A secular variation candidate model for IGRF-13 based on Swarm data and ensemble inverse geodynamo modelling

Abstract This paper describes the design of a candidate secular variation model for 13th generation International Geomagnetic Reference Field. is based upon integration an ensemble 100 numerical models geodynamo between epochs 2019.0 and 2025.0. The only difference each member lies in initial condition that used integration, all other control parameters being fixed. An defined as follows: estimate magnetic field its rate-of-change at core surface obtained from year (2018.5–2019.5) vector Swarm data. (common to members) subject prior constraints: statistical properties dynamo main geomagnetic variation, prescribed covariances sources. One next considers three-dimensional states (in terms flow, buoyancy fields) extracted different discrete times simulation not constrained by observations, with time distance state exceeding decorrelation time. Each adjusted three dimensions) order take into account. methodology provides conditions subsequent up epoch Focussing on 2020.0–2025.0 window, we use median average Gauss coefficient statistics define over frame uncertainties.