Accuracy of magnetic energy computations

摘要: Context. For magnetically driven events, the magnetic energy of system is prime reservoir that fuels dynamical evolution. In solar context, free ( i.e., in excess potential field energy) one main indica tors used space weather forecasts to predict eruptivity active regio ns. A trustworthy estimation therefore needed three-dimensional (3D) models atmosphere, e.g., coronal fields reconstructions or numerical simulations. Aims. The expression a as sum its and (Thomson’s theorem) strictly valid when exactly solenoidal. realiz ations on discrete grid, this property may be only approximately fulfilled. We show imperfect solenoidality induces ter ms can lead misinterpreting amount present configuration. Methods. consider decomposition solenoidal nonsolenoidal parts which allows unambiguous contribution energy. apply six typical cases broadly physics. quantify what extent Thomson theorem not satisfied approx imately are used. Results. quantified errors vary from negligible significant erro rs, depending component field. identify source analyz e implications adding variable divergence various fields. Finally, we pathological unphysica l situations where estimated would appear negative, found some previous works, error presence finite divergence. Conclusions. provide method quantifying effect fields, together with detailed diagnostics sources. also compare effi ciency two divergence-cleaning techniques. These results applicable broad range realizations