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%\newcommand{\sixii}{\specline{Si}{xii}{520.665}~\AA}
%\newcommand{\fexix}{\specline{Fe}{xix}{592.16}~\AA}

\newcommand{\sixii}{Si~XII {520.665}~\AA}
\newcommand{\fexix}{Fe~XIX {592.16}~\AA}


\newcommand{\SOHO}{\mbox{SOHO}}       % SOlar Heliospheric Observatory
\newcommand{\CDS}{\mbox{CDS}}         % Coronal Diagnostic Spectrometer
\newcommand{\NIS}{\mbox{NIS}}         % Normal Incidence Spectrometer
\newcommand{\GIS}{\mbox{GIS}}         % Grazing Incidence Spectrometer
\newcommand{\SUMER}{\mbox{SUMER}}     % Solar UV Measurement of Emitted Radiation
\newcommand{\SERTS}{\mbox{SERTS}}     %  Goddard Solar Extreme
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\begin{document}
\begin{article}
\begin{opening}         
\title{A multi-wavelength study of the compact M1 flare on October 22, 2002}

\author{G. \surname{Del Zanna}}  
\runningauthor{Del Zanna et al.}
\runningtitle{The compact M1 flare on October 22, 2002}
\institute{
MSSL, University College London Holmbury St. Mary Dorking UK RH5 6NT}
\author{A. \surname{Berlicki}}
\institute{Observatoire de Paris,  LESIA,
              F-92195 Meudon Principal Cedex, France}
\author{B. \surname{Schmieder}}
\institute{Observatoire de Paris,  LESIA,
              F-92195 Meudon Principal Cedex, France \\
   Institute of Theoretical Astrophysics, University of Oslo, 
   Blindern, N-0315 Oslo, Norway}

\author{H.E. \surname{Mason}}
\institute{Department of Applied Mathematics and Theoretical Physics,
University of Cambridge, Cambridge UK  CB3 0WA}

%   Astronomical Institute of the Wroc{\l}aw University, ul. Kopernika
%   11, 51-622 Wroc{\l}aw, Poland
%   Institute of Theoretical Astrophysics, University of Oslo, 
%   Blindern, N-0315 Oslo, Norway

\date{\today}

\begin{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
performed during a multi-wavelength campaign with TRACE and 
 ground-based instruments (VTT, THEMIS).
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 flare emission, 
with a pattern of progressively smaller flows at lower temperatures.
Large line-widths were observed, especially for
the Fe~XIX line, which indicate the existence of turbulent velocities. 
%
The strong upflows correspond to full shifts of the line profiles. 
%
These flows are observed at the initial phase of the flare, and 
correspond to   the ``explosive evaporation''. The regions of the
blueshifted  kernels, a few arc seconds away from the flare onset location,
could be explained by the chain reaction of successive magnetic reconnections
of growing emerging field line with  higher and higher overlying
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 magnetograms.
 \end{abstract}
\keywords{Sun: flare -- Techniques: spectroscopic -- Line: EUV}
%
\end{opening}           


\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. \opencite{doschek_etal:79}), the Solar Maximum
Mission's (SMM's) X-ray polychromator (XRP) 
 Bent Crystal Spectrometer
(BCS) (cf \opencite{antonucci_etal:82}) and the BCS on YOHKOH
(see, e.g., \opencite{bentley_etal:94}). Plasma velocities deduced from
Doppler-shift analyses were of the order of a few hundred 
$\mathrm {km\;s^{-1}}$. 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.
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, \inlinecite{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$^{\prime\prime}$). \inlinecite{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$^{\prime\prime}$) . 
\inlinecite{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.
Using CDS, it is possible
to locate the source of high temperature
blue-shifted emission seen during a solar flare. 
Such observations are however rare.
\inlinecite{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 \inlinecite{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. 
CDS and ground-based observations of 
an eruptive C2 flare were also reported by 
\inlinecite{teriaca_etal:03}. 
\inlinecite{brosius_phillips:04} also presented CDS observations
of a larger M6 flare. The position of the CDS slit was fixed,
thus sacrifying spatial coverage in favour of 
a high (10s) time resolution. 
Their observations were consistent with 
non-thermal particles 
transferring most of the energy into the chromosphere and 
creating  oppositely-directed flows. 

