Release Notes for hmi.ME_720s_fd10 HMI Magnetic Field Data (VFISV)
Definitive, science-grade, HMI vector magnetic field data are available as of May 2012 via JSOC under the series name hmi.ME_720s_fd10.
This release has now merged the full-disk and partial-disk ME data to one data series.
Major differences between 2011-Oct/Nov version (_e15w1332 series) and the FD10 version of the VFISV Milne-Eddington Inversion
- VFISV Algorithm Change
- 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.
- 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.
- 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
- 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).
These are now obsolete:
These data series contain ME inversion data processed using an adaptation of VFISV (Solar Physics Paper) using the codes implemented on April 13, 2012 and modified as described below. There are known issues with these versions of VFISV, but this remains the preferred ME release version as of the date of implementation.
- 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 (See FullDiskDisamb).
fd10 in the series name is an index of the choice we think best among those we have tested, since the last release.
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, e.g. "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 continuing improvements, there are some updates in the VFISV codes since the "April 13, 2012" version was used to make regular data production. Below are summarized the changes. All changes were made in the C-wrapper, and no changes have been made in the VFISV core logic or procedures. The date of the change appears in the INVCODEV keyword as a code version identifier.
- 2012 Jun. 23
- The wrapper was modified to host a new run-time option "-f": This option forces the VFISV module to run 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 (part of the fulldisk) and the partially processed data resided on the target data slot. No changes in the VFISV code itself.
- 2012 Nov. 28
- A few minor changes in C-language to adapt to the latest version of the 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 instrumental phasemap determined from the calibration process and used in VFISV now depends on the time of the observation. This change results in systematic differences between the data made with different phasemaps, though well within the estimated error level. A string keyword INVPHMAP tells which phasemap is used in the VFISV processesing. The VFISV wrapper versions earlier than "2013 Apr. 30", this keyword had been left blank (or may appear as a one-character space). In the new 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".
References