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Data are provided in two formats. The 11 '''~-FITS-~''' files for each time include the three vector field components, computed error estimates for each quantity, three correlations (sqrt of the covariances) between field strength, azimuth and inclination, and two quality maps (qual_map and confid_map) providing an estimate of the quality of the data at each pixel. Keywords provide other important information. Maps of additional quantities and covariances can be retrieved using JSOC. Details can be found below. For each time there are 11 '''~-FITS-~''' files that include the three vector field components, computed error estimates for each quantity, three correlations between field strength, azimuth and inclination (the square root of the covariances), and two quality maps: '''[http://hmi.stanford.edu/doc/magnetic/qual_map.pdf qual_map]''' and '''[http://hmi.stanford.edu/doc/magnetic/confid_map.pdf confid_map]''') that give information about the quality of the data at each pixel. '''~-FITS-~''' keywords provide other important information. Maps of additional quantities and covariances can be retrieved using JSOC. Details can be found in some of the links at the bottom of the page.
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Data are provided in two formats.
 

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 5-day interval of 12-minute active region patches encompassing AR 11158. The region developed rapidly from February 12-16, 2011 and produced the first X-class flare of Solar Cycle 24 at 01:56 UT on February 15.

The vector magnetic 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 code was run with very strict convergence criteria to determine the optimal values, this required additional computing resources. The disambiguation was computed with spherical geometry in a limited region with fairly generous thresholds on field strength and very gradual annealing; this also requires significant additional computing resources.

For each time there are 11 FITS files that include the three vector field components, computed error estimates for each quantity, three correlations between field strength, azimuth and inclination (the square root of the covariances), and two quality maps: [http://hmi.stanford.edu/doc/magnetic/qual_map.pdf qual_map] and [http://hmi.stanford.edu/doc/magnetic/confid_map.pdf confid_map]) that give information about the quality of the data at each pixel. FITS keywords provide other important information. Maps of additional quantities and covariances can be retrieved using JSOC. Details can be found in some of the links at the bottom of the page.

Data are provided in two formats.

  1. Cut outs of the data are provided in a tracked 650 * 600 CCD-pixel window. Components are the total flux, the inclination of the field relative to the local line of sight, and the azimuth measured counter-clockwise from 'up' on the CCD. Keywords provide information about the solar geometry. Note that solar north is down in the movie. The [http://hmi.stanford.edu/doc/magnetic/hmi_test.B_720s_cutout.keywords.pdf hmi_test.B_720s_cutout keywords] and the data can be found in JSOC.

  2. Remapped images computed with a Lambert cylindrical equal area projection centered on the uniformly tracked region. The vector field components are heliographic Br, Btheta, and Bphi. Error and quality estimates are for the nearest original pixel. The [http://hmi.stanford.edu/doc/magnetic/hmi_test.B_720s_CEA.keywords.pdf hmi_test.B_720s_CEA keywords] and the data can be found in JSOC.

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 make definitive disambiguation problematic. Additionally various 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 spatial and temporal variations in sensitivity and cross-talk due to limitations in the knowledge of instrument characteristics. Various confidence and error estimates are provided, but they do not always indicate which pixels are suspect.

AR 11158 emerged quickly in a complex way with three major centers of flux emergence. During the build-up to the flare, mixed-polarity regions intensified 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. Sections will be filled in as they become available. Pointers to the data and more detailed treatments of some aspects of the processing follow.

Measuring the Vector Magnetic Field of AR 11158 with HMI

  • by the VectorFieldTeam

  • 1 Intro – Vector magnetic fields
    • 1.1 HMI Vector Field Overview
    • 1.2 AR 11158 – X-class Flare
  • 2 Instrument and Data Processing
    • 2.1 HMI instrument
    • 2.2 Framelist for vector field
    • 2.3 Relevant calibration of HMI instrument
    • 2.4 Specifics of vector data camera, filtergrams
    • 2.5 Processing of filtergrams – dark, flat, cosmic rays, gap filling, distortion
    • 2.6 Pipeline and special HMI processing

  • 3 IQUV calculation [http://hmi.stanford.edu/doc/magnetic/observables_code.pdf Section 3]

    • 3.1 Computation of IQUV
    • 3.2 720 calculation – interpolation in time and space, averaging
    • 3.3 Other 720s quantities (very briefly)

  • 4 VFISV inversion [http://hmi.stanford.edu/doc/magnetic/section4.pdf Section 4 ]

    • 4.1 ME method and VFISV summary
    • 4.2 Specifics of implemented VFISV for this data series
      • 4.2.1 Weighting
      • 4.2.2 Filter Profile Approximation - Wavelength Hack
      • 4.2.3 Model Initialization
      • 4.2.4 Convergence Criteria, multiple minima
    • 4.3 Formal Error estimation

  • 5 Disambiguation [http://hmi.stanford.edu/doc/magnetic/disambig_longer.pdf Section 5]

    • 5.1 General method, issues, and uncertainties - planar and spherical
      • 5.1.1 Selection of Pixels to Anneal
      • 5.1.2 Potential Field Calculation
      • 5.1.3 Minimum Energy Methods
      • 5.1.4 Treatment of Weak Field Areas
    • 5.2 Computation Parameters

  • 6 HMI.B Data series and access VectorPaper6

    • 6.1 Organization of data series
    • 6.2 Details of HMI.B contents
    • 6.3 Description of HARPs
    • 6.4 Export – general

    • 6.5 HMI Vector Data Versions and Referencing Data in publications - VectorDataReference

  • 7 Projections - [http://hmi.stanford.edu/doc/magnetic/VectorTransformation.pdf Remapping and Vector Transformation]

  • 8 Known and unresolved issues with HMI data and processing [http://hmi.stanford.edu/doc/magnetic/hmivectorissues.pdf Section 8 Topics] {10.26.2011}

    • 8.1 Periodic Errors
    • 8.2 Large-scale Variations
    • 8.3 Bad Pixels
    • 8.4 Comparison of Vector and Line-of-Sight Magnetic Field
    • 8.X Inversion Dependence on Initial Guess
    • 8.X Residual Cross-talk
    • 8.X Disambiguation issues
    • 8.X Other systematic and instrumental issues that affect data
  • 9 Discussion of HMI measurements of AR 11158 - Validation
    • 9.1 General comments on determination of vector magnetic field
    • 9.2 Time Evolution of AR 11158 – features both real and otherwise
    • 9.3 Validation and limitations of HMI processing and data
    • 9.4 Qualitative comparison with B_LoS, Hinode, and other field measures
  • 10 Summary
    • 10.1 Remaining work for pipeline modules
    • 10.2 Uses of data – NLFFF, DAVE4VM, other

Access to AR 11158 Vector Field Data

Movies of the Vector Field

Vector Field Data - One-Day Tar Files of 12-minute Cadence

One-Per-Day Sample Images and FITS Files

A collection of topical discussions of the processing

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

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