SECCHI-3D reconstruction software

Orsay, 07.03.20075th SECCHI Consortium Meeting: Wiegelmann et al.:

SECCHI-3D reconstruction software

Wiegelmann, Inhester, Feng, Ruan,Thalmann, Podlipnik


• Tools to compute coronal magnetic fields

• Selfconsistent magnetohydrostatic equilibria

• Feature recognition

• Stereoscopy

• Tomography



Aim: 3D Reconstruction of Solar Corona

• The 2 Viewpoints of STEREO help usfor a 3D-reconstruction.

• But: Image data are not sufficient (see talk of Feng)• Essential: Magnetic field information.• Our tools use combined data sets of SECCHI

with photospheric B-field measurements fromvarious instruments (SOHO, HINODE, SOLIS)



Coronal magnetic field codes

• Potential, linear and nonlinear force-free extrapolation codes -Cartesian (Active Regions) and-Spherical (Full Sun) geometry

• Selfconsistent magnetohydrostatic codes:B-field + Plasma in one MHS-model-Cartesian-Spherical



Model Mathematics Observationsneeded

Validity

Potential

Fields

Line of sightmagnetogram

(Global) currentfree regions,quiet sun

Linear Force-

Free Fields

LOS magnetogram

+ observations ofplasma structures

Local in activeregions, low-betaplasma

Non Linear Force-Free

Vectormagnetogram

(3 times more data,ambiguities, noise)

Active regions,low beta plasmain low corona

MHS

Equilibrium

Vectormagnetogram

+ Tomographic Inversion of density

Helmet streamer,finite beta plasma,full solar corona0

)()( 0

B

pBB

0

)(

B

BrB 0

B

BB 0

0

B

B

Better Models More Challenging

Computational + Observational



Easy to computeRequire only

LOS-Magnetograms



Very ChallengingVector-Magnetograms

Pre-processing





Measured loops in a newly developed AR (Solanki et al., Nature 2003)

Potential field reconstruction

Linear force-free reconstruction Non-linear force-free reconstruction

Comparison of observed magnetic loops and extrapolationsfrom photospheric measurements (Wiegelmann et al., A&A 2005)

Nonlinear force-free Models are

superior.



What do coronal B-field models provide?

• 3D loop structure

• +projections on 2 images

• Length + shape of loops

• Magnetic field strength

• Electric current density

• (Free) magnetic energy

• Helicity

Stereoscopy

Scaling Laws

CME-onset



What does SECCHI provide?• Rigorous Test of B-field models.• Obtain free model parameters.• Test scaling laws.• Get plasma parameters along loops

- Temperature- Density- Pressure

• Compare selfconsistent MHS-models with coronagraph images (Talk of Ruan)

Compare real + artificial images,

Loops + B-lines

Modeling,Tomography



Single viewpoint: SOHO/EIT, TRACEUse B-Field for feature-recognition

(Wiegelmann et al., Sol. Phys. 2005)

• Compute the coronal magnetic field. • Project 3D field lines onto an EUV-image.• Emissivity and gradient along projected field lines.• Compare field lines and plasma.

How well are they aligned?

• Alternative: Extract 1-D loops out of the EUV-images (see talk of Inhester) and compare withprojections of magnetic field lines thereafter.



EIT-image and projections of magnetic

field lines for a potential field (α=0) .(bad agreement)

Linear force-free field with α=+0.01 [Mm-1](bad agreement)

We use a linear force-free model with MDI-data and have the freedomto choose an appropriate value for the force-free parameter α.



Linear force-free field with α=-0.01 [Mm-1](better agreement)

3D-magnetic field lines, linear force-free α=-0.01 [Mm-1]



SUMER Dopplergram in NeVIII ( 77 nm) and a 2-D-projection of some field lines.

(Marsch, Wiegelmann, Xia, A&A 2004)

Mass flux density inferred from Doppler-shift and intensity from SUMER observations.

up

down

3D-Loopsguide Data

Analysis



• Rates quality of magnetic field reconstruction.

• Identifies coronal loops.

• For a linear force-free model the method computes the optimal force-free parameter α.

• The method tells us also how good the assumption “linear force-free” is. (This assumption is good if the optimal value α is the same on all loops.)

• Two viewpoints will be more restrictive.Magnetic Stereoscopy, Talk of Feng

What does the method provide?



Magnetic fields and coronal tomography

a) Use only line of sight density integrals.

Wiegelmann and Inhester,Sol. Phys, 2003

b) Use only magneticfield data.

c) Use both line of sightdensity integrals andmagnetic field as regularization operator.

Magnetic Modelssupport Tomography,

Regularization



Summary

• We developed tools for the 3D-reconstructionof the solar corona (global and local).

• Combined data-analysis of SECCHI-datawith magnetic field information are morepowerful than 2 STEREO-viewpoints alone.

• It is fortunate that we have STEREO and HINODE data available at the same time.

SECCHI + HINODE+ Reconstruction Tools

= Corona in 3D



References (Selection)

Coronal magnetic field modelsT. Wiegelmann: Optimization code with weighting function for the reconstruction of coronal magnetic fields. (Sol. Phys., Vol. 219: 87-108, 2004.) T. Wiegelmann, A. Lagg, S.K. Solanki, B. Inhester, J. Woch: Comparing magnetic field extrapolations with measurements of magnetic loops. (A&A, Vol. 433, 701-705, 2005.)

T. Wiegelmann, B. Inhester, T.Sakurai: Preprocessing of vector magnetograph datafor a nonlinear force-free magnetic field reconstruction. (Sol. Phys, Vol. 233, 215-232, 2006.)

B. Inhester and T. Wiegelmann : Nonlinear force-free magnetic field extrapolations:comparison of the Grad-Rubin and Wheatland-Sturrock-Roumeliotis algorithm. (Sol. Phys., Vol. 235,201-221, 2006)

T. Wiegelmann and T. Neukirch: An optimization principle for the computation of MHD equilibria in the solar corona. (A&A, Vol. 457, 1053-1058, 2006.) T. Wiegelmann: Computing nonlinear force-free coronal magnetic fields in spherical geometry. (Solar Physics, in press, 2007)



StereoscopyT. Wiegelmann and T. Neukirch: Including Stereoscopic Information in the Reconstructionof Coronal Magnetic Fields. (Sol. Phys., Vol. 208: 233-251, 2002.)

T. Wiegelmann and B.Inhester: Magnetic Stereoscopy. (Solar Physics, Vol. 236, 25-40, 2006.)

L.Feng, T. Wiegelmann, B.Inhester, S.K. Solanki, W.Q. Gan, P. Ruan : Magnetic Stereoscopy of Coronal Loops in NOAA 8891. (Sol. Phys., accepted.)

B.Inhester: Stereoscopy Basics for the Stereo mission (ISSI publication, submitted .)

TomographyT. Wiegelmann and B. Inhester: Magnetic modeling and tomography: First steps towards a consistent reconstruction of the solar corona. (Solar Physics, Vol. 214: 287-312, 2003.)

Feature recognition T. Wiegelmann, B. Inhester, A. Lagg, S.K. Solanki: How to use magnetic field information

for coronal loop identification? (Sol. Phys., Vol. 228, 67-78, 2005.)

Documents

SECCHI-3D reconstruction software