Effects of Magnetic Fields on Seismic Signatures

Effects of Magnetic Fields on Seismic Signatures

Charles Lindsey

NWRA/CoRA

Relationship to the Dynamo• Flows Dynamo• Magnetic Fields Local Luminosity• Local Luminosity Flows• Magnetic Fields Seismic Diagnostics

Questions: Are local flows driven by luminosity variations? Is the Meridional flow driven by solar activity?

Regions with excess luminosity have inflows related to magnetic fields. Examples include plages and supergranular lanes, both of which are excessively luminous and magnetic.

Sunspots have a luminosity deficit, obviously related to magnetic fields. They have outflows. However, in the case the question is more complicated.

Seismic Holography

• Subjacent vantage holography

• The local control correlations

Travel Time Signatures into Surface Magnetic Regions

• Ingression control correlation phase shift

• Travel time reduction

• The Penumbral phase anomaly

The Phase Inequality• Travel times into

active regions are up to 30 sec greater than for outgoing waves (Duvall et al. 1996).

• Possible contributorss:

(a) downflows

(b) damping (magnetic?)

The Penumbral Phase Anomaly

• a) Continuum Intensity

• b) Line-of-sight magnetic field

• c) Square horizontal magnetic field

• d) Ingression control correlation

The Penumbral Phase Anomaly in a Small Isolated Sunspot

• a) Continuum intensity

• b) Line-of-sight magnetic field

• c) Square horizontal magnetic field

• d) Ingression control correlation

Downflows beneath Sunspots• Maps of flows

beneath sunspots computeded by time-distance tomography by Zhao, Kosovichev and Duvall (2001).

Shallow Downflows• Zhao and

Kosovichev (2003)

• Downflows of order 0.5 km/sec

• Comparable horizontal inflows

• Fractional rate of change of density up to S0.0001/sec

Mass Conservation• Considerations of mass conservation (Lindsey and Braun 1996):

Downflows appear to conflict with other signatures suggesting horizontal outflows.

2 л r vρ H = π r2 vz

vρ = r/(2H) vz

Shallow Outflows from Sunspots

• A broad range of observational results suggest a general tendency of outflows from sunspots in the upper few Mm of the subphoto-sphere.

Mode Conversion• An inclined

magnetic field perturbed by a vertically propagating wave responds with tension forces that introduce horizontal motion.

Magnet Damping

• Inclined penumbral magnetic fields suggest control experiments to discriminate magnetic effects from those of flows.

The “Schunker et al. Effect”

• Dependence of the ingression control correlation on vantage with respect to an inclined magnetic field.

The Schunker Effect and Travel Times

• As we presently understand it, the Schunker et al. effect introduces a vantage-dependence to the phase inequality.

Phase Parallax• The Schunker et al. effect heavily enhances the travel

time reduction into a sunspot on the limbward side of the penumbra, where the magnetic field is inclined both with respect to the local vertical and the line of sight.

Phase Parallax in Tomographic Sound-Speed Maps

Control Computations for the Schunker et al. Effect

• 1-dimensional numerical modeling to determine holographic signatures of waves impinging into uniform photospheric magnetic regions (Crouch et al.)

Control Considerations Respecting Locality

• The thinness of the region of effective mode conversion suggests that magnetic effects can be confined to the local magnetic field.

• Numerical tests of locality

• Locality would make corrections to the showerglass far more practical.

Conclusions• Helioseismic signatures show strong evidence of

large phase shifts introduced by photospheric magnetic fields into helioseismic signatures.

• Magnetically induced phase shifts may well predominate certain helioseismic signatures, the travel time inequality in particular.

• Helioseismic signatures show strong evidence of mode coupling between p-modes and Alfven waves suggested by Cally and Bogdan.

• A careful account for magnetically induced phase shifts is essential for subphotospheric flow diagnostics. Recent theoretical developments in this direction are highly encouraging.

Acknowledgments

• Hannah Schunker

• Doug Braun

• Aaron Birch

• Paul Cally

Questions(?)

Photo from home page of Natalia Dziourkevitch: http://www.aip.de/~nsd