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SCIENTISTS IMAGE THE THREE-DIMENSIONAL SURFACE OF THE SUN

LAUREL, Maryland, June 17, 2003 -- Solar physicists from Lockheed
Martin [NYSE: LMT], the National Center for Atmospheric Research, The
Institute of Theoretical Astrophysics of the University of Oslo, and
the Institute for Solar Physics of the Royal Swedish Academy of
Sciences have analyzed the highest resolution images ever taken near
the solar limb (or visible edge of the sun), and found a surprising
variety of structure. Their results, which are being reported today
at the American Astronomical Society's Solar Physics Division meeting
in Laurel, MD, address long-standing theories on how the brightness
of the Sun varies over the course of its magnetic cycle. Such changes
may influence the Earth's climate on long timescales. "Until recently
we thought of the solar photosphere as the relatively flat and
featureless 'surface' of the Sun, punctuated only by an occasional
sunspot," said Dr. Tom Berger, principal investigator on the study,
and solar physicist at the Lockheed Martin Solar and Astrophysics
Lab (LMSAL) at the company's Advanced Technology Center in Palo Alto,
Calif. "Now, using the newly commissioned Swedish one-meter Solar
Telescope (SST) on the island of La Palma, Spain, we have, for the
first time, imaged the three-dimensional structure of the convective
'granules' that cover the photosphere.

The solar surface consists mostly of an irregular cellular pattern
caused by temperature variations. The cells, called granules, are
evidence of convection that transports heat to the surface in the
same manner as boiling water on a stovetop or thermal plumes rising
over hot fields to form thunderstorms. Each granule on the sun is
about the size of Texas. At the 75 km resolution of the SST, sunspots
and smaller dark "pores" are seen to be sunken into the surrounding
granulation. This so-called "Wilson depression" has been inferred
from lower resolution observations of large sunspots but never
directly resolved until now. 

Most importantly from a terrestrial climate perspective, the images
show clearly that the granulation in regions of smaller magnetic
fields outside of sunspots is both raised up and has brighter walls
than the granulation in non-magnetic regions. Bright structures near
the limb of the Sun have been seen for centuries in lower resolution
images and are called "faculae" (Latin for "little
torches"). Faculae
are significant because scientists believe that their brightness is
responsible for the increased solar irradiance (on the order of 0.1
to 0.15%) that occurs during periods of maximum solar magnetic
activity. 

At solar maximum, the Sun is covered by the greatest amount of dark
sunspots in its 11-year cycle. It would be expected that the solar
irradiance reaching Earth during that time might decrease. But
beginning in the 1980s, satellite radiometer instruments, such as the
Active Cavity Radiometer Irradiance Monitor instrument (ACRIM I) on
the Solar Maximum Mission (SMM) spacecraft, revealed that while
sunspots cause a decrease in the solar irradiance on time scales of
days to weeks, the long-term solar irradiance actually increases as
sunspot (magnetic) activity increases. 

The source of this "extra" irradiance has been traced to the bright
faculae near the limb of the Sun. Based on earlier low resolution
images of faculae, scientists have created models that attribute most
of the brightness of faculae to small magnetic "flux tubes" or "
micropores". These models suggest that micropores act like tiny holes
in the surface of the photosphere. When looking at disk center, we
see only the relatively cool "floors" of the flux tubes. When seen at
an angle near the limb, the models predict that the "hot walls" of
the magnetic holes shine brightly compared to the relatively cooler
surrounding granules. 

The SST images may help resolve discrepancies between the "hot-wall"
flux tube model and observations of facular brightness near the solar
limb. Most of the bright structures seen are between 150 and 400 km
tall and are typically elongated towards the limb. Simultaneous
measurements of the magnetic field establish that the bright faculae
are exactly aligned with the magnetic fields. However the faculae in
these images appear more like bright walls of granulation that have
somehow been "piled up" by the presence of magnetic fields than like
micropores seen at an angle. 

Theoretical models of solar convection developed by Dr. Neal Hurlburt
of LMSAL support this "raised wall" picture. "The model that has been
used to explain the brightness of faculae," Dr. Hurlburt reflects, "
usually assumed that the rest of the solar atmosphere was an innocent
bystander. However it is known that magnetic fields are swept aside
as hot gas rises and spreads across the solar surface and confines
the field to regions of down-flows. Many groups have modeled the
dynamics of such magnetoconvection, but we have never gotten around
to detailed comparison with sources of irradiance variations. We
frequently find that the gas in our models is denser or hotter at the
edges of the magnetic fields -- which might result in brightenings
very much like what these images show." 

As the ultimate source of all energy input to the Earth,
understanding solar irradiance and its variation with magnetic
activity on the Sun is an important factor in understanding climate
variation on Earth. "Raising the hot material above the photosphere
enhances facular emission at low angles to the solar surface"
according to Prof. John Lawrence of California State University
Northridge. "Low angles cover the greater part of the solar 'sky' as
seen from the perspective of a facula, so this discovery impacts our
estimate of the contribution of faculae to solar brightness changes.
With this new discovery, we can hope to incorporate the effects of
magnetoconvection into solar irradiance models to better predict
variations in solar output."

Preliminary analyses of the some of the images are in a paper by Dr.
Bruce Lites of NCAR, Prof. Göran Scharmer of the Royal Swedish
Academy of Sciences, and Drs. Alan Title and Tom Berger of Lockheed
Martin Solar and Astrophysics Lab that has been submitted for
peer-review to the journal Solar Physics.

Lockheed Martin Space Systems Company is one of the major operating
units of Lockheed Martin Corporation. Space Systems designs,
develops, tests, manufactures, and operates a variety of advanced
technology systems for military, civil and commercial customers.
Chief products include a full-range of space launch systems,
including heavy-lift capability, ground systems, remote sensing and
communications satellites for commercial and government customers,
advanced space observatories and interplanetary spacecraft, fleet
ballistic missiles and missile defense systems. 

Headquartered in Bethesda, Md., Lockheed Martin is a global
enterprise principally engaged in the research, design, development,
manufacture, and integration of advanced-technology systems,
products, and services. The Corporation's core businesses are systems
integration, space, aeronautics, and technology services. Employing
about 125,000 people worldwide, Lockheed Martin had 2002 sales
surpassing $26.6 billion. 

NOTE TO EDITORS: Low- and high-resolution JPEG image files of the
discovery are available at the following URL:

http://www.lmsal.com/Press/SPD2003.html

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Media Contact: Buddy Nelson, (510) 797-0349;
e-mail, buddynelson{at}mac.com

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