A Comparison of Sparse and Non-sparse Techniques for Electric-Field Inversion from Normal-Component Magnetograms

Abstract An important element of 3D data-driven simulations solar magnetic fields is the determination horizontal electric field at photosphere. This used to drive and inject energy helicity into corona. One outstanding problem localisation such that it consistent with Ohm’s law. Yeates ( Astrophys. J. 836 (1), 131, 2017) put forward a new “sparse” technique for computing from normal-component magnetograms minimises number non-zero values. aims produce better representation law compared previously “non-sparse” techniques. To test this approach we apply active region (AR) 10977, along developed non-sparse Mackay, Green, van Ballegooijen 729 (2), 97, 2011). A detailed comparison two techniques coronal observations determine which most successful. Results show (2011) produces best formation structure sigmoid above AR 10977. In contrast, (2017) injects strong between spatially separated, evolving polarities. injection highly twisted unphysical lines significantly higher helicity. It also demonstrated different results can be inconsistent depending on whether solved directly or indirectly through vector potential. method using either approach. The sparse has significant pitfalls when applied resolved data, where future studies need investigate why these problems arise.