HMI Active Region Patches

Michael TurmonJPL/Caltech

2

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)

3

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)

4

Delivering the HARPs as a Data Product

Instantaneous bounding box

HARP bounding box (bigger)

HARP origin

Mag: 2011/02/14 12:00

5

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.

6

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.

7