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Magnetic Field Extrapolation

Description

  • Inputs: Magnetic image from HMI

  • Outputs: list of endpoints (area defined by circle or polygon of solar coordinates) and time plus image with overlay of magnetic field lines

  • Problem: Magnetic field extrapolation begins with a magnetic image from HMI. Magnetic field lines are identified between active regions and highlighted as an overlay on the original magnetic image.

The loops identified in LoopRecognition will be associated with magnetic field lines found in MagneticFieldExtrapolation during the HelicityComputation analysis.

Literature Search

Algorithms:
Title
How to use magnetic field information for coronal loop identification ?
Author(s)
T.Wiegelmann, B.Inhester, A.Lagg and S.K.Solanki
Publication
Uncredited
URL
http://www.mps.mpg.de/homes/wiegelmann/H2010eti_rev.pdf
Date published
Jan 2005
Description
Discusses the correlation between potential field, linear force-free and nonlinear force-free magnetic field extrapolations and observed coronal loops on TRACE images, and recommends the nonlinear force-free method as a possible tool for coronal loop recognition.

Title
Comparing magnetic field extrapolations with measurements of magnetic loops
Author(s)
T.Wiegelmann, A.Lagg, S.K.Solanki, B.Inhester and J.Woch
Publication
Astronomy & Astrophysics manuscript no. CR AA2421
URL
http://www.mps.mpg.de/homes/wiegelmann/CR_AA2421.pdf
Date published
Dec 2004
Description
Discusses the relative merits of potential field, linear force-free and nonlinear force-free magnetic field extrapolations against a benchmark 3-D reconstruction of observed solar magnetic fields.

Title
Extrapolation of a nonlinear force-free field containing a highly twisted magnetic loop
Author(s)
G.Valori, B.Kliem and R.Keppens
Publication
Astronomy & Astrophysics manuscript no. 2008
URL
http://www.aip.de/~kli/2008.pdf
Date published
Dec 2004
Description
Discusses a new implementation of the "Stress and Relax" technique of nonlinear force-free magnetic field extrapolation from vector magnetograms.

Title
Optimization code with weighting function for the reconstruction of coronal magnetic fields
Author(s)
T.Wiegelmann
Publication
Solar Physics, volume 219, number 1, pages 87-108
URL
http://star.mpae.gwdg.de/secchi/publications/H1690e.pdf
Date published
Jan 2004
Description
Discussion of combined Optimization method for nonlinear force-free and non force-free magnetic field extrapolations.

Title
A quantitative method to optimise magnetic field line fitting of observed coronal loops
Author(s)
L.Carcedo, D.S.Brown, A.W.Hood, T.Neukirch and T.Wiegelmann
Publication
Uncredited
URL
http://www.mps.mpg.de/homes/wiegelmann/laura.pdf
Date published
Sept 2003
Description
Discusses the problems and techniques for matching extrapolated magnetic fields with coronal loops.

Title
Computing nonlinear force free coronal magnetic fields
Author(s)
T.Wiegelmann and T.Neukirch
Publication
Nonlinear Processes in Geophysics (2003) 10:313-322
URL
http://www.mps.mpg.de/homes/wiegelmann/npg02041.pdf
Date published
Nov 2002
Description
Discussion of Direct Extrapolation, MHD-relaxation and Optimization methods of nonlinear force-free magnetic field extrapolation, with particular emphasis on the latter two techniques.

Title
Magnetic Field Extrapolation
Author(s)
P.A.Sturrock
Publication
Uncredited
URL
http://
Date published
2001
Description
Informal discussion and comparison of several methods for nonlinear force free magnetic field extrapolation from vector magnetograms, including the Grad-Rubin, quasi-MHD, Optimization and "Stress & Relax" techniques.

Title
Extrapolation of the solar magnetic field within the potential-field approximation from full-disk magnetograms
Author(s)
G.V. Rudenko
Publication
arX1v:astro-ph/0004222v1
URL
http://
Date published
Apr 2000
Description
Discussion of potential field extrapolation using a combination of Galerkin's Projection and Trefftz's methods on synoptic maps and full-disk magnetograms, with a comparison of the results obtained.

Title
The Coronal Heating Mechanism as Identified by Full-Sun Visualizations
Author(s)
Carolus J. Schrijver , Anne W. Sandman , Markus J. Aschwanden , and Marc L. DeRosa
Publication
Astrophysical Journal 615: 512-525
URL
http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v615n1/59982/59982.html
Date published
Nov 2004
Description
Contains useful references to the Potential Field Solar Surface (PFSS) method of magnetic field extrapolation, which is available as a suite of Solarsoft IDL software routines (see 'Routines and Libraries' below)

Title
Photospheric and Heliospheric Fields
Author(s)
Carolus J. Schrijver and Marc L. DeRosa
Publication
Solar Physics, Volume 212, Number 1: 165-200
URL
http://www.springerlink.com/media/99EQAC4TLMDQXNKGED4T/Contributions/T/R/2/G/TR2G4167166VQ212.pdf
Date published
Jan 2003
Description
Contains references to the algorithms used in the Solarsoft IDL PFSS routines (see 'Routines and Libraries' below).

