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is a coherent magnetic structure at the scale of a solar active region identified in one or more HMI line-of-sight magnetograms. HARPs are typically observed over an extended time interval (e.g., days), and tracked from one image to the next. is a coherent magnetic structure at the scale of a solar active region identified in one or more HMI line-of-sight magnetograms. HARPs are typically observed over several days (possibly as much as a disk passage), and tracked from one image to the next.  At each time, the HARP bounding box and a mask that encloses the HARP are recorded.
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The HARPs are in the data series `hmi.MHARP_720s`, which is indexed by an integer identifier, `HARPNUM`, and by `T_REC`. The HARP will often be linked with a NOAA Active Region. This data series provides pointers to information covering the entire disk passage for each HARP in the HMI catalog, as well as summary information (e.g., integrated flux over the HARP), for each `HARPNUM` at each `T_REC`. The data series contains one segment, `MASK`, which is a mask image of the extent of the HARP at a given time. The HARPs are in the data series `hmi.MHARP_720s`, which is indexed by an integer identifier, `HARPNUM`, and by `T_REC`. The HARP will often be linked with a NOAA Active Region. This data series provides pointers to information covering the entire disk passage for each HARP in the HMI catalog, as well as summary information (e.g., integrated flux over the HARP), for each `HARPNUM` at each `T_REC`. The data series contains one segment, `BITMAP`, which is a mask image of the extent of the HARP at a given time.
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from `hmi.M_720s` and corresponding intensitygrams.) All three of these data products are full-disk images, in helioprojective-tangent coordinates (that is, as projected on the focal plane, from `hmi.M_720s` and corresponding intensitygrams, `hmi.Ic_noLimbDark_720s`.) All three of these data products are full-disk images, in helioprojective-tangent coordinates (that is, as projected on the focal plane,
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The `MASK` segment of the
HARP data series indicates exactly which pixels in the magnetogram are part of the HARP.
The `BITMAP` segment of the
HARP data series indicates exactly which pixels in the 720s magnetogram are part of the HARP.

HARP - HMI Active Region Patches

Note

This data product was released in April, 2012.

Overview

A HARP (short for HMI Active Region Patch) is a coherent magnetic structure at the scale of a solar active region identified in one or more HMI line-of-sight magnetograms. HARPs are typically observed over several days (possibly as much as a disk passage), and tracked from one image to the next. At each time, the HARP bounding box and a mask that encloses the HARP are recorded.

The HARPs are in the data series hmi.MHARP_720s, which is indexed by an integer identifier, HARPNUM, and by T_REC. The HARP will often be linked with a NOAA Active Region. This data series provides pointers to information covering the entire disk passage for each HARP in the HMI catalog, as well as summary information (e.g., integrated flux over the HARP), for each HARPNUM at each T_REC. The data series contains one segment, BITMAP, which is a mask image of the extent of the HARP at a given time.

The HARPs are found by analyzing the active region masks in hmi.Marmask_720s. (The masks are in turn derived from hmi.M_720s and corresponding intensitygrams, hmi.Ic_noLimbDark_720s.) All three of these data products are full-disk images, in helioprojective-tangent coordinates (that is, as projected on the focal plane, and not remapped to a latitude-longitude system). The BITMAP segment of the HARP data series indicates exactly which pixels in the 720s magnetogram are part of the HARP. It is a rectangular cutout from the full-disk images referred to above, typically several hundred pixels in each dimension, with special values indicating whether a pixel is on-HARP or not.

The data series can be used by following the links to associated vector, line-of-sight, and intensity data. For diagnostic or summary purposes, plots of individual keywords, such as integrated flux or size of the HARP, are also useful.

Methodology

Once localized sites that are magnetically active have been found (i.e., building on the full-disk active region masks) the HARP identification problem consists of two pieces: spatially grouping magnetic activity into objects on the scale of active regions, and tracking these objects from image to image. The grouping problem is harder, because flux emergence can cause formerly isolated ARs to merge. This means that a given HARP cannot be declared complete until it has disappeared in view of the observer, or rotated off the visible disk. Consequently, final HARPs are delayed by about a month.

It is important to track HARPs up to the limb, so that all the history of the HARP can be taken in to account in making grouping decisions. Consequently, the grouping criterion takes the spherical geometry into account.

We expect it will be useful to have easy access to the precursors and successors of the HARP. So, we extrapolate the area containing the HARP backwards in time from where it was first detected, and forward from the time where it vanished, two days in each direction. (Or less, if the entire region would rotate off-disk in this time.) This has the effect of expanding the range of T_REC associated with each HARP.

