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of SOHO `Waves, Oscillations Small­Scale Transient
in Solar Atmosphere:
A Joint SOHO TRACE',
Palma Mallorca, Balearic Islands (Spain),
29 September
-- October 2003 SP­547, January 2004)
STUDY TRANSITION REGION AND CORONAL DOPPLER SHIFTS SOLAR CORONAL HOLE
Popescu
1,2 Doyle
1 Armagh Observatory, College Armagh 9DG, Ireland
2 Astronomical Institute Romanian Academy, RO­75212 Bucharest Romania
ABSTRACT
present
a study spatial resolution raster
taken on­disk with SoHO/SUMER spectrograph
in
a polar Coronal (CH) region.
shifts and widths emitting
### 703.87 706.02 results confirm
plasma outflows
In particular, correlation
between intensity Doppler velocity
in
constitute lowest precise indication
wind streams seen originating from network
boundaries transition region.
words: radiation; Doppler line­shifts;
coronal holes; chromospheric network; fast solar wind.
1. INTRODUCTION
identified
as source
a velocity
wind stream
by Krieger (1973), who compared
X­ray data taken during sounding rocket flight
November 1970 wind velocity measured
outside terrestrial atmosphere. Further improvements
construction spectrographs allowed
determination coronal plasma Doppler velocities.
taken with
a sounding rocket August 1973
to
determination outflow velocity from
#
-1 303
## 368
lines (Cushman
& Rense, 1976).
Recently, observations collected SoHO spec­
trometers have greatly helped achieving more precise
results about properties plasma from di#erent layers
solar atmosphere. high spatial, tempo­
especially spectral resolution, SUMER (Solar
Ultraviolet Measurements Emitted Radiation) grating
spectrograph
on SoHO (Wilhelm
et 1995, Wilhelm
1997, Lemaire
et 1997) currently
suitable instrument plasma velocity diagnostics
ferred from
a range
of EUV lines.
Using on­disk observations SUMER, signatures
of
outflows CHs deduced Warren
et
al. (1997),
Dammasch (1999), Hassler
et
al. (1999),
&
Judge (1999), (1999), Stucki
et
al. (2000a), Stucki
et
al. (2000b), Wilhelm (2000),
et
al. (2003)
Popescu Doyle (2003).
mentioned authors agreed about
a blue­shift
plasma between
3 and
-1
in originating
above
#
(5 -6)â
5 lower temperatures, evidence
outflow wind CHs was found
& Judge (1999) Popescu
& Doyle (2003).
spatial resolution instrumentation increased,
quest
to more precisely what small­
features responsible development
solar wind streams from CHs. purpose,
needs
to correlate plasma down motions
structures inside CHs, which
from transition region downward. di#­
of study both spectral spatial
resolution data needs enough order
cisely determine small­scale velocity patterns
chromospheric features.
Hassler
et (1999) reported correlations between
plasma outflow deduced from coronal
chromospheric network
as
Si
## 1533 line. Stucki
et (2000b) confirmed these
results, comparing line­of­sight (LOS)
locity
N
## intensity.
Here, provide evidence outflows plasma
chromospheric network boundaries, direct
comparison Doppler velocity with
intensity same low study constitute
precise indication
of wind streams orig­
inating from network boundaries such
height following explain how
were processed interpreted and give
a sum­
of results.
2. DATA
analysed solar on­disk taken
in north­
Pole region March 1999 Wilhelm)
â arcsec detector SUMER.
cause
of was clipped, final image

dimension
is (72
â arcsec
, with
a spatial resolution
#
1 arcsec spectral resolution 22.4 må.
raster taken during 01h
-- 04h 07m
having integration time
of
Standard SUMER calibration procedures applied,
described Popescu Doyle (2003).
collected
st order) spectrum covered approxi­
mative
å spectral region centered around 709
emission lines this spectral interval were identified
from SUMERAtlas Curdt (2001). studied
shifts and widths 703.87
å
8
â
4 coronal
## 706.02 å(#
6
approximative formation temperature ionization
equilibrium Mazzotta (1998).
were taken on­disk, the
O
### strong
enough additional spatial binning needed,
relatively weak intensity coronal line
allow
a similarly spatial resolution analysis. There­
706
å had
to perform
â
4)
arcsec
2 binning
on spatial
x and solar
y
coordinates. final
of study calculate intensities
Doppler velocities (line sight, LOS veloci­
of lines considered. With purpose,
determine: position spectrum center
in
(solar solar
y coordinate, calculating LOS
locity, well amplitude width
maximum (FWHM), calculating intensity.
pixel position was found applying
a Gaussian
fit
(with XCFIT program from SoHO analysis
software) binned spectrum solar
y pixels, good signal­to­noise ratio
entire raster. converted pixel taking
### 703.87 reference line.
When fitting central wavelength position
pixel along solar
y
a linear
wavelength with distance along
### Mg lines, which
rected.
