMPLE AND THE RESULT
The sample we studied in this paper is extracted from
the sample we constructed in Paper I. In constructing the
sample in Paper I, we used three catalogs available on the
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Vol. 595
TABLE 1
Flares Associated with Fast CMEs
CME
Flare
Date
Peak
Time
Class
Speed
(km s1)
Onset
Time
Observed Band(s)
(Å)
Separating
Footpoints?
2000 Feb 08...............
2000 Jun 10 ...............
2000 Jul 14 ................
2000 Nov 24 ..............
2001 Mar 24 ..............
2001 Mar 29 ..............
2001 Apr 09...............
2001 Apr 10...............
2001 Apr 11...............
2001 Aug 25 ..............
9:00
17:02
10:24
15:13
19:55
10:15
15:34
5:26
13:26
16:45
M1.3
M5.2
X5.7
X2.3
M1.7
X1.7
M7.9
X2.3
M2.3
X5.3
1079
1108
1674
1245
906
942
1192
2411
1103
1433
9:03
16:46
10:26
15:25
19:41
9:50
15:30
5:17
13:03
16:20
171, 1600
195, 1600
195, 1600
1600
171, 1600
171, 1600
171, 1600
171, 1600
171, 1600
171, 284, 1600
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
network. They are the TRACE Flare Catalog,1 provided by
Kathy Reeves at Smithsonian Astrophysical Observatory;
SOHO LASCO CME Catalog,2 provided by The Center for
Solar Physics and Space Weather, the Catholic University
of America; and the GOES Flare Catalog,3 provided by
Space Environment Center, National Oceanic and Atmospheric Administration. We used the GOES Flare Catalog
to define the flare class and the flare peak time, the latter
being defined as the time when GOES X-ray flux reaches
maximum during the flare. The CME onset time is defined
as the time when the CME is at a height of 1.1 R and is calculated by fitting the CME height-time profile from the
SOHO LASCO CME Catalog and assuming the CME is
moving at a constant speed. It is worth mentioning here that
we do not measure the height-time profiles of CMEs ourselves, but make use of the data published in the SOHO
LASCO CME Catalog, taking advantage of the efforts carried out by the Center for Solar Physics and Space Weather
group at Catholic University of America. They measured all
the visible CMEs detected by SOHO LASCO instruments,
and the details of the measurements are described on their
Web page. Finally, we used the TRACE Flare Catalog to
find flare events that have TRACE observations that we
examine in detail in this study.
It is well known that there are certain ambiguities when
relating flares to CMEs, mainly because CMEs are observed
at the solar limb by coronagraphs like SOHO LASCO,
SMM CP, MKIV, etc., while flares are often seen on the
solar disk. In constructing the sample in Paper I, we
regarded the flare and the CME as associated if the flare is
the one that happens closest in time to the CME onset and
the position of the flare lies in the range of the CME span,
defined as the position of the CME half of the CME width
15 . We further classified a CME as a fast CME if its projected linear velocity is equal to or greater than 800 km s1;
otherwise we classified the CME as a slow one. Note that
here we classify CMEs as fast or slow by their linear velocities derived from height-time profiles and ignore their other
propagation properties. This classification may be different
from those of other authors, e.g., the one in Zhang et al.
1
TRACE Movies
TRACE Flare Catalog available at http://hea-www.harvard.edu/
SSXG/kathy/flares/flares.html.
2 See http://cdaw.gsfc.nasa.gov/CME_list/readme.html.
3 Available
at
ftp://ftp.ngdc.noao.gov/STP/SOLAR_DATA/
SOLAR_FLARES/XRAY_FLARES/.
(2001). The detailed relationship between a CME’s linear
speed and its propagation properties is still a subject under
investigation, and is beyond the scope of the present paper.
In this paper, we simply apply a self-consistent classification
of the two types of CMEs and study the possible differences
between the two groups.
