Документ взят из кэша поисковой машины. Адрес оригинального документа : http://star.arm.ac.uk/~ambn/370.ps Дата изменения: Thu Dec 13 14:02:54 2001 Дата индексирования: Mon Oct 1 20:16:12 2012 Кодировка: Поисковые слова: mdi

Astronomy & Astrophysics manuscript no.
(will be inserted by hand later)
Temporal evolution of dierent temperature plasma during
explosive events
M. S. Madjarska and J. G. Doyle
Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
Abstract. High cadence observations (10 s exposure time) obtained with the SUMER spectrometer on-board
SoHO in the Ly 6 (20 000 K) and S vi (200 000 K) lines reveal new insight on the nature of explosive events. A
time delay in the response of the S vi line with respect to the Ly 6 line has been observed, with the Ly 6 line
responding with about 20-40 seconds earlier. A temporal series obtained with 30 s exposure time and covering the
entire Lyman series plus O i, C ii and S vi (temperature range from 15 000 to 200 000 K) has also been explored
showing the response of all these lines during transient phenomena. New common features linking explosive events
and blinkers were found. During explosive events, the central intensity increases between 1.6 and 2.0 times the
pre-event value while the same range of intensity increase was already reported during blinker phenomena. On
the other hand the maximum intensity increase in Ly 6 was only 13 %.
Key words. Sun: SoHO{SUMER: Explosive events: Lyman lines
1. Introduction
Observations made with the Naval Research Laboratory's
high resolution telescope and spectrograph (HRTS) re-
vealed the existence of high velocity small-scale events
seen in lines from ions formed at temperatures from
2 10 4 K (C ii) to 2 10 5 K (N v) with no signature
in chromospheric lines such as Si ii (1.3 10 4 K), C i
(6 { 10 10 3 K) and O i (1.5 10 4 K), formed below 2
10 4 K (Brueckner & Bartoe 1983). Discovered and clas-
sied by Brueckner & Bartoe (1983) as turbulent events
and jets, they are characterized by non-Gaussian proles
due to an enhancement in the blue and red wings, of-
ten observed with an oset along the slit (Dere et al.
1989; Innes et al. 1997a). Most of the events are predom-
inantly blueshifted, showing velocities up to 250 km s 1 .
Their rst identication was followed by several stud-
ies based on observations obtained with HRTS and the
spectrometer Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) on-board SoHO performed by Dere
et al. (1989), Porter & Dere (1991), Innes et al. (1997a),
Chae et al. (1998a), Perez et al. (1999), Landi et al. (2000)
and Teriaca et al. (2001). The authors extended the de-
scription of their general characteristics naming them by
the term `explosive events'.
The explosive events are located in the network lanes
at the boundaries of the super-granulation cells where the
neutral line separates regions of opposite magnetic polar-
Send oprint requests to: M. S. Madjarska, e-mail:
madj@star.arm.ac.uk
ity (Dere et al., 1991; Porter & Dere 1991). They appear
preferably in regions with weak uxes of mixed polarity
or on the border of regions with large concentration of
magnetic ux (Chae et al. 1998a). The average lifetime
of the explosive events ranges from  60 to 350 s (Dere
1994) with spatial dimensions of  2500 km. They are of-
ten observed in bursts (Innes et al. 1997a) lasting up to
30 minutes in regions undergoing magnetic cancellation
(Chae et al. 1998a). Using the density sensitive line in-
tensity ratio O iv 1401:16/1404:81, Teriaca et al. (2001)
found an electron density increase by a factor  3 during
explosive events. They also showed an increase of the line
intensity ratio O iv 1401/O iii 703 during an explosive
event which suggests a temperature increase during the
phenomena.
Explosive events seem to be a product of magnetic re-
connection (Parker 1988; Porter & Dere 1991; Dere 1994;
Innes et al. 1997b; Wilhelm et al. 1998; Roussev et al.
2001) because they tend to occur on the neutral line sep-
arating regions of opposite magnetic polarity, appear as
bi-directional jets (Innes et al. 1997b) with velocities com-
parable to the local Alfven velocity (Dere 1994), and they
are often associated with a cancellation of photospheric
magnetic ux (Dere et al. 1991; Dere 1994; Chae et al.