Trying find whether there
is
a correlation between
Doppler velocity intensity
O
### line,
made dimensional di#erent pixel positions
solar which discuss below.
order
to obtain absolute wavelength calibration,
position
as determined
at assumed
to
a zero shift. That made necessary additional
rection about
-1
å line.
also corrected measured FWHM contribu­
the instrumental profile, using provided
ware. Considering that Gaussian profile
a good approxi­
mation optically lines, applied fitting proce­
XCFIT BLOCK program from SoHO
software package). determined amplitude,
sition width, calculated Doppler velocity
intensity
O 703
å 706
å
RESULTS
finally obtained Doppler velocity intensity maps
of considered lines. The spatial resolution
images (1â1) arcsec (4â4) arcsec
2
coronal
In coronal line, seen
a reduction
intensity, surrounded the brighter (QS),
very correlated with negative Doppler velocities
(outflows) about km
s
.
In line, bright chromospheric network
is
clearly distinguishable
in intensity with coro­
showing
a quiet Sun pattern. spatial reso­
lution low
is just
at limit detec­
arcsec), intensity Doppler velocity
maps show fine characteristics which di#cult
correlated. This
is
in
to correla­
between the Doppler velocity intensity
we made dimensional di#erent
positions solar
Looking one­dimensional plots, motion
plasma from di#erent features
in very easily
recognizable.
In Figure
1 examples solar
x positions
of raster line
in
plotting intensity Doppler velocity along
y direction. selected positions solar
=
8
arcsec
2 corresponding solar
x
32 the
O
###
(1
â arcsec
panels) and solar
x
= plot, correspond­
solar
= and
O
### (right
panels). have chosen positions because
bright coronal point
as
show second selection there explosive
event. Examples
of network boundaries
found selection chosen solar
intensity plotted
a dashed Doppler
velocity
as
a continuous line, with corresponding
#
2 km
s error. We determined error from
fitting procedure
to
be more
2
s
; some
instances (depending mostly signal­to­noise
of spectra), errors were even
-1
have divided values intensity
categories. Plasma motion presents di#erent trends
of types bright features. This
is
a statistics
of plasma velocities
in relation
to values
of intensity reveal story,
a careful
examination each individual increase intensity
is
needed.
have selected
a examples those
phenomena follows Figure
1):
. coronal bright point: featureFigure Mg
##
O 703
å intensity (dotted line) Doppler velocity (solid with error bars)
selected regions. The plots represent two sections along solar axis Mg figure),
each followed three corresponding sections identified features are: coronal
(b
chromospheric network boundaries; and
f) QS network boundaries explosive event. spatial resolution
is
1 arcsec arcsec. chromospheric network boundaries: features
. chromospheric network boundaries: features
. explosive event: feature
coronal bright
is increase
in
## intensity, which corresponds
of
intensity. The chromospheric network
as
values intensity (that correspond
coronal Di#erentiating between bright
work inside outside simple, above
plots have coronal
## which
boundaries clearly appear
as increases inten­
that and
O
### spatially aligned,
as
units from Mg solar
y correspond with
units from plot.
Establishing which
of values the
O inten­
represents EUV explosive event
lenging, was done looking individual spectra.
Large fitting errors indicate
a highly dynamic environ­
ment. When visualizing spectrum, points
which fitting error high, indeed
enhanced wings
or
a double Gaussian appearance,
where single Gaussian
is evidently good
more.
Figure plot each spectra
a few solar
y
tions selected line,
at the location
of
selected features The increased line widths
position
x feature indicate presence
explosive event, which clearly despite
length scan
intensity values bright point and explo­
much higher many values
from network boundaries, meaning that intensity
alone not distinguish among those
types features.
simple visual inspection one­dimensional plots,
bearing
in the classification scheme detailed above,
reveals each four types increases
intensity, corresponding Doppler velocity has
dency display
a certain behaviour.
BP
-- feature Figure
1 surrounded
shifts around km
s middle,
velocity decreases toward zero. very interesting
observed
in lines. similar
result found Wilhelm (2000),
reported
or outward directed velocities
and Madjarska (2003), who
served more precisely dominated
shifts
s
)
in
a small area
it
is
shifted. Madjarska
et (2003) cadence
temporal series acquired with SUMER,
in
S
å
(originating
at intermediate height between
corresponding
â
5 Moreover,
authors compared their data magne­
tograms, saw the blue­shifted region was located
between magnetic polarities.
Chromospheric network boundaries
-- features
-- blue­shifted velocities varying between
s (median value
-1 Their average
dimension about arcsec
# km.
Inside one see
is
a
decrease intensity,
it corresponds increases
velocity, which, generally, becomes red­shifted.
would mean that dark inter­network plasma
moves downward, with average speed
5 km
s
.
average dimension cells around pixels
# 4000 Sun.
In features plasma behaviour
is
completely changed, with
O
### intensity increases
network being red­shifted
s
.
