Developments in the helioseismicimaging of the deep solar interiorand sunspot structure

Shravan M. HanasogeStanford University

Max-Planck-Institut For Solar System Research

Talk outline Introduction

Modeling supergranulation

Modeling meridional flow

On the complex beast that is the travel time

Conclusions

Eruption above a sunspot

From the Hinode press release (2007), observations in the G-band and Ca II H

Solar prominences (Hinode)

Granules: sources of waves

From the Hinode press release, G-band observations

Acoustic wave propagation in the interior

Figure from SOI/MDI website, created by Sasha Kosovichev

Motivation

To develop interaction and propagationtheories of waves

(Re-)evaluate, (re-)interpret observations

Hopefully discover something new

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

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

Simulated power spectra

Spectrum looks like the solar one - two thumbs way up!

Modeling Supergranulation

Large-scale coherent convection

Have wave-like properties?

Understanding their structure and dynamics via analyses of wavefield statistics

Supergranulation

Gizon, Duvall, & Schou (2001)

Feature method: MDI data analysis

Regions of divergence Travel-time map

Duvall (2006)

Modeling supergranulation

Birch, Duvall, & Hanasoge (2007)

Frequency filtering and unexplained obs.

Differential sampling

More constraints

Highly constrained situation

Observations: very precise

Conclusion: unable to matchdata with required precision

Meridional flow

Instrumental for solar cycle

Transports magnetic flux

Redistributes angular momentum

Solar cycle predictors depend on flow profiles

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?

Modeling medium-l observations

Distance Latitude Distance (Deg)

Systematics

Light travel-time delays (disk edge)

Line-of Sight (horizontal components etc.)

Fore shortening

MTF

Radiative heat transfer

Unknown!

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

Sunspots: Observational understanding

Sunspot (computational) model

Wave statistics: results

3 mHz 4 mHz 5mHz

Filtering related issues

Fast mode propagation: problems III

WKB approximation (Elena Khomenko)

Wave propagation physics is different

Leads to Large changes in travel times

Must interpret correctly!

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)

Conclusions

Details that have been neglected in the pastare gaining importance

Must develop accurate wave interactiontheories

Systematics are serious and must beconsidered

Fin