International Geomagnetic Reference Field - The Twelfth generation

Editorial Board (Oct. 2015)
Editor-in-Chief
Yasuo Ogawa, Tokyo Institute of Technology, Japan

Editorial Board
Yosuke Aoki, University of Tokyo, Japan
Stephen Bannister, GNS Science, New Zealand
Benjamin Fong Chao, Academia Sinica, Taiwan
Nobuo Geshi, Geological Survey of Japan, AIST,Japan
Lin-Ni Hau, National Central University, Taiwan
Hauke Hussmann, German Aerospace Center,
Germany
Alexey Kuvshinov, Institute for Geophysics,
Switzerland
Hiroo Kanamori, California Institute ofTechnology, U.S.A.
Kristine M. Larson, University of Colorado, U.S.A.
Takuto Maeda, University of Tokyo, Japan
Koji Matsumoto, National Astronomical
Observatory, Japan
Yasuhiro Nariyuki, University of Toyama, Japan

Nozomu Nishitani, Nagoya University, Japan
Azusa Nishizawa, Japan Coast Guard, Japan
Keiji Ohtsuki, Kobe University, Japan
Taku Ozawa, National Research Institute for Earth
Science and Disaster Prevention, Japan
Takeshi Sakanoi, Tohoku University, Japan
Martha Savage, Victoria University of Wellington,
New Zealand
Shanaka de Silva, Oregon State University, U.S.A.
Hiroshi Takenaka, Okayama University, Japan
Hiroaki Toh, Kyoto University, Japan
Yih-Min Wu, National Taiwan University, Taiwan
Zhongliang Wu, China Earthquake Administration,
China
Toshitsugu Yamazaki, University of Tokyo, Japan
Akimasa Yoshikawa, Kyushu University, Japan

Journal Scope
Earth, Planets and Space (EPS) is the official journal of the Society of Geomagnetism and Earth, Planetary
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Yours sincerely,
Prof. Yasuo Ogawa
Editor-in-Chief, Earth, Planets and SpaceEarth, Planets and Space
Thébault et al. Earth, Planets and Space (2015) 67:158
DOI 10.1186/s40623-015-0313-0

PREFACEOpen AccessSpecial issue “International Geomagnetic
Reference Field—the twelfth generation”
E. Thébault1*, CC Finlay2 and H. Toh3
data from the German satellite CHAMP (2000–2010), theDanish satellite Ørsted (1999-), the Argentine-US-Danishsatellite SAC-C (2001–2013), and most importantly forthe new 2015 model, the European Swarm constellation(launched in November 2013; https://earth.esa.int/web/
guest/missions/esa-operational-eo-missions/swarm; seealso, Friis-Christensen and Floberghagen, 2013). The
teams adopted independent data selection, processing,and modeling procedures whose details can be foundin the papers appearing in this special issue. Someteams derived their candidate models from a parent
model (Finlay et al. 2015; Gillet et al. 2015; Hamilton
et al. 2015; Sabaka et al. 2015). The parent model parameterizations are more complex in space and in timethan IGRF models. They are primarily derived for scientificpurposes and include co-estimation of various internal andexternal source fields. The candidate models to IGRF were
subsequently estimated from the parent models by selecting
the internal field contribution at the epoch and to a spatial
resolution requested by the call for IGRF-12. Other teams
focused their effort on deriving directly a model closely
meeting the IGRF specifications (Alken et al. 2015, Lesuret al. 2015; Saturnino et al. 2015; Vigneron et al. 2015).
They relied on data selected within time windows centeredon the epochs of interest. This sometimes involved drastic
data selection and preprocessing to separate empirically thevarious source fields. In general, all models relied on statistical weighting schemes to down-weight measurements
poorly fit by the model and were directly expanded inspherical harmonics, with the exception of the candidate
models derived by the IZMIRAN team (Petrov et al.
unpublished) which relied on a principal component analysis of the data that was then converted into sphericalharmonics. IGRF-12 also contains a predictive estimate forthe secular variation that covers the epochs 2015–2020.
Teams submitted prediction candidates derived using
both “physical” and “mathematical” approaches. The“mathematical” models were built by teams relying on
analytical extrapolation and who assumed that themagnetic field will evolve linearly over the next 5 years

This special issue of Earth, Planets and Space, synthesizes the efforts made during the construction of thetwelfth generation of the International Geomagnetic
Reference Field (IGRF-12) that was released online in
December 2014 (http://www.ngdc.noaa.gov/IAGA/vmod/
igrf.html). The IGRF-12 is a series of standard mathematical models describing the large scale internal part of the
Earth’s magnetic field between epochs 1900.0 and 2015.0
with a forecast to epoch 2020.0. This activity has been
maintained since 1968 by a working group of volunteer
scientists from several international institutions but grewout from discussions started in the early 1960s (Barton,
1997). The IGRF task force operates under the auspicesof the International Association of Geomagnetism andAeronomy/Association Internationale de Géomagnétisme
et d’Aéronomie (IAGA/AIGA), which is one of the International Union of Geodesy and Geophysics/Union Internationale de Géodésie et Géophysique (IUGG/UIGG), an“international organization dedicated to advancing, promoting, and communicating knowledge of the Earth system, its space environment, and the dynamical processes
causing change” (http://www.iugg.org/).
The twelfth generation of IGRF models extends andupdates the previous one (the IGRF-11, Finlay et al. 2010).
It provides a new Definitive Geomagnetic Reference Field
model for epoch 2010.0. It proposes a provisional reference
field model for epoch 2015.0 and a predictive part forepochs ranging from 2015.0 to 2020.0 (Thébault et al.
2015a). These models were derived from candidate models
submitted by 10 teams. The 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). Modelers made use of the data measured at ground geomagnetic observatories and built their models using satellite* Correspondence: Erwan.thebault@univ-nantes.fr
1
Laboratoire de Planétologie et Géodynamique de Nantes, UMR 6112-CNRS,
University of Nantes, Nantes, France
Full list of author information is available at the end of the article© 2015 Thébault et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.

