Evaluation of candidate geomagnetic field models for IGRF-12

Abstract

-2010-2015). Findings: The models were derived from weighted averages of candidate models submitted by ten international teams. Teams were led by the British Geological Survey (UK), DTU Space (Denmark), ISTerre (France), IZMIRAN (Russia), NOAA/NGDC (USA), GFZ Potsdam (Germany), NASA/GSFC (USA), IPGP (France), LPG Nantes (France), and ETH Zurich (Switzerland). Each candidate model was carefully evaluated and compared to all other models and a mean model using well-defined statistical criteria in the spectral domain and maps in the physical space. These analyses were made to pinpoint both troublesome coefficients and the geographical regions where the candidate models most significantly differ. Some models showed clear deviation from other candidate models. However, a majority of the task force members appointed by IAGA thought that the differences were not sufficient to exclude models that were well documented and based on different techniques. Conclusions: The task force thus voted for and applied an iterative robust estimation scheme in space. In this paper, we report on the evaluations of the candidate models and provide details of the algorithm that was used to derive the IGRF-12 product.

An accelerating high-latitude jet in Earth’s core

“…It has secular variation at the core surface which is stable out to at least spherical harmonic degree 16 [1]. In this article, we focus on CHAOS-6 in preference to other available models because of its continuous treatment of ground and satellite data since the start of the modern era of satellite geomagnetism in 1999, its focus on high resolution secular variation, and the generally good agreement of the CHAOS family of models with other geomagnetic reference models [33].…”

The Revised Sunspot Record in Comparison to Cosmogenic Radionuclide-Based Solar Activity Reconstructions

“…The blue and dashed-red curves show the bootstrap average and standard deviation from the pfm9k.1b (in blue, Nilsson et al, 2014) and the A_FM (dashed-red curve, Licht et al, 2013) geomagnetic-field model. The two models have been joined together with gufm1 and IGRF 12th generation data (Jackson, Jonkers, and Walker, 2000;Thebault et al, 2015, dashed-green curve) over the period 1740 -1840 C.E., highlighted by the vertical-dashed lines. The one-σ error envelopes of the original published models are shown for reference in lighter shades of blue and red, respectively, as well as the dipole moment estimates from Knudsen et al (2008) (dotted-black curve with gray error band).…”

“…and IGRF 12th generation (Thebault et al, 2015) up to 2000 C.E. To avoid discontinuities in the transition, each individual bootstrap model was joined together with the historical field estimate by spline interpolation over a 100-year period (1740 -1840 C.E.…”

On the Usage of Geomagnetic Indices for Data Selection in Internal Field Modelling

“…IGRF is updated once in every five years. The processes to determine the two latest releases of IGRF coefficients, IGRF-11 and IGRF-12, are described by Finlay et al (2010) and Thébault et al (2015). The work begins with a call for candidate models to which typically some 7-9 international teams respond with proposals for a definitive reference field for the 5 years preceding the previous call, for provisional field for the latest 5-year epoch and for a predictive secular variation field model for the coming 5-year epoch.…”