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Table 1 Comparison of the CHAOS-4 and CHAOS-5 geomagnetic field models

From: DTU candidate field models for IGRF-12 and the CHAOS-5 geomagnetic field model

  CHAOS-4 CHAOS-5
Data sources   
Observatory monthly means June 1997 - June 2013 June 1997 - Sept 2014
Ørsted vector March 1999 - Dec 2004 March 1999 - Dec 2004
Ørsted scalar March 1999 - June 2013 March 1999 - June 2013
SAC-C scalar Jan 2001 - Dec 2004 Jan 2001 - Dec 2004
CHAMP vector and scalar Aug 2000 - Sept 2010 Aug 2000 - Sept 2010
Swarm A vector and scalar Nov 2013 - Sept 2014
Swarm B vector and scalar Nov 2013 - Sept 2014
Swarm C vector and scalar Nov 2013 - Sept 2014
Time-dependent internal field   
Model time span 1997.0–2013.5 1997.0–2015.0
Spherical harmonic degree n=1–20 n=1–20
Spline basis 6th order, 0.5 year knots 6th order, 0.5 year knots
Based on CHAOS-4l CHAOS-5l
Static internal field   
Spherical harmonic degree n=21–90 n=21–90
Based on CHAOS-4l (n=21–24) CHAOS-5l (n=21–24)
  and CHAOS-4h (n=25–90) and CHAOS-4h (n=25–90)
External field   
SM n=1: 1 h, RC int + ext n=1: 1 h, RC int + ext
  5 day \(\Delta {q^{0}_{1}}\), 30 day \(\Delta {q^{1}_{1}}\), \(\Delta {s^{1}_{1}}\) 5 day \(\Delta {q^{0}_{1}}\), 30 day \(\Delta {q^{1}_{1}}\), \(\Delta {s^{1}_{1}}\)
  n=2: static n=2: static
GSM n=1–2, m=0: static n=1–2, m=0: static
Euler angles   
Ørsted Before and after Jan 24 2000 Before and after Jan 24 2000
CHAMP 10 day bins 10 day bins
Swarm 10 day bins
Regularization   
Spatial Static field n>85, \(<{B_{r}^{2}}>\) Static field n>85, \(<{B_{r}^{2}}>\)
  λ 0=1 nT−2 λ 0=1 nT−2
Temporal, interior \(<(d{B^{3}_{r}}/dt^{3})^{2}>\) \(<(d{B^{3}_{r}}/dt^{3})^{2}>\)
  λ 3=0.33 (nT/year−3)−2 λ 3=0.33 (nT/year−3)−2
  except \({g^{0}_{1}}\), λ 3=10 (nT/year−3)−2 except m=0, λ 3=100 (nT/year −3)−2
Temporal, endpoints \(<(d{B^{2}_{r}}/dt^{2})^{2}>\) \(<(d{B^{2}_{r}}/dt^{2})^{2}>\)
  λ 2=10 (nT/year−2)−2 λ 2=100 (nT/year −2)−2
  1. Contributing data, model parameterization and model regularization are presented. Improvements of CHAOS-5 compared to CHAOS-4 are shown in bold. <> indicates integration over the core-mantle boundary