1

International Geomagnetic Reference Field - The Twelfth generation
Thébault et al. Earth, Planets and Space (2015) 67:158

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failure to help guide decisions regarding the Swarm’s satellite orbit deployment (Jackson, 2015). For scientists, theIGRF update is a general opportunity to assess the scope of
geomagnetism as a discipline and to analyze the scientificand societal needs for such an operational model. The
IGRF task force, through the call for IGRF candidate
models, gives only technical and minimum specifications
but no clear recommendation about what source field IGRF
that should represent. Should IGRF represent the Earth’s
magnetic core field only? Should all large scale internal
fields, including fields induced by the external field in the
Earth’s mantle, be included? These questions again lead todebate amongst the IGRF task force members and otherscientists interested in IGRF. However, offering flexibility tomodelers arguably stimulates innovation, guarantees thatsome candidate models are independent, and aids in making the IGRF model valid on average for a wide range ofdisparate applications. This latter important aspect can beillustrated with a short investigation on how IGRF models
are used.
The IGRF models are used in scientific and societal
applications for mapping, drilling or navigation, and orientation (e.g., Meyers and Davis, 1990). During the past decade, this traditional landscape has been supplemented by
the emergence of new applications. A systematic investigation about the use of IGRF through 50 years is difficult,but a glimpse into its use in scientific studies over the last
decade can be obtained by searching the Web of Science™.
Between 2005 and August 2015, the three main papers
about the tenth generation of IGRF (Macmillan et al. 2005
and Maus et al. 2005a; Maus et al. 2005b) were cited about
246 times in peer reviewed publications (in the Web of
Sience™ Core Collection). The following IGRF-11 generation (Finlay et al. 2010) received 315 citations between
2010 and August 2015. The citing papers can be classified
in five arbitrary science categories. The first category,
Geophysics and Geochemistry, contains papers dealing
with the internal and/or deep Earth. These include research areas such as physics of the Earth’s core, mantle,
and crust. The second category, Aeronomy/Astronomy,pulls together papers on external ionospheric and magnetospheric fields and their interaction with the solar wind
on a global spatial scale. The third category, Space
Weather/Ionosphere, contains a collection of articles
dealing mostly with transient magnetic phenomena occurring in the upper atmosphere. These three categories
include almost all academic works related to the study of
the Earth system. The fourth category, Engineering/Remotesensing, includes paper about instrumentation, telecommunication, and space technologies. The last category, Life
Siences/Medecine, gathers a wide variety of topics investigating the possible links between (geo) magnetic field conditions and life. Some categories such as the second andthird contain closely related field of interests which are not(e.g., Alken et al. 2015; Finlay et al. 2015; Lesur et al. 2015;
Saturnino et al. 2015). The “physical” models were proposed by teams who considered that forecasting the chaotic
geodynamo although difficult is numerically and statisticallyachievable. Two teams applied the tools of geophysical assimilation (Fournier et al. 2015, Kuang et al. unpublished),
and two others explored a priori statistical hypotheses on
the core flow (Gillet et al. 2015; Hamilton et al. 2015).
These physically motivated models are not only attractive
for forecasting the Earth’s magnetic field but also for hindcasting it at past epochs poorly constrained by the available
magnetic field measurements. In IGRF-12, the term “definitive”, which concerns models from 1900.0 to 2010.0, is usedbecause substantial improvement is currently unlikely.
Future retrospective analyses and improvements ofthese models might be achieved by data reprocessing,of course. For instance, Stockman et al. (2015) propose
a new calibration of the POGO satellite measurements
for the late 1960s. However, the systematic revision of
the IGRF models for epochs earlier than 2010.0 will be
more likely conceivable when our understanding about
the physics of Earth’s magnetic field is sufficient to include more realistic prior information in geomagnetic
field models. Each candidate model to the IGRF model
was evaluated in order to inform the construction of
the IGRF-12 model. The variety of techniques appliedamongst the candidate models often complicated thework of the evaluators but, after some debate, all submitted models were included in the derivation of the
final IGRF-12 via a robust weighting scheme applied inspace. The evaluation procedure and the applied diagnostic tests are documented in Thébault et al. (2015b).
Users may obtain the IGRF-12 model coefficients inelectronic form, software for evaluating the model, anda “health warning” concerning the use of IGRF-12, online
at http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html.
It should be appreciated that the update of the IGRF isan enterprise of general scientific interest. It is the occasion
to strengthen the cooperation between scientists involved
in modeling the magnetic field, the institutions archiving
and disseminating the ground magnetic field data, thenational and the various space agencies, and sometimes
industry. This close link between science and industry iswell illustrated by the article of Léger et al. (2015) who
discuss and demonstrate the in-flight performances of a
new type of scalar magnetometer that is onboard the three
European Swarm satellites. The magnetometers can also be
run in a vector mode and generate measurements that were
exclusively and successfully used by Vigneron et al. (2015)
to derive their candidate model to IGRF-12 for epoch
2015.0. The malfunction of one of the absolute scalarmagnetometers on one of the three Swarm satellites has
deprived the scientific community of some of these innovative measurements but prompted a probabilistic analysis of2Earth, Planets and Space
Thébault et al. Earth, Planets and Space (2015) 67:158

