IGRF candidate models at times of rapid changes in core field acceleration

Research areas:
Earth Planets Space
We submit three candidate models following the call
for IGRF-11. We apply a simple modeling approach in
spherical harmonics based on a quadratic Taylor
expansion for the internal field time variations. We
use the Dst magnetic index as a proxy for the
external field variations. In order to compensate
for the limitations incurred by such a conventional
approach, we focus on the optimal selection of
satellite data in space and time. We also show that
some a priori knowledge about the core field state
helps us to avoid the pitfall encountered in the
case of rapid changes of core field
accelerations. Indeed, various acceleration events
of relevance for the IGRF 11th occurred between 2003
and 2010, one of them being a geomagnetic jerk. They
could entail disagreements between IGRF candidate
models for the secular variation (SV) if data prior
to 2008 are used. Our SV and main field (MF)
candidate models have a root mean square uncertainty
less than 6 nT/yr and 8 nT, respectively, with
respect to the modeled magnetic field
contributions. These values correspond to the
intrinsic error associated with truncating SV and MF
models to spherical harmonic degree 8 and 13,
respectively, as requested for IGRF models.