Title
A New Technique for a Routine Azimuth Disambiguation of Solar Vector Magnetograms
Author(s)
Manolis K. Georgoulis, Applied Physics Laboratory, John Hopkins University, Maryland USA
Publication
The Astrophysical Journal, 629:L69-L72
URL
http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v629n1/19590/19590.web.pdf
Date published
August 2005
Description
Describes a new non-potential technique to remove the PI ambiguity from vector magnetograms.

Title
On the Resolution of the Azimuthal Ambiguity in Vector Magnetograms of Solar Active Regions.
Author(s)
Manolis K. Georgoulis, Barry J. LaBonte and Thomas R. Metcalf
Publication
The Astrophysical Journal, 602:446-467
URL
http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v602n1/58845/58845.web.pdf
Date published
February 2005
Description
Describes a structure minimization technique to remove the PI ambiguity from vector magnetograms.

Title
Resolving the 180-degree ambiguity in vector magnetic field measurements: the 'minimum' energy solution
Author(s)
Thomas R. Metcalf
Publication
Solar Physics, Volume 155, Number 2: 235-242
URL
http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994SoPh..155..235M&link_type=ARTICLE&db_key=AST
Date published
December 1994
Description
Describes a technique for resolving the 180-degree ambiguity in solar vector magnetic field measurements.

Title
Vertical Lorentz Force and Non-field-aligned currents in the photospheric magnetic fields of Solar Active Regions
Author(s)
Manolis K. Georgoulis, B.J. LaBonte
Publication
The Astrophysical Journal, 615, 1029-1041
URL
http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v615n2/59281/59281.web.pdf
Date published
December 2004
Description
Describes a technique for the computation of vertical Lorentz force and corresponding cross-field electric current density from vector magnetograms. Essential precursor to 'Azimuth Disambiguation' method.

Title
Preprocessing of vector magnetograph data for a nonlinear force-free magnetic field reconstruction
Author(s)
T.Wiegelmann, B. Inhester, T.Sakurai
Publication
Solar Physics (in press)
URL
http://www.mps.mpg.de/homes/wiegelmann/H2092L_rev.pdf
Date published
In press, 2005
Description
Describes a technique for detecting and smoothing non force-free vector magnetogram data.

Title
Nonlinear force-free modelling of coronal magnetic fields. A quantitative comparison of methods.
Author(s)
C.Shrijver, M.DeRosa, T.Metcalf, Y.Liu, J.McTiernan, S.Regnier, G.Valori, M.Wheatland, T.Wiegelmann
Publication
Solar Physics (last submitted December, 2005)
URL
http://www.mps.mpg.de/homes/wiegelmann/nlfff1.pdf
Date published
???
Description
Describes the various magnetic field extrapolation methods discussed/demonstrated at Stanford University NLFFF "shootout" in 2005.

An informal writeup of a U. of Berkeley meeting to compare magnetic field extrapolation algorithms can be found at http://solarmuri.ssl.berkeley.edu/~welsch/public/meetings/FFFThinkshop/lmsal_fff_02.html.

Routines and Libraries

  • pfss_viewer.pro - this Solarsoft widget from Marc deRosa at Lockheed Martin opens up an IDL .sav file containing SOHO-MDI magnetic field data. A box is drawn to constrain latitude and longitude, and then magnetic field lines are drawn on the solar surface image. The pfss widget and supporting code are found in $SSW/packages/pfss/idl.

Test Data

Perhaps SOHO-MDI data is appropriate for testing here?

  • The pfss_viewer uses SOHO-MDI data.

Comments

Algorithm steps from Marc deRosa's PFSS Magnetic Extrapolation method (software available under the IDL Solarsoft archive) have been extracted and added to PFSSMagExtrapSteps.

  • Table 1: Summary of current Magnetic Extrapolation techniques

Model Advantages Disadvantages Comments
Potential Field Provides fast approximation Poor predictor of solar events Basis of Solarsoft PFSS package
Linear Force-Free Field Provides better results than Potential Field Model Field strength doesn't decay with distance -
Nonlinear Force-Free Field Provides much better correlation with observations than either Potential Field or Force-Free Field models Requires vector magnetogram, which is less accurate than its line-of-sight cousin Several implementations available, including:
a) Optimization method
b) "Stress and Relax" method
Parametric Transformation Analysis Allows extrapolation correction using observed coronal loops - Uses Potential Field or Nonlinear Force-Free Model extrapolations as starting point. See 'Allen.ppt' presentation under 'Attachment' for further information.

-- MikeSmith - 09 Jun 2005

Topic attachments
I Attachment History Action Size Date Who Comment
PowerPointppt Allen.ppt r1 manage 2504.0 K 2006-03-03 - 16:30 MikeSmith Parametric Transformation Analysis .ppt presentation - Allen Gary
PowerPointppt HMIproducts_mags_general.v00.ppt r1 manage 94.0 K 2006-03-03 - 16:30 MikeSmith SDO/HMI Products From Vector Magnetograms (date unknown)
PDFpdf opt_wiegelmann.pdf r1 manage 114.5 K 2006-03-03 - 16:30 MikeSmith Userguide to running NLFF optimization code - T.Wiegelmann
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Topic revision: r20 - 2006-03-30 - MikeSmith
 
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