Do magnetic waves heat the solar atmosphere?

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Do magnetic waves heat the solar atmosphere?
Dr. E.J. Zita (zita_at_evergreen.edu) The Evergreen
State College Fri.30.May 2003 at Reed
College NW Section meeting, American Physical
Society (APS) This work supported by NASA's 
Sun-Earth Connection Guest Investigator Program,
NRA 00-OSS-01 SEC
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ABSTRACT
Evergreen students and faculty are investigating
the unexplained temperature rise from 5770 K at
the photosphere to millions of degrees in the
corona. We combine theoretical calculations with
analysis of observational and numerical data to
develop a more complete understanding of the role
of magnetohydrodynamic (MHD) waves in heating the
chromosphere. One group of students analyzed
energy flux in 3D MHD simulations of pressure
modes propagating obliquely into a strongly
magnetic regions. Another student analyzed UV
oscillation data from the SUMER satellite and
found that p-modes lose power with altitude, and
that the frequency spectrum of oscillations
depends on the local field strength. Zita is
performing complementary analytic calculations of
MHD wave propagation in sheared magnetic field
regions. Taken together, these investigations
suggest that in regions where magnetic pressure
is comparable to plasma pressure (b1), p-modes
may mix into Alfvénic and magnetosonic waves.
These MHD waves may carry energy to higher
altitudes, where it is deposited by Joule heating
and field line reconnection. Processes such as
these help solve the mystery of the anomalously
high coronal temperatures.
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Magnetic dynamics may heat the solar atmosphere
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Magnetic outbursts affect Earth

• Recent Solar Max
• More magnetic sunspots
• Strong, twisted B fields
• Magnetic tearing releases energy and radiation ?
• Cell phone disruption
• Bright, widespread aurorae
• Solar flares, prominences, and coronal mass
  ejections
• Global warming
• next solar max around 2011

CME movie
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Methods Simulations

• Nordlunds 3D MHD code models effects of surface
  acoustic waves near magnetic network regions.
• Students wrote programs to analyze supercomputer
  data from ITAP ?HAO.
• Calculated energy fluxes out of each region.

Pressure (p-)mode oscillates in left half of
network region at photosphere. Waves travel up
into chromosphere.
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Results Simulations
Magnetic energy fluxes grow MS and Alfvén out of
phase.
Pressure-mode energy flux decreases with height.
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Conclusions Simulations

• Parallel acoustic waves are channeled along field
  lines
• Oblique acoustic waves can excite magnetic waves
  and lose energy
• Strong mode mixing near b1 regions
• Magnetosonic and Alfvénic waves can carry energy
  to high altitudes

Matt Johnson, Sara Petty-Powell, E.J. Zita, 2001,
Energy Transport by MHD waves above the
photosphere
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Methods Observations
UV oscillates in space (brightest in magnetic
network regions) and in time (milliHertz
frequencies characteristic of photospheric
p-modes).
SOHO telescope includes SUMER, which measures
solar UV light
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Results Observations

• Fourier analyze UV oscillations in each
  wavelength
• Shorter-wavelength UV at higher altitudes, where
  chromosphere is hotter
• P-mode oscillations weaken with height

Noah S. Heller, E.J. Zita, 2002, Chromospheric UV
oscillations depend on altitude and local
magnetic field
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Conclusions Observations

• Magnetic waves carry energy to higher altitudes
  while p-modes weaken.
• Lower frequency oscillations stronger in magnetic
  regions.
• Higher frequency oscillations stronger in
  internetwork regions.

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Methods Theory

• Model sheared field region with a force-free
  magnetic field
• Bx0, By B0 sech(ax), Bz B0
  tanh(ax)
• Write the wave equation in sheared coordinates.
• Solve the wave equation for plasma
  displacements.
• Find wave characteristics in the sheared field
  region.

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The wave equation describes how forces displace
plasma.
Results Theory
w frequency, ? displacement, cs sound
speed, vA Alfvén speed B total magnetic
field, B0 mean field, b1 magnetic oscillation






Waves transform as they move through a sheared
magnetic field region.

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Conclusions Theory

• Magnetic energy travels along or across magnetic
  field lines.
• Twisting or shearing increases magnetic energy
• Shearing ? mode transformation
• Twisting ? tearing ? explosive release of
  magnetic energy.

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Summary

• Something carries energy from the solar surface
  to heat the solar atmosphere,
• but photospheric pressure modes weaken with
  altitude.
• P-modes transform into magnetohydrodynamic
  modes, especially where b1 or vA cs
• then Alfvénic and magnetosonic waves carry
  energy from the photosphere up into the
  chromosphere.
• Magnetic waves can heat the chromosphere by
  tearing, reconnection, and Joule heating.
• Magnetic dynamics are important on the Sun and
  affect weather and communications on Earth.

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Acknowledgements
Thanks to Tom Bogdan, Phil Judge, and the staff
at the High Altitude Observatory (HAO) at the
National Center for Atmospheric Research (NCAR)
for hosting our summer visits and teaching us to
analyze numerical and satellite data, and to BC
Low for suggesting the form of the sheared field.
Thanks to computing staff at Evergreen for
setting up Linux boxes with IDL in the Computer
Applications Lab.
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References

• Tom Bogdan, Johnson, Petty-Powell, Zita, et al.,
  2002, Waves in magnetic flux concentrations,
  Astronomische Nachrichten, 323 Issues 3/4 p.196
• Dick Canfield et al., IEEE Transactions on Plasma
  Physics, special issue on Space Plasmas, 2000
• Noah Heller, E.J. Zita, 2002, Chromospheric UV
  oscillations frequency spectra in network and
  internetwork regions
• Matt Johnson, Sara Petty-Powell, E.J. Zita, 2001,
  Energy Transport by MHD waves above the
  photosphere
• B.C. Low, 1988, Astrophysical Journal 330, 992
• E.J. Zita zita_at_evergreen.edu
  http//www.evergreen.edu/z/zita/research.htm
  (links to our papers and posters)
• The Evergreen State College http//www.evergreen
  .edu
• HAO High Altitude Observatory
  http//www.hao.ucar.edu
• NCAR National Center for Atmospheric Research
  http//www.ncar.ucar.edu/ncar/
• Montana St. Univ., http//solar.physics.montana.ed
  u/canfield/
• SOHO Solar Heliospheric Observatory
  http//sohowww.nascom.nasa.gov/
• SUMER Solar Ultraviolet Measurements of Emitted
  Radiation http//www.linmpi.mpg.de/english/projek
  te/sumer/