1998a).
After the launch of the SoHO satellite it became pos-
sible to observe Lyman lines with high spectral, spatial
and temporal resolution. Using these lines as a plasma di-
agnostic tool has several advantages. They cover heights
with a strong temperature gradient and therefore can be

2 Madjarska & Doyle: Temporal evolution of explosive events
used to diagnose the time evolution of dierent temper-
ature structures. The cores of these optically thick lines
are supposed to be formed in the chromosphere or at the
base of the transition region while the wings are formed
over large atmospheric depths in regions far below the core
formation i.e. in the lower chromosphere (Vernazza et al.
1981). It was demonstrated by Heinzel et al. (1997) that
the cores of the higher Lyman lines are sensitive to tem-
perature because the upper levels of the corresponding
transitions are strongly coupled to the kinetic tempera-
ture while the wings show sensitivity to the gas pressure.
These lines are relatively strong and thus can be used for
observations which need short exposures as in the case of
explosive events. However, the observed proles can only
be interpreted correctly if multilevel NLTE (Non Local-
Thermodynamic-Equilibrium) radiative transfer calcula-
tions are performed to explain the registered line shapes
and intensities. That is why the present study is mainly
based on the response of these lines during an explosive
event through the emission changes in the blue and red
wings of the registered lines.
Recently, Chae et al. (1998b), using SUMER data in
Si iv 1402  A and Big Bear Solar Observatory (BBSO)
H spectrograph observations, found that chromospheric
up ow events rising in intranetwork areas are related to
transition region explosive events. To support the idea of
the chromospheric origin of some of the explosive events
full spectrum observations covering lines with a wide range
of formation temperature (1.5 10 4 - 2 10 5 K) have been
analysed.
A new transient phenomenon observed with the
Coronal Diagnostics Spectrometer (CDS) on-board SoHO
as enhancements in the ux of transition region lines at
network junctions was recently introduced by Harrison
(1997) named as `blinkers'. Blinkers are mainly observed
in lines of O iii, O iv and O v while lines formed at lower
and higher temperatures (such as He i and Mg x) show
only a modest increase in intensity. They show a typical
lifetime of  17 minutes over an area of  5 10 7 km 2 ,
with an average intensity increase in O v of  1:5 which,
in extreme cases, can reach values as high as ve times
the pre-event level (Harrison et al. 1999). Chae et al.
(2000) used CDS and SUMER coordinated observations
in the transition region lines O v 629  A (CDS) and Si iv
1402  A (SUMER), and Big Bear Solar Observatory mag-
netograms to examine the relation between blinkers and
explosive events showing similarities such as line proles
with enhanced wings, but on a dierent scale, suggest-
ing the same physical origin of the two events, namely
magnetic reconnection, but with dierent magnetic ge-
ometries.
This paper presents a study on the temporal evolution
of a plasma with dierent temperatures during explosive
events. In the next section we discuss the observations and
the data reduction. x 3 presents the data analysis, paying
attention on the line blends and event identication. The
results are described in x 4 and the conclusions in x 5.
2. Observations and Data Reduction
In search of high cadence observations obtained in transi-
tion region lines, we selected a series of temporal observa-
tions from the SoHO archive performed with the SUMER
spectrometer in S vi (933.38  A) and Ly 6 (930.748  A),
and a full spectrum temporal series, covering all Lyman
lines from Ly 4 up to the end of the series. The SUMER
instrument is a high resolution stigmatic normal incidence
spectrometer covering the wavelength range from 400 to
1610  A (Wilhelm et al. 1995; 1997; Lemaire et al. 1997)
with a spatial resolution 1.5 00 and spectral pixels size be-
tween 42 m A and 45 m A. The datasets have been obtained
on 1996 October 17 and 18 and 1997 June 5, pointing the
instrument on the `quiet Sun' at heliographic coordinates
X = 0 00 and Y = 0 00 and X = 696 00 .2 and Y = 158 00 .3,
respectively. In both cases the slit 1 00  120 00 was used.