The blue-shifts seen in the emission from high
temperature flare plasma are in fact thought to be driven 
by non-thermal electrons accelerated during the primary energy release
(\opencite{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 (\opencite{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} (\opencite{fisher_etal:85c}) which seem 
to be responsible for red-shifts 
of the H$\alpha$ line profiles reported by many authors 
(\opencite{svestka:76}, \opencite{ichimoto_kurokawa:84}).

%\inlinecite{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=8.0cm , 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 
Figures~\ref{fig:trace_seq} and 6;
 middle: first three TRACE images (T1,T2,T3) in the initial 
phase of the flare, see Fig.~\ref{fig:trace_seq};
bottom: H$\alpha$ slit positions during two 
consecutive VTT/MSDP rasters, see  Fig.~\ref{fig:vtt}).
}
  \label{fig:goes_plot}
% Fig.~\ref{fig:goes_plot}
\end{figure*}



In this paper we present new CDS observations of the 
initial phase of the M1 flare of October 22, 2002.
%
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,
while in Sect.~3 we present the CDS  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
obtained from THEMIS magnetograms. 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 }}
\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}




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.
RHESSI did not observe the initial phase of the M1 flare.
The morphology and evolution of the M1 
flare  during the gradual phase 
(when RHESSI was observing) were presented 
in \inlinecite{berlicki_etal:04} (Paper I).


The active region NOAA 0162 was mainly bipolar, quite extended, and
relatively active.
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 \inlinecite{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 \inlinecite{berlicki_etal:05}
(Paper II).


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$512''). 
%
 Fig.~\ref{fig:trace_seq} shows a sequence of 
TRACE 195 {\AA} difference images in the central part of the 
TRACE FOV, where the flare took place.
The location and timings of the CDS slit are also indicated 
in  Fig.~\ref{fig:trace_seq}.
The first obvious signature  in the  TRACE 195 {\AA}
occurs  at 15:32:18 UT (T2, see Fig.~1), somewhat later than the 
 increase in  the GOES X-ray flux.
However, a small brightening already appears at the same 
location on the 15:31:31 UT TRACE image (T1, see Fig.~1).
%
By 15:33 UT (T3, see Fig.~1), the entire ribbon structures (located
on either side of the neutral line) brighten up in the TRACE 195~\AA\
image. The H$\alpha$ ribbons were already 
visible at 15:31 UT (see Paper I and Figure 9). 

After this intial phase, a  system of 
 high-lying and expanding loops starts to appear 
as a weak feature in the in TRACE 195~\AA\ images (See Figures~3 and 5).
%
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 195~\AA\ 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 with the long slit an 
 area of 4\arcmin\ square within a single `raster', from west to east. 
%
The CDS observing sequences were specifically designed 
to study compact flares, and 
included a range of spectral lines, in
particular the high-temperature  Fe~XIX 592.2~\AA.
%
CDS observed NOAA 0162 
with  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}{@{}lcccccc@{}}
%[511.455, 0.116225, 7.71135e-07]
\hline\noalign{\smallskip}
                     & Si XII & He I   & Ne IV  & Al XI & O IV & O IV \\
$\lambda_{st}$  & 520.665& 522.210&  542.07& 550.06& 553.34& 555.263 \\
$\lambda_1$ & 520.675 & 522.208   &    542.031  & 550.070 & 553.365  &     555.252    \\
$v_1$  & 5 &   -1 &  -21  &   5 &   13 &   -6 \\

$\lambda_2$  & 520.664 & 522.211 & 542.061 & 550.066 & 553.354 & 555.260 \\
$v_2$      & 0 &   0 &  -4 &   3  &  7 &  -1 \\

