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Table 1 CIY4 parameterization

From: A comprehensive model of Earth’s magnetic field determined from 4 years of Swarm satellite observations

Field source/effect # Parms Description
Core/lithosphere 13,368 Spatial: geographic spherical harmonic (SH) \(N_{\max }=100\)
Temporal: order 4 B-splines SV, 6 month knot spacing from 2013.9 to 2018.0, epoch 2015.0, up to \(N_{\max }=16\)
\(M_2\) tidal 2736 Spatial: geographic SH \(N_{\max }=36\)
Temporal: period of 12.42060122 hours, Greenwich fixed phase
Ionosphere/induced 5520 Spatial: quasi-dipole (QD) frame, underlying dipole SH \(N_{\max }=60\), \(M_{\max }=12\)
Temporal: annual, semiannual, 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 165,252 Magnetosphere
 Spatial: dipole SH \(N_{\max }=1\)
 Temporal: discretized in 1 h bins
Induced
 Spatial: dipole SH \(N_{\max }=1\)
 Temporal: discretized in 1 h bins
OHM biases 465 One vector bias for each station in local spherical system
VFM-CRF alignment 1350 Three XYZ-type Euler angles every 10 days for each satellite
Total 188,691