Global Dynamics Rachel Howe, NSO Session H10. Synopsis Achievements from GONG/MDI –Nearly a full...
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Transcript of Global Dynamics Rachel Howe, NSO Session H10. Synopsis Achievements from GONG/MDI –Nearly a full...
Global Dynamics
Rachel Howe, NSO
Session H10
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
Almost a cycle of observations!
• Zonal flow residuals from MDI (yearly averages)
Migrating Zonal Flows in the Interior
• Amplitude and phase of 11yr sinusoid fits
Rotation speed variations at the tachocline?
?
• 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?
Challenges: Systematic Errors
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.
Challenges: Near-Surface Shear
• Does shear reverse at high latitudes, or not?
• How sharp is the shear really?
• Can HMI help? – high-l modes
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.
Challenges: Meridional Flow
• Return meridional flow much desired by theorists.– Not really a global-mode problem.– Possible indirect inferences from effects on
zonal flows?