1. Magnetic fields induced in the solid Earth and oceans Alexei Kuvshinov & Nils Olsen
Danish National Space Center, Copenhagen, Denmark
Predicting magnetic signals induced in 3-D conductivity Earth by various sources
- Sq and EEJ
- Geomagnetic storms
- Ocean tides and global circulation
Possible utilization of 3-D predictions in geomagnetic field modeling
Conclusions

2. Forward problem formulation and 3-D Earth’s model
Calculate EM field induced by a given in Earth’s model of a given
Governing (Maxwell’s) equations:
Basic 3-D conductivity model:
Existing numerical solutions:
Conductance
Fainberg et al., 1990;
Tarits, 1994;
Everett & Schultz, 1996;
Martinec, 1999;
Uyeshima & Schultz, 2000;
Tyler et al., 1999, 2002;
Koyama et al., 2002;
Kuvshinov et al., 2002; 2005 (VIE approach)
Yoshimura & Oshiman, 2002;
Hamano, 2002;
Weidelt, 2004;
Velimsky et al., 2005
Varies from 0.1 S up to S

3. 3D magnetic fields due to Sq current system
Source: Sq of 21 March 2000 (from CM4; Sabaka et al.,2004)
Sea level
Altitude of 400 km
3D Br (inducing + induced parts)
Ocean effect (up to 12 nT)
Ocean effect (up to 6 nT)

4. Magnetic fields due to equatorial electrojet (EEJ)
Source: EEJ of 21 March 2000 (from CM4)
Sea level
Altitude of 400 km
Ocean effect (up to 4 nT)
Ocean effect (up to 1 nT)

5. Magnetic fields due to geomagnetic storms
Source: storm of 5-6 November, 2001
Sea level
Altitude of 400 km
Ocean effect (up to 80 nT)
Ocean effect (up to 30 nT)

6. Magnetic fields due to geomagnetic storms (contd.)
Z at HER for selected storms
Z at coastal obsrvatories for storm 13 July 2000
Olsen & Kuvshinov, 2004

7. Magnetic fields due to ocean tides
Movement of sea water through the main field:
Source: S
M2 tidal model by Egbert & Erofeeva (2000)
Predictions from Kuvshinov & Olsen (2005)

8. Magnetic fields due to ocean tides (contd)
Magnetic effect of oceanic M2 tide as seen by CHAMP
Observed S
Predicted
Tyler, Maus & Luhr, 2003

9. Magnetic fields due to ocean tides (contd.)
Tidal correction for MF4 model
Tides
Period, days M2
0.5176 S2
0.5 N2
0.5274 K2
0.4986 K1
0.9973 O1
1.0758 P1
1.0027 Q1
1.1195
The spectrum of the magnetic residuals over the Indian Ocean before (black) and after (red) subtracting our predictions from 8 major tidal constituents (Maus et al., 2005).

10. Magnetic field due to ocean circulation
Ocean circulation velocities (ECCO model)
Source S
The magnetic signals are largely influenced by the Antarctic Circumpolar Current (ACC).
The largest signature is in Br with peak-to-peak values of order 3 nT.
Br at 430 km
Manoj et al., 2005

11. Possible utilization of 3-D predictions in geomagnetic field modeling
Signals due to ocean flows – subtracting the 3-D predictions from the data
Signals of magnetospheric origin – decomposition of Dst = Est + Ist (Maus & Weidelt, 2004) using 3-D conductivity model
Signals of ionospheric origin – replacement of 1-D responses by 3-D ones

12. Conclusions
3-D induction effects contribute much to near-Earth magnetic field
These effects can be predicted with required accuracy and detail by using modern numerical solutions
3-D predictions can be readily incorporated into modern geomagnetic field modeling schemes