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use IGRF so their number is unknown. IGRF model coefficients and computation codes are embedded in a numberof commercial Software packages (Matlab®, Geosoft, for instance) dedicated to engineering and operational activities.
They are also often used for educational and personal
purposes. Most GPS receivers include the IGRF or theWorld Magnetic Model (https://www.ngdc.noaa.gov/
geomag/WMM/DoDWMM.shtml) in their firmware forconverting true courses and bearings into magnetic
ones. The analytics set up on the IGRF web page (http://
www.ngdc.noaa.gov/IAGA/vmod/igrf.html) in May 2015shows that 7963 unique users navigated on the IGRF website from 28 May 2015 to 13 August 2015 (C. Manoj,
National Centers for Environmental Information, personalcommunication). If the exact number of visitors who
downloaded the coefficients file is unknown, we learn that
10 % of them cared to visit the IGRF “Health warning”
page and showed enough interest to stay there longenough to read the recommendations. A similar log
monitoring carried out by the British Geological Survey(S. Macmillan, S. Reay and C. Beggan, personal communication) indicates that the IGRF-11 online calculator received about 580 requests per month fromJanuary 2010 to July 2015 and that 7082 requests fromJanuary 2015 are associated with entries of positional data
and date using IGRF-12. All these requests were done byhumans and not visiting spider or robot programs.
This wide community of users has a range of different
needs that justifies some flexibility in the IGRF specifications. The increasing interest in IGRF for space applications may, for example, lead IAGA to consider in the
future the introduction of models for magnetic sourcesinternal to satellite orbits, including the magnetic field
generated by currents flowing in the ionosphere or also
quasi-static magnetospheric field contributions. In thiseasy to separate objectively. Some overlap between the
categories is not ruled out, and the percentage distributionof each research area provides only a crude picture of thescientific use of IGRF models through the last decade.
Figure 1 shows that between 2005 and 2015 (leftpanel), the IGRF-10 was mostly used for “traditional”
scientific purposes such as internal and external field
geophysics. These activities, comprising navigation, surveying, and prospecting, represent almost 80 % of thescientific uses of IGRF-10; IGRF-10 was apparently used
only occasionally in Engineering (6 %) and Life Sciences(3 %). The large percentage of use for fundamental geophysical research is consistent with the outcome of thestudy of Meyers and Davis (1990) relying on a survey
conducted directly with 144 users from 1 October 1987
through 6 June 1989. It can also be verified using the
Web of Science™ that the three first categories absorb
more than 80 % of the citations from the third to thetenth generation of IGRF (note that the Web of Science™
is perhaps less reliable in counting citations at older
epochs). However, from 2010 onwards, users citing the
updated IGRF-11 used the series of models also forother purposes. The proportion of papers citing IGRF11 for internal and external geomagnetic field purposesdecreased notably (down to 70 %; Fig. 1, right panel)
while the proportion of research involving the sciencearea Engineering/Remote sensing (24 %) rose. This increasing number of IGRF citations in this category inrecent years is due to primarily researches carried out inaerospace engineering that seek to address communication issues from space and challenges in positioning
miniaturized satellites. The statistics accessible fromWeb of Science™ provide only a limited insight concerning the typical IGRF user. Most users do not inform the
IAGA V-MOD working group about their intention to

Fig. 1 Percentage by category of science papers citing the IGRF-10 between 2005 and 2015 (left) and citing the IGRF-11 paper between 2010
and 2015 (right)

3

International Geomagnetic Reference Field - The Twelfth generation
Thébault et al. Earth, Planets and Space (2015) 67:158

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regard, the IGRF task force, whose role is to discuss anddefine the IGRF specifications, will seek to guarantee that
IGRF activities will stay at the forefront of geomagnetismand deliver a product that best serves science and society.
The IGRF-12 results from major collaborative effort, andwe wish in particular to thank the authors of the papers
presented here, the many referees who gave their time andshared their expertise, and the EPS Chief Editor Yasuo
Ogawa for his support with this special issue.

Sabaka TJ, Olsen N, Tyler RH, Kuvshinov A (2015) CM5 a pre-Swarm
comprehensive geomagnetic field model derived from over 12 yr of CHAMP,Ørsted, SAC-C, and observatory data. Geophys J Int 200:1596–1626.
doi:10.1093/gji/ggu493
Saturnino D, Langlais B, Civet F, Thébault E, Mandea M (2015) Main field andsecular variation candidate models for the 12th IGRF generation after 10months of Swarm measurements. Earth, Planets Space 67:96
Stockmann R, Christiansen F, Olsen N, Jackson A (2015) POGO satellite orbit
corrections: an opportunity to improve the quality of the geomagnetic fieldmeasurements? Earth Planets Space 67:102
Thébault E, Finlay CC, Beggan CD, Alken P, Aubert J, Barrois O, Bertrand F, Bondar T,
Boness A, Brocco L, Canet E, Chambodut A, Chulliat A, Coïsson P, Civet F, Du A,
Fournier A, Fratter I, Gillet N, Hamilton B, Hamoudi M, Hulot G, Jager T, Korte M,
Kuang W, Lalanne X, Langlais B, Léger JM, Lesur V, Lowes FJ et al (2015a)
International Geomagnetic Reference Field: the twelfth generation. Earth
Planets Space 67:79. doi:10.1186/s40623-015-0228-9
Thébault E, Finlay CC, Alken P, Beggan CD, Canet E, Chulliat A, Langlais B, Lesur V,
Lowes F, Manoj C, Rother M, Schachtschneider R (2015b) Evaluation ofcandidate geomagnetic field models for IGRF-12. Earth Planets Space 67:112
Vigneron P, Hulot G, Olsen N, Léger J-M, Jager T, Brocco L, Sirol O, Coïsson P,
Lalanne X, Chulliat A, Bertrand F, Boness A, Fratter I (2015) A 2015
International Geomagnetic Reference Field (IGRF) candidate model based on
Swarm’s experimental absolute magnetometer vector mode data. Earth
Planets Space 67:95

Author details
1
Laboratoire de Planétologie et Géodynamique de Nantes, UMR 6112-CNRS,
University of Nantes, Nantes, France. 2Division of Geomagnetism, DTU Space,
Technical University of Denmark, Diplomvej, 371, Kongens Lyngby, Denmark.
3
Data Analysis Center for Geomagnetism and Space Magnetism, Graduate
School of Science, Kyoto University, Kyoto 606-8502, Japan.
Received: 27 August 2015 Accepted: 27 August 2015
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Gillet N, Barrois O, Finlay CC (2015) Stochastic forecasting of the geomagnetic
field from the COV-OBS.x1 geomagnetic field model, and candidate models
for IGRF-12. Earth Planets Space 67:71
Hamilton B, Ridley VA, Beggan CD, Macmillan S (2015) The BGS magnetic fieldcandidate models for the 12th generation IGRF. Earth Planets Space 67:69
Jackson A (2015) A probabilistic analysis of the implications of instrument failures
on ESA’s Swarm mission for its individual satellite orbit deployments. Earth
Planets Space 67:113
Léger JM, Jager T, Bertrand F, Hulot G, Brocco L, Vigneron P, Lalanne X, Chulliat
A, Fratter I (2015) In-flight performance of the Absolute Scalar Magnetometer
vector mode on board the Swarm satellites. Earth Planets Space 67:57
Lesur V, Rother M, Wardinski I, Schachtschneider R, Hamoudi M, Chambodut A(2015) Parent magnetic field models for the IGRF-12 GFZ-candidates. Earth
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Earth, Planets and SpaceFRONTIER LETTER

Open Access

In-flight performance of the Absolute Scalar Magnetometer vector
mode on board the Swarm satellites
Jean-Michel Léger, Thomas Jager*, François Bertrand, Gauthier Hulot, Laura Brocco, Pierre Vigneron, Xavier Lalanne,
Arnaud Chulliat and Isabelle Fratter
Earth, Planets and Space 2015, 67:57 doi:10.1186/s40623-015-0231-1
Received: 6 February 2015, Accepted: 15 April 2015, Published: 25 April 2015

Abstract
The role of the Absolute Scalar Magnetometer (ASM) in the European Space Agency (ESA) Swarm mission is to deliverabsolute measurements of the magnetic field’s strength for science investigations and in-flight calibration of the Vector Field
Magnetometer (VFM). However, the ASM instrument can also simultaneously deliver vector measurements with no impact on
the magnetometer’s scalar performance, using a so-called vector mode. This vector mode has been continuously operated
since the beginning of the mission, except for short periods of time during commissioning. Since both scalar and vector
measurements are perfectly synchronous and spatially coherent, a direct assessment of the ASM vector performance can thenbe carried out at instrument level without need to correct for the various magnetic perturbations generated by the satellites.
After a brief description of the instrument’s operating principles, a thorough analysis of the instrument’s behavior ispresented, as well as a characterization of its environment in flight, using an alternative high sampling rate (burst) scalar modethat could be run a few days during commissioning. The ASM vector calibration
process is next detailed, with some emphasis on its sensitivity to operational
conditions. Finally, the evolution of the instrument’s performance during the firstyear of the mission is presented and discussed in view of the mission’s performancerequirements for vector measurements.

Keywords: Swarm; He4 magnetometer; Scalar absolute magnetometer;
Vector magnetometer; Vector calibration

Figure 1*Corresponding author: Thomas Jager, thomas.jager@cea.fr

FULL PAPER 

Open Access

NOAA/NGDC candidate models for the 12th generation International
Geomagnetic Reference Field
Patrick Alken*, Stefan Maus, Arnaud Chulliat and Chandrasekharan Manoj
Earth, Planets and Space 2015, 67:68 doi:10.1186/s40623-015-0215-1
Received: 30 January 2015, Accepted: 19 March 2015, Published: 12 May 2015

Abstractscalar data per 10 days

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 the2015.0 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 forconsideration in IGRF-12. The 2010 main field candidate was produced from
Temporal distribution of scalar data
25000
Challenging Minisatellite Payload (CHAMP) satellite data, while the 2015 main field
20000
and secular variation candidates were produced from Swarm and Ørsted satellite
15000
data. Careful data selection was performed to minimize the influence of
10000
magnetospheric and ionospheric fields. The secular variation predictions of our5000
parent models, from which the candidate models were derived, have been validated
0
against independent ground observatory data.
Swarm A
Swarm B
Swarm C
OerstedKeywords: Geomagnetic field; Magnetic field modeling; IGRF; Swarm

vector data per 10 days

Temporal distribution of vector data

25000
20000
15000
10000
5000
0
2013

2013.52014

Figure 1*Corresponding author: Patrick Alken, patrick.alken@colorado.edu
52014.52015

International Geomagnetic Reference Field - The Twelfth generation

FULL PAPER 

Open Access

The BGS magnetic field candidate models for the 12th generation
IGRF
Brian Hamilton*, Victoria A Ridley, Ciarán D Beggan and Susan Macmillan
Earth, Planets and Space 2015, 67:69 doi:10.1186/s40623-015-0227-x
Received: 29 January 2015, Accepted: 10 April 2015, Published: 12 May 2015

Abstract
We describe the candidate models submitted by the British Geological Survey for the 12th generation International
Geomagnetic Reference Field. These models are extracted from a spherical harmonic ‘parent model’ derived from vector andscalar magnetic field data from satellite and observatory sources. These data cover the period 2009.0 to 2014.7 and include
measurements from the recently launched European Space Agency (ESA) Swarm satellite constellation. The parent model’sinternal field time dependence for degrees 1 to 13 is represented by order 6 B-splines with knots at yearly intervals. The parent
model’s degree 1 external field time dependence is described by periodic functions for the annual and semi-annual signals
and by dependence on the 20-min Vector Magnetic Disturbance index. Signals induced by these external fields are also
parameterized. Satellite data are weighted by spatial density and by two different noise estimators: (a) by standard deviation
along segments of the satellite track and (b) a larger-scale noise estimator defined in terms of a measure of vector activity at
the geographically closest magnetic observatories to the sample point. Forecastingof the magnetic field secular variation beyond the span of data is by advection of themain field using core surface flows.
80000

Observatory pseudo-scalar

70000

Observatory vector

Keywords: IGRF; Geomagnetic field; Geomagnetic secular variation; Swarm

total number of data / month

Oersted scalar

60000

CHAMP scalar

CHAMP vector

50000

Swarm scalar
Swarm vector

40000
30000
20000
10000
0
2009

2010

2011

2012

2013

2014

years

Figure 1*Corresponding author: Brian Hamilton, bham@bgs.ac.uk

FULL PAPER 

Open Access

Stochastic forecasting of the geomagnetic field from the COV-OBS.x1
geomagnetic field model, and candidate models for IGRF-12
Nicolas Gillet*, Olivier Barrois and Christopher C Finlay
Earth, Planets and Space 2015, 67:71 doi:10.1186/s40623-015-0225-z
Received: 15 December 2014, Accepted: 4 April 2015, Published: 14 May 2015

Abstract
We present the geomagnetic field model COV-OBS.x1, covering 1840 to 2020, from which have been derived candidate models for
the IGRF-12. Towards the most recent epochs, it is primarily constrained by first differences of observatory annual means andmeasurements from the Oersted, Champ, and Swarm satellite missions. Stochastic information derived from the temporal spectra ofgeomagnetic series is used to construct the a priori model covariance matrix that complements the constraint brought by the data.
This approach makes it possible the use of a posteriori model errors, for instance, to measure the‘observations’ uncertainties in data assimilation schemes for the study of the outer core
dynamics.
We also present and illustrate a stochastic algorithm designed to forecast the geomagnetic field.
The radial field at the outer core surface is advected by core motions governed by an autoregressive process of order 1. This particular choice is motivated by the slope observed for the
power spectral density of geomagnetic series. Accounting for time-correlated model errors(subgrid processes associated with the unresolved magnetic field) is made possible thanks to
the use of an augmented state ensemble Kalman filter algorithm. We show that the envelope of
forecasts includes the observed secular variation of the geomagnetic field over 5-year intervals,
even in the case of rapid changes. In a purpose of testing hypotheses about the core dynamics,
this prototype method could be implemented to build the ‘state zero’ of the ability to forecast
the geomagnetic field, by measuring what can be predicted when no deterministic physics isincorporated into the dynamical model.

Keywords: Geomagnetic field; Secular variation; Stochastic equations;
Ensemble Kalman filter*Corresponding author: Nicolas Gillet, nicolas.gillet@ujf-grenoble.fr
6

Figure 1

Earth, Planets and Space

FULL PAPER 

Open AccessA candidate secular variation model for IGRF-12 based on Swarm dataand inverse geodynamo modelling
Alexandre Fournier*, Julien Aubert and Erwan Thébault
Earth, Planets and Space 2015, 67:81 doi:10.1186/s40623-015-0245-8
Received: 28 January 2015, Accepted: 8 May 2015, Published: 27 May 2015

Abstract
In the context of the 12th release of the international geomagnetic reference field (IGRF), we present the methodology wefollowed to design a candidate secular variation model for years 2015–2020. An initial geomagnetic field model centeredaround 2014.3 is first constructed, based on Swarm magnetic measurements, for both the main field and its instantaneous
secular variation. This initial model is next fed to an inverse geodynamo modelling framework in order to specify, for epoch
2014.3, the initial condition for the integration of a three-dimensional numerical dynamo model. The initialization phasecombines the information contained in the initial model with that coming from the numerical dynamo model, in the form of
three-dimensional multivariate statistics built from a numerical dynamo run unconstrained by data.
We study the performance of this novel approach over two recent 5-year long intervals, 2005–2010 and 2009–2014. For aforecast horizon of 5 years, shorter than the large-scale secular acceleration time scale (~10 years), we find that it is safer toneglect the flow acceleration and to assume that the flow determined by the initialization is steady. This steady flow is used toadvance the three-dimensional induction equation forward in time, with the benefit of estimating the effects of magnetic
diffusion. The result of this deterministic integration between 2015.0 and 2020.0
ayields our candidate average secular variation model for that time frame, which isthus centered on 2017.5.

Keywords: Magnetic field; Satellite magnetics; Dynamo: theories and simulations;
Inverse theory

Figure 1*Corresponding author: Alexandre Fournier, fournier@ipgp.fr

FULL PAPER 

Open Access

Parent magnetic field models for the IGRF-12 GFZ-candidates
Vincent Lesur*, Martin Rother, Ingo Wardinski, Reyko Schachtschneider, Mohamed Hamoudi
and Aude Chambodut
Earth, Planets and Space 2015, 67:87 doi:10.1186/s40623-015-0239-6
Received: 30 January 2015, Accepted: 21 April 2015, Published: 10 June 2015

Abstract
We propose candidate models for IGRF-12. These models were derived from parent models built from 10 months of Swarmsatellite data and 1.5 years of magnetic observatory data. Using the same parameterisation, a magnetic field model was built
from a slightly extended satellite data set. As a result of discrepancies between magnetic field intensity measured by theabsolute scalar instrument and that calculated from the vector instrument, we re-calibrated the satellite data. For thecalibration, we assumed that the discrepancies resulted from a small perturbing magnetic field carried by the satellite, with astrength and orientation dependent on the Sun’s position relative to the satellite. Scalar and vector data were reconciled using
only a limited number of calibration parameters. The data selection process, followed by the joint modelling of the magnetic
field and Euler angles, leads to accurate models of the main field and its secular variation around 2014.0. The obtained secularvariation model is compared with models based on CHAMP satellite data. The comparison suggests that pulses of magnetic
field acceleration that were observed on short time scales average-out over a decade.

Keywords: IGRF-12; Swarm satellite mission; Geomagnetic field models

Figure 1*Corresponding author: Vincent Lesur, lesur@gfz-potsdam.de7

International Geomagnetic Reference Field - The Twelfth generation

FULL PAPER 

Open Access

A 2015 International Geomagnetic Reference Field (IGRF) candidate
model based on Swarm’s experimental absolute magnetometer vector
mode data
Pierre Vigneron, Gauthier Hulot*, Nils Olsen, Jean-Michel Léger, Thomas Jager, Laura Brocco, Olivier Sirol,
Pierdavide Coïsson, Xavier Lalanne, Arnaud Chulliat, François Bertrand, Axel Boness and Isabelle Fratter
Earth, Planets and Space 2015, 67:95 doi:10.1186/s40623-015-0265-4
Received: 19 February 2015, Accepted: 5 June 2015, Published: 20 June 2015

Abstract
Each of the three satellites of the European Space Agency Swarm mission carries an absolute scalar magnetometer (ASM) thatprovides the nominal 1-Hz scalar data of the mission for both science and calibration purposes. These ASM instruments,
however, also deliver autonomous 1-Hz experimental vector data. Here, we report on how ASM-only scalar and vector datafrom the Alpha and Bravo satellites between November 29, 2013 (a week after launch) and September 25, 2014 (for on-time
delivery of the model on October 1, 2014) could be used to build a very valuable candidate model for the 2015.0 International
Geomagnetic Reference Field (IGRF). A parent model was first computed, describing the geomagnetic field of internal origin
up to degree and order 40 in a spherical harmonic representation and including a constant secular variation up to degree andorder 8. This model was next simply forwarded to epoch 2015.0 and truncated at degree and order 13. The resulting ASM-only
2015.0 IGRF candidate model is compared to analogous models derived from the mission’s nominal data and to the nowpublished final 2015.0 IGRF model. Differences among models mainly highlight
uncertainties enhanced by the limited geographical distribution of the selected dataset (essentially due to a lack of availability of data at high northern latitude satisfying
nighttime conditions at the end of the time period considered). These appear to becomparable to differences classically observed among IGRF candidate models. These
positive results led the ASM-only 2015.0 IGRF candidate model to contribute to theconstruction of the final 2015.0 IGRF model.

Keywords: Swarm; IGRF; Absolute vector magnetometer

Figure 1*Corresponding author: Gauthier Hulot, gh@ipgp.fr

FULL PAPER 

Open Access

POGO satellite orbit corrections: an opportunity to improve
the quality of the geomagnetic field measurements?
Reto Stockmann*, Freddy Christiansen, Nils Olsen and Andrew Jackson*
Earth, Planets and Space 2015, 67:102 doi:10.1186/s40623-015-0254-7
Received: 1 December 2014, Accepted: 20 May 2015, Published: 27 June 2015

Abstract
We present an attempt to improve the quality of the geomagnetic field measurements from the Polar Orbiting GeophysicalObservatory (POGO) satellite missions in the late 1960s. Inaccurate satellite positions are believed to be a major source oferrors for using the magnetic observations for field modelling. To improve the data, we use an iterative approach consisting of
two main parts: one is a main field modelling process to obtain the radial field gradient to perturb the orbits and the other isthe state-of-the-art GPS orbit modelling software BERNESE to calculate new physical orbits. We report results based on asingle-day approach showing a clear increase of the data quality. That single-day approach leads, however, to undesirable
orbital jumps at midnight. Furthermore, we report results obtained for a much larger data set comprising almost all of thedata from the three missions. With this approach, we eliminate the orbit discontinuities at midnight but only tiny quality
improvements could be achieved for geomagnetically quiet data. We believe that improvements to the data are probably still
possible, but it would require the original tracking observations to be found.

Keywords: Inverse theory; Satellite magnetics; Satellite orbits

Figure 1*Corresponding author: Reto Stockmann, reto.stockmann@gmx.net; Andrew Jackson, ajackson@ethz.ch
8

Earth, Planets and Space

FULL PAPER 

Open Access

DTU candidate field models for IGRF-12 and the CHAOS-5
geomagnetic field model
Christopher C Finlay*, Nils Olsen and Lars Tøffner-Clausen
Earth, Planets and Space 2015, 67:114 doi:10.1186/s40623-015-0274-3
Received: 10 February 2015, Accepted: 15 June 2015, Published: 22 July 2015

Abstract
We present DTU’s candidate field models for IGRF-12 and the parent field model from which they were derived, CHAOS-5. Tenmonths of magnetic field observations from ESA’s Swarm mission, together with up-to-date ground observatory monthly
means, were used to supplement the data sources previously used to construct CHAOS-4. The internal field part of CHAOS-5,
from which our IGRF-12 candidate models were extracted, is time-dependent up to spherical harmonic degree 20 andinvolves sixth-order splines with a 0.5 year knot spacing. In CHAOS-5, compared with CHAOS-4, we update only the lowdegree internal field model (degrees 1 to 24) and the associated external field model. The high-degree internal field (degrees
25 to 90) is taken from the same model CHAOS-4h, based on low-altitude CHAMP data, which was used in CHAOS-4.
We find that CHAOS-5 is able to consistently fit magnetic field data from six independent low Earth orbit satellites: Ørsted,
CHAMP, SAC-C and the three Swarm satellites (A, B and C). It also adequately describes the secular variation measured at
ground observatories. CHAOS-5 thus contributes to an initial validation of the quality of the Swarm magnetic data, inparticular demonstrating that Huber weighted rms model residuals to Swarm vector field data are lower than those to Ørsted
and CHAMP vector data (when either one or two star cameras were operating).
CHAOS-5 shows three pulses of secular acceleration at the core surface over the past
decade; the 2006 and 2009 pulses have previously been documented, but the 2013
pulse has only recently been identified. The spatial signature of the 2013 pulse at thecore surface, under the Atlantic sector where it is strongest, is well correlated with the2006 pulse, but anti-correlated with the 2009 pulse.

Keywords: Geomagnetism; Field modelling; IGRF; Swarm

Figure 1*Corresponding author: Christopher C Finlay, cfinlay@space.dtu.dk

LETTER

Open AccessInternational Geomagnetic Reference Field: the 12th generation
Erwan Thébault*, Christopher C Finlay, Ciarán D Beggan, Patrick Alken, Julien Aubert, Olivier Barrois,
Francois Bertrand, Tatiana Bondar, Axel Boness, Laura Brocco, Elisabeth Canet, Aude Chambodut, Arnaud Chulliat,
Pierdavide Coïsson, François Civet, Aimin Du, Alexandre Fournier, Isabelle Fratter, Nicolas Gillet, Brian Hamilton,
Mohamed Hamoudi, Gauthier Hulot, Thomas Jager, Monika Korte, Weijia Kuang, Xavier Lalanne, Benoit Langlais,
Jean-Michel Léger, Vincent Lesur, Frank J Lowes, Susan Macmillan, Mioara Mandea, Chandrasekharan Manoj,
Stefan Maus, Nils Olsen, Valeriy Petrov, Victoria Ridley, Martin Rother, Terence J Sabaka, Diana Saturnino,
Reyko Schachtschneider, Olivier Sirol, Andrew Tangborn, Alan Thomson, Lars Tøffner-Clausen, Pierre Vigneron,
Ingo Wardinski and Tatiana Zvereva
Earth, Planets and Space 2015, 67:79 doi:10.1186/s40623-015-0228-9
Received: 30 January 2015, Accepted: 13 April 2015, Published: 27 May 2015

Abstract
The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December
2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism andAeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch
2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmoniccoefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch
2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions
and discuss briefly the latest changes and possible future trends of the Earth’s magnetic field.

Keywords: Geomagnetism; Field modeling; IGRF

Figure 1*Corresponding author: Erwan Thébault, erwan.thebault@univ-nantes.fr
9International Geomagnetic Reference Field - The Twelfth generation

LETTER

Open Access

Main field and secular variation candidate models for the 12th IGRF
generation after 10 months of Swarm measurements
Diana Saturnino*, Benoit Langlais, François Civet, Erwan Thébault and Mioara Mandea
Earth, Planets and Space 2015, 67:96 doi:10.1186/s40623-015-0262-7
Received: 12 February 2015, Accepted: 3 June 2015, Published: 20 June 2015

Abstract
We describe the main field and secular variation candidate models for the 12th generation of the International Geomagnetic
Reference Field model. These two models are derived from the same parent model, in which the main field is extrapolated toepoch 2015.0 using its associated secular variation. The parent model is exclusively based on measurements acquired by theEuropean Space Agency Swarm mission between its launch on 11/22/2013 and 09/18/2014. It is computed up to sphericalharmonic degree and order 25 for the main field, 13 for the secular variation, and 2 for the external field. A selection on local
time rather than on true illumination of the spacecraft was chosen in order to keep more measurements. Data selection basedon geomagnetic indices was used to minimize the external field contributions. Measurements were screened and outliers
were carefully removed. The model uses magnetic field intensity measurements at all latitudes and magnetic field vector
measurements equatorward of 50° absolute quasi-dipole magnetic latitude. A second model using only the verticalcomponent of the measured magnetic field and the total intensity was computed.
This companion model offers a slightly better fit to the measurements. These two
03
6
9 12 15
models are compared and discussed.We discuss in particular the quality of the model
which does not use the full vector measurements and underline that this approach
may be used when only partial directional information is known. The candidateabmodels and their associated companion models are retrospectively compared to theadopted IGRF which allows us to criticize our own choices.
Meas. per 6x6 degree bin

Keywords: Magnetic field; Main field; Secular variation; Modeling; IGRF;
Time extrapolationcdFigure 1*Corresponding author: Diana Saturnino, diana.saturnino@univ-nantes.fr

LETTER

Open AccessA probabilistic analysis of the implications of instrument failures on
ESA’s Swarm mission for its individual satellite orbit deployments
Andrew Jackson
Earth, Planets and Space 2015, 67:113 doi:10.1186/s40623-015-0286-z
Received: 14 January 2015, Accepted: 29 June 2015, Published: 22 July 2015

Abstract
On launch, one of Swarm’s absolute scalar magnetometers (ASMs) failed to function, leaving an asymmetrical arrangement of
redundant spares on different spacecrafts. A decision was required concerning the deployment of individual satellites into the
low-orbit pair or the higher “lonely” orbit. I analyse the probabilities for successful operation of two of the science componentsof the Swarm mission in terms of a classical probabilistic failure analysis, with a view to concluding a favourable assignment
for the satellite with the single working ASM. I concentrate on the following two
science aspects: the east-west gradiometer aspect of the lower pair of satellites andthe constellation aspect, which requires a working ASM in each of the two orbital
planes. I use the so-called “expert solicitation” probabilities for instrument failure
solicited from Mission Advisory Group (MAG) members. My conclusion from theanalysis is that it is better to have redundancy of ASMs in the lonely satellite orbit.
Although the opposite scenario, having redundancy (and thus four ASMs) in thelower orbit, increases the chance of a working gradiometer late in the mission; it does
so at the expense of a likely constellation. Although the results are presented basedon actual MAG members’ probabilities, the results are rather generic, excepting thecase when the probability of individual ASM failure is very small; in this case, any
arrangement will ensure a successful mission since there is essentially no failure
expected at all. Since the very design of the lower pair is to enable common mode
rejection of external signals, it is likely that its work can be successfully achieved
during the first 5 years of the mission.
Figure 1

Corresponding author: Andrew Jackson, ajackson@ethz.ch
10Earth, Planets and SpaceTECHNICAL REPORT

Open Access

Evaluation of candidate geomagnetic field models for IGRF-12
Erwan Thébault*, Christopher C. Finlay, Patrick Alken, Ciaran D. Beggan, Elisabeth Canet, Arnaud Chulliat,
Benoit Langlais, Vincent Lesur, Frank J. Lowes, Chandrasekharan Manoj, Martin Rother and Reyko Schachtschneider
Earth, Planets and Space 2015, 67:112 doi:10.1186/s40623-015-0273-4
Received: 7 April 2015, Accepted: 14 June 2015, Published: 19 July 2015

Abstract
Background: The 12th revision of the International Geomagnetic Reference Field (IGRF) was issued in December 2014 by theInternational Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD (http://www.ngdc.noaa.
gov/IAGA/vmod/igrf.html). This revision comprises new spherical harmonic main field models for epochs 2010.0 (DGRF-2010)
and 2015.0 (IGRF-2015) and predictive linear secular variation for the interval 2015.0-2020.0 (SV-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). Eachcandidate 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 ofthe task force members appointed by IAGA thought that thedifferences 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 iterativerobust estimation scheme in space. In this paper, we report on theevaluations of the candidate models and provide details of thealgorithm that was used to derive the IGRF-12 product.

Keywords: Geomagnetism; Field modeling; IGRF

Figure 1*Corresponding author: Erwan Thébault, erwan.thebault@univ-nantes.fr

11

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Contents
Special issue “International Geomagnetic Reference Field—the twelfth generation” . . . . . . . E. Thébault, CC Finlay and H. Toh
In-flight performance of the Absolute Scalar Magnetometer vector mode on board the Swarm satellites. . . . . . . . . . . . . . . . . Jean-Michel Léger, Thomas Jager, François Bertrand, Gauthier Hulot, Laura Brocco, Pierre Vigneron, Xavier Lalanne,
Arnaud Chulliat and Isabelle Fratter

NOAA/NGDC candidate models for the 12th generation International Geomagnetic Reference Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Patrick Alken, Stefan Maus, Arnaud Chulliat and Chandrasekharan Manoj
The BGS magnetic field candidate models for the 12th generation IGRF
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brian Hamilton, Victoria A Ridley, Ciarán D Beggan and Susan Macmillan
Stochastic forecasting of the geomagnetic field from the COV-OBS.x1 geomagnetic field model, and candidate models
for IGRF-12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nicolas Gillet, Olivier Barrois and Christopher C Finlay
A candidate secular variation model for IGRF-12 based on Swarm data and inverse geodynamo modelling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alexandre Fournier, Julien Aubert and Erwan Thébault
Parent magnetic field models for the IGRF-12 GFZ-candidates. . . . . . . . . . . . . . . . . Vincent Lesur, Martin Rother, Ingo Wardinski, Reyko Schachtschneider, Mohamed Hamoudi and Aude Chambodut
A 2015 International Geomagnetic Reference Field (IGRF) candidate model based on Swarm’s experimental absolute
magnetometer vector mode data
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pierre Vigneron, Gauthier Hulot, Nils Olsen, Jean-Michel Léger, Thomas Jager, Laura Brocco, Olivier Sirol,
Pierdavide Coïsson, Xavier Lalanne, Arnaud Chulliat, François Bertrand, Axel Boness and Isabelle Fratter

POGO satellite orbit corrections: an opportunity to improve the quality of the geomagnetic field measurements?
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reto Stockmann, Freddy Christiansen, Nils Olsen and Andrew Jackson
DTU candidate field models for IGRF-12 and the CHAOS-5 geomagnetic field model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Christopher C Finlay, Nils Olsen and Lars Tøffner-Clausen
International Geomagnetic Reference Field: the 12th generation. . . . . . . . . . . . . Erwan Thébault, Christopher C Finlay, Ciarán D Beggan, Patrick Alken, Julien Aubert, Olivier Barrois, Francois Bertrand,
Tatiana Bondar, Axel Boness, Laura Brocco, Elisabeth Canet, Aude Chambodut, Arnaud Chulliat, Pierdavide Coïsson,
François Civet, Aimin Du, Alexandre Fournier, Isabelle Fratter, Nicolas Gillet, Brian Hamilton, Mohamed Hamoudi,
Gauthier Hulot, Thomas Jager, Monika Korte, Weijia Kuang, Xavier Lalanne, Benoit Langlais, Jean-Michel Léger,Vincent Lesur, Frank J Lowes, Susan Macmillan, Mioara Mandea, Chandrasekharan Manoj, Stefan Maus, Nils Olsen,
Valeriy Petrov, Victoria Ridley, Martin Rother, Terence J Sabaka, Diana Saturnino, Reyko Schachtschneider, Olivier Sirol,
Andrew Tangborn, Alan Thomson, Lars Tøffner-Clausen, Pierre Vigneron, Ingo Wardinski and Tatiana Zvereva

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Main field and secular variation candidate models for the 12th IGRF generation after 10 months of Swarm measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diana Saturnino, Benoit Langlais, François Civet, Erwan Thébault and Mioara Mandea 10
A probabilistic analysis of the implications of instrument failures on ESA’s Swarm mission for its individual satellite orbit
deployments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Andrew Jackson 10
Evaluation of candidate geomagnetic field models for IGRF-12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Erwan Thébault, Christopher C. Finlay, Patrick Alken, Ciaran D. Beggan, Elisabeth Canet, Arnaud Chulliat,
Benoit Langlais, Vincent Lesur, Frank J. Lowes, Chandrasekharan Manoj, Martin Rother and Reyko Schachtschneider

11

Cover image: Thébault, E. et al., Earth, Planets and Space 2015, 67:79 doi:10.1186/s40623-015-0228-9