The observations in 1996 (DS1) started on October 17
at 19:23:11 UT and nished on October 18 at 00:23:39 UT.
The spectra were obtained exposing a band of 120 spatial
 1024 spectral pixels (spectral range from 907 to 954  A)
on the central part of detector B for 200 s. A temporal
sequence consisting of two spectral windows (120 spatial
 50 spectral pixels) centered on Ly 6 930.748  A and S vi
933.38  A with 10 s exposure time was telemetred to the
ground as well. No compensation for the solar rotation
was applied and therefore for a solar rotation at this heli-
ographic latitude of about 10 00 /1h the slit covered a region
of  47 00 .
The observations on 1997 June 5 (DS2) were obtained
between 12:05:13 UT and 14:15:27 UT exposing for 30 s
120 spatial  1024 spectral pixels on detector B covering
the wavelength range from 903 to 943  A. This wavelength
range includes the Lyman lines from Ly 5 up to the series
limit, N iv, S vi and a few O i lines. In order to remain
on the same position on the Sun a rotation compensation
has been applied setting the tracking system to oset for
the X-pointing by 0.75 00 .
The reduction of SUMER raw images followed several
stages such as local gain correction, at-eld subtraction
and a correction for geometrical distortion. The signal to
noise level is determined by the photon statistics.
Michelson Doppler Imager (MDI) (Scherrer et al. 1995)
observations have been performed on 1996 October 17 and
18. The high resolution photospheric longitudinal magne-
tograms (0.6 00 per pixel) were obtained with 60 s exposure
time and eld of view of 500  1024 pixels covering all the
SUMER observing period. Magnetic cancellation during
explosive events cannot be registered because of the high
noise level (20 Gauss rms) of the MDI. Nevertheless these
observations give a general picture of explosive events for-
mation with respect to the solar magnetic network lanes
and larger concentration of magnetic ux (Figure 1, right
panel).

Madjarska & Doyle: Temporal evolution of explosive events 3
Fig. 1. Ly 6 (left) and S vi (middle) integrated line intensity images showing the network pattern and the locations of the
explosive events marked by crosses and letters together with a MDI high resolution magnetogram (right) showing the position
of explosive events with respect to magnetic ux concentrations. Note that the events `b' and `c' appear on the same position
on the raster because we integrate over 390 seconds to reproduce each position of the slit on the Sun.
3. Data analysis
DS1 consists of a full spectrum obtained with 200 s inte-
gration time, prior to every 121 temporal spectra, covering
the wavelength range from 907 to 954  A. The spectra cover
a few unblended O i lines such as O i 929.52  A and O i
936.63  A which have been used as a wavelength standard
during the calibration. Since the reference lines are in gen-
eral rather weak, we used proles averaged along the slit
to determine the centroids of these lines from a Gaussian
t. Both Ly 6 and S vi lines were registered during DS1
on the KBr part of the detector, and despite the short ex-
posure time the signal-to-noise ratio is good. During DS2,
however, the S vi line has been registered on the bare
part, but the longer exposure still results in good photon
statistics.
3.1. Line blends
Our study was based on the spectral lines listed in Table 1.
In the present paper the Lyman lines (H i Ly #) will
be written as Ly # for convenience, where # is the se-
rial number of the line. Unfortunately, the lines belonging
to the registered wavelength range are not free of contri-
bution from other emission lines, mainly He ii (T = 5.0
10 4 K) and/or O i (T = 1.5 10 4 K) lines. Table 1 gives
the blends as identied by Curdt et al. (1997, 2001) and
Warren et al. (1998). The Ly 8 line is excluded from our
analysis because it is blended by N iv lines which have a
strong contribution in the very bright network and espe-
cially during explosive events.
The Ly 6 line is not eected by Ne vii 465.22  A ap-
pearing in second order since the sensitivity of SUMER
below 500  A is very low. It is, however, blended by a rst
order O i 930.886  A in the red wing, which could not be re-
solved. In the blue wing of Ly 6 are also O i 926.295  A and
He ii 930.33  A lines which appear as one feature and could
be subtracted. These lines have a small, insignicant con-
tribution of less than 10% to the blue wing of Ly 6 (Marsh
et al. 1999). Our analysis is performed in a way (described
in x3.2) ensuring that these blends do not in uence the re-
sulting response of the wings during explosive events. The
other Lyman lines have small blends which do not eect
our analysis and subsequent conclusions.
