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FOR IMMEDIATE RELEASE

By compiling all the solar wind data gathered in the space
age, NASA scientists have concluded that even though the solar
magnetic field is constantly changing, it always returns to its
original shape and position.

“We now know that the Sun’s magnetic field has a memory
and returns to approximately the same configuration in each 11-
year solar cycle,” said Dr. Marcia Neugebauer, a Distinguished
Visiting Scientist at NASA’s Jet Propulsion Laboratory, Pasadena,
Calif. “Current theories imply that the field is generated by
random, churning motions within the Sun and should have no long-
term memory. Despite this expectation, the underlying magnetic
structure remains fixed at the same solar longitude.”

“It’s interesting that the solar magnetic field varies in
strength and direction, but not in longitude,” said Dr. Edward
Smith, senior research scientist at JPL.

The solar wind is composed of charged particles ejected from
the Sun that flow continuously through interplanetary space. The
solar wind carries part of the Sun’s magnetic field into space.
Before completing this research, scientists knew that features of
the solar wind reaching the Earth tended to repeat about every 27
days, said Neugebauer. The new information pinpoints the
repetition interval at 27 days and 43 minutes and shows that the
Sun has kept this steady rhythm, much like a metronome, for at
least 38 years.

This pattern escaped previous detection because it is a very
subtle statistical effect. There are many larger variations in
the solar wind that come and go, which largely mask the
underlying pattern. This repetitive behavior can’t be seen if
these data are examined for only a few months or years, but it
was revealed in this 38-year database.

“Why the Sun’s magnetic field behaves in this way is a
puzzle, but the answer must lie deep within the Sun,” Smith said.

“We’re trying to understand how magnetic fields are
generated in the Sun, the planets and the stars,” said
Neugebauer. “A better understanding of how the Sun generates its
magnetic field will help us better understand the solar wind and
space weather.”

Fluids conducting electricity under the Sun’s surface
generate the magnetic field, Neugebauer explained, and the
field’s apparent memory is most likely caused by a structure and
process occurring deeper inside the Sun than previously believed.
“There may be something asymmetric about the Sun’s interior,
perhaps a deep-seated lump of old magnetic field,” she said.

The findings, published in the February 1 issue of the
Journal of Geophysical Research, are based on all the solar wind
data collected from the dawn of space exploration through 1998,
both by Earth-orbiting satellites and interplanetary spacecraft.
This includes about 335,000 hours of solar wind speed data and
250,000 hours of magnetic field data. Co-authors of the article,
in addition to Neugebauer and Smith, are Drs. Alexander
Ruzmaikin, Joan Feynman and Arthur Vaughn, all of JPL.

Additional information is available at:

http://spacephysics.jpl.nasa.gov/pr/longitude.htm

This study was funded under the Supporting Research Program
of NASA’s Office of Space Science, Washington, D.C. JPL is a
NASA center managed by the California Institute of Technology,
Pasadena.

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