NGDC/GFZ candidate models for the 10th generation International Geomagnetic Reference Field

Abstract

Following the call for candidates for the 10th generation IGRF, we produced and submitted three main field and three secular variation candidate models. The candidates are derived from parent models which use a standard quadratic parameterisation in time of the internal Gauss coefficients. External magnetospheric fields are represented by combined parameterisations in Solar Magnetic (SM) and in Geocentric Solar Magnetospheric (GSM) coordinates. Apart from the daily and annual variations caused by these external fields, the model also accounts for induction by Earth rotation in a non-axial external field. The uncertainties of our candidates are estimated by comparing independent models from CHAMP and Ørsted data. The root mean square errors of our main field candidates, for the internal field to spherical harmonic degree 13, are estimated to be less than 8 nT at the Earth's surface. Our secular variation candidates are estimated to have root mean square uncertainties of 12 nT per year. A hind-cast analysis of the geomagnetic field for earlier epochs shows that our secular acceleration estimates from post-2000 satellite data are inconsistent with pre-2000 acceleration in the field. This could confirm earlier reports of a jerk around 2000.0, with a genuine change in the secular acceleration.

Modelling the Earth’s core magnetic field under flow constraints

“…(5) and (9). This number corresponds to the Gaunt and Elsasser's integral exclusion rule (see for example Moon, 1979), and the matrix formulation for Eq. (12) becomes:…”

“…Only recently has it become clear that this is possible for magnetic eld models spanning only a few years. First attempts have been made by Lesur et al (2005), Maus et al (2005), and Olsen et al (2005), but their SA models do not agree. The CHAOS model (Olsen et al, 2006) presents a more realistic SA but the use of cubic B-splines to parameterize in time the core magnetic eld precludes its continuous mapping.…”

International Geomagnetic Reference Field—the tenth generation

“…Team A applied ionospheric corrections, team B applied diamagnetic plasma correction to CHAMP data and oceanic tidal corrections to all input data, team C used observatory hourly mean data and incorporated outputs from linear prediction filters to long-term annual mean data into their secular-variation model, and team D used natural orthogonal component analysis. Sections 1 and 2 of Maus et al (2005a) give some more information about the candidate models submitted, but for detailed information the reader is referred to Olsen et al (2005), Maus et al (2005b), Lesur et al (2005) and Golovkov et al (2005) in this special issue of the journal Earth, Planets and Space.…”

Candidate models for the IGRF-11th generation making use of extrapolated observatory data

“…The abrupt change observed around 1998 at KNY may be related to a geomagnetic jerk, occurring at or near epoch 2000 (Mandea et al, 2000a;Maus et al, 2005). At CLF, this jerk occurred in 1998.0, i.e.…”