TARPs: Tracked Active Region Patches from SoHO/MDI

We describe progress toward creating a retrospective MDI data product consisting of tracked magnetic features on the scale of solar active regions, abbreviated TARPs (Tracked Active Region Patches). The TARPs are being developed as a backward-looking extension (covering approximately 3500 regions spanning 1996-2010) to the HARP (HMI Active Region Patch) data product that has already been released for HMI (2010-present). Like the HARPs, the MDI TARP data set is designed to be a catalog of active regions (ARs), indexed by a region ID number, analogous to a NOAA AR number, and time. TARPs from MDI are computed based on the 96-minute synoptic magnetograms and pseudo-continuum intensitygrams. As with the related HARP data product, the approximate threshold for significance is 100G. Use of both image types together allows faculae and sunspots to be separated out as sub-classes of activity, in addition to identifying the overall active region that the faculae/sunspots are part of. After being identified in single images, the magnetically-active patches are grouped and tracked from image to image. Merges among growing active regions, as well as faint active regions hovering at the threshold of detection, are handled automatically. Regions are tracked from their inception until they decay within view, or transit off the visible disk. The final data product is indexed by a nominal AR number and time. For each active region and for each time, a bitmap image is stored containing the precise outline of the active region. Additionaly, metadata such as areas and integrated fluxes are stored for each AR and for each time. Because there is a calibration between the HMI and MDI magnetograms (Liu, Hoeksema et al. 2012), it is straightforward to use the same classification and tracking rules for the HARPs (from HMI) and the MDI TARPs. We anticipate that this will allow a consistent catalog spanning both instruments. We envision several uses for the TARP data product, which will be available in the MDI resident archive (RA). The catalog, indexed by AR number and time, eases data subsetting, which is useful to focus computationally expensive studies on just the active parts of the Sun. The catalog will enable per-AR studies such as the relation between AR structure and energetic events like flares, in a way that can readily consider AR age and geometry. The TARP catalog, combined with the HARP catalog, could enable extended studies, such as solar irradiance, across cycles 23 and 24, and allow analyses that had been confined to just a handful of ARs to be extended to a larger set. A portion of this research was performed at the Jet Propulsion Laboratory, California Institute of Technology. All Rights Reserved. A tracked AR as described here (compare NOAA 10095). Center panel: selected appearances of the AR. Right and left panels: snapshots at times T1 and T2. At starred times, the AR contains multiple unconnected pieces.