Global Dynamics

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Global Dynamics

• Rachel Howe, NSO
• Session H10

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Synopsis

• Achievements from GONG/MDI
• Nearly a full 11yr cycle of observations
• Zonal flow pattern in bulk of convection zone.
• Tachocline oscillations(?)
• Comparisons with dynamo models
• Outstanding challenges
• Systematics
• High-l modes
• Near-surface shear
• Tachocline
• Meridional Flow

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Almost a cycle of observations!

• Zonal flow residuals from MDI (yearly averages)

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Migrating Zonal Flows in the Interior

• Amplitude and phase of 11yr sinusoid fits

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Rotation speed variations at the tachocline?
?
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Challenges Systematic Errors

• Systematic differences, e.g., between MDI and
  GONG, mostly but not all from analysis.
• Somewhat understood, but not all fixed.
• Need to offer choice of methods?
• Different methods for different regimes?

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Challenges High-Degree Modes

• Probably only f-modes.
• Need different -- and difficult -- fitting
  techniques. Rhodes, Reiter, Jefferies?
• Could be useful for inversions, particularly for
  near-surface layers.
• Need to adjust inversion codes to accommodate
  high l.

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Challenges Near-Surface Shear

• Does shear reverse at high latitudes, or not?
• How sharp is the shear really?
• Can HMI help?
• high-l modes

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Challenges Tachocline

• Longitudinal structure needs large-scale local
  methods.
• Methods need developing.
• May not be possible with rings, look at T-D?
• Radial structure just needs accurate,
  consistent measurements of lowish-degree modes.
• Improvements to fitting algorithms may help.

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Challenges Meridional Flow

• Return meridional flow much desired by theorists.
• Not really a global-mode problem.
• Possible indirect inferences from effects on
  zonal flows?