\noalign{\smallskip}

  & Ca X     & Ne VI   & Ne VI & Fe XII & Mg X & O V \\
$\lambda_{st}$  &  557.765& 558.594& 562.803& 592.60& 624.941& 629.732 \\
$\lambda_1$ &  557.758 &  558.590 & 562.791 &   592.590 &   624.936&629.735 \\
$v_1$  &    -3  &  -2 &   -6 &   -5 &   -2  &   1 \\
$\lambda_2$  & 557.769 & 558.622 & 562.812 & 592.597 & 624.932 & 629.747 \\
$v_2$      &   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.
The NIS data were processed using the standard 
corrections.
%
Line-fitting techniques have been used
to determine the moments of each of the spectral 
lines  by removing the  scattered light 
component.
%
In SOHO post-recovery spectra the 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.
Significant line broadening can still be 
measured.
%
The CDS radiometric calibration of \inlinecite{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}

In order to deduce velocities, it is necessary to 
have an accurate wavelength calibration for the CDS spectra.
CDS does not have an absolute wavelength calibration,
nor does it have any photospheric or chromospheric lines
(except He~I) which could be used as wavelength references.
This means that the CDS wavelength calibration has to
be carried out using the observed transition region and 
coronal lines for each set of observations. Changes in CDS
wavelength calibration have been observed (up to 0.1~\AA\ in NIS~2)
due to temperature changes in the CDS instrument (C.D.Pike,
priv. comm.), in particular when moving from disk to off limb 
and visa-versa.

For the wavelength calibration, it is important to have accurate 
'standard' rest wavelengths. We have adopted the values shown in Table~\ref{tab:list_lines}, 
mainly from the CHIANTI database (v 4.2) which in turn incorporates 
most values from NIST. Special care has been taken to assertain an accurate 
rest wavelength value for the Fe XIX 592.2~\AA\ line. Our calibration gives a 
value of 592.16~\AA, consistent with the careful flare studies of Skylab NRL 
spectroheliogram data by \inlinecite{widing:78}, but different from other 
work (e.g. \inlinecite{sandlin_etal:76} who reported a value of 592.24~\AA\ 
and \inlinecite{lawson_peacock:80} who's laboratory work implied a value of 
592.522~\AA). An extra complication in the line profile fitting for the 
Fe~XIX line is the presence of a line 
(\opencite{delzanna02_cospar}), recently identified with
an Fe~XII transition at 592.6~\AA (\opencite{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 of the observations. 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 to approximately 0.1~\AA, which is equivalent to 
about 10 km/s. There may be some other systematic uncertainties (for
example due to geometrical distortions within CDS) but these are difficult 
to quantify. We note that spectral resolution of CDS does not easily
allow a stationary and shifted component to be resolved simultaneously.
Hence, our results refer to the average displacement of each line 
profile. We note that Fe~XIX is only present during flares, and that
otherwise the Fe~XII line dominates.



\begin{figure}[!htbp]
\centerline{
\epsfig{file=s26058r00_HeI_int.ps, width=6.5cm,angle=0 }
%\epsfig{file=s26058r00_HeI_pos_mdi.ps, width=8.0cm,angle=0}
\epsfig{file=s26058r00_OV_int.ps, width=6.5cm,angle=0}}
%
\centerline{\epsfig{file=s26058r00_SiXII_int.ps, width=6.5cm,angle=0 }
\epsfig{file=s26058r00_FeXIX_int.ps, width=6.5cm,angle=0 }}
\caption{Monochromatic images (negative) 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. 
Note the bright emission, cospatial with the ribbon 
and the Fe XIX intensity. Also note the weaker 
 high-lying loops connecting the two ribbons.
}
  \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=7.0cm,angle=0}
\epsfig{file=s26058r00_SiXII_vel_HeI_int.ps, width=7.0cm,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.
The left image shows the \sixii\ map with contours of the 
He~I intensities.}
  \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.cm , angle=90}
\epsfig{file=s26058r00_fe_xix_win.ps, width=5.cm, angle=90 }}
\caption{Left: 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.
Right: 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:oiv_win}
\end{figure}
% Fig.~\ref{fig:oiv_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}
\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}  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: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.
Line velocities are also plotted in Fig.~\ref{fig:vel}.


