developments in the helioseismic imaging of the deep solar...
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Developments in the helioseismicimaging of the deep solar interiorand sunspot structure
Shravan M. HanasogeStanford University
Max-Planck-Institut For Solar System Research
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Talk outline Introduction
Modeling supergranulation
Modeling meridional flow
On the complex beast that is the travel time
Conclusions
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Eruption above a sunspot
From the Hinode press release (2007), observations in the G-band and Ca II H
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Solar prominences (Hinode)
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Granules: sources of waves
From the Hinode press release, G-band observations
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Acoustic wave propagation in the interior
Figure from SOI/MDI website, created by Sasha Kosovichev
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Motivation
To develop interaction and propagationtheories of waves
(Re-)evaluate, (re-)interpret observations
Hopefully discover something new
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Simulating the solar wavefield
Incredible breadth of scales and wide range ofphenomena
Cannot simulate the entire Sun yet!
Pick battles: simulate wave propagation inappropriate geometry
Differential studies
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Mimic observed modal distribution
SOI/MDI website
Forget non-linear magneto-convection
Model purely linear wave interactions
Stochastically excite waves in the Sun
Place time-stationary perturbations inthe simulation box
Analyze the resultant wavefield
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Simulated power spectra
Spectrum looks like the solar one - two thumbs way up!
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Modeling Supergranulation
Large-scale coherent convection
Have wave-like properties?
Understanding their structure and dynamics via analyses of wavefield statistics
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Supergranulation
Gizon, Duvall, & Schou (2001)
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Feature method: MDI data analysis
Regions of divergence Travel-time map
Duvall (2006)
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Modeling supergranulation
Birch, Duvall, & Hanasoge (2007)
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Frequency filtering and unexplained obs.
Differential sampling
More constraints
Highly constrained situation
Observations: very precise
Conclusion: unable to matchdata with required precision
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Meridional flow
Instrumental for solar cycle
Transports magnetic flux
Redistributes angular momentum
Solar cycle predictors depend on flow profiles
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Analysis and models
Differential measurement of travel times
Many systematics such as light travel time
delays and projection effects
Previous analyses did not take into account?
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Modeling medium-l observations
Distance Latitude Distance (Deg)
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Systematics
Light travel-time delays (disk edge)
Line-of Sight (horizontal components etc.)
Fore shortening
MTF
Radiative heat transfer
Unknown!
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The complex beast that is the travel time
Travel time is not raypath travel time
Signal contributions from disparate location
Non-homogeneity of sources leads tocomplex effects
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Sunspots: Observational understanding
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Sunspot (computational) model
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Wave statistics: results
3 mHz 4 mHz 5mHz
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Filtering related issues
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Fast mode propagation: problems III
WKB approximation (Elena Khomenko)
Wave propagation physics is different
Leads to Large changes in travel times
Must interpret correctly!
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Non-sequitur: convection as seen by waves
ASH simulations
Miesch et al. (2000)
No waves in the ASHsimulations.
Difference travel-timemap
Waves are scattered bythe convective cells.
Unpublished, private communication (Duvall, 2007)
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Conclusions
Details that have been neglected in the pastare gaining importance
Must develop accurate wave interactiontheories
Systematics are serious and must beconsidered
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Fin