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\newcommand{\CDS}{\mbox{CDS}}         % Coronal Diagnostic Spectrometer
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\begin{document}

\title{A multiline study of flows  of the M 1.0 flare on October 22, 2002}

\author{G. Del Zanna
\inst{1}\thanks{Previous address: DAMTP, University of Cambridge} 
\and
A.\ Berlicki \inst{2,3} 
\and
H. E. Mason
\inst{4}  
\and
          B.\ Schmieder  \inst{2,5}
}
\institute{
MSSL, University College London Holmbury St. Mary Dorking UK RH5 6NT
\and
Observatoire de Paris, Section de Meudon, LESIA,
              F-92195 Meudon Principal Cedex, France
   \and
   Astronomical Institute of the Wroc{\l}aw University, ul. Kopernika
   11, 51-622 Wroc{\l}aw, Poland
\and
Department of Applied Mathematics and Theoretical Physics,
University of Cambridge, Cambridge UK  CB3 0WA
   \and
   Institute of Theoretical Astrophysics, University of Oslo, 
   Blindern, N-0315 Oslo, Norway
}


\offprints{G. Del Zanna \\ (G.Del-Zanna@damtp.cam.ac.uk)}

\date{\today}

\titlerunning{The M~1 flare on October 22, 2002 }

\abstract{
In this paper we present a further study of the M1 class flare
observed on October 22, 2002. We focus on the SOHO Coronal 
Diagnostic Spectrometer (CDS) spectral observations
and the ground-based (VTT/MSDP) observations 
performed during a multi-wavelength campaign with TRACE.
Strong blue-shifts are observed in the CDS coronal 
 lines in  flare kernels during the impulsive phase of this flare.
From a careful wavelength calibration  
we deduce upflows of 140 km/s for the Fe~XIX emission, less for the
cooler lines and  downflows in the  He I line  (13 km/s). The
upflows correspond to full shifts of the line profiles. The large
line-widths, specially for
the Fe~XIX line indicate the existence of  strong turbulence velocities. 
These flows are observed at the launch time of the flare, and 
correspond to   the ``explosive evaporation''. The location of these
blueshifted  kernels, few arc seconds far from the flare onset location is
explained by the chain reaction of successive magnetic reconnections
of growing emerging field line with  higher and higher overlaying
field. This interpretation is evidenced  by the
analysis of the magnetic topology of the active region using  a
linear force-free-field extrapolation of THEMIS magnetogram.
In other kernels reached during the late phase of the flare by CDS we
observed small upflows (maximum 50 km/s) which  we interpreted  as due
to ''gentle evaporation''.
 
\keywords{Sun: corona -- Techniques: spectroscopic -- Line: profiles}
}

\maketitle



\section{ Introduction }

The broadening and blue-shifting of spectral lines for high temperature
emission during the initial phase of solar flares has been
extensively studied in the X-ray wavelength range
using data from SOLFLEX (cf. \citealt{doschek_etal:79}), the Solar Maximum
Mission's (SMM's) X-ray polychromator (XRP) 
 Bent Crystal Spectrometer
(BCS) (cf \citealt{antonucci_etal:82}) and the BCS on YOHKOH
(see, e.g., \citealt{bentley_etal:94}). Plasma velocities deduced from
Doppler-shift analysis were of the order of a few hundreds 
$\mathrm {km\;s^{-1}}$. This blueshifted emission was interpreted as
evidence for chromospheric evaporation. However,
these BCSs had no spatial resolution, so it was not possible 
to locate the source 
of the blueshifted X-ray emission, or to spatially separate this 
from any stationary components. 
A further complexity in the interpretation of BCS spectra 
was due to the superposition (at different wavelengths)
 of stationary components originating from different locations.
In general asymetric line profiles
were observed, rather than totally shifted lines.
Without spatial resolution in the BCS X-ray observations, 
any weak blue-shifted X-ray emission would swiftly be swamped by 
the strong stationary emission from the flare X-ray loops.
In a  recent paper, \cite{warren_doschek:05}
interpret these blue-shifted asymetries as a succession 
of independently heated
threads within flare loop structures. To progress further, it
is essential to spatially locate the high temperature 
blue shifted emission in relation to the flare loops and structures.


The SMM XRP Flat Crystal Spectrometer (FCS) had a limited
spatial resolution (14$^{\prime\prime}$). \cite{zarro_etal:88} 
reported spatially confined Mg XI blue-shifted 
emission during the impulsive phase of a small flare.
The Fe~XXI line at 1354.1~\AA\, emitted at
about $10^7$~K, was studied with the SMM Ultraviolet
Spectrometer and Polarimeter (UVSP) instrument (with spatial 
resolution down to 3$^{\prime\prime}$) . 
\cite{mason_etal:86} deduced upward flows
in Fe~XXI emitting plasma in excess of 200~km/s.
Their observations supported the hypothesis of 
chromospheric evaporation in the
'footpoint region' of what subsequently became soft X-ray emitting loops.


The Coronal Diagnostic Spectrometer (CDS) instrument 
on SOHO has the capability to simultaneously 
obtain spatial and spectral information for emission over a 
wide range of plasma temperatures. One of the  hottest lines recorded
with CDS is the Fe~XIX flare line at 592.2~\AA. This is formed at a
temperature around $8 \times 10^6$~K. Using CDS, it is possible
to locate the source of high temperature
blue-shifted emission seen during a solar flare. 
\cite{czaykowska_etal:99} reported SOHO/CDS 
observations of blue-shifts in Fe XVI 
($3 \times 10^6$~K) and Fe~XIX ($8 \times 10^6$~K) lines.
These observations were however performed 
more than one hour after the maximum 
of a two-ribbon M6.8 flare. The blue-shifts appeared to be 
located at the outer edges of the flare ribbons.

Spatially-resolved spectral information from CDS were 
reported by \cite{delzanna02_cospar}
covering the entire evolution of a small flare.
Long-lasting (over an hour) blue-shifts of 
30~km/s in coronal lines (Mg~X, Si~XII, emitted at 
1-2~MK) were located at the footpoints of a small loop system.
These could be interpreted as indirect evidence of chromospheric evaporation. 


