Abstract
As a part of the 11th generation IGRF defined by IAGA, we propose a candidate model for the DGRF 2005, a candidate model for IGRF 2010 and a candidate model for the mean secular variation between 2010 and 2015. These candidate models, the derivation of which is described in the following, are based on the latest model in the CHAOS model series, called “CHAOS-3”. This model is derived from more than 10 years of satellite and ground observatory data. Maximum spherical harmonic degree of the static field is n = 60. The core field time changes are expressed by spherical harmonic expansion coefficients up to n = 20, described by order 6 splines (with 6-month knot spacing) spanning the time interval 1997.0–2010.0. The third time derivative of the squared magnetic field intensity is regularized at the core-mantle boundary. No spatial regularization is applied.
Highlights
The 11th generation IGRF is based on seven candidate models for DGRF 2005 and for IGRF 2010, and eight candidate models for the mean secular variation (SV) for 2010–2015
CHAOS-3 is derived from more recent satellite data and using “revised observatory monthly mean values”
Compared to CHAOS-2, most significant is the decrease of the observatory misfit by a factor 2 for the horizontal components Xand Yand by about 30% for Z, which is probably due to the use of revised monthly mean values compared to traditional monthly means
Summary
The 11th generation IGRF is based on seven candidate models for DGRF 2005 and for IGRF 2010, and eight candidate models for the mean secular variation (SV) for 2010–2015. During the evaluation procedure of the IGRF candidate models it has been found that the degree-1 internal terms of the preliminary model version CHAOS-3α—derived in September 2009 and used as parent model for our IGRF candidate models—for epoch 2010.0 are rather different from those of the other candidate models. This is most probably due to the fact that only data until summer 2009. The resulting final model, CHAOS-3, allows us to make a further assessment of our model candidates (which are based on CHAOS-3α) and of the final adopted IGRF model for epoch 2010.0
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