The S vi line at 933.38  A is blended in the red wing by
He II Balmer 12 at 933.44 (Curdt et al. 1997, 2001). The
blend eect is variable, ranging between 10 and 20 % (W.

4 Madjarska & Doyle: Temporal evolution of explosive events
Table 1. The analysed lines and their corresponding blends.
Lines  (  A) Blend
Ly 11 918.129 He II 917.74
Ly 10 919.35 O I 919.65
Ly 9 920.963 He II 920.62
Ly 7 926.84 He II 925.84
O I 926.295
Ly 6 930.748 O i 926.295
He ii 930.33
O I 930.886
S VI 933.378 Ne VII 465.22
He II 933.44
O I 929.52 -
O I 936.63 -
C II 903.63 -
C II 903.96 -
C II 904.14 -
C II 904.48 -
Curdt, private communication). It can only be responsible
for an overestimation of the count rate in the red wing of
S vi. On the blue wing at 932.9  A there is a faint uniden-
tied line (W. Curdt, private communication) which has
insignicant contribution to S vi. Both O i lines as well
as the C ii lines are clean from any blends.
3.2. Event identication
Whereas CDS blinkers have already been associated with
small-scale short-lived SUMER `unit brightening events'
with a size of a few arc seconds and a lifetime of a few
minutes (Chae et al. 2000, Teriaca et al. 2001) charac-
terised by proles with enhanced wings, explosive events
show broader short- and longward shifted wings with ve-
locities higher than 50 km s 1 . As will be shown later
in this paper, the central line intensities, however, show
a strong intensity increase in explosive events just like in
blinkers, which has been reported to increase by about a
factor of two, depending on the emission line under con-
sideration (Harrison et al. 1999). From the point of view
of spatial relationship, blinkers are found in the center of
the network junctions (Harrison et al. 1997, 1999; Chae
et al. 2000; Teriaca et al. 2001) while the explosive events
tend to appear on the border of the network junctions and
the super-granulation cells. Besides the location, the two
events have also dierent size and duration. That is why a
precise identication through a visual inspection is needed
to correctly select each single event.
We selected a few explosive events by visual inspection
of both S vi and Ly 6 slit images in the DS1, using the
above mentioned wings at velocities > 50 km s 1 as a
criterion.
As was mentioned above, the observations were per-
formed without applying rotational compensation, so the
slit pointing at X = 0 00 and Y = 0 00 during 5.05 hr of
observations resulted in a drift raster scan with a width of
about 47 00 . Figure 1 shows the reproduced rasters in both
Table 2. Time dierence in the response of the blue and red
wing of Ly 6 compared to the S vi line.
Event Blue wing Red wing
Time (s) Time (s)
a 409 402
b 136 111
c 7921 3310
d { 196
e 3114 164
f 397 {
g 164 286
Ly 6 and S vi lines with the corresponding locations of the
explosive events marked by crosses and letters. The net-
work pattern is visible on both rasters, less clear in Ly 6
due to the optical thickness of the Lyman line. An MDI
image is also presented on this gure showing the region
covered by the SUMER slit.
The events have a dimension along the slit Solar Y 
4 00 -5 00 appearing in the network lanes away from larger
concentration of magnetic ux. At the observed helio-
graphic latitude the 1 00 slit needs about 390 s to move to
the neighboring position on the Sun which makes it im-
possible to evaluate the Solar X dimension of the events.
In order to follow the temporal evolution of the phe-
nomena through the emission changes in both wings, the
total emission in the wings was estimated as the line in-
tensity over 0.17  A wide intervals centered 0.22  A away
from the central position on the blue and red sides of the
spectral line. In this way we avoid most of the contribution
of the blends. In the case of the Ly 6 line, the blends He ii
930.32  A and O i 930.26  A are observed as one feature at
0.44  A from the center of Ly 6. This blend was evaluated
to be only  3%. In order to evaluate the central intensity
increase, the centroids of the lines have been determined
by a Gaussian t of the line prole averaged along the slit
in absence of high velocity events. The central intensity is
that obtained within 0.13  A around the central position.