Recently, \cite{teriaca_etal:03} published
CDS and ground-based observations of 
an eruptive C2 flare.
The main findings were quasi-simultaneous and co-spatial 
measurements of upflows in the flare line (Fe~XIX) 
and downflows in the chromosphere, as seen in the 
He~I 10830~\AA\ line. 
\cite{brosius_phillips:04} presented CDS observations
of a larger M6 flare.
These authors kept the position of the CDS slit fixed,
thus sacrifying spatial coverage in favour of 
a high (10s) time resolution. They used TRACE observations
to track the evolution of the flare.
Their main results were measurements of upflows ($\simeq$60 km/s) 
in flare lines and downflows ($\simeq$40 km/s) in cooler
transition region lines during the impulsive phase.
The X-ray emission appeared $\simeq$1m after the start of 
the impulsive intensity rise in the cooler lines.
They concluded that their observations were consistent with 
non-thermal particles 
transferring most of the energy into the chromosphere and 
creating these oppositely-directed flows. 

The ''explosive'' evaporation seen in the emission from high
temperature flare plasma is thought to be driven 
by non-thermal electrons accelerated during the primary energy release
(\citealt{antonucci_etal:84}) and may occur when the heating rate due 
to collisions of non-thermal 
electrons with the ambient plasma in upper layers of the 
chromosphere exceeds the chromospheric
radiative losses (\citealt{fisher:87}). This occurs 
when the temperature of the heated region is 
above \mbox{$2 \times 10^{5}$ K} and thus this kind of 
evaporation cannot be seen in chromospheric spectral lines which are
formed in a cooler plasma.

If a region of the chromosphere heated by non-thermal electrons 
is thick enough, then the 
rapid temperature increase produces an enhanced pressure 
in the heated region. This overpressure, 
besides the evaporation, also drives downward-moving cool and dense 
{\it chromospheric condensations} (\citealt{fisher_etal:85c}) which seem 
to be responsible for red-shifts 
of the H$\alpha$ line profiles reported by many authors 
(\citealt{svestka:76}, \citealt{ichimoto_kurokawa:84}).
\cite{fisher_etal:85a} modelled the hydrodynamic 
and radiative response of the atmosphere to short impulsive injections 
of non-thermal electron beams. They showed that only the high-energy 
flux of non-thermal electrons drives explosive evaporation, 
accompanied by the formation of 
cool chromospheric condensations in the flare chromosphere.


\begin{figure*}[!htbp]
\centerline{\epsfig{file=goes3_bw.ps, width=10.0cm , angle=90 }}
%  \resizebox{\hsize}{!} {\includegraphics{goes2_bw.ps}}
\caption{Time evolution of the GOES 8  X-ray fluxes
on October 22, 2002 during the M1 flare and the CDS raster 
scan.
The dot-dashed curve is the time derivative of the 
0.5--3 \AA\ light curve, and can be used as a proxy for the 
hard X-ray emission. 
 The timings of a few 
key observations are indicated 
(top: CDS slit positions, see 
Fig.~\ref{fig:trace_seq}; middle: TRACE images, see Fig.~\ref{fig:trace_seq_zoom};
bottom: H$\alpha$ slit positions during two 
consecutive rasters, see  Fig.~\ref{fig:vtt}).
}
  \label{fig:goes_plot}
% Fig.~\ref{fig:goes_plot}
\end{figure*}




A coordinated observational campaign
was organised to follow the evolution of the 
NOAA 0162 active region during October 22, 2002.
Ground based instruments (THEMIS and Vacuum Tower Telescope - VTT - 
on Tenerife, Canary islands, Spain) and
space observatories (SOHO, TRACE and RHESSI)
were involved. 
The active region had several flares, including an M1 flare.
The morphology and evolution of the M1 
flare in particular during the gradual phase 
(when RHESSI was observing) were presented in \cite{berlicki_etal:04}.
Here, we focus in particular on the nature of the emission from
the high temperature plasma, as seen in the initial 
phase of the M1 flare with the CDS on SOHO.


In this paper we focus primarily on the nature of the blue shifted
emission from high temperature plasma and its relationship with 
 the cool chromospheric emission and the hot flare emission.
In Sect.~2 we summarise the observing campaign for the 22nd October
2002.
In Sect.~3 we present the CDS observations and results in detail, 
paying particular attention to the measurement of wavelength shifts.
In Sect.~4 we discuss the magnetic topology of the flare according to
a non linear force free field extrapolation of the magnetic field with
an observed THEMIS magnetogram as boundary conditions. The flows of
the flare plasma are presented and discussed in this context
(Sect.~5).




\section{Co-ordinated observing campaign for 22nd October 2002}


\begin{figure}[!htbp]
\centerline{\epsfig{file=trace1534_themis1541.ps, width=8.5cm,angle=0 }}
%\centerline{\epsfig{file=trace_1529.ps, width=8.5cm,angle=0 }}
%\centerline{\epsfig{file=trace_1529_ovl.ps, width=8.5cm,angle=0 }}
\caption{ TRACE 195 \AA\ image of the active region during  the M1 flare.
 with contours ($\pm$ 200, 500, 1000 G) 
from the THEMIS magnetogram obtained in the Na D1 line.
The fields of view of the TRACE sequence of images (Z1, see 
Fig.~\ref{fig:trace_seq}), of the region of the  M1 flare 
and of the CDS raster are also shown.
}
  \label{fig:trace_over}
% Fig.~\ref{fig:trace_over}
\end{figure}


\begin{figure}[!htbp]
\centerline{\epsfig{file=trace_seq.ps, width=9.0cm , angle=0 }}
\caption{Sequence of TRACE 195~\AA\ difference images (negative) 
of the region Z1 (cf. Fig.~\ref{fig:trace_over}) 
and  centred during the peak of the M1 flare. 
The image that has been subtracted was taken at 15:29:59 UT,
before the start of the flare.
The timings indicate the initial exposure time 
for each TRACE image, and the corresponding nearest CDS exposure.
The location of the CDS slit is also shown.
}
  \label{fig:trace_seq}
% Fig.~\ref{fig:trace_seq}
\end{figure}






The active region NOAA 0162 was mainly bipolar, quite extended, and
relatively active.
It was observed on October 22, 2002 with SOHO, TRACE, RHESSI,
and from the ground with  THEMIS and VTT.
The SOHO/CDS sequence of observations 
was extensive and ran during 08:02-13:07~UT and 15:18-18:13~UT
(see Table~\ref{tab:list_files}).
The CDS observations, described in detail below,
 consisted of 'rasters' during which the slit
was scanning the active region.

