A.A. Norton
W.W. Hansen Experiment Physics Laboratory, Stanford University, Stanford, CA 94305-4085
In order to make the properties of magnetic features observed by SDO/HMI more accessible, the Solar Photospheric Ephemeral and Active Region (SPEAR) catalogue has been created as an easy-to-read tabulated text file. Both active regions and smaller magnetic features such as ephemeral regions are included in the catalogue from the beginning of HMI science data acquisition, 2010.05.01, until 2020.12.31. More recent data will be added at regular intervals.
The catalogue currently contains information on nearly four thousand magnetic regions, SHARPs, at their nearest central meridian crossing time for Carrington Rotations 2096 – 2239. SPEAR-CR.txt is available here: http://sun.stanford.edu/~norton/SPEAR/ with a ReadMe text file and a Jupyter notebook, READ-SPEAR.ipynb for use in reading and plotting the data.
Some notes on the data are as follows. All of the latitude and longitude quantities are flux-weighted centroids. Many smaller magnetic regions are not associated with an assigned NOAA number and as such have a NOAA value of 0. If a quantity cannot be calculated for any reason, it is assigned the value of -999 in order to be easily flagged. A single SHARPs region may contain multiple NOAA regions; only one is listed in the SPEAR entries* (footnote).
The catalogue was created using the SPEAR code, modified from Anthony Yeates’ BMRS code that is available to the public ( https://github.com/antyeates1983/sharps-bmrs ) and described in Ref. [1]. The SPEAR code then accesses Spaceweather HMI Active Region Patches (SHARPs)[2] and associated keywords in JSOC in order to create the text catalogue. The SPEAR data differ from Yeates’ BMRS catalogue in several ways: first, it includes all SHARPs regardless of their polarity balance and second, different quantities are included such as the flux-weighted centroids of the positive and negative polarity regions, the sum of the line-of-sight magnetic field, and more. The quantities included in the SPEAR catalogue are found in the following table.
Table 1| The characteristics of the SHARPs magnetic regions that are included in the SPEAR catalogue.
As an example of the SPEAR data, a butterfly diagram showing the location of magnetic regions as a function of time and sin latitude is shown in Figure 1. The leading polarity determines the color so anti-Hale regions show up easily. The top ten rogue regions (Nagy et al., 2017, and Yeates, A., personal communication), whose axial dipole moment contributions are highly influential, are shown in yellow. The evolution of Cycle 24 is evident as is the beginning of Cycle 25.
Figure 1| A butterfly diagram created from the SPEAR data shows the magnetic regions as a function of time vs. sin (latitude). The leading spot polarity is shown in red (blue) with total flux indicated by symbol marker size. Anti-Hale regions are obvious as the non-dominant color in each hemisphere. The top ten rogue active regions are shown in yellow.
Additionally, tilt angle data from the SPEAR catalogue are shown in Fig. 2. The tilt angles of bipolar magnetic regions are thought to be crucial for the operation of the α-effect in the solar dynamo, and the distribution of tilts provides insight into the origins of strong magnetic fields and the influence of turbulent convection on the magnetic flux as it rises.
Figure 2|
Tilt angles shown as a histogram (top) and as a function of latitude (bottom) with colors indicating all bipolar magnetic regions (blue), those regions with anti-Joy tilts (red), and anti-Hale (purple) tilts. The range of values is 0-360 degrees. See inset in top plot for interpretation of angle values with P (N) indicatng a positive (negative) polarity. The lower scatter plot shows the latitude, and therefore the hemispheric contribution, of tilt angles found in the histogram.
In the SPEAR catalogue, the tilt was determined for 1811 regions. Anti-Joy tilts are found for 31% of the regions while 11% are anti-Hale, a value higher than reported by Ref. [4]. It’s worth pondering why more than 40% of magnetic regions disobey the laws of Joy and Hale.
More characteristics of the data, including a more advanced analysis of tilts, can be determined with the use of the SPEAR catalogue.
References
[1] Yeates, A. 2020, Solar Phys, 295, 119
[2] Bobra, M.G., Sun, X., Hoeksema, J.T., Turmon, M., Liu, Y., Hayashi, K., Barnes, G., and Leka, K.D. 2014, Solar Phys, 289, 3549.
[3] Nagy, M., Lemerle, A., Labonville, F., Petrovay, K., and Charbonneau, P. 2017, Solar Phys, 292, 167
[4] McClintock, B.H., Norton, A.A., and Li, J. 2014, ApJ, 797, 130
Footnote: * A list of HARP regions that contain multiple NOAA regions can be found here:
http://jsoc.stanford.edu/doc/data/hmi/harpnum_to_noaa/all_harps_with_noaa_ars.txt