After the visual identication, the duration of a single
explosive event was dened as the period of a strong in-
crease of the integrated emission in one of the wings until
its decay.
4. Results
The DS1 consists only of one Lyman line (Ly 6) and the
S vi line, but this temporal series has the advantage of
a high temporal resolution (10 s exposure time) and con-
taining two lines which have one order of magnitude dier-
ence in formation temperature. These two facts permit us
to determine whether Ly 6 shows a response to explosive
events, and if it does, what is the line prole shape and
what is the temporal evolution of a dierent temperature
plasma during these transient events?
First the strongest event was analysed, because a re-
sponse of the optically thick Lyman lines could only be
identied when the event is so strong that its emission is

Madjarska & Doyle: Temporal evolution of explosive events 5
Fig. 2. Ly 6 and S vi proles in explosive event `a' during (solid line) and before the event (dashed line), obtained by binning
over 7 pixels along the slit.
shifted far enough to be visible against the high back-
ground emission (Brueckner & Bartoe 1983). Figure 2
shows Ly 6 and S vi proles during the event. We over-
plotted a pre-event prole in order to visualise the line
shape and intensity changes. An increase in the blue wing
in Ly 6 is clearly visible whereas the central intensity of
the line does not show any signicant change. The analy-
sis of all line proles showed that an increase in Ly 6 only
becomes visible when at the same time the S vi central
intensity increases by  100% or more above the pre-event
value.
All identied events were searched for a Lyman line
response through the emission increase in the blue and
red wings. In order to identify the start of a single event
the background emission in the wing before or/and af-
ter the event was evaluated rst. Note that the growth
of the intensity in the wings for the two lines is dierent
because of the dierent optical thickness of the Ly 6 and
S vi lines. Through a visual inspection we determined the
beginning of each event. It was dened as a point from the
ascending branch of the intensity curve showing an obvi-
ous increase above the background emission. In order to
improve the signicance of the time delay measurements
a few points above the starting one were also evaluated.
Figure 3 presents the smoothed integrated intensity curves
for all the registered events. The time dierences for all
events are given in Table 2. The time dierence of the in-
tensity peaks are easy distinguishable for events 'a', `b',
`c', and `e'. The blue wing of event 'd' has a very complex
behaviour and it is diфcult to dene its starting time.
Events `f' and `g' already started before the observations
begun (remember that a reference spectrum was obtained
before each 121st spectrum). The time dierences for these
events are also given in Table 2, but have to be consid-
ered as lower limits. The general picture of the evolution
of all events is characterised by a blueshift accompanied
by a redshift with the emission in the red wing often lower
than in the blue one.
Concerning the intensity changes of the stationary
component of the line we have determined a mean inten-
sity increase in S vi of about 0.6 above the pre-event inten-
sity. During the strongest one it reaches 0.9{1.0. However,
only very small changes of the order of  0.13 have been
registered in Ly 6 due to the optical thickness of this line.
Therefore, the observed self-absorption during the explo-
sive events in Lyman lines may be mainly due to an emis-
sion increase in the wings. Figure 4 shows the intensity
changes of the stationary component obtained in the way
as described in x3.2. As was mentioned already, Harrison
et al. (1999) have registered the same intensity increase of
0.2 - 0.3 above the pre-event value in the optically thick
He i 584  A and 1.0 in optically thin lines such as O v
629  A, O iii 599  A and O iv 554  A during blinker tran-
sient phenomena.
We dened the duration of a single event as the time
from the intensity increase in the wing until its decay.
Dened in that way, it was found that events with duration
of more than 100 s show spikes in the wing intensity curve
as was already observed by Dere et al. (1991). They are
found to last between 40 and 100 s. Similar peaks, but on a
dierent time scale, have also been observed during blinker
events (Harrison et al. 1999). The authors suggested that
this could be the result of the superimposed intrinsic solar
variability.