During October 22  the active region  produced at least 
3 flares. The main M1 flare occurs at 15:30 UT during 
 the CDS raster at 
15:18:16--15:43:16 UT.
%
Fig.~\ref{fig:goes_plot} shows the X-ray light curves from GOES~8 
during the CDS scan.
The time derivative of the 
0.5--3 \AA\ light curve can be used as a proxy for the 
hard X-ray emission, and indicates a peak at 15:33 UT.
The timings  of some  CDS  slit positions and 
some TRACE and ground-based observations are also shown.


\begin{table}[ht]
\caption[]{CDS rasters analysed - 22 Oct 2002.}
\begin{center}
\begin{tabular}{ccl}
\hline\noalign{\smallskip}
 Time (UT) & CDS files  & CDS study \\
\hline\noalign{\smallskip}


8:02:50--8:27:54 & s26053r00  & SIG\_FT44 \\
 & s26054r00  & ARDIAG\_2 \\
 & s26054r01  & ARDIAG\_2 \\
 & s26055r00  & ARDIAG\_2 \\
 & s26056r00  & SIG\_FT44 \\

15:18:16--15:43:16  & s26058r00  & SIG\_FT44 \\
15:43:30--17:07:33  & s26059r00  & ARDIAG\_2 \\
17:08:03--18:32:46  & s26059r01  & ARDIAG\_2 \\

\hline\noalign{\smallskip}

\end{tabular}
\end{center}
\label{tab:list_files}
\end{table}
%Table~\ref{tab:list_files}


%and has been discussed in \cite{berlicki_etal:04}.
%
%THEMIS observed continuously between 15:41--17:26~UT 
%in the Na I ${\rm{D_{1}}}$ spectral line. 
%These observations were used to obtain  
% the line--of--sight (LOS) magnetic field  from the observed Stokes profiles.
%
VTT/MSDP observations in H$\alpha$ consisted of 
9 raster scans between 15:30 and 16:17 UT and a field-of-view
of about 380''$\times$170'' (exposure time of 0.5s).
The rastering was performed from east to west, in the 
opposite direction compared to CDS.
Below we will concentrate on the first VTT spectral raster,
which scanned the active region during 15:30-15:37 UT, i.e. 
in the impulsive phase. Results from the follow-up raster 
(gradual phase) have been presented by Berlicky et al. (2005).


TRACE 195~\AA\ images were obtained at high-cadence (40~s) 
between 15:29 and 15:41 UT (with a FOV
384''$\times$384'' and a 1'' resolution)(see  Fig.~\ref{fig:trace_over} for the full TRACE FOV). 
Before and after this time the TRACE observations were
obtained with slightly lower time resolution (50 s) and larger FOV
(512''$\times$512''). 


%
 Fig.~\ref{fig:trace_seq} shows a sequence of 
TRACE 195 {\AA} difference images in the central part of the 
TRACE FOV, where the flare took place.
The location and timings of the CDS slit are also indicated 
in  Fig.~\ref{fig:trace_seq}.
The first obvious signature  in the  TRACE 195 {\AA}
occurs  at 15:32:18 UT, somewhat later than the 
 increase in  the GOES X-ray flux.
However, a small brightening already appears at the same 
location on the 15:31:31 UT TRACE image.


%
By 15:33 UT, the entire ribbon structures (located
on either side of the neutral line) brighten up in the TRACE 195~\AA\
image. The H$\alpha$ ribbons were already 
visible at 15:31 UT (see \citealt{berlicki_etal:04}). 


CDS had the slit positioned over the main area of the flare 
during the peak and gradual phase (cf.  Fig.~\ref{fig:goes_plot}
and Fig.~\ref{fig:trace_seq}) and can therefore be used to 
estimate the temperatures of the various features recorded by TRACE.
%(note that these features are lasting long enough for this 
As shown below, CDS observed strong Fe~XIX emission in the 
locations of both the ribbons and the higher-lying loops
observed by TRACE, which suggests that  most likely 
the TRACE images are dominated by hot emission from Fe~XXIV.

.


\section{CDS instrument and data analysis}

The CDS observations were performed with the 
normal incidence spectrometer (NIS).
%The slits are  normally oriented along the solar N-S direction.
The internal scan mirror allows CDS  to scan an 
 area of 4\arcmin\ square within a single `raster', from west to east. 
The N-S coverage was provided by the use of 
the long slit 4\arcsec x240\arcsec. 

The NIS is composed of two gratings, that  
produce two wave-bands  
(NIS~1: 308  -- 379 \AA\ and NIS~2: 513 -- 633 \AA;).



The CDS observing sequences were specifically designed 
to study the spatial and spectral characteristics of small flares.
They included a range of spectral lines from different ions and in
particular the high temperature flare line, Fe~XIX 592.2~\AA.
%
CDS observed NOAA 0162 
with the two types of rasters (see Table~\ref{tab:list_files}):
1) a slow diagnostic raster
(1hour 20 m, CDS study name ARDIAG\_2)
that extracts many diagnostic lines;
 2) a fast raster
(slit exposure of 18s for a total duration of 
20 m, CDS study name SIG\_FT44) that 
only extracts a few lines, selected to cover a wide  range of
temperatures (see Table~\ref{tab:list_lines}).





\begin{table*}[ht]
\caption[]{List of the main lines used for the wavelength calibration.
The first row gives the reference wavelengths ($\lambda_{st}$, \AA) adopted.
The second row gives the wavelengths ($\lambda_{1}$, \AA) as obtained from the 
pre-flare raster s26055 and the calibration curve adopted.
The third row gives the corresponding relative velocities ($v_1$, km/s).
The following two rows give wavelengths ($\lambda_{2}$, \AA) and
relative velocities ($v_2$, km/s) as obtained 
from the post-flare raster s26059 and using the same 
  calibration curve. Note the small differences in the 
measured wavelengths, giving confidence in the stability of the 
wavelength calibration.
}
\begin{center}
\footnotesize
%\tiny
%\scriptsize
\begin{tabular}{@{}lcccccccccccc@{}}
%[511.455, 0.116225, 7.71135e-07]
\hline\noalign{\smallskip}
\hline\noalign{\smallskip}
                     & Si XII & He I   & Ne IV  & Al XI & O IV & O IV&
Ca X     & Ne VI   & Ne VI & Fe XII & Mg X & O V \\

$\lambda_{st}$  & 520.665& 522.210&  542.07& 550.06& 553.34& 555.263&
 557.765& 558.594& 562.803& 592.60& 624.941& 629.732 \\

$\lambda_1$ & 520.675 & 522.208   &    542.031  &     550.070   &    553.365  &     555.252    &   557.758     &  558.590    &   562.791    &   592.590   &    624.936
   &    629.735 \\

