CalcDeltaB: An efficient postprocessing tool to calculate ground‐level magnetic perturbations from global magnetosphere simulations

Abstract Ground magnetic field variations can induce electric currents on long conductor systems such as high‐voltage power transmission systems. The extra electric currents can interfere with normal operation of these conductor systems; and thus, there is a great need for better specification and prediction of the field perturbations. In this publication we present CalcDeltaB, an efficient postprocessing tool to calculate magnetic perturbations Δ B at any position on the ground from snapshots of the current systems that are being produced by first‐principle models of the global magnetosphere‐ionosphere system. This tool was developed during the recent “d B /d t ” modeling challenge at the Community Coordinated Modeling Center that compared magnetic perturbations and their derivative with observational results. The calculation tool is separate from each of the magnetosphere models and ensures that the Δ B computation method is uniformly applied, and that validation studies using Δ B compare the performance of the models rather than the combination of each model and a built‐in Δ B computation tool that may exist. Using the tool, magnetic perturbations on the ground are calculated from currents in the magnetosphere, from field‐aligned currents between magnetosphere and ionosphere, and the Hall and Pedersen currents in the ionosphere. The results of the new postprocessing tool are compared with Δ B calculations within the Space Weather Modeling Framework model and are in excellent agreement. We find that a radial resolution of 1/30 R E is fine enough to represent the contribution to Δ B from the region of field‐aligned currents.