%
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}). 
%
The blueshifts in region B show an exponential behaviour 
with increasing temperature of line formation.
They are 27 km/s in He I, 
60 -- 88 km/s in Mg~X, Si~XII, and 140 km/s in Fe XIX. 
Region A shows a similar behaviour but 
with a slight downflow in the cooler line (He~I). 
The downflows in O~IV and Mg~X are questionable 
because of detector saturation.
%
As observed in other cases (\opencite{del_zanna_etal_prague}), 
upflows are seen in both  Si~XII and Mg~X lines. 
We note that in contrast to our results,
 \inlinecite{brosius_phillips:04} 
found conflicting line shifts in these lines, 
thus discouraging the use of the Mg~X 625~\AA\ line 
because of blending with O~IV.

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 \inlinecite{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}). 


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 involved in 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 
592.6~\AA).
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$^{-3}$.



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



For the analysis of the H$\alpha$ Dopplershifts we used the observations of 
VTT/MSDP obtained at 15:30-15:36 UT and followed the methods
described in Paper II.
 We selected areas (Fig.~\ref{fig:vtt})
corresponding to the regions observed by SOHO/CDS.
These regions were not observed at the same time
as CDS because of the opposite direction of the scanning of these two
instruments. 
The profiles in areas 1 and 2 (east ribbon) 
are observed close to  the onset of the
flare. They are very flat or asymmetric and cannot be 
fitted  because they cover a rather
small wavelength range ($\pm0.6${\AA}). Nevertheless, the shape of the 
profiles is consistent with strong downflows (30-40 km/s).

Regions 6,7,8 in the west ribbon 
correspond to region A in the CDS spectra; 4,5 to region B;
and 3 to region L1. 
For those regions (3-8) we have obtained very similar values as those
obtained in the successive raster (Paper II), i.e.
smaller upflows in regions 4,5 (3 km/s) and higher upflows 
(7 km/s) in regions 6,7,8.


In Paper I we presented 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 the THEMIS
magnetogram (cf. Figure \ref{extrapol}) 
provides an explanation of the asymmetry of the east (1,2)
 and west (3-8) ribbons
and of the fast propagation of the brightening along the west ribbon 
(of the order of a few  min) from the emerging bipole 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.


\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=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=6cm , angle=0}
\epsfig{file=vel_temp_C_D_LP, width=6cm , 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. The measurements in parentheses are uncertain due to saturation
of the CDS detector.}
  \label{fig:vel}
\end{figure}
% Fig.~\ref{fig:vel}



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

\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}
% Fig.~\ref{sketch}

We have presented multi-wavelength 
observations of a compact M1 flare, mainly with CDS, TRACE,
VTT/MSDP and THEMIS.
In two earlier papers (Paper I and II)
we discussed the gradual phase.
In this paper,  we concentrate mainly on SOHO/CDS flow analysis
during the initial phase.
With CDS we could make some accurate measurements
of velocities over a range of temperatures
(10$^4$ K to 8 $\cdot$ 10$^6$ K), for which we
have proposed an explanation.


As seen in the X-rays (GOES), 
the flare started at 15:31 UT and reached peak emission in just
3 minutes.
Soon after the peak X-ray emission, long-lasting
chromospheric (H$\alpha$) ribbons form across the neutral line. 
Strong TRACE 195~\AA\ emission, cospatial with  
H$\alpha$ also forms as a  brightening along the ribbons. 
The simultaneous CDS 
observations show that the hot (8 MK) Fe~XIX 
emission is cospatial with TRACE 195~\AA, and we can therefore
propose that the bulk of the TRACE emission is due to
the Fe~XXIV 192.0~\AA (12 MK) flare line. 

It is a rare opportunity to observe with CDS 
 during the initial (peak) phase of a flare (15:33-15:36 UT).
%
We find upflows concentrated in small spatial areas 
in the ribbon (in regions A,B, 15:33-15:36 UT). 
%
The blueshifts in region B show an 
exponential increase with temperature of line formation
(27 km/s in He I, 
60 -- 88 km/s in Mg~X, Si~XII, and 140 km/s in Fe XIX).
Region A shows a similar pattern, 
with a possible downflow in the cooler lines (Figure~11).
%

We stress the fact that  the
observed upflows correspond to full shifts of the line profiles,
in regions where the coronal/flare line intensities are relatively weak.
Instruments (such as the above-mentioned BCS or FCS)
without the CDS spatial resolution would have not been able to 
observe these localised blue-shifts. 
%
The large line-widths in the 
 Fe~XIX line indicate the existence, in the upflow regions,
 of  strong turbulent
velocities at high temperatures, in addition to the overall flows. 