$v_1$  & 5 &   -1 &  -21  &   5 &   13 &   -6 &   -3  &  -2 &   -6 &   -5 &   -2  &   1 \\

$\lambda_2$  & 520.664 & 522.211 & 542.061 & 550.066 &
 553.354 & 555.260 & 557.769 & 558.622 & 562.812 & 592.597 & 624.932 & 629.747 \\

$v_2$      & 0 &   0 &  -4 &   3  &  7 &  -1  &  1 &  15  &  5  & -1 & -4  &  6 \\

\hline\noalign{\smallskip}
\end{tabular}
\end{center}
\normalsize
\label{tab:wvl_cal}
\end{table*}
%Table~\ref{tab:wvl_cal}



\begin{table}
\caption{Some of the prominent  lines in the CDS/NIS wavelength bands,
used in this paper.
Wavelengths are taken from the CHIANTI database unless otherwise
stated.
Those indicated with an asterisk have been used for the 
wavelength calibration.
When only one decimal 
place is indicated, the lines are blends of at least two transitions.
The approximate temperature of maximum ion abundance 
(in ionization equilibrium) is also
indicated, together with the channel and the CDS study that 
recorded the lines (FR: fast raster; DR: diagnostic raster, see text).
%
%*************************
}
\begin{center}
%\footnotesize
%\tiny
%\scriptsize

\begin{tabular}{llrccc}
\hline\noalign{\smallskip}
Ion & wavelength (\AA) & log T$_e$  & NIS  &  \\
\hline\noalign{\smallskip}

%Fe XIV & 334.172 & 6.2 &   1  &  DR \\

Si X & 347.402 & 6.1 &   1  &  FR,DR \\
Si X & 356.0 & 6.1 &   1  &  FR,DR \\

%Fe XVI & 360.761 & 6.3 &   1  &  DR \\
%Fe XII & 364.467  & 6.1 &   1  &  DR \\

%Mg VII  & 367.7 & 5.8 &   1  &  DR \\
%Mg IX  & 368.070 & 6.0 &   1  & DR  \\

Si XII & 520.665$^*$ & 6.3 &   2  & FR,DR \\
He I  & 522.210$^*$ & 4.5 &   2  & FR,DR \\

%Ne IV & 542.07$^*$ & 5.3 &   2  & DR \\

%Al XI & 550.06$^*$ & 6.2 &   2  & DR \\

O IV  & 553.34$^*$ & 5.3 &   2  & FR,DR \\
O IV  & 554.076 & 5.3 &   2  & FR,DR \\
O IV  & 554.513 & 5.3 &   2  & FR,DR \\
O IV & 555.263$^*$ & 5.3 &   2  & FR,DR \\

%Ca X & 557.765$^*$ & 5.8 &   2  &  DR\\
%Ne VI  & 558.594$^*$ & 5.6 &   2  &  DR\\

%Ne VII  & 561.728 & 5.7 &   2  &  DR\\
%Ne VI  & 562.803$^*$ & 5.6 &   2  &  DR \\

Fe XIX & 592.16 & 6.9 &  2  & FR,DR \\

Fe XII & 592.60$^*$ & 6.1 &  2  & FR,DR \\

Mg X & 624.941$^*$ & 6.0 &   2  & FR,DR \\
O IV &  625.853   & 5.3 &   2  & FR,DR \\
O V  & 629.732$^*$ & 5.4 &   2  & FR,DR \\
\hline\noalign{\smallskip}
\end{tabular}
\end{center}
\normalsize
\label{tab:list_lines}
\end{table}
% Table~\ref{tab:list_lines}



One important aspect of CDS is that lines emitted from 
the chromosphere up to the corona are observed. 
This is very useful for a proper co-alignment 
with other datasets, e.g. photospheric magnetic fields 
from SOHO/MDI, and coronal images from TRACE.
A series of standard  corrections was applied to the raw NIS data.
These include de-biasing, flat-fielding, corrections for 
the burn-in of the lines and high count rates, cosmic ray removal.
%
Multiple-line-fitting techniques have been used
to determine the moments of each of the spectral 
lines in the spectra by removing the {\it `continuum' }
 intensity, which is mainly  due to scattered light in the NIS.
%
In SOHO post-recovery spectra,  the CDS/NIS line profiles
are no longer gaussians, and show a broadened and asymmetrical
long wavelength wing, which is approximately
constant and can therefore be accounted for.
%
The CDS calibration of \cite{delzanna01_cdscal}
has been adopted here,  with a correction to take
into account the effects on the NIS detector of the gain depression caused by
exposures with the wide slit.




\subsection{Wavelength calibration}


For a correct interpretation of the velocities observed,
an accurate wavelength calibration is necessary.
%
CDS does not have an absolute wavelength calibration.
%
Changes in the  wavelength calibration 
have been observed (up to 0.1~\AA\ in NIS 2), 
and caused primarily by on-board
temperature changes (and their history),
which are due to the variable illumination
received from the Sun (D. Pike, priv. comm.).
Also, the wavelength calibration often 
requires a `scan mirror correction', 
which also  appears to vary.
%
In addition, there are no photospheric or chromospheric lines within 
the CDS wavelength bands (except He~I).

The above means that the calibration has to be done using the 
observed transition region and coronal lines, and that 
it is necessary to obtain/check the
wavelength calibration for each set of observations.


For the calibration, it is important to have accurate `standard'
rest wavelengths for the spectral lines concerned, which is 
a non-trivial issue if very accurate measurements are 
sought. 
We have adopted the values shown in Table~\ref{tab:list_lines}.
For most lines we adopt the wavelengths as in the CHIANTI 
database, which in turn has values mostly from NIST. 
We note, however, that 
the values in NIST are taken from the literature, where 
many measurements have been obtained from solar spectra and present
some inconsistency.



The case of the important \ion{Fe}{xix} {592.2}\AA\ line
is emblematic. 
%This line was observed by ...
%and identified for the first time by ... 
%However, accurate measurements are sparse in the literature,
%the few available being inconsistent with each other.
%
Our calibration, based on a small sample,
provides a wavelength of 592.16 \AA, in excellent 
agreement with the accurate measurements of \cite{widing:78}, 
but different from e.g. the value previously reported 
by  \cite{sandlin_etal:76},  592.24~\AA.
We note that \cite{widing:78} averaged many flare observations taken with 
the NRL spectroheliogram on Skylab.
On the other hand, 
\cite{lawson_peacock:80}, in their review of the $n=2 \to n=2$ 
transitions, based on  solar and
laboratory measurements,  suggested an energy 
for the \orb[2s 2] \orb[2p 4] $^1$D$_{2}$ level 
of 168770 \cm. This energy is equivalent to a rest wavelength of 592.522 \AA,
i.e. at  the considerable difference of  
 183 km/s, compared to our result, 592.16~\AA.
%
% {sandlin_etal:76}  592.24 
%
An extra complication is due to the presence, in the 
red wing of the  \ion{Fe}{xix} line, of a coronal 
line only recently identified as due to \ion{Fe}{xii}
(see Fig.~\ref{fig:fe_xix_win} below and 
\citealt{delzanna02_cospar}, \citealt{del_zanna_mason_fexii}).