The strong response of Ly 6 rises the question about
the registration of the explosive events at lower temper-
ature (below 2 10 4 K). To explore this idea we searched
a full spectrum temporal series covering simultaneously
Lyman lines (< 20 000 K), O i ( 15 000 K) lines and
S vi ( 200 000 K) line for explosive events. Only one

6 Madjarska & Doyle: Temporal evolution of explosive events
Fig. 3. Integrated intensity in the blue (solid line) and red (dashed line) wings of Ly 6 and S vi during the explosive events. The
beginning of the events `f' and `g' are not registered because a reference spectrum was obtained before each temporal series.
event has been selected. Figure 5 displays the line proles
of the Ly 11 and S vi lines together with the correspond-
ing slit negative images. The proles were obtained by
binning over 3 spectra and 5 pixels along the slit (note
that S vi is registered on the bare part of detector B).
The line prole before the explosive event does not show
the presence of the faint feature at 932.9  A and therefore
we do not expect any signicant contribution during the
explosive event. Some of the Lyman lines show strong self-
absorption, but as was mentioned above, this may be due
to an increase of the emission in the wings as the central
intensity slightly increases during the event.
Figure 6 shows the integrated intensity in the blue
wings of Ly 11, Ly 10, Ly 9, Ly 7, Ly 6 and S vi obtained
as described in x3.2. The total intensity of C ii includes
the intensity of four blended C ii lines at 903.59, 903.99,
904.14, 904.46  A (Curdt et al. 1997, 2001). We were espe-
cially interested in the response of the O i (15 000 K) lines.
The visual inspection of these lines suggested some inten-
sity increase during the explosive event, but this is uncer-
tain because of the low emission of these lines. Therefore
we used the total intensity in the two selected unblended
oxygen lines O i 929.52 and 936.63  A. As was shown above,
the central intensity of optically thin lines increases by at
least 1.6 and in optically thick lines by less than 1.2 times

Madjarska & Doyle: Temporal evolution of explosive events 7
Fig. 4. Two examples of the stationary component intensity changes of the Ly 6 (solid line) and S vi (dashed line) lines during
explosive events `a' and `g'.
Fig. 5. Ly 11 and S vi line proles before (dashed line) and during (solid line) the explosive event. The proles are obtained
by binning over 3 spectra and over the region along the slit as shown by the horizontal lines on the right panel slit negative
images. Right panels: Slit negative images before and during the explosive event in Ly 11 (a, b) and S vi (c, d), respectively.
during an explosive event. Therefore, when it is impossible
to detect blueshifted and redshifted emission as in the case
of faint lines such as oxygen, and the event is already reg-
istered by other simultaneously recorded lines, the total
intensity in these lines is a good indicator for the pres-
ence of the event in this spectral line. As can be seen from
Figure 5, the continuum also shows an increase during the
explosive event, which made it necessary to evaluate and
subtract the background for each line. This is especially
important in the case of the faint oxygen lines. The plots
in Figure 6 show that during the event, a plasma with
a temperature from 15 000 to 200 000 K is registered.
Unfortunately, the longer exposure time during these ob-
servations does not permit us to follow the temporal evo-
lution of the dierent temperature plasma.
5. Conclusions
During the last decades numerous solar activity phenom-
ena (solar ares, surges, sprays etc.) have been consid-
ered as manifestation of magnetic reconnection processes
(Giovanelli 1946; Gold & Hoyle 1960; Priest 1981; Parker
1988; Forbes 1991, Priest & Forbes 2000) resulting from

8 Madjarska & Doyle: Temporal evolution of explosive events
Fig. 6. Integrated intensity in the blue wing of Ly 11, Ly 10, Ly 9, Ly 7, Ly 6 and S vi in the region of the explosive event (5
pixels along the slit) for the all analysed dataset. We also show the total intensity of the O i and C ii (includes four blended
C ii lines) lines .
the formation of a current sheet formed by magnetic ux
tubes with opposite polarities pushed together by inten-
sive photospheric motions. Such a current sheet may also
occur between a new emerging ux tube and a pre-existing
one. It is believed that the explosive events appearing as
bi-directional jets with velocities comparable to the local
Alfven velocity are such events resulting from magnetic re-
connection. This belief is due to their appearance on the
super-granulation cell boundaries and the fact that they
are often associated with the cancellation of the photo-
spheric magnetic eld.
