A Solar Wind Source Tracking Concept for Inner
Heliosphere Constellations of Spacecraft
J.G. Luhmann1, Yan Li1, C.N. Arge2, Todd Hoeksema3 and Xuepu Zhao3
(1) Space Sciences Laboratory, University of California Berkeley, (2) CIRES, University of Colorado and NOAASEC, (3) Stanford University
Abstract.
During the next decade, a number of spacecraft carrying in-situ particles and fields instruments, including the
twin STEREO spacecraft, ACE, WIND, and possibly Triana, will be monitoring the solar wind in the inner heliosphere. At the
same time, several suitably instrumented planetary missions, including Nozomi, Mars Express, and Messenger will be in either
their cruise or orbital phases which expose them at times to interplanetary conditions and/or regions affected by the solar wind
interaction. In addition to the mutual support role for the individual missions that can be gained from this coincidence, this set
provides an opportunity for evaluating the challenges and tools for a future targeted heliospheric constellation mission. In the
past few years the capability of estimating the solar sources of the local solar wind has improved, in part due to the ability to
monitor the full-disk magnetic field of the Sun on an almost continuous basis. We illustrate a concept for a model and web-based
display that routinely updates the estimated sources of the solar wind arriving at inner heliospheric spacecraft.
disk data are also used for this purpose, and moreover
provide the possibility of updates at 96 minute cadence
- or better during limited campaign periods. Figures
1a-b show some of the standard displays from the
aforementioned websites. The programs to generate
these run automatically on standard platforms.
Looking ahead to STEREO and the Heliospheric
Sentinels, this capability can be exploited toward
identification of likely sites of solar wind sources for
each spacecraft location.
DISPLAY TOOLS FOR EVALUATING
SOLAR WIND SOURCES
Several web-based space weather tools for
corona and solar wind monitoring have been
developed over the last few years that take advantage
of regular full-disk magnetograph observations and the
Potential Field Source Surface Model (e.g. Altschuler
et al., 1969; Wang and Sheeley, 1992). One of these, at
SSL-UCB, keeps track of the coronal hole and coronal
magnetic field configuration, including changes in the
open and closed regions between full-disk
observations (currently available at the URL
http://sprg.ssl.berkeley.edu/mf_evol ). The other is part
of a Rapid Prototyping Center activity at NOAA-SEC
where it is used to make predictions of solar wind
speeds and magnetic field polarities at the Earth (URL
http://solar.sec.noaa.gov/ws/index.html ).
While the Potential Field Source Surface Model
has well-understood limitations, it provides an
excellent approximation to the observed coronal holes
(e.g. Levine, 1982), and projected interplanetary
magnetic field polarities {3}. Such mappings of the
inferred coronal hole flows to the source surface, and
then into the heliosphere, were first demonstrated in
the era of SkyLab {7,4}. In these mappings, the
coronal potential field model open field lines are
regarded as solar wind streamlines in the corona.
Kinematic extrapolations from the source surface,
typically assumed at ~2.5 solar radii, provide the
connection to heliospheric sites where in-situ plasma
and field measurements are made by spacecraft.
These applications are possible because of the
typically daily construction of “updated” photospheric
magnetic field synoptic maps that occurs at Wilcox
Solar Observatory, and at the NOAA-SEC for other
magnetic observatories including Mt. Wilson, Kitt
Peak, and the GONG network. The SOHO-MDI full-
CP679, Solar Wind Ten: Proceedings of the Tenth International Solar Wind Conference,
edited by M. Velli, R. Bruno, and F. Malara
© 2003 American Institute of Physics 0-7354-0148-9/03/$20.00
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Although the MHD models are based on more
physically rigorous treatments (e.g. Usmanov, 2000),
the good agreement on the solar wind source locations
obtained with the much less computationally
demanding potential field source surface model
approach establishes its credibility as a first-order
source mapping tool. Moreover, the latter is much
more amenable to the higher spatial resolution coronal
field modeling required during active periods of the
solar cycle.
FIGURE
1A.
Sample
page
from
the
The displays shown in Figures 2 through 7
illustrate the types of visualizations possible with only
modest extensions of the framework developed for the
above-mentioned websites. The advantage of these
displays is that they are all 3-dimensional. They can be
shown as rotating Sun movies, to give the viewer a
sense of the longitudinal variation of the solar wind
sources at a particular time, or with new applications
like Java 3D, can be manipulated to any orientation by
the website viewer using their mouse.
website
http://sprg.ssl.berkeley.edu/mf_evol that tracks changes
in the coronal magnetic fields based on magnetograph
observations and the potential field source surface model.
The general philosophy represented by these
displays is the use of available synoptic data from
magnetographs and other full-disk imagers, together
with the Potential Field Source Surface model, to infer
the solar connections of interplanetary features. Setting
up the mechanisms now, using solar observations of
the type we expect to have available to us in 2006, will
prepare us to exploit the observations from STEREO
and its partners in the heliosphere, including
Messenger at Mercury, Nozomi at Mars, and
especially the near-Earth spacecraft ACE and WIND.
Description of Figures
FIGURE 1B.