To calibrate the CDS observations, 
average CDS spectra containing a large number of lines 
(the diagnostic rasters) of two rasters taken before and 
after the flare have been analysed and wavelength-calibrated.
We assumed for the CDS pixel-wavelength calibration 
a quadratic function.
The  wavelength calibration was remarkably stable over the 
period. Table~\ref{tab:wvl_cal} shows that in most cases the 
line centres were within a few km/s the assumed reference 
values.

In terms of uncertainties, we note that  
the positions of the line centres can be calculated with 
approximately 1/10 of a pixel accuracy 
(1  pixel in the NIS~2 channel is approximately equivalent to 0.11 \AA),
and the average differences between the predicted and 
standard wavelengths are of the same order, 0.01 \AA.
This accuracy results in an uncertainty 
in the derivation of velocities of the order of 
10 km/s.
An additional systematic uncertainty is due to the 
spatially-dependent effects due to the geometrical 
distortions within the instrument. 
This is more difficult to quantify, because it depends on the 
type of relative measurement that is done, but is again 
of the same order.
Finally, we note that the resolution of the CDS instrument 
does not allow simultaneous measurements of 
stationary and non-stationary components. Hence, our 
results refer in most cases to the average main displacement of 
each line profile. 
This is not true in the case of the Fe~XIX emission, since 
it is present only during flares.
Significant line broadening can however be 
measured even in post-recovery spectra.

\begin{figure}[!htbp]
\centerline{
\epsfig{file=s26058r00_HeI_int_mdi.ps, width=4.7cm,angle=0 }
%\epsfig{file=s26058r00_HeI_pos_mdi.ps, width=8.0cm,angle=0}
\epsfig{file=s26058r00_OV_int_mdi.ps, width=4.7cm,angle=0}}
%
\centerline{\epsfig{file=s26058r00_SiXII_int_mdi.ps, width=4.7cm,angle=0 }
\epsfig{file=s26058r00_FeXIX_int_mdi.ps, width=4.7cm,angle=0 }}
\caption{Monochromatic images obtained from the CDS raster.
Contours from the SOHO/MDI magnetograms are superimposed.
}
  \label{fig:cds_ima}
% Fig.~\ref{fig:cds_ima}
\end{figure}


\begin{figure}[!htbp]
\centerline{\epsfig{file=trace_195_1539_FeXIX_int.ps, width=6.0cm,angle=90 }}
\caption{ TRACE 195 \AA\ difference (negative) image
 with contours of Fe XIX intensity.
}
  \label{fig:trace_fe_xix_int}
% Fig.~\ref{fig:trace_fe_xix_int}
\end{figure}

\begin{figure}[!htbp]
%\centerline{\epsfig{file=s26058r00_SiXII_pos_mdi.ps, width=8.0cm,angle=0}}
%\centerline{\epsfig{file=s26058r00_SiXII_pos.ps, width=8.0cm,angle=0}}
\centerline{\epsfig{file=s26058r00_sixii_areas.ps, width=8.0cm,angle=0}}
%\centerline{\epsfig{file=s26058r00_FeXIX_int_SiXII_pos.ps, width=8.0cm,angle=0}}
\caption{\sixii\  velocity map in the flare region,
 with the areas selected for further  analysis.
Areas A,B,C correspond to regions of strong blue-shifts,
while area D of red-shift. Region LP corresponds to 
the area of peak \fexix\ intensity, while region L1 is where 
the central part of the flare loop is located. 
Region BG is a `background' reference region.}
  \label{fig:si_xii_pos}
% Fig.~\ref{fig:si_xii_pos}

\end{figure}


%\begin{figure}[!htbp]
%\centerline{\epsfig{file=s26058r00_FeXIX_pos_SiXII_pos.ps, width=7.0cm,angle=0}}
%\centerline{\epsfig{file=trace_195_154039_SiXII_pos.ps, width=8.0cm,angle=0}}
%\centerline{\epsfig{file=s26058r00_FeXIX_int_SiXII_pos.ps, width=8.0cm,angle=0}}
%\caption{ Fe~XIX image with superimposed the
%  contours of the Si~XII blue- and red-shifts. }
%  \label{fig:over_SiXII_pos}
%% Fig.~\ref{fig:over_SiXII_pos}
%\end{figure}


\subsection{Overview of the CDS results}


\begin{figure}[!htbp]
%\centerline{\epsfig{file=s26058r00_oiv_win.ps, width=5.cm , angle=90 }}
\centerline{\epsfig{file=s26058r00_mgx_win.ps, width=5.5cm , angle=90 }}
\caption{Spectra of three different regions, A,B,BG. 
Note that in region A the profiles of the strongest lines are 
nearly saturated. The O~IV line has been used for density measurements
at transition-region temperatures.}
  \label{fig:oiv_win}
\end{figure}
% Fig.~\ref{fig:oiv_win}

\begin{figure}[!htbp]
\centerline{\epsfig{file=s26058r00_fe_xix_win.ps, width=5.5cm, angle=90 }}
\caption{Spectra of the region L1 (peak flare),
and of the background BG (multiplied by ten), showing the
\fexix\ and the previously unidentified Fe~XII line.
Outside of the flaring region, all the intensity is due to Fe~XII.}
  \label{fig:fe_xix_win}
\end{figure}
% Fig.~\ref{fig:fe_xix_win}

\begin{figure}[!htbp]
%\centerline{\epsfig{file=s26058r00_he_i_prof.ps, width=5.5cm , angle=90 }}
\centerline{\epsfig{file=s26058r00_si_xii_prof.ps, width=5.cm , angle=90 }}
\centerline{\epsfig{file=s26058r00_fe_xix_prof.ps, width=5.cm , angle=90 }}
\caption{Line profiles in regions A,B,D showing the evident
 blue-shifts in the coronal (Si~XII) and flare (Fe~XIX) lines in
 regions A,B. }
  \label{fig:prof}
\end{figure}
% Fig.~\ref{fig:prof}




Fig.~\ref{fig:cds_ima} shows monochromatic images obtained from the
CDS raster, in lines emitted over a broad temperature range.
The ribbon structure is so bright in He~I and also at 
transition region temperatures (e.g. O~V) that the brightest 
lines saturated the detector in some positions 
(region A, defined below). 
The hot emission from Fe~XIX is only present in the 
ribbon and high-lying loop  structures seen in the TRACE 195 \AA\ band 
(see Fig.~\ref{fig:trace_fe_xix_int}).

