Validation of AMPERE Magnetic Perturbations Using Swarm

The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) provides continuous global maps of Birkeland currents, using magnetic field perturbations (d B ) obtained by calibrating and detrending data from engineering magnetometers on the 66 polar‐orbiting Iridium satellites in the communications constellation. Here, we provide an assessment of AMPERE d B accuracy, as compared with magnetic field observations from the Swarm satellite mission. The CHAOS v8.1 model (Finlay et al., 2020, https://doi.org/10.1186/s40623‐020‐01252‐9 ) was used to remove the main field and other non‐ionospheric contributions from both data sets. In a nearest‐neighbor comparison covering August 2022, AMPERE's calibrated and detrended d B data from the Iridium NEXT satellites are found to have root‐mean‐square deviations of 31 and 33 nT (for d B θ and d B φ , respectively) as compared with data from Swarm, while the biases are −7 and −2 nT. For the same interval, AMPERE's fitted maps have root‐mean‐square errors of <40 nT, rising to 109–185 nT in active conditions (defined as Swarm d B > 250 nT). However, there is evidence that small scale (<400‐km along Swarm track direction) d B structures are not fully resolved. Overall, we find that the AMPERE d B data and fitted products are unbiased and are typically in excellent agreement with the Swarm data.