“snowfall” in f layer

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“Snowfall” in F Layer. CIDER Post-AGU 2012. 2:57 PM, Dec. 8 , 2012 . Jie (Jackie) Li University of Michigan. Advanced Photon Source. Collaborators. Jeffrey Pigott – Mineral Physics (Ohio State) Jie (Jackie) Li – Mineral Physics (U of Michigan) - PowerPoint PPT Presentation

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2:57 PM, Dec. 8, 2012 CIDER Post-AGU 2012Snowfall in F LayerJie (Jackie) LiUniversity of MichiganAdvanced Photon Source

1Whats so special about ICB?What is equivalent of F-layer

CollaboratorsAdvanced Photon Source

Jeffrey Pigott Mineral Physics (Ohio State)Jie (Jackie) Li Mineral Physics (U of Michigan)Bin Chen Mineral Physics (U of Michigan)Matt Armentrout Mineral Physics (UCLA)Antonio Buono Mineral Physics (MIT)

John Hernlund Geodynamics (UC-Berkeley)Jodi Gaeman Geodynamics (U of Maryland)

Lauren Waszek Seismology (Cambridge)

Louis Kellogg, Barbara Romanowicz, Jeroen Tromp, Vernon Cormier 2For the XES experiments, Yuming Xiao helped me with the experiments. Yu Meng (Sector 16), Zhiguo Liu (Sector 13) (Harbin Institute of Technology), and Yingxia Shi (Sector 16) (Stanford) gave me some beamtime to characterize the sample. Michael Hu , Jiyong Zhao, and Dongzhou Zhang helped me with the experiments.Seismic features of the F-layer

Outer CoreInner CoreF-layerPREMAK135PREM2Zou et al. 08Krasnoshchekov et al. 05Cao et al. 07Sun and Song 08Gubbins et al. 08

,31D: V gradient2D: mosaic3D: topography

anisotropy: directional

Wen 06Wookey & Helffrich 08 NatureDuess et al. 10 Science

Snowing cores in Solar SystemWilliams 09Hauck et al. 06 JGR

Chen et al. 08 GRL

Stewart et al. 07 Science

4Occurrence of snowfall in Earths core?

Case 1

Case 2Case 1Melting gradientdecreases

Case 2Adiabatic gradient increases

5Case 1 Gubbins et al (2008) requires T increase in F layer, but with no explanation?

Case 2 T increase near ICB by viscomagnetic frictional power (Greff-Lefftz and Legros, 1999 ScienceIntegrative approachMP- Adiabat, melting curve for snow criterion- Density for dynamic modeling- Velocity for seismic comparisonSeismo- Compare PKIKP-PKiKP differential travel time with PREM- Compare PKIKP-PKiKP differential travel time b/w east-west hemispheresDynamics- Evolution of thermal, compositional, and structural profiles with time- Origin of stratified layer- Stability of F-layer 6crystallization and evolution as T drops- Fe crystals settle downwards through liquid- light elements percolate upwards- chemical stratification

Adiabatic temperature gradientCore adiabat(dT/dP)S = gthT/Kliqgth: 1.65Kliq: 1343T: geotherm

Perturbation to geothermDziewonski and Anderson 81Anderson O. 98Greff-Lefftz and Legros 99, 7Gruneisen parameterMelting curveLindemanns Law for fixed compositiondTm/dP = 2(gSL 1/3)Tm/Ksol2(gSL 1/3) = K -1, K = 1.7 to 3.6Ksol: 1500Tm: melting temperature

Binary solution

Dziewonski and Anderson 81Seagle et al. 098experimental

theory: Lindmann law

Seismic PREM

Grneisen parameters9Snowing Fe-S, Fe-C?, Fe-Si?No snow Pure Fe, Fe-H, likely Fe-C and Fe-Si

Case 1a: Wide Snowing zone

Parameter space for snowing10Snowing Fe-S, Fe-C?, Fe-Si?No snow Pure Fe, Fe-H, likely Fe-C and Fe-Si

Case 1b: Narrow snowing zone

Chen et al. 08

11Snowing Fe-S, Fe-C?, Fe-Si?No snow Pure Fe, Fe-H, likely Fe-C and Fe-Si

Case 2:

Greff-Lefftz and Legros 99, Temperature near ICBincreases due to resonant period and viscomagnetic friction power12Looking back2010 July-Aug: CIDER Boundary Layer, KITP2010 Nov: MP Mini-Meeting Umich2010 Dec: AGU presentation, meeting2011 Nov: MP Mini-Meeting Umich2011 Dec: AGU presentation, Post-AGU CIDER Workshop2012 Sep: MP Mini-Meeting Umich

13Tips and TrapsAccomplishments- Cross-discipline exchange- MP collaboration that otherwise would not have occurred- AGU presentations (Li, Hernlund)- SEDI grant (Hernlund and Cormier)- Thesis project (Piggot)

Obstacles- Define leadership role- Follow up- Generate a concrete product

For discussion- Group, ungroup, regroup14

Looking forward

2012 has been an eventful year for the groupnew-year resolutionArron and Cynthia ChenJeff and his bride15

Looking forward

2012 has been an eventful year for the groupnew-year resolutionArron and Cynthia ChenJeff and his bride16

PKPCdiff PKPDF differential travel time (Zou et al., 2008)A recent seismological study on PKP_Cdiff DF differential travel times. -Top Left: ray paths. PKP_Cdiff grazing F-layer. -Top Right: dots and crosses: measurements; solid line: prediction of PREM (as ref); dashed line: prediction of AK135. AK135 fits obsrv better than PREM. Not focus on the hemispherical pattern for the scope of this presentation. -Bottom: difference between PREM and AK135 predictions is majorly attributed to F-layer rather than the top of inner core or D.

Problems- Though the F layer model fits the data better than PREM, the PKIKP-PKiKP method is not ideal- Cannot use PKIKP as a reference phase due to the hemispherical inner core structure, detected in PKIKP-PKPbc phases and normal modes (e.g. Deuss et al, 2010)- Better method use waveform modelling of PKiKP to search for scatter within F layer, and examine for precursors reflected from top of F layer (e.g. Poupinet & Kennett 2004)

17Previously proposed mechanisms

A thermochemical F-layerGubbins et al. 2008, GJIA slurry F-layerInner core freezing must occur above the solid boundary (Loper and Roberts, 1981 PEPI)CMBICB

Slurry zone

A thermochemical F-layerGubbins et al. 2008, GJIA slurry F-layerInner core freezing must occur above the solid boundary (Loper and Roberts, 1981 PEPI)CMBICB

Geodynamics

20Origin of Vp gradientCan solid/liquid fraction account for Vp gradient?

213rd order B-M Mie Grneisen EOS

pure Fe and FeS liquid endmembers

Large extrapolations but still fits well

Examine which parameters are insensitive

Figure3.11

Relations

amon

gthevariou

sdefin

itions

oftheGruneisen

parameter.

4.0

3.5

3.0

2.5

2.0

1.5

1.0

K'

2.52.01.51.00.50.0th

Snow

Bottom-Up crystallization

Fe-S

Fe-H

Fe-CFe-O

Fe-Si

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