HMI Vector Magnetic Field Products
For the most up-to-date information on all the vector data products, including current release information,
see the wiki.
The vector magnetic field is derived from full-disk filtergrams collected in a 135-second sequence.
The observations are obtained in polarized light at several wavelengths across a spectral line.
The filtergrams are calibrated and registered to account for solar rotation before being combined
to provide Stokes polarization parameters.
The parameters are used to determine the magnetic and other plasma parameters using VFISV, a Milne-Eddington inversion code.
The final step is to disambiguate the data, that is infer the azimuthal direction of the transverse field.
Vector Field Quantities Described in More Detail Below
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Stokes Vector:
The Stokes parameters are available for the whole mission.
-
ME Inversion:
The full disk inverted quantities are available since April, 2012 and earlier for selected intervals.
-
Full Disk Vector B:
The full disk vector field is not yet available.
-
SHARP for Space Weather:
Definitive vector field in HMI Active Region Patches (HARPS) will be available starting in the fall of 2012.
Starting 14 September, 2012 quick-look vector analysis of near-real time HARPS is being completed for space-weather purposes.
The vector field and a set of quantities useful for predictions are computed quickly using HMI nrt data.
These data are available in both native CCD coordinates and Cartesian heliographic coordinates.
Early Vector B in HARPs:
Science-grade vector field is currently available only for selected regions.
The first region for science data was AR 11158, observed in February, 2011.
Since then a few regions have been fully processed, most with early versions of code.
These are desribed at ReleaseNotes2.
SHARP Data - Tracked Space-weather HMI Active Region Patches.
Available Fall, 2012.
Vector magnetic field in HMI Active Region Patches tracked during their disk transit will become available in fall 2012.
These data have been available for near real time applications in a non-science quality version since mid September.
The disambiguated vector data will be provided in native CCD coordinates every 12 minutes
and also in standard Cartesian projected CEA (Cylindrical Equal Area) coordinates centered on the tracked region.
The SHARP data series provide several maps of other HMI observables and derived space weather indices for each HARP at each time step.
For a more complete description of SHARPs, look here.
See HARPS for a description of HMI Active Region Patches.
Go to the VectorMagneticField Wiki entry for more details.
For release of early Science-quality active region data, see
ReleaseNotes2.
-
hmi.sharp_720s_nrt
and hmi.sharp_720s
provide vector magnetic field in the active region as it transits the disk.
The size of the nrt SHARP will change with time, but
the definitive SHARP will enclose a constant heliographic area on the Solar surface during the entire disk passage.
The SHARP includes map cut-outs of the full set of vector field components, uncertainties, and covariances as well as other useful
quantites, such as continuum intensity, velocity, and line-of-sight magnetic field; there are maps of 31 quantities.
The three prime vector components are total magnetic flux density, inclination of the field to the line of sight, and azimuth angle.
The SHARP also provides convenient space-weather indices for the region at each time step such as
total flux, area, and vertical current.
-
hmi.sharp_720s_cea_nrt
and
hmi.sharp_cea_720s_
have been projected and remapped to a cylindrical equal area Cartesian coordinate system
centered on the tracked active region.
The size of the nrt regions will evolve with time.
At each time step the definitive SHARPs will enclose the maximum extent of the region during it's disk passage.
The three prime vector components are Bx, By, and Bz.
HARP maps of 8 additional quantities are also provided at each time step:
the three estimated component errors, the line-of-sight magnetogram, a Dopplergram, the continuum intensity,
a map of the active pixels, and an estimate of the confidence in the disambiguation.
ME Data - Milne-Eddington Inversions:
Currently our most complete definitive vector field product is the ME inversion data processed using the
Very Fast Inversion of the Stokes Vector (VFISV)
scheme. VFISV provides the primary data segments of field strength, inclination and azimuth.
No disambiguation of the azimuth has been performed in the ME data product, so azimuths are in the range 0-180, not 0-360.
- hmi.ME_720s_fd10
represents our most up-to-date pipeline vector data product. fd10 in the product name refers to a version of the VFISV code.
Updates in the fd10 inversion code include a regularization of the minimization function to bias the solution towards a lower eta0 in the case of double minima.
- hmi.ME_720s_e15w1332
is an earlier older, beta-test version of the data product that was released in fall of 2011. The e15 in the series name
indicates a strict convergence criteria that forced the number of iterations at each pixel to 200;
the w1332 in the name referred to relative weights of I,Q,U,V of 1,3,3,2 in the inversion.
Only a very limited selection of e15w1332 data are available.
Stokes Profile Data:
- hmi.S_720s
provides maps of each of the Stokes profile parameters, I, Q, U, and V, for each wavelengths position. Data are available from
the start of the HMI mission every 12 minutes. These data are most convenient for those preferring non-inverted values.
Coverage Maps:
-
HMI Data Coverage Maps
Monthly charts showing if data was available or missing or of low quality.
Currently the coverage maps are available for Line-of Sight magnetograms and for inverted ME_720s_fd10.
Our JSOC Wiki provides an overview of the
HMI Magnetic Field Products
and links to more detailed information.
Joint Science Operations Center (JSOC)
