Evaluation of candidate geomagnetic field models for IGRF-11

Abstract

Here, we report the evaluations of candidate models carried out by the IGRF-11 task force during October/November 2009 and describe the weightings used to derive the new IGRF-11 model. The evaluations include calculations of root mean square vector field differences between the candidates, comparisons of the power spectra, and degree correlations between the candidates and a mean model. Coefficient by coefficient analysis including determination of weighting factors used in a robust estimation of mean coefficients is also reported. Maps of differences in the vertical field intensity at Earth's surface between the candidates and weighted mean models are presented. Candidates with anomalous aspects are identified and efforts made to pinpoint both troublesome coefficients and geographical regions where large variations between candidates originate. A retrospective analysis of IGRF-10 main field candidates for epoch 2005.0 and predictive secular variation candidates for 2005.0-2010.0 using the new IGRF-11 models as a reference is also reported. The high quality and consistency of main field models derived using vector satellite data is demonstrated; based on internal consistency DGRF-2005 has a formal root mean square vector field error over Earth's surface of 1.0 nT. Difficulties nevertheless remain in accurately forecasting field evolution only five years into the future.

A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

“…Whereas seeking for inverse problem analytical solutions is commonly impracticable, numerical modeling may provide meaningful results. He et al (1996) show an optimization approach to solve a 1D consists of a spherical harmonics expansion of the geomagnetic potential, whose coefficients are determined empirically (Finlay et al, 2010). The model provides the 3D geomagnetic field distribution from the core to the magnetosphere, including the secular variation rate.…”

Forecasting secular variation using core flows

“…To ascertain how accurate previous forecasts have been, it is useful to examine how the IGRF-10 field model and its SV prediction compares against the DGRF and IGRF-11 models (Finlay et al, 2010). The models are compared using a root mean square (RMS) difference (or misfit) metric ( √ d P) calculated by Maus et al (2008):…”

Swarm SCARF Dedicated Lithospheric Field Inversion chain

“…In principle, there is a better consistency between the data selection detailed in the previous section and the data selection applied in the dedicated chain for the core field Rother et al, 2013), particularly at night times. This consistency is important if one keeps in mind that differences in data selection are acknowledged to be one of the major sources of discrepancies between main field models yet parameterized in similar ways (e.g., Finlay et al, 2010). In the course of the Swarm preparation phase, we tested the influence of each of the input main field models and the results were similar.…”

“…These length scales are typically dominated by the magnetic field created by the spatial variation in structure and composition of the Earth's crust and upper mantle for a review). The previous CHAMP (Reigber et al, 2002) satellite mission allowed impressive progress towards mapping the Earth's lithospheric magnetic field (e.g., Maus et al, 2008), understanding their geological sources (e.g., Hemant and Maus, 2005), and inferring other physical quantities such as the equivalent global Curie depth (Purucker et al, 2002) or the heat flow anomalies of the Earth's crust in remote regions (e.g., Fox-Maule et al, 2005). The Earth's lithospheric field at large wavelengths (>400 km) is conceptually simple because mostly static in time (e.g., Thébault et al, 2009).…”