Release Notes for HMI Vector Magnetic Field Data Files for AR 11158

This page describes the data files being released for AR 11158 and provides information about how to use them. For more information about the way the data have been computed and the uncertainties in them, please refer to VectorPaper.

We have computed a 5-day time series of 12-minute cadence disambiguated vector magnetic field and associated quantities.

• Data are provided as either CCD cut-outs or as remapped and projected values.
• There are also one-per-day samples in the same formats.
• Movies show summaries of the vector data and provide context information.

• Please make use of this [http://hmi.stanford.edu/doc/magnetic/guide.pdf Practical Guide] for reading HMI Vector Magnetograms and interpreting geometry information.

Description of Vector Field Cut-outs - ''hmi_test.B_720s_cutout''

This data series is in the original CCD coordinate system, virtually 'cut out' of the original full disk images. It is most appropriate for those who want to compare with other disk images and reconstruct the heliographic geometry themselves.

• A single ~900 MB tar file is provided for each of the 5 days from February 12 - 16, 2011.
• Each tar file contains 120 sets of 10 FITS files (1220 files), one set for each 12-minute interval of the day.
• Also included are 5 summary files:

  • The three index.* files list the contents of the directory

  • The JSOC_*.drmsrun and JSOC_*.qsub files give information about the export processing of the data series.

• ClickHereForDataRelease

• The names of the FITS data files indicate the data series (hmi_test.B_720s_cutout), an HMI region code (1984), time, and data quantity.
• An example of a file name is
  • hmi_test.B_720s_cutout.1984.20110212_000000_TAI.azimuth.fits
  • where hmi_test.B_720s_cutout is the series name, 1984 is the region number, 20110212_000000_TAI is the center time of the observation, and azimuth is the data quantity in that map.
• Each cut out is 650 * 600 pixels.
• Pixels that are not inverted are NANs.
• The files are RICE compressed.
• Each file contains keywords that provide geometry and other necessary information (described below).

  • A sample compressed cutout file has [http://hmi.stanford.edu/doc/magnetic/Btot.cutout.fitsheader.txt these keyword values]

• Ten Individual Data and Error Quantities
  • The three field components are:

    • field is the total average field strength for the pixel measured in Gauss.

    • inclination is the angle of the field vector relative to the line of sight in degrees from 0-180.

    • azimuth is angle of the field vector relative to 'up' on the CCD measured counterclockwise in degrees from 0-360, i.e. a values of 0 is nearly solar south at disk center.

  • The computed uncertainties of the individual components are given in

    • field_err

    • azimuth_err

    • inclination_err

  • The square root of the three covariances are given in combined names

    • field_az_err

    • field_inclination_err

    • inclin_azimuth_err

  • The Quality map gives information about the results of each processing step. See [http://hmi.stanford.edu/doc/magnetic/qualmap_description.pdf Qual_Map] for details.

    • qual_map contains 32-bit integers providing encoded information for each pixel:

      • Bits 28-31 - The Stokes vector computation
      • Bits 24-27 - The VFISV inversion results
      • Bits 0-7 - The disambiguation results (bits 0-7).
• KEYWORDS - Keywords in each FITS file provide information about the data.

  • Annotated list of [http://hmi.stanford.edu/doc/magnetic/hmi.B_720s.KeywordsSegments.pdf HMI_B Keywords]

  • General information about [http://jsoc.stanford.edu/doc/keywords/JSOC_Keywords_for_metadata.pdf JSOC Keywords]

  • Standard HMI [http://sun.stanford.edu/~beck/JSOC/HMI_WCS_Dummies.pdf WCS Coordinates]

  • See also the [http://hmi.stanford.edu/doc/magnetic/guide.pdf Practical Guide] for HMI Vector Field Data.

Description of CEA Projected and Remapped Vector Magnetic Field - ''hmi_test.B_720s_CEA''

The active region is mapped using a Lambert Cylindrical Equal Area Projection centered on the midpoint of the active region tracked at the Carrington rotation rate for the duration of the data series. This data series is most appropriate for those who wish to do modeling in a uniform geometry.

• A single ~650 MB tar file is provided for each of the 5 days from February 12 - 16, 2011.
• Each tar file contains 120 sets of 6 FITS files (720 files), one set for each 12-minute interval of the day.
• Also included are 5 summary files:

  • The three index.* files list the contents of the directory

  • The JSOC_*.drmsrun and JSOC_*.qsub files give information about the export processing of the data series.

• ClickHereForDataRelease

• The names of the FITS data files indicate the data series (hmi_test.B_720s_CEA), region (1984), time, and data quantity.
• An example of a file name is
  • hmi_test.B_720s_CEA.1984.20110212_000000_TAI.Br.fits
  • where hmi_test.B_720s_CEA is the series name, 1984 is the region number, 20110212_000000_TAI is the center time of the observation, and Br is the data quantity in that map.
• Each map is 600 * 600 pixels, in equal 0.03 degree steps of latitude and longitude at the center pixel.
• Pixels that are not inverted are NANs.
• The files are RICE compressed.
• Each file contains keywords that provide geometry and other necessary information (described below).

  • A sample compressed cutout file has [http://hmi.stanford.edu/doc/magnetic/Br.CEA.fitsheader.txt these keyword values]

• Six Individual Data and Error Quantities

  • The three field field components measured in Mx/cm2 or Gauss.

