1. Do magnetic waves heat the solar atmosphere? Dr. E.J. Zita (zita@evergreen.edu) The Evergreen State College American Geophysical Union SF, Dec.2003 This work supported by NASA's Sun-Earth Connection Guest Investigator Program, NRA 00-OSS-01 SEC

2. How does the temperature rise to millions of degrees in the corona from under 6000 K at the photosphere? We investigate the role of magnetohydrodynamic (MHD) waves in heating the solar atmosphere. Evergreen students and faculty work with HAO-NCAR on complementary theoretical calculations and analysis of observational and numerical data. Analysis of UV continuum from the SOHO/SUMER satellite reveals that pressure modes lose power with altitude. We show how the oscillation frequency spectrum varies with magnetic field strength. Energy flux analysis of 3D MHD data reveals that p-modes excite Alfvénic and magnetosonic waves. These modes can carry energy into the chromosphere, where field line reconnection may drive Joule heating. Analytic solutions of the wave equation in twisted and sheared magnetic field geometries may shed light on mode transformations. Taken together, these analyses may help solve the mystery of anomalous coronal heating. ABSTRACT

3. Magnetic dynamics may heat the solar atmosphere

4. 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

5. Methods: Simulations Nordlund et al. 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.

6. Results: Simulations Magnetic energy fluxes grow; MS and Alfvén out of phase. Pressure-mode energy flux decreases with height.

7. Conclusions: Simulations Parallel acoustic waves are channeled along field lines Oblique component of acoustic waves can excite magnetic waves Strong mode mixing near  =1 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

8. Methods: Observations SOHO telescope includes SUMER, which measures solar UV light UV oscillates in space (brightest in magnetic network regions) and in time (milliHertz frequencies characteristic of photospheric p-modes).

9. 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 T h

10. 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: magnetic shadowing?

11. Methods: Theory ObservationsSchematicMathematical model x Model sheared field region with a force-free magnetic field: B x =0, B y = B 0 sech(ax), B z = B 0 tanh(ax) Write the wave equation in sheared coordinates. Solve the wave equation for plasma displacements. Find wave characteristics in the sheared field region.

12. The wave equation describes how forces displace plasma.  = frequency,  = displacement, c s = sound speed, v A = Alfvén speed B = total magnetic field, B 0 = mean field, b 1 = magnetic oscillation Alfvén waves Magnetosonic waves B v B v k || B k ||  Waves transform as they move through a sheared magnetic field region. Results: Theory

13. Conclusions: Theory Magnetic energy travels along or across magnetic field lines. Twisting or shearing increases magnetic energy Shearing  mode transformation Twisting  tearing  release of magnetic energy. Critical frequencies: p 2 = 0 when  2 = and p 0 = 0 when  2 = Waves oscillate along x when k x = real (p 0 > 0 and p 2 > 0), for frequencies  2 >  2 2 and  2 >  0 2 (high frequencies). Waves damp along x when k x = imaginary: LF case: (p 0 0)  2 <  0 2 MF case: (p 0 > 0 and p 2 < 0)  0 2 <  2 <  2 2

14. 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  ~1 or v A ~ c s … … then Alfvénic, magnetosonic, and hybrid waves carry energy from the photosphere up into the chromosphere. Magnetic waves may heat the chromosphere by tearing, reconnection, and Joule heating. Magnetic dynamics are important on the Sun and affect weather and communications on Earth.

15. 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.

16. References Bogdan, T.J., Rosenthal, C.S., Carlsson, M, Hansteen, V., McMurray, A, Zita, E.J., Johnson, M.; Petty-Powell, S., McIntosh, S.W., Nordlund, Å., Stein, R.F., and Dorch, S.B.F. 2002, “Waves in magnetic flux concentrations: The critical role of mode mixing and interference,” Astron. Nachr. 323, 196 Bogdan, T.J., Carlsson, M, Hansteen, V., McMurray, A, Rosenthal, C.S., Johnson, M., Petty-Powell, S., Zita, E.J., Stein, R.F., McIntosh, S.W., Nordlund, Å. 2003, “Waves in the magnetized solar atmosphere II: waves from localized sources in magnetic flux concentrations”, ApJ 597 Canfield, R.C., Hudson, H.S., McKenzie, D.E. 1999, “Sigmoidal morphology and eruptive solar activity,” Geophysical Research Letters, 26, 627 * 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 * Zita, E.J. 2002, “Magnetic waves in sheared field regions” * papers: http://academic.evergreen.edu/z/zita/research.htm (zita@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.edu/canfield/ SOHO = Solar Heliospheric Observatory: http://sohowww.nascom.nasa.gov/ SUMER = Solar Ultraviolet Measurements of Emitted Radiation: http://www.linmpi.mpg.de/english/projekte/sumer/