The Mag.num core field model as a parent for IGRF-13, and the recent evolution of the South Atlantic Anomaly

Abstract We present the GFZ candidate field models for $$13{\mathrm{th}}$$ 13 th Generation International Geomagnetic Reference Field (IGRF-13). These candidates were derived from geomagnetic core model, which is constrained by Swarm satellite and ground observatory data November 2013 to August 2019. Data selected magnetically quiet periods, model parameters have been obtained using an iteratively reweighted inversion scheme approximating a robust modified Huber norm as measure of misfit. The root mean square misfit in order 3–5 nT mid low latitudes, with maximum 44 east component at high latitudes. time-varying described 6 splines spherical harmonic coefficients up degree 20. note that temporal variation strongly damped shows smooth secular suits well IGRF, where represented constant over 5-year intervals. Further, external parameterised slowly varying part more rapidly controlled magnetic activity interplanetary proxies. Additionally, Euler angles sensor orientation are co-estimated. A widely discussed feature South Atlantic Anomaly, zone weak decreasing strength stretching southern Africa America. IGRF indicate anomaly has developed second, less pronounced eastern minimum Earth’s surface since 2007. observe while strong western continues drift westwards, currently drifts eastward surface. This does not seem be linked any motion core–mantle boundary, but rather intensity changes westward drifting flux patches contributing observed field. Also, we report sudden change measured two observatories around 2015.0, occurred shortly after well-known jerk 2014.0.