    • Br - the magnitude of the radial field component, positive is out of the solar surface.
    • Bt - the magnitude of the theta (southward) component of the field.
    • Bp - the magnitude of the phi (westward) component of the field.
  • The three computed error estimates (also in Gauss). Errors in the CEA projection are those of the nearest pixel before re-mapping.
    • Br_err - the error in the radial component of the field
    • Bt_err - the error in the theta component of the field
    • Bp_err - the error in the phi component of the field

  • The Quality map gives information about the results of each processing step. See [http://hmi.stanford.edu/doc/magnetic/qualmap_description.pdf Qual_Map] for details. Note, in CEA the values is for the nearest pixel before the remap.

    • qual_map contains 32-bit integers providing encoded information for each pixel:

      • Bits 28-31 - The Stokes vector computation
      • Bits 24-27 - The VFISV inversion results
      • Bits 0-7 - The disambiguation results (bits 0-7).
• KEYWORDS - Keywords in each FITS file provide information about the data.

  • Annotated list of [http://hmi.stanford.edu/doc/magnetic/hmi.B_720s.KeywordsSegments.pdf HMI_B Keywords]

  • General information about [http://jsoc.stanford.edu/doc/keywords/JSOC_Keywords_for_metadata.pdf JSOC Keywords]

  • Standard HMI [http://sun.stanford.edu/~beck/JSOC/HMI_WCS_Dummies.pdf WCS Coordinates]

  • See also the [http://hmi.stanford.edu/doc/magnetic/guide.pdf Practical Guide] for HMI Vector Field Data.

Sample Data

For those interested in surveying the data, we have provided shorter (~30MB) sample files that hold data for just five times, 00:00 TAI on each of the five days. The format of each data series is the same as that described above, except that there is one tar file for the entire data set. There is a file for the cut-out projection and another for the CEA projection. For each of the five 0:00 TAI times the cut-out tar file contains 10 fits files with the computed quantities outlined above. The CEA tar file contain for each time the same six fits files described above.

The sample.png file shows the intensity, radial component of the cut-out, and vector map of the CEA projection at each time.

• ClickHereForDataRelease

Summary and Context Movies

• Br Cutout Movie

  • The Br Cutout Movie shows the polarity of the radial field in black (inward) and white (outward). The color table saturates and a contour is drawn at the 600 G level. The cut-outs are in native CCD coordinates on a fixed 600 by 600 grid. The center pixel is the one nearest a point tracked at the Carrington rate, but of course some jitter remains. The HMI CCD is rotated such that solar north points very nearly to the bottom of the frame. Toward the end of the movie a dark region appears at the edge of the frames where data were not inverted. Each frame is labeled with the UT time. Note the 20s offset due to the use of TAI time in the original data series.

• Vector Field Movie

  • The Vector Field Movie shows the radial field in black (negative) and white (positive) with a contour at 600 G. The transverse component is shown by small vectors whose length is related to strength and whose color depends on the radial field direction (blue = positive, red = negative). Vectors are shown only when the transverse field is greater than 200 G. These data have been remapped and interpolated at high resolution onto a cylindrical equal area Lambert projection centered at a fixed point at the center of the region that is tracked at the Carrington rate. The vector field components have been transformed to Br, Btheta and Bphi. The UT time is shown for each frame.

• Hedgehog

  • There are three hedgehog versions of the field movie. In each movie red and blue indicate the direction and strength of the radial component of the field. At each grid point a small line shows the direction of the field originating on the surface. The length of the line corresponds to the total field strength. Vectors are shown only for points with total field strength greater than 200 G. The glyph on the lower left shows the orientation and projection of the movie relative to the a standard disk and indicates time of day with the small point in the outer circle that moves around on a 24-hour cadence. TAI time is indicated at the top of each frame. The movies show the full region at two scales and focus in on the east and west part of the region as it evolves.

• Intensity and Blos

  • The side-by-side frames show the continuum intensity (corrected for limb darkening) in shades of yellow, orange, and black on the left and the line-of-sight component of the magnetic field in black and white on the right. These are cut outs of the field rotated to place north at the top of the frame. The tracking is at the Carrington rate and some jitter remains due to rounding. The time of each frame is indicated.

• Tracked Patches

  • Two movies show the full disk magnetic field evolution during the first and second halves of the month of February. The colored regions are HMI Active Region Patches (HARPs) identified and tracked automatically from one image to the next. Each HARP is assigned a number (shown on the right) and color coded for ease of identification. Active pixels above a threshold are shown in black and the pixels inside the colored blobs show the instantaneous HARP boundary. The rectangular box around each region encloses the blob. The gray areas suggest how the region is changing in time. The northern and southern HARP numbers are indicated at the top and bottom right. Regions with a + near the center are numbered NOAA active regions and the NOAA numbers are shown on the right, near the HARP numbers. The + shows the NOAA-provided location and the NOAA numbers are listed from from left to right in the appropriate hemisphere. AR 11158 is the orange region labeled as HARP 883 in the southern hemisphere that crosses central meridian on February 14.

Additional Resources

• If you have trouble reading Rice compressed FITS files on your Mac, check [http://hmi.stanford.edu/doc/magnetic/fitsio.pdf here] for a guide to compiling fitsio.so

• Back to VectorMagneticField

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