Документ взят из кэша поисковой машины. Адрес оригинального документа : http://star.arm.ac.uk/preprints/457.ps Дата изменения: Mon Sep 19 13:31:09 2005 Дата индексирования: Mon Oct 1 21:30:19 2012 Кодировка: Поисковые слова: coronal hole

SEARCHING FOR THE ORIGINS OF THE FAST SOLAR WIND
M. D. POPESCU 1;2 and J. G. DOYLE 1
1 Armagh Observatory
College Hill, Armagh BT61 9DG, N. Ireland
2 Astronomical Institute of the Romanian Academy
RO-75212 Bucharest 28, Romania
Abstract. Here we present the lowest evidence, observed in the solar atmosphere, of the
fast solar wind streams. They originate from coronal holes (CH) network boundaries, as
seen in the low transition region (TR) line, O iii 703.87  A (Te  8  10 4 K). Higher in
the solar corona, the plasma out ow is seen in the Mg ix 706.02  A line (Te  10 6 K),
as an increased blue-shift inside the CH region. An interesting change in behaviour is
observed at the quiet Sun (QS)/CH boundaries, where plasma from the network changes
its velocity sign, and, following the closed magnetic structures, falls back to the Sun. This
is also the site where signature of magnetic reconnection between the open CH lines and
the closed QS loops is seen, in the form of an increased number of bi-directional jets,
which represent evidence for the slow solar wind origins.
1. Introduction
Today there is general agreement that the fast solar wind originates mainly
from magnetically open regions in the coronal holes (CHs) (Krieger et al.,
1973). In order to nd more precisely what are the small-scale features
responsible for the development and rise of the fast solar wind streams, one
needs to correlate the plasma motions with the ne structures inside the
CHs, which are only seen from the transition region (TR) downward.
Hassler et al. (1999) reported correlations between the plasma out ow
as deduced from the coronal Ne viii 770  A line (originating at 63  10 4 K)
and the chromospheric network as seen in the Si ii 1533  A line (1:310 4 K).
The results we present here indicate that we indeed see the fast solar
wind streams originating from the magnetic network boundaries, at a tem-
perature as low as  8  10 4 K (that means, not far away from the base
of the TR). This constitutes the lowest temperature (and height) at which
those out ows have ever been observed. Moreover, we also see an increased
number of bi-directional jets at the quiet Sun (QS)/CH boundary, which
searching2.tex; 19/12/2003; 15:57; p.1

2 M. D. POPESCU AND J. G. DOYLE
Figure 1. The raster location as seen on the EIT Fe xii 195  A image (left), together
with the raster intensity in the SUMER Mg ix 706  A line (right). The white contour
represents the QS/CH boundary.
represent evidence for the slow solar wind origins, as very recently observed
for rst time by Madjarska et al. (2004).
2. Data
We analysed a solar on-disk raster taken in a northern polar CH region on
17 March 1999 with detector B from the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) grating spectrograph on SoHO. The nal
image has a dimension of (108  292) arcsec 2 , with a spatial resolution
of  1 arcsec and a spectral resolution of 22.4 m A. Each spectrum has
an integration time of 150 s. We studied a low TR line O iii 703.87  A
( 8  10 4 K) and a coronal line, Mg ix 706.02  A( 10 6 K).
The nal aim of our study was to calculate the intensities and the
Doppler velocities (LOS velocities) of both lines considered. More details
searching2.tex; 19/12/2003; 15:57; p.2

SEARCHING FOR THE ORIGINS OF THE FAST SOLAR WIND 3
Figure 2. Top left: three example spectra, representing (a) a bi-directional jet, (b) a CH
network boundary blue-shift and (c) a QS network boundary red-shift. Top right: intensity
(dotted line) and Doppler velocity (continuous line) for the Mg ix line at solar x = 10.
The vertical lines mark the QS/CH boundary. Bottom: intensity and Doppler velocity
for the O iii line, where the selected examples are again marked.
on the calibration procedures applied, as well as on how we extracted the
information from the data, are given in Popescu & Doyle (2004).
The location of the raster on the Sun is given in Figure 1, as seen in
the EIT Fe xii 195  A image (left). To the right of the gure, we give the
Mg ix 706  A intensity, as derived from our data.
3. Results
In the coronal line, the CH is seen as a reduction in the intensity, sur-
rounded by the brighter QS, and very well correlated with negative Doppler
velocities (out ows) of about {4 km s 1 .
In order to see the correlation between the Doppler velocity and the
intensity for the O iii line, we made a one dimensional cut at solar x = 10
(see the vertical line in Figure 1, right).
searching2.tex; 19/12/2003; 15:57; p.3

4 M. D. POPESCU AND J. G. DOYLE
We selected as examples three type of phenomena, where the O iii
intensity has high values, but the plasma moves dierent (see features (a),
(b) and (c) on Figure 2, bottom). On the top left plot of Figure 2, we also
present the spectra of the selected features.
In the bi-directional jet (a), plasma undergoes rapid movements, both
up and down. The spectrum shows a double peak structure, and when tted
with a double Gaussian, the out ow velocities are about {100 km s 1 .
In the CH network boundaries (b), plasma is blue-shifted. In the chosen
example, the highest out ow is {15 km s 1 . This blue-shift represents the
plasma up-ward motion seen originating from the CH network boundaries,
representing evidence of the fast solar wind origins. In the CH, one can see
that every time there is an increase in the intensity, it corresponds to a
decrease in the velocity, which generally becomes blue-shifted.
In the QS network boundaries (c) the plasma behaviour is completely
changed. The spectrum of the feature (c) is red-shifted up to 13 km s 1 .
Also, here signature of magnetic reconnection between the open CH lines
and the closed QS loops is seen, in the form of an increased number of
bi-directional jets, which represent evidence for the slow solar wind origins.
4. Conclusions
Our results (see also Popescu & Doyle, 2004) constitute the rst precise
indication of fast wind streams seen originating from the CH network
boundaries at such a low height in the TR. We have derived this conclusion
from direct correlation between the O iii 703  A Doppler velocity and the
intensity of the same ion.
Acknowledgements
Research at Armagh Observatory is grant-aided by DCAL. This work was
supported in part by PPARC grant PPA/G/S/1999/00055 and by the
Programme for Research in Irish Third Level Institutions for Grid-enabled
Computational Physics of Natural Phenomena (CosmoGrid). The SUMER
project is nancially supported by DLR, CNES, NASA, and PRODEX.
MDP wishes to acknowledge nancial support partially given by the orga-
nizers for attending the school.
References
Krieger, A. S., Timothy, A. F., Roelof, E. C.:1973, Sol. Phys., 29, 505.
Hassler, D. M., Dammasch, I. E., Lemaire, P., et al.:1999, Science, 283, 810.
Madjarska, S. M., Doyle J. G., van Driel-Gesztelyi, L.: 2004, Astrophys. J. L. (submitted).
Popescu, M. D., Doyle J. G.: 2004, Astron. & Astrophys. (accepted).
searching2.tex; 19/12/2003; 15:57; p.4