For the purpose of this study we further confine our sample to those flares that happen near disk center. We define a
flare as being near disk center if both its longitude and latitude are within 40 of disk center. The reason for this selection is to limit the projection effect on the flare morphology,
which is the main subject of this paper. We then further confine our sample by ignoring those events whose associated
CME speeds are between 700 and 900 km s1, in order to
have a clearer separation between fast and slow CMEs.
Now our flares associated with fast CMEs are those whose
CME linear speeds are greater than 900 km s1, and flares
associated with slow CMEs are those whose associated
CME linear speeds are lower than 700 km s1. After applying these cuts, we are left with a sample of 28 flares, of which
6 are X-class flares and 22 M-class. Ten of them are associated with fast CMEs and 18 are associated with slow CMEs.
From Paper I, we know that flares associated with fast
CMEs all happened within 30 minutes of the CME onsets.
This is of course the case for the 10 events in the present
sample. For the 18 flares associated with slow CMEs, the
time of occurrence of the flare spreads over a wide range,
and we then further classify them into two groups. One
group contains those flares that occurred within half an
hour of the CME onset; we call them ‘‘ flares associated with
slow CMEs.’’ The other group contains those flares that
occurred more than half an hour from the CME onset; we
call them ‘‘ flares loosely associated with CMEs or without
CMEs.’’ As a result, we are left with a sample of 28 flares,
and they are classified into three groups: a group of 10 that
we call ‘‘ flares associated with fast CMEs ’’; a group of 10
flares associated with slow CMEs; and a group of 8 flares
loosely associated with CMEs or without CMEs.
2.1. Flares Associated with Fast CMEs
Table 1 lists details of the 10 flares associated with fast
CMEs. Among them, five are X-class flares and five are
M-class flares. Most were observed in both ultraviolet (1600
Å) and extreme-ultraviolet (171, 195, or 284 Å) wavelengths
by the TRACE satellite. The TRACE mission explores the
No. 2, 2003
MORPHOLOGIES OF FLARES ASSOCIATED WITH CMEs
1253
Fig. 1.—TRACE observations of the event on 2000 July 14. The flare is an X5.7 flare, associated with a v ¼ 1674 km s1 CME. The top panels (a–d ) show
the time-series TRACE observations at 195 Å. The bottom panels (e–h) show the time-series TRACE observations at 1600 Å. The arrows in each panel indicate
where the separation of footpoints can be clearly seen. The field of view is 38400 38400 for each image.
dynamics and evolution of the solar atmosphere from the
photosphere to the corona with high spatial and temporal
resolution (Handy et al. 1999). Its spatial resolution is 0>5
pixel1 for all observed wavelengths, and the time resolution
can be as high as several seconds per image. For most observations of flares in this sample, the cadence is about 30 s,
with some sequences as high as 2–3 s in 1600 Å wavelength.
These high temporal and spatial resolution observations
benefit us in studying the highly dynamical morphological
variations.
By carefully examining the movies of these 10 flares in all
wavelengths available, we find that all 10 flares associated
with fast CMEs clearly show the dynamical morphology of
footpoint-separating, two-ribbon flares. The typical process
is as follows. A ribbon first lights up, and then separates into
two. The two ribbons separate from each other, and the
rapid separation process typically stops around the flare
peak time. After the flare peak, the two ribbons elongate
and the space between then becomes filled with postflare
loops (e.g., Zirin 1988).
Figure 1 shows an example of a flare associated with a fast
CME. This is an X5.7 flare associated with a v ¼ 1674 km
s1 CME. This is the famous Bastille Day flare and has been
discussed by several authors (e.g., Fletcher & Hudson
2001). Here we focus on its dynamical morphology, which
shows the rapid spreading of footpoints identified as a classic two-ribbon flare. Figures 1a–1d show the time-series
images observed at 195 Å. Figures 1e–1h are the time-series
images observed at 1600 Å. The arrows in each panel indicate where the separation of footpoints can be clearly seen.
The field of view is 38400 38400 for each image. The separation of the footpoints began when the filament began to
TABLE 2
Flares Associated with Slow CMEs
CME
Flare
TRACE Movies
Date
Peak
Time
Class
Speed
(km s1)
Onset
Time
Observed Band(s)
(Å)
Separating
Footpoints?
