NOAA/NGDC candidate models for the 12th generation International Geomagnetic Reference Field

Abstract

The International Geomagnetic Reference Field (IGRF) is a model of the geomagnetic main field and its secular variation, produced every 5 years from candidate models proposed by a number of international research institutions. For this 12th generation IGRF, three candidate models were solicited: a main field model for the 2010.0 epoch, a main field model for the 2015.0 epoch, and the predicted secular variation for the five-year period 2015 to 2020. The National Geophysical Data Center (NGDC), part of the National Oceanic and Atmospheric Administration (NOAA), has produced three candidate models for consideration in IGRF-12. The 2010 main field candidate was produced from Challenging Minisatellite Payload (CHAMP) satellite data, while the 2015 main field and secular variation candidates were produced from Swarm and Ørsted satellite data. Careful data selection was performed to minimize the influence of magnetospheric and ionospheric fields. The secular variation predictions of our parent models, from which the candidate models were derived, have been validated against independent ground observatory data.

Evidence for a new geomagnetic jerk in 2014

“…In order to remove as much external field signal as possible, in previous analyses of geomagnetic jerks it was common to compute monthly means only from nightside data and quiet time intervals [Chulliat and Maus, 2014;Alken et al, 2015] or by employing a dedicated two-step method [Brown et al, 2013]. However, here use has been made of the complete data set, because the changes on the trends are equally evident, and the extra time needed to select the data would have affected the promptness with which we wanted to present our results.…”

Evaluation of candidate geomagnetic field models for IGRF-12

“…Some teams nevertheless considered a physics-based approach applying the tools of geophysical assimilation or setting a priori hypothesis on the core flow (e.g., Gillet et al 2015;Hamilton et al 2015). Other teams (e.g., Alken et al 2015;Finlay et al 2015;Lesur et al 2015;Saturnino et al 2015) relied on simple analytical extrapolation assuming that the magnetic field will evolve linearly over the next 5 years. From October to early December 2014, some members of the task force and interested parties carried out evaluations of the candidate models submitted by the different teams.…”

First results from the Swarm Dedicated Ionospheric Field Inversion chain

“…Data corrections were applied for the core, crustal and magnetospheric fields using the following models: (a) a Swarm-based, core field model derived by Patrick Alken (University of Colorado Boulder) using an algorithm recently developed for the IGRF project (Alken et al 2015a), (b) the MF7 lithospheric field model, which can be retrieved from https://geomag.colorado.edu/magnetic-field-model-mf7. html and uses more recent CHAMP data but a similar methodology as the earlier MF6 model (Maus et al 2008); (c) the POMME-6 magnetospheric field model (Maus and Lühr 2005;Lühr and Maus 2010).…”