HMI Active Region Patches
Michael TurmonJPL/Caltech
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Mask and Patch Data Products
• Magnetograms (M_720s) + intensitygrams (Ic_720s) yield activity masks (Marmask_720s).
• Active clumps in Marmask_720s are grouped into “instantaneous patches” (Mpatch_720s)
• The instantaneous patches are linked temporally using an overlap metric to produce HARPs (HMI AR Patch)
• A HARP is about the scale of a NOAA active region.
• We have its entire history.
Mask: 2011/02/14 12:00
HARP
zoom
(text overlayin this image
is flipped)
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HARP Geometry
• HARPs are a simple concept, but their geometry can be complex.
• They are often not “simply connected”– I.e., a single HARP can consist of multiple compact blobs
• Their configuration is unknown until final demise– HARPs are retrospectively pasted together (“merged”) as future growth is observed
HARPs: 2011/02/14 12:00One Day Earlier One Day Later
• HARPs are a sequence of cut-outs from the original image set.
• To use, you shift the cut-out to the correct place in M_720s, etc.– There is no complex transformation. Just a shift in pixel coordinates.
• In JSOC, the HARP data series is indexed by HARP number, analogous to NOAA AR number, and time.
• Encoding: on-HARP (orange patch) is ≥ 64; active area within HARP is 66; inactive within HARP is 65. (Using symbolic KWs)
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Delivering the HARPs as a Data Product
Instantaneous bounding box
HARP bounding box (bigger)
HARP origin
Mag: 2011/02/14 12:00
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What the HARP is aimed at
• Why is the HARP bounding box larger than the instantaneous bounding box? How is that size determined?– Note: You do need not to know or remember these details.
• We want the HARP to be in image coordinates for ease-of-use, but we also want the HARP to be a consistent size for AR studies
• Key: The HARP cutout is made as if seen by observer hovering above the AR, moving at a constant angular rate (deg. lon/day).– Per-HARP angular rate determined from differential rotation formula in powers
of sin2(lat) evaluated at HARP centroid in latitude, and encoded in HARP KWs.
• The dimensions (degrees lon X degrees lat) of the HARP is given by the smallest lat-lon bounding box that encompasses all presentations of the HARP from birth to death.
• HARPs have equal extent in longitude => they are “tall” at the limb.
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Graphical Overview of HARP Sizing
• Orange pixels are on-HARP; black pixels are active. The white line marks the instantaneous bounding box (in image-pixel coordinates).
• The blue dots mark the lat-lon center of the HARP. The center has a constant latitude and advances in longitude with constant rate.
• The red boxes show a fixed-size lat-lon bounding box, centered on the blue dots, which encompasses all HARP pixels at all times.
• The HARP is the smallest image-domain box containing the red boxes.
Time S
ame lat/lon
Acknowledgement
The research described in this paper was carried out in part by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.
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