The HARP identification component consists of two parts, a grouping/tracking component, implemented in Matlab, and a data ingestion component, implemented as a JSOC module.

HARP Feature Scale

The following images show how the convolution kernel used for spatial grouping of active regions compares to a small active region at disk center. The units on the top two plots are HMI pixels. The bottom plot shows the convolution kernel at the same scale.

[http://sun.stanford.edu/~turmon/jsoc-wiki/kernel-scale-ar-mag-small.png] [http://sun.stanford.edu/~turmon/jsoc-wiki/kernel-scale-ar-mask-small.png]

[http://sun.stanford.edu/~turmon/jsoc-wiki/ar-grouping-kernel-center-small.png]

When at the limb, the convolution kernel is foreshortened as shown below:

[http://sun.stanford.edu/~turmon/jsoc-wiki/ar-grouping-kernel-limb-small.png]

Example

The following images are approximate data segments extracted from the large February 2011 active region. The corresponding HARP contains hundreds of T_REC values; we only show five. The orange blob outlines the contents of the HARP. The black pixels, most of which are inside the HARP, are all pixels declared active in the mask. Some clumps of active pixels are not large enough to constitute a HARP.

The white rectangle is not part of the data segment. It is the bounding box in pixel coordinates which contains the entire HARP, and its coordinates are part of the keywords. There is a corresponding bounding box, not shown, in Stonyhurst latitude-longitude coordinates, which is also recorded in the keywords, as MINLON0, MINLAT0, etc.

[http://sun.stanford.edu/~turmon/jsoc-wiki/track-movie-2011-feb-066-zoom.png] [http://sun.stanford.edu/~turmon/jsoc-wiki/track-movie-2011-feb-126-zoom.png] [http://sun.stanford.edu/~turmon/jsoc-wiki/track-movie-2011-feb-186-zoom.png] [http://sun.stanford.edu/~turmon/jsoc-wiki/track-movie-2011-feb-246-zoom.png] [http://sun.stanford.edu/~turmon/jsoc-wiki/track-movie-2011-feb-306-zoom.png]

Keywords

Besides the standard HMI keywords (observation geometry, time, and WCS), we have these keywords for HARP at each T_REC where it was observed:

Name

unit

Description

MINLON

degree

Minimum longitude for disk transit

MINLAT

degree

Minimum latitude for disk transit

MAXLON

degree

Maximum longitude for disk transit

MAXLAT

degree

Maximum latitude for disk transit

OMEGA

degree/day

Rotation rate

NPIX

none

Number of pixels within the identified region

SIZE

mH

Projected area of identified region on image in micro-hemisphere

AREA

mH

De-projected area of identified region on sphere in micro-hemisphere

NACR

none

Number of active pixels

SIZE_ACR

mH

Projected area of active pixels on image in micro-hemisphere

AREA_ACR

mH

De-projected area of active pixels on sphere in micro-hemisphere

MTOT

weber

Sum of absolute LoS flux within the identified region

MNET

weber

Net LoS flux within the identified region

MPOS_TOT

weber

Absolute value of total positive LoS flux

MNEG_TOT

weber

Absolute value of total negative LoS flux

MMEAN

gauss

Mean of LoS flux density

MSTDEV

gauss

Standard deviation of LoS flux density

MSKEW

none

Skewness of LoS flux density

MKURT

none

Kurtosis of LoS flux density

MINLAT0

degree

Minimum Stonyhurst latitude of pixels within the patch

MINLON0

degree

Minimum Stonyhurst longitude of pixels within the patch

MAXLAT0

degree

Maximum Stonyhurst latitude of pixels within the patch

MAXLON0

degree

Maximum Stonyhurst longitude of pixels within the patch

FWT_LAT

degree

Stonyhurst latitude of flux-weighted center of active pixels

FWT_LON

degree

Stonyhurst longitude of flux-weighted center of active pixels

FWTPOS_LAT

degree

Stonyhurst latitude of flux-weighted center of positive flux

FWTPOS_LON

degree

Stonyhurst longitude of flux-weighted center of positive flux

FWTNEG_LAT

degree

Stonyhurst latitude of flux-weighted center of negative flux

FWTNEG_LON

degree

Stonyhurst longitude of flux-weighted center of negative flux

T_FRST

TAI

T_REC of first frame of HARP

T_LAST

TAI

T_REC of last frame of HARP

JsocWiki: HARPDataSeries (last edited 2015-05-23 07:42:08 by MichaelTurmon)