Large amplitude transverse oscillations

1
Large amplitude transverse oscillations in a
multi-stranded EUV prominence
J. M. Harris C. Foullon, V. M. Nakariakov, E.
Verwichte
2
Prominence Oscillations

• Solar prominences float in the corona, held in
  place by the magnetic field
• They are cooler and denser than the coronal
  plasma, therefore appearing
• bright against a dark background in 304 Å
  (70,000 K),
• but dark against the bright corona in 195 Å
  (1.5 million K).
• Oscillations traditionally observed in Ha lines
  as winking filaments
• e.g. Dyson et al (1930), Brusek (1951), Ramsey
  Smith (1966).
• The line of sight velocity can be measured using
  the Doppler shift.

EUV images of a prominence on the NE limb
(SOHO/EIT)?
3
Prominence Oscillations

• Now also observed by EUV imagers
• e.g. Foullon et al (2004, 2010), Isobe
  Tripathi (2006), Pinter et al (2008).
• This enables long periods and the field of view
  velocity to be measured.
• Small amplitude oscillations velocity 2-3
  km/s.
• Large amplitude oscillations velocity gt 20km/s.
• can be triggered by nearby flares or EIT waves,
• observational analyses are scarce, see Tripathi
  et al (2009) for a review.
• Analysis of these oscillations enables us to
• measure plasma parameters (e.g. magnetic field)
  via coronal seismology,
• understand more about solar prominences (e.g.
  link to prominence eruptions),
• verify oscillation and damping theories.

4
Prominence Oscillation on 30th July 2005

• Observed using SOHO/EIT
• 195 Å, 12 min cadence,
• 304 Å, 6 hour cadence.
• Two successive trains of transverse oscillations,
• triggered by EIT waves from two flares in the
  same remote active region
• X1.3 class flare at 0617
• C8.9 class flare at 1639

5
EIT Waves

• 1st EIT wave seen over only 1 frame using running
  difference images (Type II radio burst, 1801
  km/s)
• 2nd EIT wave seen over 4 fast frames (no Type
  II reported)
• Intensity depletion is larger following the 1st
  EIT wave

1635 - 1635
EIT Wave 2
EIT Wave 1
6
Evolution of the Apparent Height
position over the limb when
rotation
Image using ratio of 304/195 Å with region of
interest indicated
Foullon Verwichte (2006)?
7
Evolution of Apparent Height
Region of interest moves with the rotation of the
prominence
8
Time - Distance Plots slit 1
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Time - Distance Plots slit 4
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Analysis of Time Series slit 1
P 122 23 min ? 131 94 min v 12 5 km/s
P 101 1 min ? 218 47 min v 32 10 km/s
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Analysis of Time Series slit 4
P 97 21 min ? 274 497 min v 5 4
km/s
P 94 2 min ? 119 19 min v 30 4
km/s
P 108 2 min ? 277 80 min v 17 3
km/s
P 111 4 min ? 362 212 min v 11
3 km/s
12
Results Amplitude Period
13
Results Damping Times
Coronal loop oscillation data Nakariakov et al
(1999)? Aschwanden et al (2002)? Wang Solanki
(2004)? Verwichte et al. (2004)? Van
Doorsselaere et al. (2007)? Hori et al.
(2007)? Van Doorsselaere et al (2009)? Verwichte
et al. (2009)? Verwichte et al.
(2010)? Prominence oscillation data Harris et
al (2010)?
consistent with damping via resonant absorption
14
Conclusions

• Large amplitude transverse (horizontal)
  prominence oscillation.
• Velocity amplitudes
• Generally increasing with height, up to 32km/s
  following the X1.3 class flare and up to 12km/s
  after the C8.9 class flare, as expected due to
  the difference in flare energy.
• Periods of around 100 minutes (10 minutes)
• Generally increasing with height and varying for
  different strands, indicating that the prominence
  doesnt oscillate as a solid body but according
  to its filamentary structure.
• Around 10 shorter during the 1st oscillatory
  train than the 2nd (c.f. 15x flare energy, 5x
  amplitude), suggesting the period is largely
  dependent on the properties of the prominence
  rather than the triggering mechanism, as expected
  for an MHD mode.
• Damping times
• 2 to 3 periods for most strands.
  when combined with data from loop
  oscillations, this is consistent with damping via
  resonant absorption.
• Other strands exhibit much longer decay times,
  but the errors in these cases are very large.

Harris et al. 2010, in preparation