Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean...
-
Upload
julie-sharp -
Category
Documents
-
view
215 -
download
0
Transcript of Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean...
![Page 1: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/1.jpg)
Boundary Layers & Magnetic Fields: Observations
Catherine L. JohnsonDepartment of Earth and Ocean Sciences
University of British Columbia, Vancouver
A Few Overview References - Treatise on Geophysics, 2007
1. Core energetics, Nimmo, vol 8, ch. 2 (sections 2,4,5)
2. Core-mantle interactions: Buffett, vol 8, ch. 123. Comparison w/ dynamo simulations: Christensen, vol
8, ch. 8, secn 44. Secular variation and historical field: Jackson &
Finlay, vol 5, ch. 55. Paleofield (kyr time scales): Constable, vol 5,
ch. 9 6. Paleofield (Myr time scales): Johnson & McFadden,
vol 5, ch. 11
![Page 2: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/2.jpg)
Boundary layers & dynamos
1. Mantle convective style: relationship of Qcmb to Qad
2. Inner core solidification: latent heat and compositional buoyancy3. Radioactivity in the core
plate tectonicsEarth - dynamo
stagnant-lid convection Mars - no dynamo, remanent fieldVenus - no dynamo, no remanenceMercury - likely dynamo
conduction: Moon - no dynamoremanent field
from Buffet, 2007
![Page 3: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/3.jpg)
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?
![Page 4: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/4.jpg)
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 kyrlake sediments, lavas: direction, |B| kyrlavas D, I, |B| Myrdeep sea sediments I, relative |B|, D Myr
Issues: temporal, spatial distribution, not full vector measurement, paleo-site position
![Page 5: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/5.jpg)
Longevity and Mean Intensity of Earth’s Field
1. Since 3.5 Ga2. Intensity variations on both long and short time
scales
0 - 3.5 Ga
0 - 160 Ma
0 - 5 Ma
from Tauxe and Yamazaki, 2007
![Page 6: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/6.jpg)
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, hl
m
Simulate distributions of observables: D, I, |B|, dispersion
Global Field Models
![Page 7: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/7.jpg)
Persistent high latitude flux lobe => thermal coupling?
Low secular variation, Br, in Pacific => EM or thermal coupling?
Historical Geomagnetic Field Behavior (Centuries)
Br in T at CMB: 1590-1990 time average
Model gufm1Jackson et al., 2000
![Page 8: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/8.jpg)
Persistent high latitude flux lobes?
Paleo-Field Behavior: I (Millenia)
Model CALS7K.2Korte & Constable, 2005
Br in T at CMB: 0 - 7 ka time average
DATA
lake sediments
archaeomag directions
archaeomag intensity
![Page 9: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/9.jpg)
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
![Page 10: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/10.jpg)
Paleo-Field Behavior: I (Millions of Years)
Models: time-averaged b/c limited temporal information
Johnson & Constable, 1995Kelly & Gubbins, 1997
Johnson & Constable, 1997Historical Field: Jackson et al., 2000
![Page 11: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/11.jpg)
Records of Reversals
Br at CMB: UFM1: 1840-1980
Confined VGP paths due to thermal or electromagnetic coupling?
e.g., Costin & Buffett, 2004
![Page 12: Boundary Layers & Magnetic Fields: Observations Catherine L. Johnson Department of Earth and Ocean Sciences University of British Columbia, Vancouver A.](https://reader036.fdocuments.us/reader036/viewer/2022062423/5697bf9a1a28abf838c920f6/html5/thumbnails/12.jpg)
Paleofield Models: Next Generation….
Continuous global models for 0 - 2 Ma: temporal evolution, spectrum, statistics
Reconcile / Merge different data types 1. Time series of direction and relative intensity2. Large collection of new data from volcanics