%This suggests that the brightest emission seen in the 
%TRACE 195 \AA\ band is dominated by Fe~XXIV emission.

The velocity maps show a consistent pattern.
Large velocities, mainly upflows, are only visible in 
lines formed above 1~MK, and in the  Fe~XIX flare line.
Fig.~\ref{fig:si_xii_pos} (top) shows as an example a velocity
map in the flare area obtained from a Si~XII line,
and the regions selected for further study. 
Line fitting was performed on the 
 averaged spectra of these selected regions.
Figs.~\ref{fig:oiv_win},\ref{fig:fe_xix_win},\ref{fig:prof} 
show some line profiles in a few selected regions.
Table~\ref{tab:areas} presents some results of the line 
fitting, in particular  velocities,  intensities and 
line widths.

%
Regions A,B were  associated with 
the brightest emission in the chromospheric-TR lines,
and with strong upflows in the Fe~XIX flare line.
Region A was observed by CDS during 15:33:20--15:34:10 UT  
(see Fig.~\ref{fig:trace_seq} for the correspondence with TRACE),
 i.e. in the impulsive phase of the flare
 (Fig.~\ref{fig:goes_plot}).
%
Region B was observed during 
15:35:00--15:35:50 UT, i.e. at the time of the peak
X-ray  emission (Fig.~\ref{fig:goes_plot}). 

As observed in other cases (\citealt{del_zanna_etal_prague}), upflows are also 
seen in the lower-temperature Si~XII and Mg~X lines. 
Our findings are contrary to those of 
\cite{brosius_phillips:04}, that  
discouraged the use of  Mg~X lines because of 
blends with O~IV emission. 

In terms of line widths, aside from a few notable exceptions,
the  full-width at half maximum ($FWHM$) values are close to 
the value of the instrumental width (0.5~\AA\ in post-recovery 
spectra). The exceptions are in regions A,B,D and mostly in 
the coronal lines. Interestingly, the Fe~XIX line has a large
width in all of the regions, suggestive of large turbulent 
motions.
As also noted by \cite{brosius_phillips:04}, the 
observed blue-shifts are not superimposed on a stationary 
component, but appear as 
shifts of the entire line profiles
 in Mg~X, Si~XII and Fe~XIX  (see Fig.\ref{fig:prof}). 


We also find upflows  (although smaller) in the TR lines
in region B.
Interestingly, in region A, during the impulsive phase, He~I, O~IV and O~V
 lines show small downflows. However, these results should 
be considered with some caution because the detectors were nearly 
saturated (completely saturated in the O~V case).


The other regions were close to the flare site.
Region L1 shows near-zero line-of-sight velocities 
in all lines.
The region LP corresponds to the area of peak X-ray  emission,
as judged from the TRACE 195~\AA\ images and the 
Fe~XIX emission, observed by CDS 7 minutes later, around 15:42 UT.
It is interesting to notice that, on the opposite sides of the 
peak emission, flows of opposite directions are observed 
(region C, upflow; region D, downflow) in all the lines, emitted 
from TR to flare temperatures.
%

Region BG was chosen as a background reference 
region, not interested by the flare.
The lines 
show near-zero line-of-sight velocities.  
Note that the intensity of the Fe~XIX line is 
an upper limit (the emission being dominated by the  Fe~XII).
We have compared the line intensities of the background 
region with other observations of the quiet Sun, and found that,
for the transition region lines, the values are very close 
to those of the average quiet Sun. 



\begin{table*}[!htbp]
\caption[]{Results from the averaged spectra of the various 
regions displayed in Fig.~\ref{fig:si_xii_pos}.
For each of the selected spectral lines, we display
the averaged velocities  $v$ (in km/s; negative corresponds to blue-shift),
the calibrated line intensities $I$ (erg cm$^{-2}$ s$^{-1}$
sr$^{-1}$), and the full-width at half maximum  $FWHM$ (\AA).
O IV(a) indicates the 553.4~\AA\ line, while 
O IV(b) indicates the 625.8~\AA\ line, used to obtain the 
electron densities $N_{\rm e}$ (cm$^{-3}$).
Large blue-shifts are mostly observed in regions A,B,C.
Note, however, that some of the lines are close to saturation
in region A, and values are uncertain (they are indicated in 
parentheses).
 }
\begin{center}
%\footnotesize
%\tiny
%\scriptsize

\begin{tabular}{rrrrrrrr}
\hline\noalign{\smallskip}

\hline\noalign{\smallskip}
Region       & A  &   B  & C   & D   & L1 & LP  & BG  \\
\hline\noalign{\smallskip}
%
 He I $v$  &  13  & -27  & -30 & -17   & -17   & -36   &  -22   \\
      $I$  & 2393 & 770  & 112 & 377   & 751   & 1293   &  16   \\
   $FWHM$  & 0.61 & 0.53 & 0.51& 0.56  & 0.51   & 0.51   &  0.50    \\
\\
% 553.4:
 O IV(a) $v$ & (33) & -21  & -24 & 13    &  0   &  -20  &  0    \\
      $I$  & (9818) & 598  & 80  & 237   & 252   & 686   & 33    \\
%   $FWHM$  & (0.65) & 0.64 & 0.65& 0.65  & 0.65   & 0.65   &  0.56    \\
%625.853 :
\\
 O IV(b) $I$ & 2333 & 111  &  -  &  -    &  -  & -   &   -   \\