In explosive event feature
-- solar plasma under­
movements. seen Figure
3 solar
x spectrum shows
a double structure.
region, single Gaussian
is appropriate,
it obviously gives very errors. When fitted
spectra from explosive event
a double Gaussian,
found outflow velocities --120
s
.
In Figure line shifts toward right) indi­
redshifts (downward motion)
in QS
boundaries: features toward
left) indicate blue­shifts (upward motion)
explosive event CH network boundaries: features
(e).
have observed dimension inter­network
is generally smaller that bright CH
boundaries. regards velocity structures,
observe smaller than intensity
they have tendency asymmetric. Similar
characteristics reported Gontikakis
et (2003)
in
of structures
in
## 1533
C
##
å
å lines). They suggest
larger width network boundaries
to opening magnetic lines from
vective cells boundaries, when they reach higher levels
atmosphere, while smaller velocity structure
asymmetry could
to that di#erent struc­
show di#erent Doppler shifts even
comparable intensities, also asymmetric heat­
induce di#erent flows
in di#erent locations.
4. CONCLUSIONS
results agreement blue­shifts
observed corona,
as with
red­shifts reported the regions. case
of outflows correspond
bright, highly structured network boundaries, while
coronal upward velocity seen
area CH.
outflows
s were previously reported.
Dammasch
et
al. (1999) reports outflow speeds
regions
#
9
s
. blue­shift 3--6
-1
is
reported Hassler
et
al. (1999) sameFigure Spectra positions solar
y axis selected solar given
spatial pixels. blue­ and red­shifted wings each increase intensity easy distinguish. The shifts
toward right) indicate redshifts (downward motion)
in network boundaries
-- features
-- and toward indicate blue­shifts (upward motion)
in the explosive event and network
boundaries
-- features increased widths, together with
a double Gaussian shape solar
x
signature explosive event.
blue­shifts large samples lines were found
Peter Judge (1999) and Stucki (2000).
blue­shift deduced
by Wilhelm (2000)
is
of
#
3
s both The
equatorial analysed
by (2003)
is
blue­shifted with average velocity
of
#
s
.
data,
## 706 velocity
s (average over velocity values
from CH). blue­shifted material alone
average velocity
s
.
From characteristics
of radiation emitted
### define following: network
boundaries, plasma
is blue­shifted average veloc­
-1 network outside
responding LOS velocity
is red­shifted with
5
s
;
explosive events dislocate plasma outflow velocities
as
as --120
s
; X­ray corresponds
a small
portion
of zero LOS velocities,
in middle struc­
surrounded positive (upward) values about
5­
-1
reported Popescu &Doyle 2003, work provided
of plasma motion
at such atmospheric
height (close TR,
#
8
4
a spatial resolution high enough
to distinguish the
scale correspondence between network patterns
plasma up­flows.
Previous works showed strong evidence favour
solar wind outflow observed
in CHs, none
of
found correlation between network inten­
Doppler velocity lines.
that
is coarse spatial scale
in which
characteristics determined. correla­
reported between plasma outflow chro­
mospheric network
of Doppler velocities from
coronal intensities from lower tempera­
tures.
if Peter Judge (1999) analysed large sample
whole data were taken while
SoHO rolling,
so small­scale spatial structures
along largely smeared 100 arcsec
arcsec. This allowed them determine varia­
Doppler shift over
a large spatial scale,
spatial resolution su#cient finding
relation between line width intensity.
Hassler
et
al. (1999) clearly observed the outflow
in ####,
in other anal­
ysed:
C
### and
##, therefore correlated Doppler
velocity
of with network boundaries
inferred intensities
of
Si
##. data
binned over arcsec
. Similarly, Stucki
(2000b) compared velocities intensities
lower heights found same correlation
between those quantities. Moreover, they show
in temperature range
2
4
K
to
5
is
a di#erence between CH Their
were binned pixels.
(2003) correlated intensitiesLOS velocities with solar magnetograms, finding
larger blue­shifts mainly regions
concentrations unipolar magnetic field.
results Popescu Doyle, 2003) constitute
precise indication wind streams
inating network boundaries
at such
height derived conclusion
direct correlation between Doppler veloc­
the intensity same
ACKNOWLEDGMENTS
work was supported PPARC
PPA/G/S/1999/00055 Programme
search Irish Third Level Institutions Grid­enabled
Computational Physics Natural Phenomena (Cosmo­
Grid). The SUMER project financially supported
DLR, CNES, NASA, PRODEX. Research
at Armagh
Observatory grant­aided
by Ireland Dept.
of
Culture, Leisure.
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