Sample page from the website
http://solar.sec.noaa.gov/ws/index.html that predicts
solar wind speeds and interplanetary field polarities
based on magnetograph observations and the potential
field source surface model.
The figures in this brief report show various
combinations of 3D information from observations
and the potential field source surface model of the
coronal hole sources of solar wind. The example of
Carrington Rotation 1932 (22 Jan-17 Feb, 1998) is
used for illustration. Mt. Wilson Observatory synoptic
maps provide both the photospheric magnetic fields
shown on the globe of the photosphere, as well as the
basis for the coronal field model. They were chosen
because of their particularly well-characterized polar
field corrections (e.g. see Arge and Pizzo, 2000). The
other synoptic maps shown are from the EIT
experiment on SOHO. These are available through the
NRL LASCO EIT website. The 195 Angstrom maps
are used because they often exhibit dark areas similar
to the coronal hole footprints obtained with the
potential field source surface model.
Arge and Pizzo {2} and Fry et al. {8} recently
applied the Wang and Sheeley {11} method of
estimating the solar wind velocity from the divergence
of coronal open flux tubes, and then used a modified
kinematic mapping corrected for the effects of stream
interactions to obtain quantitative predictions of solar
wind speed and interplanetary field polarity. Another
application to Ulysses data analysis by Neugebauer et
al. {6} compared the results of similar mappings with
those from a global MHD model. They found that for
the moderate solar activity interval studied, the
inferred sources of the measured solar wind obtained
with both models were very similar.
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FIGURE 5. Like Figure 2, but including the last
closed field lines of the coronal helmet streamer belt
for context. This display emphasizes the location of
the mapped points relative to the closed/open field line
boundaries.
FIGURE 2. Illustration of the solar wind source
tracking tool concept described in this report.
Hypothetical spacecraft locations are mapped back to
the source surface, and then to their coronal hole
footpoints along interplanetary and coronal magnetic
field lines. The coronal hole pattern on the inner
boundary of the potential field source surface model is
included, together with some other open coronal field
lines for context. Only the coronal part of the mapping
is shown here.
FIGURE 6. Illustration of a subsequent mapping of
magnetic field lines from the coronal model source
surface out to 1 AU using a modified kinematic
approach, More sophisticated techniques, especially
MHD models, can be substituted here for more
physical realism.
FIGURE 3. Like Figure 2, but including a synoptic
map of the photospheric magnetic field from the Mt.
Wilson Observatory website at UCLA for context, and
eliminating all but the mapped coronal field lines that
connect the spacecraft to the Sun. The relationship of
the connection points to active regions is the aim of
this display.
The fine dotted lines are coronal magnetic field
lines from the spherical source surface (Rss=2.5 solar
radii) potential field model. The green dotted line
represents the trace of the heliospheric neutral sheet on
the source surface, while red-dotted circles indicate
either the source surface equator or Earth's orbit at 1
AU. The remaining colored dotted lines are those that
map to near-term inner heliospheric spacecraft at
hypothetical locations in their orbits. These mappings
can be used to infer the arrival of wind from a
particular feature such as a polar coronal hole
extension, and the context of the spacecraft with
respect to the stream structure and magnetic sector
boundaries. Our extrapolation from the spacecraft
FIGURE 4. Like Figure 3, but including a synoptic
map of 195 Angstrom EUV flux from the SOHO EIT
website at NRL for context. The EIT maps show the
coronal holes as dark features, for comparison with the
calculated coronal holes.
170
these visualizations. The solar wind extrapolations also
allow 3D rendering of the prevailing heliospheric
current sheet configuration with respect to the mapped
field lines, akin to those of Riley et al. {9, also this
volume}.
Altogether, this source tracking toolkit can be
regularly updated in a space-weather forecasting
fashion or used for retrospective analyses. With
multipoint (e.g. SOHO and STEREO) mission images
on the horizon, the ability to illustrate and examine the
inferred 3D solar wind structure will be a key part of
tying the in-situ measurements into our "picture" of the
inner heliosphere.
FIGURE 7. Heliospheric current sheet inferred
from the potential field source surface coronal model
and modified kinematic interplanetary mapping. The 1
AU circle and spiral line segments indicate the Earth's
orbit and mapped interplanetary field lines intersecting
the 3 dimensional opaque structure used to render the
current sheet.
ACKNOWLEDGMENTS
The visualizations described here could not have been
done without open access to solar data provided by
Mt. Wilson Observatory (Roger Ulrich and coworkers
at UCLA), and the SOHO EIT investigators (Nathan
Rich at NRL, especially). This work was supported in
part by the Space Weather Program at NSF as part of
award 164766 to Boston University, and by the Solar
MURI project at UC Berkeley, sponsored by the Air
Force Office of Scientific Research.
location back to the source surface uses a modified
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solar wind flow with an initially heliomagnetic
latitude-dependent speed. The results from more
rigorous approaches can of course be substituted in
6. Neugebauer, M., et al., Spatial structure of the solar wind
and comparisons with solar data and models, J. Geophys.
Res., 103, 14,587, (1998).
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