$N_{\rm e}$ (O~IV)  & 2 10$^{11}$ & 0.9 10$^{11}$ & - & - & -  & -  & - \\
\\
 O V  $v$  & (23)   & -25  & -21 &  0    &  -12   & -28   &  -4      \\
      $I$  & (33226) & 5038 & 721 & 2490 & 2840   & 6782   & 387    \\
   $FWHM$  & (0.70) & 0.50 & 0.50& 0.55  & 0.50   & 0.50   &  0.50   \\
\\
Mg X  $v$  & (14)   & -62  & -51 & 29    & -17   &  -37  &  -5    \\
      $I$  & (5910) & 1630 & 656 & 1205  & 1781  & 17093   & 118    \\
   $FWHM$  & (0.80) & 0.59 & 0.53& 0.58  & 0.58  &  0.52  &   0.52 \\
\\
 Si XII $v$ & -64  & -84  & -54  &  17   &   -6  & -40   & -10      \\
      $I$  & 2756 & 1847 & 839   &  1378 & 2818  & 16748 & 63     \\
   $FWHM$  &  0.59& 0.55 & 0.50  & 0.55  & 0.51  & 0.50   & 0.50    \\
\\
 Fe XIX $v$ & -141 & -140 & -56  & 22    & -13  & -26    & -     \\  
       $I$  & 294  & 272  & 694  & 1271  & 2721 &  7544  & $\le$ 0.5     \\
   $FWHM$   & 0.68 & 0.65 & 0.56 & 0.59  & 0.57 &  0.55  &  -   \\

%  &  & & & & & & & \\
 
%

\hline\noalign{\smallskip}
\end{tabular}
\end{center}
\normalsize
\label{tab:areas}
\end{table*}
% Table~\ref{tab:areas}

%
The O~IV lines (cf. Fig.~\ref{fig:oiv_win}) 
are an useful density diagnostic at 
transition region temperatures, and in the locations 
of strong brightenings. 
For both the upflow regions A and B we obtain  
 averaged line-of sight electron 
densities of $\simeq$10$^{11}$ cm$^{-3}$.
Interestingly,  the two O~IV intensities increase respectively  by 
factors of $\simeq$300, 20,  while the density 
increases by an order of magnitude compared to 
quiet Sun values (cf. \citealt{delzanna_jgr99a}).
This means that the filling factor of the two regions 
could be different. This is an added complexity that 
a detailed flare interpretation should take into account.
%Accurate measurements of filling factor require, however,
%much higher spatial resolution than the CDS one.







\section{ Magnetic topology and H$\alpha$ ribbons}

In Berlicki \etal 2004  we present the magnetic topology of the active
region. The magnetic field shows that this active region was highly
sheared. The trigger of the flare was the emergence of a locally very
twisted magnetic flux (bipole). The linear force-free-field
extrapolation of the magnetic field lines obtained from THEMIS
magnetogram provides an explanation of the   fast propagation
 of the brightening along the ribbon 
(of the order of few  min) from the emerging dipole towards the leading
spot.  This propagation can be explained by the reconnection of the
growing emerging field lines with the higher and higher overlying
magnetic field (Figure \ref{themis}).  We mentioned that RHESSI emission was 
also shifted and confirmed successive reconnections and favouring the fast
brightening of the ribbon. 
The points A and B were reached by CDS at the time of the new bursts of
the flare (15:33-15:35 UT) and correspond to an impulsive phase of the
flare.

For the analysis of the H$\alpha$ Dopplershifts we used the observations of 
VTT/MSDP obtained at 15:30-15:36 UT. We selected areas (Fig.~\ref{fig:vtt})
corresponding to the regions observed by SOHO/CDS 
 (see Fig.~\ref{fig:vtt_over}). 
Regions 6,7,8 in the H$\alpha$ spectra 
correspond to region A in the CDS spectra; 4,5 to region B;
and 3 to region L1. These regions were not observed at the same time
than CDS because of the opposite direction of the scanning of these two
instruments. Thus it is not possible to compare directly the velocities.

\begin{figure}[!htbp]
\centering
\includegraphics[width=9cm]{vtt_points_landscape_1530_times.ps}
\caption{VTT/MSDP image of AR 0162 taken between 15:30 and 15:36 UT with dots
 which mark the areas where the H$\alpha$ line profiles were obtained.
 The timing and scanning direction are also indicated.}
 \label{fig:vtt}
% Fig.~\ref{fig:vtt}
\end{figure}


\begin{figure}[!htbp]
%\centerline{\epsfig{file=cds1518_heI_vtt1530_dots.ps, width=6.5cm,angle=0}}
\centerline{\epsfig{file=cds1518_vel_si_vtt1530_dots.ps, width=6.5cm,angle=0}}
\caption{{ 
SOHO/CDS velocity map in the  Si XII 520.7~{\AA} line obtained 
between 15:18 and 15:43 UT. 
The darker structures represent upflows.
The dots (1-8) mark the 
areas where the H$\alpha$ line profiles were obtained
The contours represent the H$\alpha$ flare ribbons
as observed by VTT during 15:30-15:36 UT.}}
 \label{fig:vtt_over}
% Fig.~\ref{fig:vtt_over}
\end{figure}
 
The profiles in areas 1 and 2 are observed nearly at the onset of the
flare. They are very flat or asymmetric and cannot be 
fitted with satisfactory quality because the profile cover a rather
small wavelength range ($\pm0.6${\AA}). Nevertheless, the shape of the 
profiles is consistent with strong downflows.
The other regions  6,7,8 are observed during the gradual phase and
exhibit similar shape as the profiles analysed in the previous 
paper (Berlicki \etal 2005) by using non-LTE radiative transfer codes.


\begin{figure}[!htbp]
\centerline{\epsfig{file=Figure_new_d.ps, width=6.5cm,angle=0}}
\caption{ Extrapolated field lines over the active region explaining the
fast propagation  of the brightening of the flare ribbon by the rise
of the emerging flux, in the plane is represented the photospheric
longitudinal magnetic field observed  with THEMIS in the Na D1 line}
\label{extrapol}
\end{figure}


\begin{figure}[!htbp]
\centerline{\epsfig{file=vel_temp_A_B.ps, width=8.5cm , angle=0 }}
\centerline{\epsfig{file=vel_temp_C_D_LP, width=8.5cm , angle=0 }}
\caption{Flows observed in  flare kernels over a large temperature
  range for  different CDS lines: strong
 blue-shifts in regions A and  B for hot lines, weak blueshifts in
 regions C,and LP, slight redshifts in region D. The error bar is +/-
 10 km/s}
  \label{fig:vel}
\end{figure}
% Fig.~\ref{fig:vel}



\section{Discussion and conclusions}
\label{sec:disc}

During a coordinated observing campaign, a compact and 
short-duration M1.0 flare was observed from the
ground and in space using spectrographs. 


