1. Boundary Layers & Magnetic Fields: Observations
Catherine L. Johnson
Department of Earth and Ocean Sciences
University of British Columbia, Vancouver
A Few Overview References - Treatise on Geophysics, 2007
Core energetics, Nimmo, vol 8, ch. 2 (sections 2,4,5)
Core-mantle interactions: Buffett, vol 8, ch. 12
Comparison w/ dynamo simulations: Christensen, vol 8, ch. 8, secn 4
Secular variation and historical field: Jackson & Finlay, vol 5, ch. 5
Paleofield (kyr time scales): Constable, vol 5, ch. 9
Paleofield (Myr time scales): Johnson & McFadden, vol 5, ch. 11

2. Boundary layers & dynamos
Mantle convective style: relationship of Qcmb to Qad
Inner core solidification: latent heat and compositional buoyancy
3. Radioactivity in the core
from Buffet, 2007
conduction:
Moon - no dynamo
remanent field
stagnant-lid convection
Mars - no dynamo, remanent field
Venus - no dynamo, no remanence
Mercury - likely dynamo
plate tectonics
Earth - dynamo

3. Boundary Layers and the Geodynamo
Are there observable geomagnetic diagnostics of boundary conditions?
qcmb (mean and spatial variations), IC growth
=> time-averaged morphology and intensity, TAF
=> (paleo) secular variation, (P)SV
=> reversal rates & field structure during a reversal
Are there observational constraints useful for building models of the geodynamo?

4. Boundary Layers and the Geodynamo
Are there observable geomagnetic diagnostics of boundary conditions?
qcmb (mean and spatial variations), IC growth
DATA:
satellites: Bx, By, Bz since 1980
observatories, surveys: Bx, By, Bz centuries
archaeomagnetic artefacts: |B|, direction kyr
lake sediments, lavas: direction, |B| kyr
lavas D, I, |B| Myr
deep sea sediments I, relative |B|, D Myr
Issues: temporal, spatial distribution,
not full vector measurement, paleo-site position

5. Longevity and Mean Intensity of Earth’s Field
0 - 5 Ma Ga Ma
from Tauxe and Yamazaki, 2007
Since 3.5 Ga
Intensity variations on both long and short time scales

6. Global Field Models
TAF: Regularized inversions for SH coefficients (Guy - next week)
Linear - Bx, By, Bz; non-linear - D, I, |B|
PSV: Forward model statistical distributions of glm, hlm
Simulate distributions of observables: D, I, |B|, dispersion

7. Historical Geomagnetic Field Behavior (Centuries)
Br in T at CMB: time average
Model gufm1
Jackson et al., 2000
Persistent high latitude flux lobe => thermal coupling?
Low secular variation, sBr, in Pacific => EM or thermal coupling?

8. Paleo-Field Behavior: I (Millenia)
DATA
lake sediments
archaeomag directions
archaeomag intensity
Model CALS7K.2
Korte & Constable, 2005
Br in T at CMB: ka time average
Persistent high latitude flux lobes?

10. Paleo-Field Behavior: I (Millions of Years)
Models: time-averaged b/c limited temporal information
Johnson & Constable, 1995
Kelly & Gubbins, 1997
Johnson & Constable, 1997
Historical Field: Jackson et al., 2000

11. Records of Reversals
Br at CMB: UFM1:
If ULVZ patches are metallic or metal-rich then during reversals, as dipole field decays currents are generated in patches resulting in a secondary field. Costin and Buffett (2003, submitted):
Geometry of secondary field, generated in metallic or metal-rich patches during reversals and superposed onto transitional field due to dynamo, can govern VGP paths as observed.
Confined VGP paths due to thermal or electromagnetic coupling?
e.g., Costin & Buffett, 2004

12. Paleofield Models: Next Generation….
Continuous global models for Ma:
temporal evolution, spectrum, statistics
Reconcile / Merge different data types
Time series of direction and relative intensity
Large collection of new data from volcanics
Calibration, spectrum