Kalmag: a high spatio-temporal model of the geomagnetic field

Earth, Planets and Space

Table 3 Magnetic sources parameters as described in "Dynamical model" section and evaluated by Baerenzung et al. (2020)

Field	Spectrum	Radius a (km)	A (nT)	M	\(\alpha\)
Core	Flat	3456	D: \(1.12 \times 10^5\) \(9.74 \times 10^4\)	\(\tau _c(1)\): 935 yrs \(M(\ell \ge 2) = 514\) yrs	1.06
Lithospheric \(1 \le \ell \le 74\)	C-based	6287	0.16	\(\infty\)	0
\(75 \le \ell \le 1000\)	Flat	6367.9	6.5	\(\infty\)	0
Close magnetospheric	C-based	12524	D: 9.16 1.88	\(\tau _m(1)\): 1.54 days \(M(\ell \ge 2) = 18\) min	0
Remote magnetospheric	C-based	235570	7.3	10.31 yrs	0
Fluctuating magnetospheric	C-based	13028	D: 3 4.56	\(\tau _{fm}(1)\): 0.36 day \(\tau _{fm}(2)\): 0.55 days \(M(\ell \ge 3) = 4\) days	1.15
Residual ionospheric/ induced	Flat	6324	D: 5.48 4.39	\(\tau _s(1)\): 0.71 day \(M(\ell \ge 2) = 1.76\) day	0.93
Field-aligned currents	C-based	7917	D: 0 1.22	\(\tau _{fac}(1)\): 0 \(M(\ell \ge 2) = 1\) min	0

The prior spatial covariance matrices are derived from energy spectra expressed at some radii \(a_s\) which are either flat with \(E_s^\infty (\ell ) = A_s^2\) or of the C-based type [see Holschneider et al. (2016)] with the form \(E_s^\infty (\ell ) = A_s^2 (2\ell +1) R(\ell )\), where \(R(\ell )=\ell +1\) and \(R(\ell )=\ell\) for, respectively, internal and external sources
The characteristic timescales are parameterized by \(\tau _s(\ell ) = M_s \ell ^{-\alpha _s}\)