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== Measuring the Vector Magnetic Field of AR 11158 with HMI == = Measuring the Vector Magnetic Field of AR 11158 with HMI =

The first disambiguated vector field data released by the HMI project for science analysis is a 6-day interval of 12-minute active region patches including AR 11158. The region developed rapidly from February 12-17, 2011 and produced the first X-class flare of Solar Cycle 24.

The field is derived from the standard HMI IQUV 720-second data series. Patches on the Sun that include AR 11158 were identified using the HMI Active Region Patch (HARP) code and then enlarged to provide a surrounding buffer of weak field. The VFISV inversion was run with very strict convergence criteria to provide the optimal values, this required additional computing resources. The disambiguation was computed with spherical geometry in a limited region with fairly strict thresholds on field strength to determine the method of annealing.

Data Files are provided in two formats.
 1. Cut outs of the data are provided in a 650 * 600 window. The native coordinate system is CCD pixels. The inclination of the field is relative to the local line of sight and the azimuth is measured clockwise from up on the CCD. Keywords provide information about the solar geometry. Note that solar north is down in the movie.
 1. Remapped images computed with a Lambert equal area projection centered on the tracked region. The vector field components are heliographic Br, Btheta, and Bphi.

Vector field data must be used with care. There are several issues with vector magnetic field data that make inversions fail in some pixels and definitive disambiguation problemmatic. Additionally several systematic errors must be considered when using the data. These include daily, 12-hour, and other long-period variations associated with SDO's orbital velocity that cause large-scale satial and temporal variations in sensitivity and cross-talk due to limitations in the knowledge of instrument characteristics. Various confidence and error estimates do not always indicate which pixels are suspect.

AR 11158 emerged quickly in a complex way with several centers of flux emergence. During the build-up to the flare mixed-polarity regions strengthened and horizontal flows were apparent. At the time of the flare significant long-lasting changes in the horizontal magnetic field occurred.

The following paper describing the analysis of the vector field for this region will be submitted to Solar Physics shortly. Details will be filled in as they become available. More detailed treatments of some aspects of the processing follow.

Movie of the Radial Field: [ftp:pail.stanford.edu/pub/HMIvector FTP Directory]

=== Measuring the Vector Magnetic Field of AR 11158 with HMI ===
Line 57: Line 75:
=== A collection of topical discussions of the processing ===

Details of some aspects of the processing can be found below. Watch for updates:

 . ''' [http://hmi.stanford.edu/doc/magnetic/observables_code.pdf IQUV Computation] ''' {updated 9/2011}
 . ''' [http://hmi.stanford.edu/doc/magnetic/section5.RCE.pdf VFISV Most complete] ''' {updated 09/2011},
  . ''' [http://hmi.stanford.edu/doc/magnetic/VFISVdescription.doc VFISV Inversion Method Overview] ''' {updated 7/2011},
  . ''' [http://hmi.stanford.edu/doc/magnetic/weights.pdf Weighting Scheme for IQUV in VFISV Inversion] ''' {updated 8/2011}
  . ''' [http://hmi.stanford.edu/doc/magnetic/hack.pdf Filter / Line Profile Approximation (''the Hack'')] ''' {updated 8/2011}
 . ''' [http://hmi.stanford.edu/doc/magnetic/hmi.ME.Segments.doc hmi.ME inverted data detailed description] ''' {updated 7/2011}
 . ''' [http://hmi.stanford.edu/doc/magnetic/disambig_overview.pdf Disambiguation Overview]''' {updated 8/2011}
 . ''' [http://hmi.stanford.edu/doc/magnetic/disambig_longer.pdf Disambiguation Detail (incomplete)]''' {updated 8/2011}
 . ''' [http://hmi.stanford.edu/doc/magnetic/hmivector.YLiu.pdf Systemic Effects]''' {updated 9/2011}
  . A rough collection of ''' [http://sun.stanford.edu/~yliu/hmi/doc/hmivector_summaryV00.html Vector Field Systematic Issues ]''' {updated 7/2011}
 . ''' [http://hmi.stanford.edu/doc/magnetic/VectorTransformation.pdf Remapping & Coordinate Transformation]''' {updated 9/2011}

Measuring the Vector Magnetic Field of AR 11158 with HMI

The first disambiguated vector field data released by the HMI project for science analysis is a 6-day interval of 12-minute active region patches including AR 11158. The region developed rapidly from February 12-17, 2011 and produced the first X-class flare of Solar Cycle 24.

The field is derived from the standard HMI IQUV 720-second data series. Patches on the Sun that include AR 11158 were identified using the HMI Active Region Patch (HARP) code and then enlarged to provide a surrounding buffer of weak field. The VFISV inversion was run with very strict convergence criteria to provide the optimal values, this required additional computing resources. The disambiguation was computed with spherical geometry in a limited region with fairly strict thresholds on field strength to determine the method of annealing.

Data Files are provided in two formats.

  1. Cut outs of the data are provided in a 650 * 600 window. The native coordinate system is CCD pixels. The inclination of the field is relative to the local line of sight and the azimuth is measured clockwise from up on the CCD. Keywords provide information about the solar geometry. Note that solar north is down in the movie.
  2. Remapped images computed with a Lambert equal area projection centered on the tracked region. The vector field components are heliographic Br, Btheta, and Bphi.

Vector field data must be used with care. There are several issues with vector magnetic field data that make inversions fail in some pixels and definitive disambiguation problemmatic. Additionally several systematic errors must be considered when using the data. These include daily, 12-hour, and other long-period variations associated with SDO's orbital velocity that cause large-scale satial and temporal variations in sensitivity and cross-talk due to limitations in the knowledge of instrument characteristics. Various confidence and error estimates do not always indicate which pixels are suspect.

AR 11158 emerged quickly in a complex way with several centers of flux emergence. During the build-up to the flare mixed-polarity regions strengthened and horizontal flows were apparent. At the time of the flare significant long-lasting changes in the horizontal magnetic field occurred.

The following paper describing the analysis of the vector field for this region will be submitted to Solar Physics shortly. Details will be filled in as they become available. More detailed treatments of some aspects of the processing follow.

Movie of the Radial Field: [ftp:pail.stanford.edu/pub/HMIvector FTP Directory]

Measuring the Vector Magnetic Field of AR 11158 with HMI

A collection of topical discussions of the processing

Details of some aspects of the processing can be found below. Watch for updates:

JsocWiki: VectorPaper (last edited 2013-05-01 04:35:25 by localhost)