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|| Some data products suitable for space weather applications are available in near real time. ||
|| More details are provided at VectorMagneticField, LineofsightMagneticField, ["HARPDataSeries"], and SpaceWeatherProducts. ||		 || 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. ||
|| More details are provided at LineofsightMagneticField, VectorMagneticField, SynopticMaps, ["HARPDataSeries"], and SpaceWeatherProducts. ||
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 . 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 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.
 . The latest HMI images are available at http://jsoc.stanford.edu/data/hmi/images/latest/
. 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 ([http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.M_720s 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 ([http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.M_720s 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/
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 . VectorMagneticField : 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.
. VectorMagneticField : 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 ([http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.S_720s hmi.S_720s]) are computed. Then a Milne-Eddington inversion is performed to determine the field and other plasma parameters ([http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.ME_720s_fd10 hmi.ME_720s_fd10]). Finally disambiguation is performed to determine the field angles (TBA, preliminary data at [http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.B_720s_e15w1332_CEA hmi.B_720s_e15w1332_CEA]).
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 . SynopticMaps : 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.
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===== SHARP - HMI Active Region Patches with Space Weather Quantities =====  . SynopticMaps : 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 synoptic chart.
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 . ["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 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. ===== SHARPs - HMI Active Region Patches (HARPs) with Computed Space Weather Quantities =====

 . ["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. The SHARP data series collects the mapped data for the region along with computed space-weather quantities.

 . SpaceWeatherProducts - SHARPs - '''Still to come'''. Space weather quantities computed from the vector magnetic field for each HARP time step are stored in SHARP keywords. The SHARP data series will also provide links to cut-outs and remapped images of the HARPS. Details still to come.

HMI Magnetic Field Products

http://jsoc.stanford.edu/data/hmi/images/latest/HMI_latest_Mag_256x256.gif

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 (nrt). Such data products always have nrt in the series name.

More details are provided at LineofsightMagneticField, VectorMagneticField, SynopticMaps, ["HARPDataSeries"], and SpaceWeatherProducts.

Line-of-sight Magnetograms

Vector Magnetic Field Image Data

  • VectorMagneticField : 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 ([http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.S_720s hmi.S_720s]) are computed. Then a Milne-Eddington inversion is performed to determine the field and other plasma parameters ([http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.ME_720s_fd10 hmi.ME_720s_fd10]). Finally disambiguation is performed to determine the field angles (TBA, preliminary data at [http://jsoc.stanford.edu/ajax/lookdata.html?ds=hmi.B_720s_e15w1332_CEA hmi.B_720s_e15w1332_CEA]).

Synoptic Maps

  • SynopticMaps : 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 synoptic chart.

SHARPs - HMI Active Region Patches (HARPs) with Computed Space Weather Quantities

  • ["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. The SHARP data series collects the mapped data for the region along with computed space-weather quantities.

  • SpaceWeatherProducts - SHARPs - Still to come. Space weather quantities computed from the vector magnetic field for each HARP time step are stored in SHARP keywords. The SHARP data series will also provide links to cut-outs and remapped images of the HARPS. Details still to come.

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.

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