Every explosive event shows some particularities and
it is not possible to dene a general picture of their be-
haviour. Two datasets complementing each other have
been explored in this study trying to identify new com-
mon features for all of the events. We have examined the
temporal evolution of dierent temperature plasmas dur-
ing explosive events taking the advantage of having reg-
istered these phenomena with a short exposure time (10
s) in lines with one magnitude dierence in the formation
temperature. Another temporal series but covering simul-
taneously lines with a wide range of formation tempera-
tures has been used to nd out which temperature plasma
is involved in this phenomenon. Our analysis revealed that
the explosive events appear rst at chromospheric temper-
atures. After some time delay which diers from event to
event a hotter plasma is registered.
Solar ares are another solar activity phenomena, re-
sulting from magnetic reconnection. During their impul-
sive phase they are also registered in many EUV spec-
tral lines ranging from neutral hydrogen and oxygen to
highly ionised ions of metals (Priest 1981 and the ci-
tations therein). Results, with quite large uncertainties,
from OSO-III observations (Hall 1971) suggest that prob-
ably similar time delays in the response of EUV emission
lines exist during solar ares as well. The similarities be-
tween explosive events and ares suggest a common mech-
anism of their generation. This may help to nd out why
a plasma exists at such a wide temperature range dur-
ing explosive events although not necessarily at coronal
temperatures and how that is related to their generation.
Our study has been based on only a few events. In
order to dene the time evolution of plasma with dif-
ferent temperatures during explosive events further spec-
troscopic observations simultaneously covering lines with
a wide range of formation temperatures obtained with
high temporal resolution (exposure time around 10 s) are
needed. Koutchmy et al. (1997) provided evidence for the

Madjarska & Doyle: Temporal evolution of explosive events 9
existence of a new type of soft X-ray brightening event
with duration and size comparable to the explosive events
and called them `soft X-ray coronal ashes'. To nd out
whether these phenomena are the coronal counterpart of
the explosive events simultaneous multi-instrumental and
spectroscopic multi-wavelength observations have to be
obtained.
Such observations are also needed to explore the con-
nection and similarities between explosive events and
blinkers. Chae et al. (1998) using SUMER and CDS ob-
servations have already revealed some similarities between
explosive events and blinkers. CDS blinkers have been as-
sociated with small-scale short-lived SUMER `unit bright-
ening events' with a size of a few arc seconds and a lifetime
of a few minutes (Chae et al. 2000, Teriaca et al. 2001)
characterised by proles that are not as broad as those
of explosive events but still with signicantly enhanced
wings. In this work two more common features of the two
events have been identied. We compared the intensity
increase of the `line at rest' during explosive events and
blinkers (reported by Harrison et al. 1999) and found out
that the same intensity increase takes place during both
events. The existence of intensity peaks during an explo-
sive event, registered also with HRTS by Dere et al. (1989),
is another link between explosive events and blinkers.
Further eorts are required regarding time delays of
the response of dierent spectral lines during explosive
events as well as a more detailed NLTE study concern-
ing the line formation of optically thick lines such as the
Lyman series. The present observational dataset suggests
a time delay with the chromospheric feature being de-
tected rst as a blueshifted plasma several seconds before
a response to the magnetic reconnection is observed at
transition region temperatures.
Acknowledgements. Research at Armagh Observatory is grant-
aided by the N. Ireland Dept. of Culture, Arts and Leisure,
while partial support for software and hardware is pro-
vided by the STARLINK Project which is funded by the
UK PPARC. This work was supported by PPARC grant
PPA/GIS/1999/00055. The SUMER project is nancially sup-
ported by DLR, CNES, NASA, and PRODEX. Thanks to Prof.