1999 Oct 26 ...............
2000 Jul 25 ................
2001 Mar 28 ..............
2001 Mar 29 ..............
2001 May 15..............
2001 Aug 25 ..............
2001 Sep 28 ...............
2001 Oct 26 ...............
2001 Nov 28 ..............
2001 Dec 16...............
7:45
2:49
12:40
15:25
3:00
9:28
10:14
14:35
16:35
1:24
M1.2
M8.0
M4.3
M1.2
M1.0
M1.2
M2.4
M2.0
M6.9
M1.5
212
528
519
441
381
513
665
350
500
343
8:05
2:41
12:26
15:36
3:22
9:42
9:50
14:18
16:37
1:20
171, 1600
171, 195, 1600
171, 1600
171, 1600
171, 1600
171, 284, 1600
171
171
1600
1600
no
yes?
no
no
no
no
no
no
no
yes?
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ZHANG & GOLUB
Vol. 595
Fig. 2.—TRACE time-series observation at 171 Å of the 2001 October 26 flare. The flare is a M2.0 flare, associated with a v ¼ 350 km s1 CME. The field of
view is 32000 25600 for each image. The arrows in panels b–d indicate the positions of tubular emissions addressed in the text. The square in panel b shows the
position and range of images shown in Fig. 6.
erupt at about 10:08 UT (Figs. 1b and 1e). The fast footpoint separation process stopped when the flare reached its
peak flux (Figs. 1c and 1g). After that, postflare loops
appeared (Figs. 1d and 1h), possibly with a very mild further
separation of the footpoints. The whole process of separation of footpoints is very typical in our sample for flares
associated with fast CMEs, regardless of whether the flare is
of M or X class.
clear footpoint-separating ribbons as seen in Figure 1 and
the 10 flares associated with fast CMEs. Instead, we see
upward-moving tubular emission at the flaring position,
indicated by the arrows in the upper part of each panel.
These tubular emissions are not seen before the eruption
(Fig. 1a), but are quite obvious during the flare (Figs. 1b
and 1c). After the flare, a cusplike structure formed, as
shown in Figure 1d.
2.2. Flares Associated with Slow CMEs
2.3. Flares Loosely Associated with CMEs or without CMEs
Table 2 lists details of the 10 flares associated with slow
CMEs. These flares do not show common morphological
features as do flares associated with fast CMEs; rather, they
show a variety of morphologies. Some show brightenings
along two-ribbon channels. Some show a compact bulge
and tubular structures. A common feature they have is that
they look different from those flares associated with fast
CMEs; e.g., most of them do not show the obvious rapid
separation of two ribbons. Although in two cases (the 2000
July 25 and the 2001 December 16 flares in Table 2) we see
some evidence of footpoint separation, in these two cases
the two ribbons do not elongate after the flare peak and the
ribbons are relatively short compared to those in flares associated with fast CMEs. Another major difference between
the flares associated with fast and slow CMEs is that some
of slow-CME flares show compact bulgelike structures with
clearly seen tubular emissions above the bulge. None of this
tubular emission is seen in flares associated with fast CMEs.
Figure 2 gives an example of a flare associated with a slow
CME. This is a M2.0 flare, associated with a v ¼ 350 km s1
CME. The flare is observed by TRACE at 171 Å, and the
field of view is 32000 25600 for each image. We do not see
Details of the eight flares loosely associated with CMEs
or without CMEs are listed in Table 3. We find that the morphologies of most of the flares in this group look similar to
those flares associated with slow CMEs. Recalling what we
found in Paper I, that the timing of flares associated with
slow CMEs spreads over a wide range relative to CME
onsets, the similarity of the morphologies here indicates that
some of the flares in this group may be ‘‘ wrongly ’’ grouped
here. They are closer to the group of flares associated with
slow CMEs, which implies that even though some flares
happened more than 30 minutes after the CME onsets, the
flare may still be CME-related and may be a result of the
CME expulsion.
