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. from Buffet, 2007 Boundary layers & dynamos Mantle convective style: relationship of Qcmb toQad Inner core solidification: latent heat and compositional buoyancy 3. Radioactivity in the core 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 0 - 3.5 Ga 0 - 160 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: 1590-1990 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. DATA lake sediments Br in T at CMB: 0 - 7 ka time average archaeomag directions Model CALS7K.2 Korte & Constable, 2005 archaeomag intensity Paleo-Field Behavior: I (Millenia) Persistent high latitude flux lobes?

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

11. Records of Reversals Br at CMB: UFM1: 1840-1980 Confined VGP paths due to thermal or electromagnetic coupling? e.g., Costin & Buffett, 2004

12. Paleofield Models: Next Generation…. • Continuous global models for 0 - 2 Ma: • temporal evolution, spectrum, statistics • Reconcile / Merge different data types • Time series of direction and relative intensity • Large collection of new data from volcanics