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?