Figure 3 gives an example of a flare that we classify as a
flare without a CME. It is a M1.2 flare, and no CME is
found associated with this flare within 2.5 hr of the flare
peak time. Similarly to Figure 1, Figures 3a–3d show the
time series of images observed at 195 Å. Figures 3e–3h are
the time series of images observed at 1600 Å. The field of
view is 38400 38400 . The arrows in each panel indicate
where the flare brightens along a two-ribbon channel.
TABLE 3
Flares Loosely Associated with CMEs or without CMEs
CME
Flare
TRACE Movies
Date
Peak
Time
Class
Speed
(km s1)
Onset
Time
Observed Band(s)
(Å)
Separating
Footpoints?
1999 Dec 21...............
1999 Dec 22...............
2000 Jul 12 ................
2000 Nov 23 ..............
2001 May 05..............
2001 Oct 19 ...............
2001 Nov 01 ..............
2001 Nov 13 ..............
17:19
19:04
5:02
23:28
8:56
1:05
23:52
6:26
M1.1
M5.3
M1.2
M1.0
M1.0
X1.6
M1.1
M1.5
291
605
613
690
617
558
453
416
16:40
18:23
2:30
22:58
5:27
0:19
22:01
5:15
171, 195, 1600
171, 1600
195, 1600
1600
171, 1600
171
171
1600
no
no
no
no
no
no
no
no
No. 2, 2003
MORPHOLOGIES OF FLARES ASSOCIATED WITH CMEs
1255
Fig. 3.—TRACE observation of the 2000 July 12 M1.2 flare. The top panels (a–d ) show the time-series TRACE observations at 195 Å. The bottom panels
(e–h) show the time-series TRACE observations at 1600 Å. The field of view is 38400 38400 for each image. The arrows in each panel indicate the position of a
two-ribbon brightening channel but with no separation from each other.
However, no separation of the footpoints, as seen in Figure
1, is found in this event. Note that this flare happens in the
same region as the flare in Figure 1. Although we can see the
similarity of the large-scale structures in both 195 and 1600
Å TRACE images, the flaring morphologies are quite
different for the two events.
3. INTERPRETATION AND DISCUSSION
We interpret our observations within the context of the
Low & Zhang theory. It is worth mentioning here that, even
though we are motivated to do this observation to test the
Low & Zhang theory, the observational result itself is
independent of our interpretations.
3.1. Flares Associated with Fast CMEs
Figure 4 shows a sketch of the fast CME model, based on
Figure 2 in Low & Zhang (2002). Low & Zhang (2002) treat
the normal prominence configurations as the initial state of
fast CMEs. The pre-eruption magnetic flux ropes are held in
equilibrium by heavy prominences treated as vertical sheets
(Fig. 4, left). By an assumed mass loss from the prominence,
the flux rope will be released up into the atmosphere, forming a current sheet ahead of the flux rope. The current sheet
Fig. 4.—Sketch of the fast CME model, based on Fig. 2 in Low & Zhang (2002). Shown are the initial state prior to eruption where the massive prominence
sheet in the flux rope presented a normal prominence (left); the lift-off of the flux-rope due to mass-loss from the prominence, forming a current sheet ahead of
the flux-rope (center); and further development with magnetic reconnection having removed the fields ahead of the flux rope and the left-over flux rope running
away as an expulsion (right). Note that the reconnection of the current sheet will happen continuously, from the very beginning when the footpoints of the
sheet are still close to each other (center), through stages in which the heated footpoints of newly reconnected flux separate from each other (right) and behave
as a two-ribbon flare.
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Fig. 5.—Sketch of the slow CME model, based on Fig. 1 in Low & Zhang (2002). Shown are the initial state prior to eruption with a massive prominence
sheet in the flux rope presented an inverse prominence (left); the lift-off of the flux-rope due to mass loss from the prominence, forming a current sheet behind
the flux-rope (center); and further development of the expulsion with magnetic reconnection producing closed bipolar fields anchored to the atmospheric base
(right). Note in this configuration the occurrence of reconnection of the current sheet can be delayed to a very late stage in the right panel, and the heated
footpoints are confined to those regions of newly reconnected flux behind the rope.
separates the flux rope flux from the external coronal field
of opposite polarity. Having two flux systems of opposite
polarity is a characteristic necessary to produce a normal
flux-rope prominence. Then, with the magnetic reconnection of the current sheet setting in, the opposite-polarity
fields ahead of the flux rope will be removed and the flux
rope will run away as an expulsion. Note that in this configuration the reconnection of the current sheet is necessary to
release the flux rope, and the reconnection will happen continuously, from the very beginning when the footpoints of
the current sheet are still close to each other (Fig. 4, center),
to a stage at which the flux rope has been totally expelled. In
this process, the heated footpoints of continuously newly
reconnected flux will separate from each other (Fig. 4, right)
and behave as a two-ribbon flare.
3.2. Flares Associated with Slow CMEs
Figure 5 shows a sketch of the slow CME model, based
on Figure 1 in Low & Zhang (2002). Here the inverse prominences are treated as the initial state of slow CMEs (Fig. 5,
left). Mass loss from the prominence will lift the flux rope
and form a straight current sheet behind the flux rope (Fig.
5, center). This current sheet has the same sign of current as
does the current in the flux rope and will attract the flux rope
and hence resist its outward motion. This is the reason we
conjecture that this configuration will produce a slow CME.
Note that in this configuration magnetic reconnection is not
necessary for the flux rope expulsion, so its occurrence may
be delayed to a very late stage of the expulsion (Fig. 5, right).
This means we may have a chance to find some slow CMEs
that have no indication of reconnection until the late stage
of its expulsion. When the reconnection of the current sheet
finally sets in, the reconnection point may be high in the atmosphere and the plasma be attracted to move along the
straight current sheet and nearby field lines to reach the
reconnection point and appear as tubular emission (Fig. 5,
center).
However, below the reconnecting point, the heated footpoints of the newly reconnected flux behind the rope might
still behave as a two-ribbon flare. This brings us to ask, even
though we do not find in our sample obvious footpoint-
separating two-ribbon configurations in flares associated
with slow CMEs, to what extent this topology is found in all
flares associated with slow CMEs. We note that previous
authors have found examples of large-scale, long-duration,
two-ribbon flares (Kahler 1992; Hudson, Acton, & Freeland
1996; Hundhausen 1999), which can be explained in terms
of the reclosing of the anchored magnetic field left behind
by the expulsion (Low 1996, 2001), a process similar to our
slow CME case. To reconcile these results, we point out that
our sample contains events of a subset of the various types
of flares. The events in our sample are all large (X- or
M-class) flares occurring in active regions. None of the
events in our sample is a long-duration event, like the one
discussed in Hudson et al. (1996), whose associated flare is
of C2 level. Also, none of the events in our sample is from
outside active regions, as is the example shown in Hundhausen (1999), where a slow CME originates from the disruption of polar crown filaments. Notably, in the latter event
the CME-associated flare is again of C class.
It might be instructive to examine Figure 6, where subimages of TRACE observations of the 2001 October 26 event
(the one in Fig. 2) are shown. If we examine the small-scale
structures inside the bulge structure in Figure 2 (inside the
square in Fig. 2b), we can see a possibly slight separation of
the footpoints inside the bulge. This small-scale separation
of footpoints began about 4 minutes before the flare peak
time (Fig. 2a) and also ended at the flare peak time (Fig. 2c).
There is also a postflare looplike structure formed after the
flare peak (Fig. 2d). This implies that the reason we do not
see obvious footpoint-separating two-ribbons in flares associated with slow CMEs might be that they are happening on
a small scale for the events in our sample. In this sense, our
sample, by taking advantage of the TRACE observations’
high temporal and spatial resolutions and by selecting big
flares, may have selected a subset of flares that provide us a
better chance to see those tubular structures associated with
slow CMEs.
3.3. Flares Loosely Associated with CMEs or without CMEs
For those flares in this group that show morphologies
similar to those of the group of flares associated with slow
No. 2, 2003
MORPHOLOGIES OF FLARES ASSOCIATED WITH CMEs
1257
Fig. 6.—Subimages of TRACE time-series observation at 171 Å of the 2001 October 26 flare. The field of view is 5000 5000 for each image, and its position
is shown by the square in Fig. 2. These time-series images indicate that there may be a tiny two-ribbon flare inside the bulge of this flare.
CMEs, we interpret them as the same phenomenon as
the flares associated with slow CMEs. The existence of this
similarity is consistent with our understanding that the
occurrence of the reconnection can be delayed until the late
stage of the expulsion for slow CMEs.
If the flare happens without a CME and is not in a filament channel, then it is not necessary to relate the flare to
flux ropes. The flare may just be caused by the field releasing
its free magnetic energy and hence has nothing to do with
the expulsion mechanism. However, if the flare happens
within a filament channel or has a filament associated with
it, then we may also interpret it under the same scheme of
flux-rope expulsion. We note that, for the fast CME (in Fig.
4) to happen under the Low & Zhang picture, the flux in the
flux rope must exceed the flux of the surrounding coronal
field. If the flux in the flux rope is less than the flux of the surrounding field, by mass loss from the prominence the current sheet will still form, as shown in the center panel of
Figure 4. However, the reconnection of the current sheet
will not result in a flux rope expulsion because there will be
no flux left over for the rope after the reconnection between
the flux rope and the surrounding field of opposite polarity.
This will result in a flare without expulsion, a process of
magnetic relaxation through reconnection similar to that
discussed in Zhang & Low (2003).
4. SUMMARY
High-cadence TRACE disk center observations of a sample of 28 X- and M-class flares are studied in this paper. This
sample has 6 X-class flares and 22 M-class flares: 10 are
associated with fast CMEs, 10 are associated with slow
CMEs and 8 are only loosely associated with CMEs.
We find that flares associated with fast and slow CMEs
show different dynamical flaring morphologies. While all
flares associated with fast CMEs clearly show footpointseparating two-ribbon configurations during the flare, this
feature is not generally observed in flares associated with
slow CMEs or flares without CMEs. At the same time,
while some flares associated with slow CMEs show upward-
moving tubular emission features during the flare, these features are not observed in our sample for flares associated
with fast CMEs. This result suggests that the morphologies
of flares, and hence possibly the magnetic field topologies,
are different for events associated, respectively, with fast
and slow CMEs.
We interpret our observations within the context of Low
& Zhang (2002), a theory that relates the two types of prominences to the two types of CMEs in terms of the interplays
between flux rope expulsion and magnetic reconnection in
topologically different magnetic environments. From that
theory, we expect to see the timing difference of flares associated with the two types of CMEs as we did in Paper I. The
morphologies of the flares associated with the two types of
CMEs are also expected to be different, as we examined in
this paper. Magnetic field environments of the source
regions of the two types of CMEs might also show the differences, and this will be another testable aspect of the theory
(M. Zhang & J. Burkepile 2003, in preparation). Of course,
a very direct approach to test the theory might be checking
whether the prominences associated with the fast and slow
CMEs are normal and inverse prominences respectively.
However, until recently, instrumental constraints had limited prominence field measurements to prominences at the
limb. New polarimetric methods of field measurement are
being pursued, including the measurement of fields in filaments against the solar disk and in the corona around a
prominence at the limb (Lin, Penn, & Kuhn 1998; Judge
1998; Trujillo Bueno 2001). Thus, in the next few years there
may be unprecedented magnetic field observations that will
put the Low & Zhang theory to a direct test.
We thank B. C. Low and L. Acton for helpful comments
and suggestions that improved the manuscript. This work
was supported by the U.S. National Science Foundation
under Grant ATM-9819909 and ATM-0203489, the Chinese National Key Basic Research Science Foundation
(G2000078404), and a contract from Lockheed Martin to
the Smithsonian Astrophysical Observatory.
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