Chromospheric UV oscillations depend on altitude and local magnetic field Noah S. Heller and E.J. Zita, The Evergreen State College, Olympia, WA Philip Judge, HAO, NCAR, Boulder, CO ABSTRACT

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. Introduction: UV continuum emissions: Are brighter where gas is hotter, that is at higher altitudes Intensity is greater in strong magnetic regions (network) Intensity oscillations track photospheric waves traveling up through chromosphere Image courtesy of WHO at T h

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. Background: Photospheric oscillations Supergranules excited by convection at He + layer:  x~ __ Mm,  t ~ 1 day, f << 2 mHz Granules excited by convection at H + layer:  x~ __ Mm,  t ~ 10 minutes, f ~ 1.5 mHz p-modes at photosphere:  x~ __ Mm,  t ~ 5 minutes, f ~ 3 mHz Image courtesy of WHO at

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. SUMER measures chromospheric UV emissions Image courtesy of Max-Planck-Institut für Aeronomie Text

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. UV oscillations vary in space and time Sumer slit… Greyscale intensity plot for a given wavelegnth Timeseries at a give position x i and wavelength

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. Strong field regions correlate with bright regions MDI nw bright

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. Fourier transform  frequency spectra I f Integrated power Power spectrum shows frequency peaks for each x i and  Integrate power spectrum over all positions, for each  Sum power over each of three frequency ranges: LF (0-2 mHz), MF (2-5 mHz), HF (5-10) mHz

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. 2-5 mHz oscillation power increases with wavelength do this for LF, MF, HF do it for NW and INW note trend Network + Internetwork

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. Oscillation power depends on local field strength note trend: power decreases further from photosphere  p-modes are source of UV oscillations ratios: LF stronger in NW (granulation) HF stronger in INW (…)

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. Magnetic environment can transform waves Parallel acoustic waves can propagate freely to field lines Oblique acoustic waves can excite magnetic waves and lose energy

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. DISCUSSION

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. Nonlinearities: p-modes  shocks  heating p-modes  transformed to magnetic waves  less power to UV oscillations

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. SUMMARY: chromospheric UV oscillations reveal: Significance: p-modes heat chromosphere and weaken as they rise Magnetic field strength and topology affects mode propagation and transformation

Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug. Next steps: Compare to MDI data on local magnetic fields: check correspondence between intense UV and strong “network” fields investigate magnetic topology: expect p-modes to propagate freely in regions with weak or vertical fields expect p-modes to transform to MHD waves in regions with strong and oblique fields, as evident in 2D MHD code data (Johnson, Petty-Powell, Zita)

References and Acknowledgements B.C. Low, High Altitude Observatory (HAO), NCAR, Astrophysical Journal 330, 992 E.J. Zita, 2002, The Evergreen State College, Dick Canfield et al., 1999, Montana St. Univ., This work is supported by NASA under the Sun-Earth Connection Guest Investigator Program, NRA 00--OSS--01 SEC Thanks to Dr. B.C.Low (HAO) for suggesting this sheared field for analysis, and to Dr. Tom Bogdan (HAO and NSF) for discussions and solution strategies. Heller, Zita (TESC) and Judge (HAO), SHINE meeting, Banff CA, 2002 Aug.