IRBEM computes magnetic coordinates and traces field lines by combining an internal field model (representing Earth’s main field) with an optional external field model (representing magnetospheric current systems). TheDocumentation Index
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kext integer parameter passed to most IRBEM routines selects the external model, while options[4] selects the internal model.
External Field Models (kext)
The table below lists all 14 external models supported by IRBEM. Models that require driving parameters source those values from the maginput array — see the maginput reference for the full parameter list.
kext | Model Name | Notes / Valid Range |
|---|---|---|
| 0 | No external field | Internal field only |
| 1 | Mead & Fairfield [1975] | Uses Kp (0–9); valid for r_GEO ≤ 17 Re |
| 2 | Tsyganenko short [1987] | Uses Kp (0–9); valid for r_GEO ≤ 30 Re |
| 3 | Tsyganenko long [1987] | Uses Kp (0–9); valid for r_GEO ≤ 70 Re |
| 4 | Tsyganenko [1989c] | Uses Kp (0–9); valid for r_GEO ≤ 70 Re |
| 5 | Olson & Pfitzer quiet [1977] | Valid for r_GEO ≤ 15 Re |
| 6 | Olson & Pfitzer dynamic [1988] | Uses dens (5–50 cm⁻³), velo (300–500 km/s), Dst (−100 to 20 nT); valid for r_GEO ≤ 60 Re |
| 7 | Tsyganenko [1996] | Uses Dst (−100 to 20 nT), Pdyn (0.5–10 nPa), |By| ≤ 10 nT, |Bz| ≤ 10 nT; valid for r_GEO ≤ 40 Re |
| 8 | Ostapenko & Maltsev [1997] | Uses Dst, Pdyn, Bz, Kp |
| 9 | Tsyganenko [2001] | Uses Dst (−50 to 20 nT), Pdyn (0.5–5 nPa), |By| ≤ 5 nT, |Bz| ≤ 5 nT, G1 (0–10), G2 (0–10); valid for x_GSM ≥ −15 Re |
| 10 | Tsyganenko [2001] storm | Uses Dst, Pdyn, By, Bz, G2, G3; no upper/lower limit on inputs; valid for x_GSM ≥ −15 Re |
| 11 | Tsyganenko [2004] storm | Uses Dst, Pdyn, By, Bz, W1–W6; no upper/lower limit on inputs; valid for x_GSM ≥ −15 Re |
| 12 | Alexeev [2000] / Paraboloid | Uses dens, velo, Dst, BzIMF, AL |
| 13 | Tsyganenko [2007] | |
| 14 | Mead-Tsyganenko | Uses Kp; ONERA model where T89 is best-fitted by a Mead model |
Python String Aliases
In the PythonMagFields class, kext can be specified as either an integer or a string alias from the extModels list. The aliases map to kext values in order:
kext | String alias |
|---|---|
| 0 | 'None' |
| 1 | 'MF75' |
| 2 | 'TS87' |
| 3 | 'TL87' |
| 4 | 'T89' |
| 5 | 'OPQ77' |
| 6 | 'OPD88' |
| 7 | 'T96' |
| 8 | 'OM97' |
| 9 | 'T01' |
| 10 | 'T01S' |
| 11 | 'T04' |
| 12 | 'A00' |
| 13 | 'T07' |
| 14 | 'MT' |
Internal Field Models (options[4])
The fifth element of the options array selects the internal (main) field model applied beneath every external model:
options[4] | Model |
|---|---|
| 0 | IGRF (default) |
| 1 | Eccentric tilted dipole |
| 2 | Jensen & Cain 1960 |
| 3 | GSFC 12/66 updated to 1970 |
| 4 | User-defined myOwnMagField routine |
| 5 | Centered dipole |
When
options[4] = 4, IRBEM calls a user-supplied Fortran routine myOwnMagField(xGEO, Bxint). The inputs are xGEO, a 3-element double array of geocentric geographic (GEO) cartesian coordinates in Re, and the output is Bxint, a 3-element double array of magnetic field components (Bx, By, Bz) in GEO cartesian coordinates in nT.The TS07d Model
The Tsyganenko [2007] model (kext=13, alias 'T07') requires additional coefficient files that are not bundled with the base IRBEM distribution. Before using this model you must run the setup script included in the repository root: