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\title{Study of Ribbon Separation of a Flare Associated with
a Quiescent Filament Eruption}

\author{Haimin Wang$^{1,2,3}$, Jiong Qiu$^3$, Ju Jing$^{2,3}$ and Hongqi
Zhang$^1$}

\affil {1. National Astronomical Observatory of China, Beijing, China}

\affil{2. Big Bear Solar Observatory, New Jersey Institute of Technology
    \\ 40386 North Shore Lane, Big Bear City, CA 92314-9672, USA}

\affil {3. Center for Solar Research, New Jersey Institute of Technology,
Newark, NJ 07102}

\email{haimin@flare.njit.edu -- Version on April 9,  2003}


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%    ABSTRACT
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\begin{abstract}

In this paper, we present a detailed study of a two-ribbon flare in the
plage region observed by Kanzelhohe Solar Observatory (KSO)
which is one of the stations in our Global H$\alpha$ Network.
We select this event due to
its very clear filament
eruption, two-ribbon separation, and association with a fast CME. We study
the separation between the two ribbons seen in H$\alpha$ as a function of
time, and find that the separation motion consisted of a fast stage of
rapid motion at a speed of about 15 km s$^{-1}$ in the first 20 minutes and
a slow stage with a separation speed of about 1 km s$^{-1}$ lasting for 2
hrs.  We then estimate the rate of the magnetic reconnection in the corona,
as represented by the electric fields $E_c$ in the reconnecting current
sheet, by measuring the ribbon motion speed and the magnetic fields
obtained from MDI. We find that there were two stages as well in evolution
of
the electric fields: $E_c = 1 V cm^{-1}$ averaged over 20 minutes in the
early stage followed by $E_c = 0.1 V cm^{-1}$ in the subsequent two hours.
The
two stages of the ribbon motion and electric fields coincide with the
impulsive and decaying phases of the flare respectively, yielding clear
evidence that the impulsive flare energy release is governed by the fast
magnetic reconnection in the corona. We also measure the projected heights
of the erupting filament from KSO H$\alpha$ and SoHO/EIT images. The
filament started to rise 20 minutes before the flare. After the flare
onset, it was accelerated quickly at a rate of 300 m s$^{-2}$, and in 20
minutes reached a speed of at least 540 km s$^{-1}$ when it disappeared
beyond the limb in the EIT observations. The acceleration rate of the CME
is estimated to be 58 m s$^{-2}$ during the decay phase of the flare. The
comparison of the height and velocity profiles between the filament and CME
suggests that fast acceleration of mass ejections occurred during the
impulsive phase of the flare when the magnetic reconnection rate was also
large with $E_c = 1 V cm^{-1}$.


\end{abstract}
\keywords{Sun: activity -- Sun: magnetic fields -- Sun: flares -- Sun:
filaments -- Sun: CME}

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%  SECTION I: INTRODUCTION
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\section{INTRODUCTION}

	Eruptive two-ribbon flares provide a lot of information on the
physical picture of the eruptive solar phenomena. Since the 1970s, 
some have suggested that two-ribbon flares are caused by magnetic
reconnection between coronal field lines which are forced open by erupting
filaments (see a review by Svestka \& Cliver 1992).
In the last two decades, the discovery and numerous studies of the
Coronal Mass Ejections (CMEs) and their relationship with specifically
long-duration two-ribbon flares and filament eruptions lead to a
further developed idea that CMEs provide a powerful mechanism to
stretch the coronal magnetic fields into an open configuration for
magnetic reconnection to occur subsequently (Hundhausen 1988, 1999;
Harrison et al. 1990; Low 1996 and references therein). 
Hundhausen and colleagues have proposed that the
CME opens the field rather than the erupting filament;  backward extrapolations
of velocity diagrams indicate that the CME probably begins before the filament
eruption and has stronger magnetic fields and more potential and kinetic energy
than the erupting filament. Very recently, the simulation by Cheng et al. 
(2003) showed that flux rope's accelerated rising motion enhanced magnetic 
reconnection rate.

 The often observed
flare ribbon expansion is the chromospheric signature of the progressive
magnetic reconnection in the corona in which new field lines reconnect at
higher and higher altitudes.  How quickly the ribbon expands in the
chromosphere is then related to how fast the reconnection proceeds in the
corona. Since the magnetic reconnection in the corona is hardly observable
directly, many chromospheric observations have been conducted and analyzed
in an effort to indirectly map the coronal magnetic reconnection
(Schmieder et al. 1987; Svestka 1989; Falchi, Qiu \& Cauzzi 1997; Qiu et
al., 2002).

	Physically speaking, the velocity of the foot-point motion
sweeping through the magnetic field lines corresponds to the rate of the
magnetic flux convected into the diffusion region at the reconnection
point in the corona where the reconnecting current sheet (RCS) is
generated. With some assumptions and approximations, Forbes and colleagues
(Forbes \& Priest 1984, Forbes \& Lin 2000) derive a very simple
relationship between the electric field strength (E$_c$) along the current
sheet and two observables $V_t$ and $B_n$ as $E_c = V_t B_n$, where $B_n$
is the normal component of magnetic field strength of the ribbon and $V_t$
represents the transverse velocity of the flare ribbon motion. In the
past, very few attempts have been made to explore the electric field in
the RCS from the flare foot-point kernel motion.  Using the above
relation, Poletto \& Kopp (1986) derived the maximum E$_c$ of 2 V
cm$^{-1}$ in a large two-ribbon flare. Recently Qiu et al. (2002) studied
an impulsive flare with high cadence H$\alpha$ observations at BBSO. They
estimated the maximum electric field at RCS to be 90 V cm$^{-1}$, which
occurred around the peaking time of hard X-rays. The derived $E_c$ is
proportional to the magnetic reconnection rate, which is fundamentally
controlled by the coronal magnetic fields and dynamics.

	The association between eruptive two-ribbon flares and coronal
mass ejections (CMEs) is frequently addressed, although so far most
observations failed to establish a systematic correlation among the onset
of solar flares, filament eruptions and CMEs (Verma, 1990;  Feynman and
Hundhausen, 1994; Harrison, 1995;  McAllister et al., 1996). Detecting the
early manifestation of CMEs on the solar disk and their relationship with
solar surface phenomena is essential to understanding the physical origin
of CMEs. Theoretically, there are two kinds of CME models which also
underline different flare-CME relationships. In the flux rope model (e.g.,
Forbes \& Priest 1995, Amari et al. 2000), mass ejections force open the
magnetic field arcade, leaving behind large-scale magnetic reconnection
between open-field lines. The subsequent feedback of the magnetic
reconnection to the mass ejection is discussed by Lin \& Forbes (2000).
In the break-out model (e.g., Antiochos et al. 1999), magnetic
reconnection occurs first to open the coronal magnetic structure for mass
to escape. Therefore in this model the magnetic reconnection precedes the
mass ejection, and how quickly the mass moves out of the surface system
should be related to how rapidly the magnetic reconnection proceeds. These
two models depict different magnetic configurations which also regulate
the energy budget carried by mass ejections and released by dissipation
via magnetic reconnection. Although demanding, the models need to be
tested by observations that compare the dynamics of the mass ejection and
the magnetic reconnection responsible for flare energy release (e.g.,
Zhang et al. 2001).

	In this paper, we present the result on the analysis of a
quiet-sun flare associated with an erupting filament and a fast CME. The flare
exhibits a clear two-ribbon separation motion over several hours, 
which can be used to infer the evolution of the coronal magnetic 
reconnection. We select this clear case to avoid complex magnetic
structures. The Kanzelhohe Solar Observatory (KSO) and Solar and 
Heliospheric Observatory (SoHO) observations also provide continuous 
observations of the filament activation and eruption, which can be
used to infer the dynamics of the CME at its take-off. Combinations of 
ribbon separation and filament/CME height would give us a 3-D physical 
picture associated with the eruptive flare. It is also possible to investigate 
the physical connection between the flare dynamics, filament eruption 
and CME quantitatively. 

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% % SECTION II: OBSERVATIONS AND DATA REDUCTION % 

\section{OBSERVATIONS AND DATA REDUCTION}

In the past two and a half years, we have
successfully installed and are continuously operating a high resolution
global H$\alpha$ network. The stations are at Big Bear Solar
Observatory (BBSO),  KSO in Austria,
Catania Astrophysical Observatory (CAO) in Italy, Yunnan Observatory
(YO) and Huairou Solar Observing Station (HSOS) in China. Nominally,
each station obtains H$\alpha$ image every minute with 1 arcsec pixel
resolution. The data are calibrated using standard procedures at BBSO.

The primary data source used in the current study are from full disk
H$\alpha$ data obtained from
KSO station on September 12, 2000. KSO had complete coverage of the M1
flare and the associated filament eruption at about 12UT. Figure 1 is the
time sequence of KSO H$\alpha$ images
showing the evolution of the event. It is a classical two-ribbon flare
accompanied by the filament eruption.

The same event was covered by SOHO EIT, MDI and LASCO observations. It is
clearly associated with a fast Halo CME. MDI data provides full disk
magnetograms, which are aligned with H$\alpha$ data for the study of
magnetic properties of moving ribbons.  Figure 2 compares H$\alpha$ image
during the flare and the corresponding MDI magnetogram.


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%  SECTION III: RESULTS
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\section{RESULTS}

\subsection{Dynamical Evolution} %[PROBABLY NOT A BEAUTIFUL TITLE]

We first study the temporal evolution of the flare ribbon separation,
filament eruption and CME height with respect to flare energy release. In
Figure 3, we plot the time profiles of the flare emission, ribbon
separation distance, and heights of the filament and CME. We fit these
distance/height profiles to hyperbolic functions of time, and derive and
compare their velocity profiles in Figure 4. The GOES soft X-ray light
curve is used to represent the time profile of the flare energy release.
To investigate the electron acceleration in the impulsive phase of the
flare, the hard X-ray and microwave observations are essential.  
Unfortunately, we did not have such data. We therefore use the time
derivative of GOES soft X-ray light curve to represent the hard X-ray time
profile, assuming that the so-called Neupert effect is valid in this
event.

In the top panel of Figure 3, we plot GOES soft X-ray light curve of 1 to
8 \AA~ and its derivative. The middle panel shows the average ribbon
separation distance as a function of time. The position of the ribbon was
defined by the location of the moving front. This flare exhibits a rather
regular pattern of ribbon-separation motion, with both ribbons moving away
from and nearly perpendicular to the magnetic neutral line. Therefore
there is only a small ambiguity in the the measurement of the separation
motion. As we can see from Figures 3 and 4, there are two stages in the
ribbon-separation motion: a fast separation stage in the first 20 minutes
of the event and a substantially slower stage afterwards. The fast stage
coincides with the rising phase of the derivative of the soft X-ray light
curve, i.e., the impulsive phase of the flare energy release when most of
the flare non-thermal electrons are accelerated. On average, the speed of
the ribbon separation during the impulsive phase of the flare is over 10
km s$^{-1}$, and the average speed in the later stage is about 1 km
s$^{-1}$. Our observations therefore indicate that the fast ribbon motion
corresponds to a greater energy release rate.

Then let us take a look at the erupting filament and halo CME. In the
lower two panels in Figure 3, we plot the heights of the filament and CME
front. The solid line denotes the measurements of the filament height in
H$\alpha$ images with 1-minute cadence, and the '+' symbols represent
measurements from EIT 195\AA~ images with a 12 minute cadence. The
measurement was not easy, because the contrast of the filament decreased
rapidly as it moved up. We measured the lateral displacement, and project
it to the vertical direction based on the disk position of the filament.
Of course, we had to assume that the filament moved up exactly vertically
in the local solar coordinate system. Given the uncertainties in the
measurements, the figure shows that the filament height profiles measured
from the two kinds of images are consistent. The fits to the filament
heights and the velocity profiles are shown in Figure 4. The filament
started to rise about 30 minutes before the appearance of the flare
ribbons, reaching a velocity of several tens of km s$^{-1}$. However,
after the flare onset ($\sim$1120~UT), it was rapidly accelerated to over
200~km s$^{-1}$ before becoming invisible in H$\alpha$ ($\sim$1140~UT),
and to at least 540~km s$^{-1}$ when it moved beyond the limb in the EIT
field of view around 12~UT.

The triangle symbols in the bottom panel of Figure 3 indicate the heights
of the associated halo CME front measured by Dr. Seiji Yashiro
($http://cdaw.gsfc.nasa.gov/CME\_list/$).  According to his measurements,
the CME was first seen in LASCO C2 field at 1154~UT, and the front speed
measured from a linear fit is 1,500~km s$^{-1}$. Because of the limited
FOVs of EIT and LASCO, one cannot identify the filament and CME
in the same image. However, EIT and LASCO observations overlapped at
around 12 UT when the filament and CME were observed by the two
instruments separately. Seen in Figure 4a, at this time, the displacement
between the filament and CME is about 1.4 to 2 solar radii taking into
account the projection effects. This roughly gives the scale of the
expanding system at that time.

With certain assumptions, the above observations also allow us to
reasonably estimate the acceleration rate of the CME at its takeoff in
several ways. In the first way, we may treat the filament eruption and CME
as mass ejections driven by the same mechanism in the same system at the
early stage of the mass ejections. Estimated from the velocity profiles in
Figure 4b, from 1100 to 1200 UT, the average acceleration rate was 260 m
s$^{-2}$. The filament was not accelerated at a constant rate. From 1140
to 1200~UT, the average acceleration rate reached 380 m s$^{-2}$. In the
second way, we may regard that the CME took off at 11~UT when the filament
was observed to start rising in the EIT field of view. Accordingly, to
accelerate the CME to 1270 km s$^{-1}$ at around 12~UT requires an average
acceleration rate of 350 m s$^{-2}$. The acceleration rates estimated from
these two methods are basically consistent, with the CME acceleration rate
possibly a little higher than the filament due to the rapid expansion of
the system. After 12~UT, the acceleration rate of the CME was estimated to
be 58 m s$^{-2}$ using the hyperbolic fit of the CME velocity profile in
Figure 4b. Dr. Yashiro also estimated the CME acceleration rate to be 58 m
s$^{-2}$ from a second order fit of the height-time profiles
($http://cdaw.gsfc.nasa.gov/CME\_list/$). These estimates suggest that
fast acceleration of the mass ejections occurred before 12 UT, most likely
during the impulsive phase of the flare. The rate of the fast acceleration
is about five times that of the slow acceleration. This result is
consistent with Zhang et al. (2001), yet our measurements are made with a
better data coverage, under the assumption that the erupting filament and
CME can be regarded as being accelerated in the same framework.

\subsection{Electric Field Along the Current Sheet}

Our results in the last section show that the speed of the ribbon
separation resembles the rate of the flare energy release through magnetic
reconnection. It is also of our interest to explore the spatiality of the
ribbon motion representative of the energy release rate from the
observational point of view. For this purpose, we track the separation
speed at all locations along the ribbon as a function of time. We find
that the speed of the separation was not uniform along the flare ribbon,
but at every point, the motion exhibits the same evolution pattern as the
averaged separation mode shown in Figures 3 and 4. Therefore, we divide
the data into two time bins: fast and slow separation stages. In Figure 5
we plot the speeds of the ribbon motion (away from the magnetic neutral
lines) as a function of position along the ribbon. The positive and
negative numbers represent the upper (north) and lower (south) ribbons,
respectively. The thick lines represent the fast moving stage
corresponding to the impulsive phase of the flare, and thin lines, the slow
moving stage during the decay phase of the flare. In the first stage,
the maximum speed $V_t$ along the ribbon was over 10~km s$^{-1}$, while in
the following stage the maximum $V_t$ was about 1~km s$^{-1}$.

Forbes \& Priest (1984) and Forbes \& Lin (2000) suggested that the ribbon
motion can be used to infer the electric field $E_c$ of the coronal
current sheet in a 2D assumption. In the middle and bottom panels of
Figure 5, we plot the derived electric field $E_c = V_t B_n$ as a function
of ribbon position, by assuming that at each point along the ribbon (or
along the arcade axis), the 2-D approximation is still valid. The
line-of-sight magnetic field B$_n$ was measured from MDI observations.
First, we find that the evolution of $E_c$ exhibits the same pattern as
the speed. During the early time bin, the flare has a much stronger electric field of order
1 V cm$^{-1}$ on average, while in the later time bin $E_c$ is around 0.1
V cm$^{-1}$. Since $E_c$ is proportional to the magnetic reconnection rate
at the reconnecting point, our results confirm that the flare energy
release is most efficient when the magnetic reconnection rate is also big.
While during the decay phase lasting for about 2 hrs, the magnetic
reconnection still continues at a slow rate. Second, Figure 5 shows that
$E_c$ is inhomogeneous along the ribbon, most likely indicating the
inhomogeneity in the magnetic reconnection rate along the ribbon. Such
inhomogeneity should be determined by the magnetic configuration in the
corona.

The values of the electric field derived for this event are much smaller
than 90 V cm$^{-1}$ as derived by Qiu et al. (2002), but are comparable to
the value by Polletto \& Kopp (1986). According to these values, the
electric fields in the current sheet in these events are super-Dreicer
fields in which electrons can be efficiently accelerated. Unfortunately
there were no hard X-ray observations to allow further
studies on the thermal/non-thermal properties of accelerated electrons.
Concerning the large difference between the results for this
event and the values by Qiu et al. (2002), we recognize a few points in
deriving $E_c$. First, Qiu et al. used data with much higher cadence and
the ribbon separation motion in their study is much faster. Second, in Qiu
et al. (2002), the flare occurred in strong magnetic fields. Whereas $V_t$
is measured in the chromosphere, $B_n$ is measured in the photosphere. In
strong field regions, the magnetic fields may vary more drastically from
the photosphere to the chromosphere, leading to an over-estimate of the
electric fields in Qiu et al. (2002). The event studied in this paper
occurred in the decayed region where the magnetic fields are rather
diffuse, yielding a relatively smaller error than the estimates by Qiu et
al. (2002).

\section{CONCLUSIONS AND DISCUSSIONS}

In this paper, we present the detailed study on the temporal and spatial
properties of a quiet-sun two-ribbon flare. This event exhibits a good
example of a standard solar flare characterized by the long duration,
filament eruption, two-ribbon separation, and its association with a fast
CME. Observations from various instruments provide an almost complete
coverage of the dynamic evolution of this event. The most important result
is the differences in the two evolution stages of the event, which is
evident in several aspects. 

- We studied the separation of flare ribbons observed at the chromosphere
as a function of time and found that there were two stages of separation:
a rapid stage at a speed of about 10 km s$^{-1}$ in the first 20 minutes
corresponding to the impulsive phase of the flare energy release, and a
much slower speed of about 1 km s$^{-1}$ at the later stage lasting for
more than 1.5 hrs when flare emission decayed. These numbers are similar
to the values derived for the July 29, 1973 two-ribbon flare (Moore et
al., 1980; Svestka et al., 1982).

- We derived the electric fields by measuring the ribbon motion and the
magnetic fields along the ribbon. We found the average electric fields at
the two evolution stages to be 1 and 0.1 V cm$^{-1}$ respectively. As the
rise of the flare emission coincides with the duration of the strong
electric field, we therefore conclude that the impulsive flare energy
release occurred when the electric field was in the order of 1 V
cm$^{-1}$. The sudden drop in the electric field is not due to the fact
that flare ribbons hit a strong magnetic field region and stopped the
motion. Instead the ribbon motion in the chromosphere was a consequence of
the evolution of the magnetic reconnection in the corona, which consisted
of a fast stage and a slow stage in this event. In general, the result of
the two-stage electric current agrees with the modeling of Lin et al.
(1995). However, the details need to be mapped out by case specific
models.

- We also studied the projected heights of the erupting filament, finding
that with available observations, the erupting filament was rapidly
accelerated to over 540 km s$^{-1}$ during the impulsive phase of the
flare, which is very close to the escape velocity. Comparing the time
profiles of the flare emission, ribbon motion, and the height of the
top of filament, we believe that magnetic reconnection was switched on when the
filament was in the height range of 1.5$\times$10$^5$ to 2.5$\times$10$^5$
km. Around this time, we also observed the onset of fast acceleration of
the filament mass.

- Comparing the velocity profiles of the filament and CME, it is also
likely that fast acceleration of the mass ejections, with an acceleration
rate of over 300 m s$^{-2}$, coincided with the flare impulsive phase with
a large magnetic reconnection rate as represented by the strong electric
field. During the long decay of the flare when the magnetic reconnection
rate reduced by an order of magnitude, the acceleration rate of the mass
ejections dropped to 58 m s$^{-2}$.

The parameters derived in this study for the two-stage evolution of the
dynamics and magnetic reconnection should provide information for theoretic
modeling.  We notice a few questions stemming from this study and seeking
their answers may help reveal the underlying physics. First, the two
evolution stages are distinguished by the sudden switch of the electric
field amplitude and mass acceleration rate. What is the mechanism of such
switch? Is it due to a sudden change in the magnetic configuration, such as
opening of the magnetic field lines, at that particular time? What is the
physics behind the apparent coincidence between the magnetic reconnection
rate and the dynamical evolution of the mass ejections?  Second, apart from
the two-stage evolution, Figure 4b also shows that during the first stage,
while the velocity profile of the filament shows the filament being
accelerated, the velocity profile of the ribbon motion suggests a
deceleration. From an observational point of view, we should enlarge the
sample of such studies to understand whether such anti-correlation can be
established or it is purely an accident due to uncertainties in data
analysis. Theoretically, shall we or shall we not expect such results?

Answers to these questions are important for understanding the physical
mechanisms governing the dynamical evolution and magnetic reconnection in
eruptive solar events. Some CME models have been presented which do not
involve magnetic reconnection (e. g., Low 1994), but in many other cases,
CMEs and flares are associated though in a way yet unclear to us. In the
first place, even given the sharp contrast between the spatial scales of
CMEs and flares, the radiative energy in a typical eruptive flare, which is
released mainly through magnetic reconnection, is comparable to the kinetic
energy carried by ejected masses. More importantly, even though past
studies have found it hard to conceive a causal relationship between flares
and CMEs, it remains intriguing what role the magnetic reconnection plays
in the framework of the large-scale eruption. 
The configurations
invoked by both the flux rope and break-out models, if correctly depicting
the real situation, would naturally address the link between the rate of
the magnetic reconnection and the rate of mass acceleration at least during
the early stage of the event, because the laws of magnetic flux and mass
conservation are to be observed.  The direct relationship between the two,
such as the time profiles of magnetic reconnection and CME acceleration may
be calculated given a specific magnetic configuration.

A somewhat different but not unrelated issue raised in this study also
deserves further investigation in the future. In Figure 5, one can see
that the amplitude of the electric field, nominally representative of the
magnetic reconnection rate, is not uniform along flare ribbons, indicating
a large inhomogeneity in the coronal magnetic reconnection. So far
theoretical models mentioned above only deal with 2.5-D configurations
with a translational symmetry along the axis of the arcade. Our
observations show that at least in the case of the magnetic reconnection,
such a translational symmetry may not exist. Taking into consideration the
real 3-D configuration may result in some different theoretical arguments.
Furthermore, very recently, Asai et al. (2002) found that hard X-ray
sources only concentrates in some parts of H$\alpha$ radiation source,
where the magnetic fields, and consequently the magnetic reconnection
rates, are strong. It is interesting to derive the electric fields at
these locations to compare with other locations along the ribbon. It is
also worthwhile to compare with other events for which the photospheric
magnetic fields are more homogeneous, in order to understand what agent
plays the role of controlling the magnetic reconnection rate.

%###############################################################################
% % ACKNOWLEDGEMENTS %

\acknowledgments We are grateful to the KSO observing staff for their
support in obtaining the data. We thank Dr. J. Lin for helpful discussion 
and the referee for valuable comments.
The work is supported by NSF under grants ATM-0076602, ATM-0233931, and
AST-9987366, NASA under grants NAG5-10910 and
NAG5-12733, ONR under grant N00014-03-1-0093 and Chinese NSF. The first
draft of the
paper was finished
while HW was visiting National Astronomical Observatory of China. He wishes
to thank the staff of the observatory for the support.

\newpage

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%
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\end{references}

%###############################################################################
%
%   FIGURES     
%

\begin{figure}
\epsscale{0.8} 
\plotone{f1.eps} 
\figcaption {A sequence of H$\alpha$ images showing the evolution of the
flare and the disappearance of filament. The field of view is 512 by 512
arcsec.
\label{F1}}
\end{figure}


\begin{figure}
\epsscale{0.6} 
\plotone{f2.eps} 
\figcaption{Comparison of a H$\alpha$ image with corresponding magnetogram
at 1000UT.
\label{F2}}
\end{figure}

\begin{figure}
\epsscale{0.7} 
\plotone{f3.eps} 
\figcaption{Top panel: GOES X-ray flux as a function of time in the energy
channel of 1 to 8 \AA.
Second panel: mean flare ribbon separation as a function of time. Third
panel: filament height as a function of time. The solid lines are KSO
H$\alpha$ measurements and the pluses are from SOHO EIT measurements.  
Bottom panel: EIT filament height and LASCO CME Height.
\label{F3}}
\end{figure}

\begin{figure}
\epsscale{0.8} 
\plotone{f4.eps} 
\figcaption{Left panel: time profiles of the flare ribbon separation, filament 
heights measured from KSO and EIT images, and CME heights measured by Dr.
Yashiro 
($http://cdaw.gsfc.nasa.gov/CME\_list/$). The lines indicate the least-squares
fits to hyperbolic functions. Right: velocity profiles of the ribbon separation,
filament, and CME derived from the fits of the height profiles. 
\label{F4}}
\end{figure}

\begin{figure}
\epsscale{0.7} 
\plotone{f5.eps}
\figcaption{Top panel: the mean ribbon moving speeds along ribbons. Thick
lines are for the time period of 1125 to 1200UT (time bin 1), and thin
lines are for the time period of 1200 to 1350UT (time bin 2). Middle and 
bottom panels
are derived electric fields for the lower and upper panels, respectively.
Again the thick lines are for the time bin 1 and thin lines are for the
time bin 2. The electric fields are derived from the ribbon moving speed
and line-of-sight magnetic fields measured at the location of ribbons.
\label{F5}}
\end{figure}


\end{document} 


