Release Notes for Initial Milne Eddington Inversion of HMI Magnetic Field Data (VFISV)

hmi.ME_720s_e15w1332 ([http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.ME_720s_e15w1332 click here for data]) and hmi.ME_720s_e15w1332_HARP ([http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.ME_720s_e15w1332_HARP click here for data])

These two data series contain ME inversion data processed using VFISV ([http://hmi.stanford.edu/doc/magnetic/section4.pdf details]) using the codes implemented through 27 November, 2011. There are known issues with these versions of VFISV, but this remains the best ME release version as of February 27, 2012.

• The prime data products are field strength, inclination, and azimuth.
• No disambiguation has been performed, so azimuths are in the range 0-180, not 0-360.
• e15 in the series name indicates that the number of iterations at each pixel was 200.
• w1332 in the series name indicates that the relative weights of I,Q,U,V were 1,3,3,2 in the inversion

Our efforts to optimize the VFISV for the HMI data pipeline are on going, and we will create the series to fill the data processed by the newer codes when ready. We will announce the release of the new data through Solar News.

Temporal ''coverage charts'' for these two series

Charts in [http://jsoc.stanford.edu/doc/data/hmi/coverage_maps/inversion/ this directory] show the 12-minute time slots for which the ME inversion data processed with the VFISV module are available. The coverage charts also contain the status flags of the HMI observation, thus the quality and availability of input [http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.S_720s Stokes] data. See [:ME720se15w1332CoverChart: details] for an explanation of the coverage charts.

• hmi.ME720s_e15w1332 - Full Disk

  • Synoptic data, on twice per day basis at 7 and 19UT daily, are stored in this series. The latest (Oct. 14, 2011 or later) version of VFISV was used to process the full-disk data since October 1st, 2011. The latest version of VFISV is being used to extend this series using the latest definitive Stokes data, on the 2 per day basis, usually about a week after the observation. An older version (May 26, 2011) was used to process most of the Stokes data from May 2010 to September 2011, however, the latest version was used to process some data this 17-month period. Data for scattered additional time periods are also available. Differences between the versions are described below. Checking the version of VFISV codes is strongly recommended.

• hmi.ME720s_e15w1332_HARP - HMI Active Region Patches

  • The latest version (Oct. 14, 2011) of VFISV has been used to generate the ME data stored in this series. Many of the active regions were recognized automatically by the [:HARPDataSeries:HARP module], while some were defined manually. This series includes 12-minute (720s) cadence data for several of the ARs that created X-class flares in 2011, including the one occurring on 2011 February 15 (at NOAA AR11158). The ME data stored at this series were used for preparing [:ReleaseNotes:the test data release] of the 3-component disambiguated vector data for the AR 11158.

Versions of VFISV in the FITS files exported at JSOC database

• The VFISV version is stored as a string value in the keyword INVCODEV.

  • The ME data for the two series were processed with one of three versions, labeled with a date, "May 26, 2011", "Oct 14, 2011" or "Nov 27, 2011".

  • On IDL, for example, if the exported data is read with [http://hmi.stanford.edu/doc/magnetic/fitsio.pdf fitsio_read_image()] then, the version can be printed with sxpar(),

    IDL> img=fitsio_read_image('img.fits',header)
    IDL> print, sxpar(header,'INVCODEV')

• Differences between 2011-May-26 version and 2011-October-14 version

  • VFISV core part
    1. Some of initial guess values for the iterative residual minimization were changed.
    2. Derivatives of residual square-chi is calculated with the best-fitting parameters instead of those at the last iteration stage.
  • Other change in the JSOC context
    1. The 32-bit quality flag for each pixel (segment name : qual_map) was redefined. This change is adjustable without rerunning VFISV, thus, the published data at the two series have the quality flag map given with the latest definition.

• Differences between 2011-October-14 version and 2011-November-27 version

  • The changes were limited to the JSOC data interface and MPI parallelism, and thus did not affect the output data values.