Magnetic fields induced in the solid Earth and oceans Alexei Kuvshinov & Nils Olsen

1. Magnetic fields induced in the solid Earth and oceansAlexei 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: Conductance Existing numerical solutions: 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 35000 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) Altitude of 400 km Sea level 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 The spectrum of the magnetic residuals over the Indian Ocean before (black) and after (red) subtracting our predictionsfrom 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