E. Priest and Dr. W. Curdt for fruitful discussions.
References
Brueckner, G.E. & Bartoe, J.-D.F., 1983, ApJ, 272, 329
Chae, J., Wang, H., Lee, C.Y., Goode, P.R. & Schuhle, U.,
1998a, ApJ, 497, L109
Chae, J., Wang, H., Lee, C.Y., Goode, P.R. & Schuhle, U.,
1998b, ApJ, 504, L123
Curdt, W., Feldman, U., Laming, J.M., Wilhelm, K., Schuhle,
U., & Lemaire, P., 1997, A&AS, 126, 281
Curdt, W., Brekke, P., Feldman, U., Wilhelm, K., Dwideli, B.
N., Schuhle & Lemaire, P., 2001, A&A, 375,591
Dere, K.P., Bartoe, J.-D.F. & Brueckner, G.E., 1989, Solar
Phys., 123, 41
Dere, K.P., Bartoe, J.-D., Brueckner, G.E., Ewing, J. & Lund,
P., 1991, J. Geophys. Res., 96, 9399
Dere, K.P., 1994, Adv. Space Res., 14(4), 13
Forbes, T.G., 1991, Geophys. Astrophys. Fluid Dyn., 62, 15
Giovanelli, R.G., 1946, Nature, 158, 81
Gold, T. & Hoyle, F., 1960, MNRAS, 120, 89
Hall, L.A., 1972, Solar Phys., 21, 1971
Harrison, R.A., Sawyer, E.C., Carter, A.M. et al., 1995, Solar
Phys., 162, 233
Harrison, R.A., 1997, Solar Phys., 175, 467
Harrison, R.A., Fludra, A. & Pike C.D., et al., 1997, Solar
Phys., 170, 123
Harrison, R.A., Lang, J., Brooks, D.H. & Innes, D. E., 1999,
A&A, 351, 1115
Heinzel, P., Schmieder, B. & Vial, J.-C., 1997, Proc. Fifth
SoHO Workshop (ESA SP-404); Nordwijk: ESA, 427
Innes, D.E., Brekke, P., Germerott, D. & Wilhelm, K., 1997a,
Solar Phys., 175, 341
Innes, D.E., Inhester, B., Axford, W.I. & Wilhelm, K., 1997b,
Nature, 386, 811
Koutchmy, S., Harra, H., Suematsu, Y. & Reardon, K., 1997,
A&A, 320, 33
Lemaire, P., Wilhelm, K., Curdt, W. et al., 1997, Solar Phys,
170, 105
Marsh, E., Tu, C.-Y., Heinzel, P., Wilhelm, K. & Curdt, W.,
1999, 347, 676
Parker, E.N., 1988, ApJ, 330, 474
Perez, M.E., Doyle, J.G., Erdelyi, R. & Sarro, L.M., 1999a,
A&A, 342, 279
Porter, J.G. & Dere, K. P., 1991, ApJ, 370, 775
Priest, E.R., 1981, Solar Flare Magnetohydrodynamics,
Gordon & Breach, London
Priest, E.R. & Forbes, T., 2000, Magnetic Reconnection: MHD
theory and applications, Cambridge Univ. Press
Roussev, I., Galsgaard, K., Erdelyi, R. & Doyle, J.G., 2000,
A&A, 370, 298
Sherrer, P.H., et al. 1995, Sol. Phys., 162, 129
Teriaca, L., Madjarska, M. S. & Doyle, J.G., 2001, Solar Phys.,
200, 91
Vernazza, J.E., Avrett, E. H. & Loeser, R., 1981, ApJS, 45,635
Warren , H. P., Mariska, J. T. & Wilhelm, K., 1998, ApJS,
119, 105
Wilhelm, K., Curdt, W., Marsch, E., Schuhle, U., Lemaire,
P., Gabriel, A., Vial, J.-C., Grewing, M., Huber, M.C.E.,
Jordan, S.D., Poland, A.I., Thomas, R.J., Kuhne, M.,
Timothy, J.G., Hassler, D.M. & Siegmund, O.H.W., 1995,
Solar Phys. 162, 189
Wilhelm, K., Lemaire, P., Curdt, W. et al., 1997, Solar Phys.,
170, 75
Wilhelm, K., Innes, D.E., Curdt, W., Kliem, B. & Brekke,
P., 1998, in Solar Jets and Coronal Plumes, Guadalupe,
France, ESA-SP 421, 103