HMI Magnetic Field Products
Four basic types of magnetic field products are described below.
Some data products suitable for space weather applications are available in near real time (nrt). Such data products always have nrt in the series name.
Quick access to HMI magnetic field catalogs and data products can be found at http://hmi.stanford.edu/magnetic
Notes for users of HMI Magnetic field pipeline data can be found at PipelineCode
LineofsightMagneticField : 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 (hmi.M_45s) in which twelve 4096*4096 filtergrams from the HMI Doppler camera are combined, one in each circular polarization at each of six wavelengths. A lower noise version (hmi.M_720s) is calculated every 720s using selected filtergrams from nine 135s vector field sequences from the other HMI camera.
The latest nrt HMI images are available at http://jsoc.stanford.edu/data/hmi/images/latest/.
A browsable image catalog ofHMI magnetic field and intensity
Vector Magnetic Field Image Data
VectorMagneticField : The vector magnetic field 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 six fixed 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 (hmi.S_720s) are computed from level 1 filtergrams. Then a Milne-Eddington inversion is performed to determine the field and other plasma parameters (hmi.ME_720s_fd10). Finally disambiguation is performed to determine the field azimuth angle See Vector Field Pipeline Overview for a description.
FullDiskDisamb : Full-disk disambiguated vector magnetic field images are available every 12 minutes starting on 19 December 2013 and can be found at hmi.B_720s. Magnetograms for earlier times can be computed upon request. These full disk disambiguation results are used to produce SHARPs starting on Jan 15, 2014.
SynopticMap : HMI synoptic maps are computed from the 720s line-of-sight magnetograms. Standard radial field synoptic charts are assembled by combining the 20 best 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. The basic SynopticRadial chart is used to compute the other kinds. DailySynopticMaps insert data observed within 60 degrees of central meridian averaged over a 4-hour interval into the most recent synoptic chart.
A browsable catalog of MDI and HMI synoptic maps.
HARPs - HMI Active Region Patches (HARPs)
HARPDataSeries : 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 disappearance. HARPs are often associated with one or more NOAA active regions. For each numbered HARP at each time step a rectangular bitmap indicates which pixels on the CCD are part of the HARP and above a threshold.
SHARPs - HMI Active Region Patches (HARPs) with Computed Space Weather Quantities
The SHARP data series collects maps of vector and scalar data products for each HARP region along with computed space-weather quantities. See the SHARP paper for details.
SpaceWeatherProducts - SHARPs - Active regions quantities computed from the vector magnetic field for each HARP time step are stored in SHARP keywords. The SHARP data series also provides links to cut-outs and remapped images of the HARPS. For more detail, see SHARP Explanation.
Source code is available for the SHARP module
Links to Currently Available Magnetogram Data
Magnetic Image Data
Links to lookdata
Line of sight Magnetograms
VFISV Inversion - ME
Disambiguated Vector B SHARP
Old Disambiguated Vector B
Obscure Data Products
Summary Information about Some ObscureDataProducts
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
Assumed Radial component of LoS map
Daily Update LoS Synoptic Map
Daily Update Radial Synoptic Map
Daily NRT Synoptic Maps
Daily Update NRT Los Synoptic Map
Daily Update NRT Radial Synoptic Map
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 (hmi.ME_720s_fd10) and for near real time processing (hmi.ME_720s_fd10_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.