Release Notes for hmi.ME_720s_fd10 HMI Magnetic Field Data (VFISV)

Definitive, science-grade, HMI vector magnetic field data are now (May, 2012) available via JSOC under the series name hmi.ME_720s_fd10.

We recently merged the full-disk and partial-disk ME data to one data series. Please see descriptions at a temporal Wiki page.

Major differences between 2011-Oct/Nov version (_e15w1332 series) and the current FD10 version

• VFISV Algorithm Change
  1. A regularization term, whose purpose is to penalize high values of the parameter eta_0, was added to the merit function in order to tackle a double-minima problem.
  2. The selection process that decides when the inversion of a given pixel needs to be re-started with a different (randomized or tailored) initial guess atmosphere, has been implemented and fine-tuned.
  3. We have settled on a convergence criterion based on the value of the Levenberg-Marquardt Lambda parameter. The algorithm exits the iteration loop when Lambda becomes too large and no re-start of the inversion is enforced for any other reason. The average number of iterations per pixel is now about 30.
• Implementation/Computing Change
  1. Parallelism, by means of MPI, has been modified and optimized to allocate the tasks to each Process Element as evenly as possible.

Temporal Coverage for Three Series below

Monthly charts 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 Stokes data. See details for an explanation of the coverage charts (* the color and legends in the coverage charts for version FD10 are same as those for the previous version of ME data).

hmi.ME_720s_fd10 (click here for data), hmi.ME_720s_fd10_HARP (click here for data), and hmi.ME_720s_fd10_HARP_nrt (click here for data).

These three data series contain ME inversion data processed using VFISV (details) using the codes implemented on April 13, 2012. There are known issues with these versions of VFISV, but this remains the best ME release version as of the date of implementation. We consider this a beta-test version of the HMI vector field inversion.

• The prime data products are field strength, inclination, and azimuth. Errors and other quantities are included.
• No disambiguation has been performed, so azimuths are in the range 0-180, not 0-360.

• fd10 in the series name is an index of the choice we think best among those we had tested, since the last release.

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. The eventual pipeline code for HMI vector inversions will be different. We will announce the release of the new data through Solar News.

• hmi.ME_720s_fd10 - Full Disk

  • Synoptic data, on 4 per day basis at 1, 7, 13 and 19UT daily since 2010 May 1st, are stored in this series. Since 2012 April 25, the latest version of VFISV is being used to extend this series using the latest definitive Stokes data, on one-per-12 minute basis, usually about a week after the observation. Data for scattered additional time intervals, one of which is from 2011 February 1st to March 10, are also available.

• hmi.ME_720s_fd10_HARP - HMI Active Region Patches

  • The latest version of VFISV has been used to generate the ME data stored in this series. Many of the active regions were recognized automatically by the HARP module. This series includes 1-per-hour ME data at the active regions for most of the period from 2010 May 1st until 2012 April 25. Also this series contains 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).

• hmi.ME_720s_fd10_HARP_nrt - Near-Real-Time HMI Active Region Patches

  • The latest version of VFISV has been used to generate the ME data stored in this series. The input Stokes data and the HARP info. are of preliminary near-real-time ones, though the time lag between observation and ME process is minimized. As of May 31, this module is set to start processing at 7AM (7PM) Pacific Time for the first (second) half of a day in UT.

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 series above were processed with the latest version, labeled with a date, "Apr 13, 2012".

  • In IDL, for example, if the exported data is read with fitsio_read_image() then, the version keyword can be printed with sxpar():

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

Changes in VFISV, since the "April 13 2012" version.

As results of our continuing effort, there are some updates in the VFISV codes since the "April 13, 2012" version was used to make regular data production. Belows are summarized the changes. All changes were made in the C-wrapper, and no changes in the VFISV core logics and procedures. The date of the change might be appearing in the INVCODEV keyword as a code version identifier.

• On 2012 Jun. 23
  • The wrapper was added lines to host a new run-time option "-f": This option will force VFISV module running even when a processed data for a time slot exists. This option was made to process the full disk VFISV for a time slot for which the VFISV had been applied to the HARP (partial of the fulldisk) and the partially processed data resides on the target data slot. No changes in the VFISV itself.
• On 2012 Nov. 28
  • A few minor changes in C-language to adopt the latest version of intel compiler. Information of a paper regarding the VFISV implemented to the JSOC pipeline is updated, i.e."Solar Physics 2011, vol 273 pp 267-293, Borrero et.al." No changes in the VFISV itself.
• On 2013 Mar. 13
  • A few minor changes, for preparing for very very rare cases in the DSDS data file system when the input Stokes data files are not on the disk. No changes in the VFISV itself.
• On 2013 Apr. 30
  • Two changes. The first one might affect the output from the VFISV. (1) The phasemap determined from the calibration process and used in the VFISV are now dependent on the time of the observation. This changes may result in systematic differences between the data made with different phasemaps, well within the estimated error level. A string keyword INVPHMAP will tell which phasemap is used in the VFISV processes: The VFISV wrapper version earlier than "2013 Apr. 30", this keyword had been left blank (or 1-length space). In this version, the string keyword will have a value of 7 or 8-digit number identifying the phasemap data stored in another JSOC internal data series, hmi.phasemaps_corrected[]. (2) The string keywords for unit of physical variables had been updated: For example, from "degree" to "deg", from "gauss" to "Mx/cm^2", from "adim" to "dimensionless".