HMI Magnetic Field Products

• There are four basic types of magnetic field products described below.
• Some data products suitable for space weather applications are available in near real time.

• More detail is provided at VectorMagneticField, LineofsightMagneticField, and SpaceWeatherProducts.

Line-of-sight magnetic field

• 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 fastest line-of-sight observing cadence is 45 seconds in which twelve filtergrams from the HMI Doppler camera are combined, one in each circular polarization at each of six wavelengths. A lower noise version is calculated every 720s using selected filtergrams from nine 135s vector field sequences from the other HMI camera.

Vector magnetic fields

• 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 135 seconds and uses images from HMI's Magnetic camera. The 36 filtergrams measure six polarization states, I plus or minus Q,U,and V, at the same six wavelengths. All filtergrams are corrected for instrumental effects and interpolated to the proper time. Most analysis is done with weighted averages computed every 720s using data collected over 1215 seconds (nine 135s intervals). The processing happens in three steps. First Stokes parameters are computed. Then an inversion is performed to determine the field and other plasma parameters. Finally disambiguation is performed to determine the field angles.

Synoptic maps

• Synoptic maps are computed from the 720s line-of-sight magnetograms. Standard charts are assembled by combining the 20 observations made nearest central meridian at each longitude. It takes approximately 27.27 days to complete a solar rotation. Synoptic maps are provided in two resolutions and as line-of-sight and inferred radial field. Daily update charts insert data observed within 60 degrees of central meridian averaged over a 4-hour interval into the most recent synopic chart.

HARP & SHARP - HMI Active Region Patches

• A HARP provides location information about a magnetic active region throughout its disk passage. Each 720s line-of-sight magnetogram is analyzed to generate a mask that indicates coherent regions of strong activity. The time series of masks is analyzed to identify persistent active regions. After the region rotates off the disk, a definitive time series is created that provides consistent geometric information about the HARP from before its first emergence to after its dissappearance. HARPs are often associated with one or more NOAA active regions. The SHARP data series collects the mapped data for the region along with computed space-weather quantities.

Links to Currently Available Magnetogram Data

• Magnetic Image Data	Links to lookdata
  Line of sight Magnetograms	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.M_720s hmi.M_720s]	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.M_45s hmi.M_45s]
  Stokes Parameters	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.S_720s hmi.S_720s]
  VFISV Inversion - ME	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.ME_720s_fd10 hmi.ME_720s_fd10]	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.ME_720s_fd10_nrt hmi.ME_720s_fd10_nrt]
  Disambiguated Vector B	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.B_720s_e15w1332_cutout hmi.B_720s_e15w1332_cutout]	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.B_720s_e15w1332_CEA hmi.B_720s_e15w1332_CEA]
  Obsolete Data	ObsoleteMagneticData

Links to Synoptic Maps

• HMI synoptic maps provide a composite view of the entire observable solar surface. They are computed from the 720s line-of-sight magnetic field measurements and come in 3600*1440 and 720*360 sizes.

  Standard HMI Photospheric Field Carrington Synoptic Maps
  Line of sight synoptic map	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Synoptic_Ml_720s hmi.Synoptic_Ml_720s]	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Synoptic_Ml_720s_small hmi.Synoptic_Ml_720s_small]
  Assumed Radial component of LoS map	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Synoptic_Mr_720s hmi.Synoptic_Mr_720s]	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Synoptic_Mr_720s_small hmi.Synoptic_Mr_720s_small]
  DailySynopticMaps
  Daily Update LoS Synoptic Map	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mldailysynframe_720s hmi.Mldailysynframe_720s]	Coming soon: [http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mldailysynframe_720s_small hmi.Mldailysynframe_720s_small]
  Daily Update Radial Synoptic Map	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mrdailysynframe_720s hmi.Mrdailysynframe_720s]	Coming soon: [http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mrdailysynframe_720s_small hmi.Mrdailysynframe_720s_small]
  Daily NRT Synoptic Maps
  Daily Update NRT Los Synoptic Map	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mldailysynframe_720s_nrt hmi.Mldailysynframe_720s_nrt]	Coming soon: [http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mldailysynframe_720s_nrt_small hmi.Mldailysynframe_720s_nrt_small]
  Daily Update NRT Radial Synoptic Map	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mrdailysynframe_720s_nrt hmi.Mrdailysynframe_720s_nrt]	Coming soon: [http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mrdailysynframe_720s_nrt_small hmi.Mrdailysynframe_720s_nrt_small]

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.

• HARP Data Series	Definitive	NRT
  Line of Sight	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mharp_720s hmi.HMarp_720s]	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.Mharp_720s_nrt hmi.HMarp_720s_nrt]
  Vector - ME	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.ME_720s_fd10_HARP hmi.ME_720s_fd10_HARP]	[http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.ME_720s_fd10_HARP_nrt hmi.ME_720s_fd10_HARP_nrt]

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