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Table 1 CM6 parameterization

From: CM6: a comprehensive geomagnetic field model derived from both CHAMP and Swarm satellite observations

Field source/effect

# Parms

Description

Core/lithosphere

30, 480

Spatial

Geographic spherical harmonic (SH) \(N_{\text{max}} = 120\)

Temporal

Order 4 B-splines SV, 6-month knot spacing from \(1999.0-2019.5\), epoch 2015.0, up to \(N_{\text{max}} = 18\)

\(M_2\) tidal

2, 736

Spatial

Geographic SH \(N_{\text{max}} = 36\)

Temporal

Period of 12.42060122 h, Greenwich fixed phase, complex coefficients

\(N_2\) tidal

2, 736

Spatial

Geographic SH \(N_{\text{max}} = 36\)

Temporal

Period of 12.65834751 h, Greenwich fixed phase, complex coefficients

\(O_1\) tidal

2, 736

Spatial

Geographic SH \(N_{\text{max}} = 36\)

Temporal

Period of 25.81933871 h, Greenwich fixed phase, complex coefficients

Ionosphere/induced

5, 520

Spatial

Quasi-dipole (QD) frame, underlying dipole SH \(N_{\text{max}} = 60\), \(M_{\text{max}} = 12\)

Temporal

Annual, semi-annual, 24, 12, 8, and 6 h periodicities with \(F_{10.7}\) scaling plus induction via a priori 3D conductivity model (“1D+oceans”) and infinite conductor at depth

Magnetosphere/induced

685, 110

Magnetosphere

Spatial:

dipole SH \(N_{\text{max}} = 1\)

Temporal:

Discretized in 1-h bins

Induced

Spatial:

dipole SH \(N_{\text{max}} = 1\)

Temporal:

Discretized in 1-h bins

OHM biases

597

One vector bias for each station in local spherical system

VFM-CRF alignment

4, 755

Three XYZ-type Euler angles every 10 days for each Swarm satellite and CHAMP satellite single- and double-headed star trackers

Total

734, 670