Solar Physics

, 293:9 | Cite as

Active Region Photospheric Magnetic Properties Derived from Line-of-Sight and Radial Fields

  • J. A. Guerra
  • S.-H. Park
  • P. T. Gallagher
  • I. Kontogiannis
  • M. K. Georgoulis
  • D. S. Bloomfield


The effect of using two representations of the normal-to-surface magnetic field to calculate photospheric measures that are related to the active region (AR) potential for flaring is presented. Several AR properties were computed using line-of-sight (\(B_{\mathrm{los}}\)) and spherical-radial (\(B_{r}\)) magnetograms from the Space-weather HMI Active Region Patch (SHARP) products of the Solar Dynamics Observatory, characterizing the presence and features of magnetic polarity inversion lines, fractality, and magnetic connectivity of the AR photospheric field. The data analyzed correspond to \({\approx\,}4{,}000\) AR observations, achieved by randomly selecting 25% of days between September 2012 and May 2016 for analysis at 6-hr cadence. Results from this statistical study include: i) the \(B_{r}\) component results in a slight upwards shift of property values in a manner consistent with a field-strength underestimation by the \(B_{\mathrm{los}}\) component; ii) using the \(B_{r}\) component results in significantly lower inter-property correlation in one-third of the cases, implying more independent information as regards the state of the AR photospheric magnetic field; iii) flaring rates for each property vary between the field components in a manner consistent with the differences in property-value ranges resulting from the components; iv) flaring rates generally increase for higher values of properties, except the Fourier spectral power index that has flare rates peaking around a value of \(5/3\). These findings indicate that there may be advantages in using \(B_{r}\) rather than \(B_{\mathrm{los}}\) in calculating flare-related AR magnetic properties, especially for regions located far from central meridian.


Active regions, magnetic fields Flares, forecasting Flares, relation to magnetic field Magnetic fields, photosphere 



This research was funded by the European Union Horizon 2020 research and innovation programme under grant agreement No. 640216 (FLARECAST). SHARP data were provided by courtesy of NASA/SDO and the HMI science team, and hosted for FLARECAST ( ) by the MEDOC data and operations centre ( ; CNES/CNRS/Univ. Paris-Sud). We thank the anonymous referees for their comments; they certainly helped improve the manuscript.

Disclosure of Potential Conflicts of Interest

The authors declare that they have no conflicts of interest.


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© Springer Science+Business Media B.V., part of Springer Nature 2018

Authors and Affiliations

  1. 1.School of PhysicsTrinity College DublinDublin 2Ireland
  2. 2.Research Center for Astronomy and Applied Mathematics (RCAAM)Academy of AthensAthensGreece
  3. 3.Northumbria UniversityNewcastle upon TyneUK

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