HMI Vector Magnetic Field Data Products

Overview of Vector Field Pipeline

The HMI instrument collects filtergrams in various wavelengths and polarizations sufficient to determine the Stokes parameters, I, Q, U, & V, as rapidly as every 90 seconds. Currently a 135-second base sequence is collected using the HMI side camera. The sequence measures I+-Q, I+-U, I+-V at 6 wavelengths. Level1 filtergrams are interpolated in time and space, correcting for solar rotation, cosmic rays, and other instrumental effects. Every 12 minutes data collected over a 16-minute tapered interval are averaged to reduce noise to produce the Stokes IQUV parameters in a 720-second data series, hmi.S_720s.

From many of the same filtergrams are determined the line-of-sight magnetic field (hmi.M_720), the continuum intensity (hmi.Ic_720s), line width (hmi.Lw_720s), and line depth (hmi.Ld_720s). The pipeline produces near real time version of some of these data series.

The Stokes parameters are inverted to determine the prime magnetic field parameters: B-Total, Inclination, and 180-degree Azimuth relative to the line of sight along with uncertainties on each quantity. Several other [http://hmi.stanford.edu/doc/magnetic/hmi.ME.Segments.doc hmi.ME plasma parameters and co-variances] are also determined. The Milne-Eddington inversion code is called VFISV, the Very Fast Inversion of the Stokes Vector. [:VectorDataReference:{Ref}]

These inverted data are disambiguated to fully determine the 360-degree azimuth. [:VectorDataReference:{Ref}]

The method of computation may differ for quick-look and final data products, for full-disk and selected patches, and for strong and weak field regions. Routines are available to export the data in useful heliographic coordinates, either in rectilinear {Bx, By, Bz} for patches or for full-disk observations in spherical coordinates, either {Br, Btheta, Bphi} or {Br, inclination, and azimuth}. Data can also be exported after remapping to standard synoptic or synchronic map coordinates. Averaging vector field maps in time and/or space can also be accomplished. A module will exist to merge the various methods.

The first release of disambiguated data for science analysis will be in October, 2011. That release includes 6-days of 12-minute vector magnetograms of AR 11158, the X-class flare producing region from February 12-17, 2011. The processing is not completely standard. A skeleton of the VectorPaper "Measuring the Vector Magnetic Field of AR 11158 with HMI" describing the processing is available. Presently the data are available only for testing purposes, not for science analysis. Links to the test data are available at VectorPaper.

These data will be combined to produce Carrington charts, synoptic maps, and synchronic frames of the vector field components. A long-term estimate of the polar field will be available for applications requiring global coverage.

From the photospheric data various products and models will be computed, including local and global harmonic coefficients, global potential field - source surface models, global and local magnetostatic models (including NLFFF on patches), global and local MHD models of various types.

Methods for tracking surface features will include local correlation tracking, ILCT, and DAVE4M. Interfaces to other models will be provided as practical.

Near real time SpaceWeatherProducts will be produced from quick look data. These will include indices calculated for the full disk and patches of interest.

Older Documentation

The following are from 2010 and many items are outdated. Use with care and only if newer documentation is unavailble.

Status of various modules can be found in the ["HMIModuleTable"]

Vector Magnetic Field Modules

Associated HMI Pipeline Modules

Line of Sight Magnetic Field Modules