“snowfall” in f layer

2:57 PM, Dec. 8, 2012

CIDER Post-AGU 2012

“Snowfall” in F Layer

Jie (Jackie) LiUniversity of Michigan

Collaborators

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

Seismic features of the F-layer

Outer Core

Inner Core

F-layer

PREMAK135PREM2

Zou et al. 08Krasnoshchekov et al. 05Cao et al. 07Sun and Song 08Gubbins et al. 08,

“Snowing” cores in Solar System

Williams 09 Hauck et al. 06 JGRChen et al. 08 GRL

Stewart et al. 07 Science

Occurrence of “snowfall” in Earth’s core?Case 1

Case 2

Case 1Melting gradient

decreases

Case 2Adiabatic gradient

increases

Integrative approachMP

- Adiabat, melting curve for snow criterion- Density for dynamic modeling- Velocity for seismic comparison

Seismo- Compare PKIKP-PKiKP differential travel time with PREM- Compare PKIKP-PKiKP differential travel time b/w east-west hemispheres

Dynamics- Evolution of thermal, compositional, and structural profiles with time- Origin of stratified layer- Stability of F-layer

Adiabatic temperature gradient

Core adiabat(dT/dP)S = gth•T/Kliqgth: 1.65Kliq: 1343T: geotherm

Perturbation to geotherm

Dziewonski and Anderson 81Anderson O. 98

Greff-Lefftz and Legros 99,

Melting curveLindemann’s 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 81

Seagle et al. 09

Grüneisen parameters

Case 1a: Wide “Snowing zone”Parameter space for “snowing”

Case 1b: Narrow “snowing” zone

Chen et al. 08

Case 2:

Greff-Lefftz and Legros 99,

Temperature near ICBincreases due to resonant period and viscomagnetic friction power

Looking back 2010 July-Aug: CIDER Boundary Layer, KITP 2010 Nov: MP Mini-Meeting Umich 2010 Dec: AGU presentation, meeting 2011 Nov: MP Mini-Meeting Umich 2011 Dec: AGU presentation, Post-AGU CIDER

Workshop 2012 Sep: MP Mini-Meeting Umich

Tips 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, regroup

Looking forward2012 has been an eventful year for the groupnew-year resolution

Arron and Cynthia ChenJeff and his bride

Looking forward2012 has been an eventful year for the groupnew-year resolution

Arron and Cynthia ChenJeff and his bride

PKPCdiff – PKPDF differential travel time

(Zou et al., 2008)

Previously proposed mechanisms

A thermochemical F-layerGubbins et al. 2008, GJI

A slurry F-layerInner core freezing must occur above the solid boundary (Loper and Roberts, 1981 PEPI)

CMB

ICB

Slurry zone

A thermochemical F-layerGubbins et al. 2008, GJI

A slurry F-layerInner core freezing must occur above the solid boundary (Loper and Roberts, 1981 PEPI)

CMB

ICB

Geodynamics

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