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HMI Magnetic Field Products

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Synoptic Maps Available

General Description of HMI Magnetic Field Data Products

The line-of-sight magnetic field, hmi.M, is computed from the difference of the Doppler velocities observed in two circular polarizations, as was done for MDI. The filtergrams are obtained by the Doppler camera on HMI. The basic line-of-sight observing cadence is 45 seconds.

The vector magnetic field, hmi.B, is computed from Stokes parameters derived from an independent set of polarized filtergrams. The basic vector field observing cadence is currently 135 seconds and uses HMI's Magnetic camera. Most analysis is done with 720s averages.

The possibility of combining filtergrams from the two cameras will be explored.

Vector field data products include the following quantities (and at least 23 others, including uncertainties)

  • |B| - total flux
  • Inclination (gamma) to the line of sight
  • Azimuth (phi) relative to 'up' on the CCD
  • Magnetic line-of sight velocity

Data will be exported in a variety of coordinate systems: [Bx,By,Bz], [B_total,gamma,phi], and [Br,Btheta,Bphi]

More detail is provided at VectorMagneticField and LineofsightMagneticField and SpaceWeatherProducts.

HMI Active Region Patches

A HARP (short for HMI Active Region Patch) is an enduring, coherent magnetic structure at the size scale of a solar active region. The primary purpose of the HARP data series is to provide the practical geometric information needed to follow an evolving region as it crosses the solar disk. A HARP is initially identified automatically in a sequence of HMI line-of-sight magnetograms. HARPs are typically observed over several days (possibly as long as a disk passage) and tracked from one image to the next. At each time step, the rectangular HARP bounding box is provided and a BITMAP that characterizes the pixels of the HARP is recorded. The bounding box encloses the maximum heliographic extent of the region during its life time. The BITMAP indicates which pixels in the box are part of the HMI active region patch and can be applied to an HMI image. Keywords provide summary information about the patch (e.g. the total line-of-sight magnetic flux) as well as geometric and heliographic specifics.

The HARP information is being used to determine regions of interest for vector field inversion processing, both for past data (see hmi.ME_720s_fd10_HARP) and for near real time processing (hmi.ME_720s_fd10_HARP_nrt). Near real time HARPs (hmi.Mharp_720s_nrt) are a little different than definitive HARPs because the entire history or each region is not known; NRT and definitive HARP numbers differ.

See ["HARPDataSeries"] for details.

Selected HMI Science Data Products

Standard Pipeline

  • 45-second - full disk
    • Blos (hmi.M_45s)
    • Vlos (hmi.V_45s)
    • Continuum intensity (hmi.Ic_45s), line depth (hmi.Ld_45s), and line width (hmi.Lw_45s)
  • 12 - minute
    • Line-of-sight magnetic field (hmi.M_720s)
    • Doppler velocity (hmi.V_720s)
    • Continuum intensity (hmi.Ic_720s), line depth (hmi.Ld_720s), and line width (hmi.Lw_720)
    • Stokes vector (hmi.S_720s), the IQUV values at each of 5 wavelengths
    • Inverted Vector Field (hmi.ME_720s) VFISV - Milne-Eddington Inversion (not yet released)
    • Disambiguated Vector Field (patches), hmi.Bharp_720s (not yet released)
  • 3 (TBD) - hour
    • Disambiguated B on full disk, hmi.B (not yet released)

On Demand

  • 3-second filtergrams
  • 3-minute vector B on patches
  • 6-minute disambiguated patches
  • 12-minute full-disk disambiguated vector field

On Request

  • 135-second disambiguated patches
  • 135-second Stokes Vectors
  • Anything else


JsocWiki: MagneticField (last edited 2014-11-18 05:17:51 by ToddHoeksema)