The  SOHO/CDS and the
VTT/MSDP instruments do allow us to make 
detailed studies of e.g. 
the velocities in the ribbons over a wide range of 
temperatures (10$^4$ K to 8 $\cdot$ 10$^6$ K).
However, due to the scanning method of the spectrographs, 
we were only not able to obtain spectra from the ribbons
during the same phase of the flare.
Nontheless we are able to make some accurate measurements
of velocities over a range of temperatures, for which we
have proposed an explanation. We concentrate this paper
mainly on
 SOHO/CDS flow analysis. 

CDS has measured flows in this flare in spectral lines formed
over a range of temperatures (log T=5.4-6.9)
with an accuracy $\simeq$10 km/s. 
%As seen in our observations of many other small flares, 
We find upflows in `hot' lines that are 
concentrated in small spatial areas, at the footpoints 
of coronal/flare loops.
Stronger upflows are in the Fe~XIX line,
indicating that  most of the action 
takes place in the hotter lines. 


The large broadenings of the Fe~XIX line
are in fact indicative of the presence of turbulent motions,
in addition to the overall flows.
The  co-spatiality between the  CDS  Fe~XIX and the 
TRACE 195~\AA\ emissions suggests that 
the bulk of the  TRACE 195~\AA\ emission 
at the flare site is due to Fe~XXIV.


We selected the areas in CDS which exhibit strong flows.
The areas (A,B) that were observed simultaneously 
by CDS   during the peak 
X-ray emission presented blueshifts.
The blueshifts are of the order of
27 km/s in He I, 
60 -- 88 km/s in Mg~X, Si~XII, and 140 km/s in Fe XIX in 
region B. Region A shows slight downflows in the cooler lines. 

These regions are relatively far from the flare onset site
(location of a small emerging dipole) but they became bright in 2 or 3
minutes after the onset of the flare and this rapid propagation could
be explained by a chain of reaction of successive reconnections in the
high corona as the emerging flux field lines reconnected with higher
and higher preexisting magnetic field.

We suggest that the upflows observed in hot lines in A and B 
correspond to the so
called ``explosive evaporation'' and the slight downflow observed in
cooler lines is due to the overpressure of the chromosphere
and even the transition region can be disturbed if that region is thick enough.
An important diagnostic tool available with spectroscopic instruments 
is the possibility
of measuring electron densities over a range of temperatures.
We were able to use the  CDS
O~IV diagnostic lines to obtain electron densities of 
the order of 10$^{11}$ cm$^{-3}$ for the regions A,B.
These are somewhat lower that the values of 10$^{12}$ cm$^{-3}$
derived from the H$\alpha$ data but relatively high compared to the
quiet sun electron density (1 or 2 orders more).
The exponential increase of the velocity versus the temperature
should give constrains to the modelling of the atmosphere above the
ribbons.

The eastern parts of the ribbons (areas C, D, LP in the CDS image)
are closest to the onset
site of the flare but are reached ten minutes later than the onset of
the flare.
Areas C and and LP exhibited upflows between -30 to -55 km/s according
to the temperature of formation of lines with a slight increase versus
temperature.
Such upflows  could correspond to the so called ``gentle evaporation''
(Fisher et al 1985, Schmieder et al 1987). When
the flux associated with non-thermal electrons is low or the
non-thermal electrons are not accelerated, then only a weak
chromospheric evaporation takes place. Antiochos \& Sturrock (1978)
suggested that the 
gentle chromospheric evaporation may occur after the primary energy 
release when the non-thermal 
electron flux has stopped. This evaporation could be driven 
by the large conductive 
heat flux from a high-temperature flare plasma contained 
in magnetic tubes above the 
chromosphere. 
The small downflows observed in point D are ambiguous and difficult to
be explained in this context. Their low values are at the limit of
the error bars.
 

The H$\alpha$ ribbons are not observed simultaneously with  CDS even
their observations times are overlapping.
The scanning of both instruments were done in opposite
directions thus the kernels are not reached at the same time. Therefore it is
difficult to have a direct comparison.
The asymmetry of H$\alpha$ line profiles in points 1 and 2  
suggests  some redshifts of the chromospheric plasma. These profiles  were observed at 15:31 UT. This time 
corresponds to the increase of the GOES soft X-ray flux and this
redshift could correspond to the flow that is expected for cool plasma
during the impulsive phase.
The H$\alpha$ line profiles in points 5, 6, 7,8  are similar to those
analysed by Berlicki et al 2004 during a later phase of this flare.
The Doppler-shifts
 derived from the profiles of H$\alpha$ using a non-LTE
radiative transfer code with a flare model correspond to small upflows
(2 to 10 km/s) 
(\citealt{berlicki_etal:05}) and could correspond to the ``gentle
evaporation'' observed during the gradual phase of flare in the ribbons. 


Other authors (e.g. \citealt{brosius_phillips:04}) 
have adopted a different observing approach, i.e. to fix the slit 
position and rely on the imaging instruments to study the 
morphology of an event. The slit was apparently fortuitously positioned
right where the flare took place but they have no indication of the 2D
behaviour of the flare.

Our observing campaign and analysis emphasises the importance of
combining chromospheric and coronal observations in order to
understand the dynamics of a solar flare. It is also essential to use
spectroscopic observations to obtain an unambiguous determination of
the plasma properties. With this set of observations, we were
able to get the exponential variation of the velocity of flaring plasma with
temperature during chromospheric evaporation (the ''gentle and the 
explosive'' evaporations). The main
problem with scanning instruments like VTT/MSDP and CDS is to be in the right
place at the right time! Neither the scanning approach or the
sit-and-stare approach is entirely satisfactory.
We look to future projects, such as SOLAR-B, which
will enable us to study active regions and flares in much more detail
through all layers of the solar atmosphere.
\begin{figure}
\centerline{\epsfig{file=schem1.ps, width=9.0cm}}
\caption{ Sketch of the precipitation of the electrons from the site of
         reconnection towards the low atmosphere and the expected
         flows according the temperature of formation of the observed lines.}
\label{sketch}
\end{figure}

\begin{acknowledgements}

GDZ and HEM acknowledge support from  PPARC. 

This research was partially supported by the European Commission
through the RTN programme ESMN (European Solar Magnetism
Network, contract HPRN-CT-2002-00313).  AB and BS are
members of ESMN.
SOHO is a project of international collaboration between ESA and NASA.
These observations were performed during a MEDOC
campaign (JOP 157). The magnetic field extrapolations were obtained
from the code FROMAGE (FRench Online MAGnetic Extrapolations)
We acknowledge the use of the SURF, TRACE, SOHO on-line databases.


\end{acknowledgements}



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