In both A,B regions the cooler transition region lines 
show concentrated brightenings with intensities increased 
by factors of $\simeq$300, 20.
%
We were able to use the  CDS
O~IV  line ratios to measure electron densities of 
the order of 10$^{11}$ cm$^{-3}$ for the regions A,B,
i.e. a factor of 10 higher than the quiet Sun values
(cf. \opencite{delzanna_jgr99a}).
These are somewhat lower that the values of 10$^{12}$ cm$^{-3}$
derived from the H$\alpha$ data (Paper II).
Such measurements of densities and velocities at different 
temperatures should  
give important constraints to the modelling of the atmosphere above the
ribbons.


Based on the above measurements, we interpret 
 the upflows observed in regions A and B 
(Fig.~\ref{fig:vel}) as due to chromospheric evaporation.
%
We suggest that the upflows observed in hot lines in A and B 
correspond to the so
called ``explosive evaporation'' and the small
 downflow observed in
He~I (area A) is due to the overpressure of the chromosphere.
%
These regions are relatively far from the flare onset site
(location of a small emerging bipole) but they became bright 
2-3 minutes after the onset of the flare. 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.
This is confirmed by a linear force-free
 analysis of the magnetic topology.

Non-thermal electrons are probably responsible for the 
high flows in the ribbons (Fig.~\ref{sketch}). 
%
A system of  high-lying and expanding loops in TRACE 195~\AA\ forms 
subsequently (Figure~\ref{fig:trace_fe_xix_int}). 
Cospatial  CDS observations in  Fe~XIX
suggest that these are high-temperature loops and could be 
associated with the reconnecting loops.

%In the initial phase of the flare, when CDS observed 
%the evaporation in areas A,B, thee hot loops are still 
%not present


The areas  C, D, LP in the ribbon 
 were observed by CDS ten minutes after the onset of
the flare, and do not exhibit strong flows.
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.
%
This evaporation could be driven 
by the large conductive 
heat flux from the  flare plasma contained in the  
high-temperature loops. 
%
The small downflows observed in point D are ambiguous and difficult to
be explained in this context.

The H$\alpha$ ribbons were not observed with 
 VTT/MSDP simultaneously with  CDS even
if their observations times were overlapping (cf. Fig.1).
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 the H$\alpha$ line profiles in points 1 and 2  
suggests  strong 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 Paper II 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, Paper II) and could correspond to the ``gentle
evaporation'' observed during the subsequent 
gradual phase of the flare. 



Our observing campaign and analysis emphasises the importance of
combining multi-wavelength  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, in particular flows.
Spatially-resolved observations are also fundamental to 
establish the locations of the flows, to relate them to the 
hot flare emission.


Other authors (e.g. \opencite{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.
Flows at the  slit position persisted on time-scales of minutes
after the onset of the flare. Upflows ($\simeq$60 km/s) 
in flare lines and downflows ($\simeq$40 km/s) in cooler
transition region lines were observed during the impulsive phase.
However, a fixed position of the CDS slit makes it impossible
to study the 2D behaviour of the flows within the flare.

%
% With this set of observations, we were
%able to get the exponential variation of the velocity of flaring plasma with
%temperature during chromospheric evaporation.
%
Neither the scanning approach or the
sit-and-stare approach is however 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.


\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.

\theendnotes

\bibliographystyle{klunamed}

%\bibliography{bib}
\bibliography{paper_sp}

\end{article}
\end{document}



Some of the results presented in this paper were included in a 
much longer paper that was previously submitted to A&A.
That paper was rejected, but without detailed reasons (the referee's
comments and the previous version can be provided if necessary).
The main criticism was the length of the paper and the lack of focus.

The present paper constitutes a newly-rewritten manuscript, with some new added material but mostly shorter and focused on original new spectroscopic observations during the initial phase a flare, and their interpretation. The general morphology of the active region and the subsequent gradual phase have already been discussed in two earlier papers published by A&A.

Best regards,
Giulio Del Zanna 
