Chromospheric UV oscillations depend on altitude and local magnetic field Noah S. Heller and E.J....
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Transcript of Chromospheric UV oscillations depend on altitude and local magnetic field Noah S. Heller and E.J....
Chromospheric UV oscillations depend on altitude and local magnetic fieldNoah S. Heller and E.J. Zita, The Evergreen State College, Olympia, WA 98505
Philip Judge, HAO, NCAR, Boulder, CO 80301
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
http://WHERE
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
http://WHERE
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
http://www.linmpi.mpg.de/english/projekte/sumer/pictures/SUM_SOHO.HTML
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 xi 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 xi 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.
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
Results Interpretation
mHz UV oscillationsweaken with altitude
strong field regions havemore LF oscillations
weak field regions havemore HF oscillations
photospheric p-modes lose energyto heating and mode transformationas they rise into chromosphere
granulation / supergranulation -secular variations
HF modes transform to MHDwaves where field is strong &oblique
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, http://www.hao.ucar.edu1988 Astrophysical Journal 330, 992
E.J. Zita, 2002, The Evergreen State College, http://192.211.16.13/individuals/zita/research.htm
Dick Canfield et al., 1999, Montana St. Univ., http://solar.physics.montana.edu/canfield/
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.