TY - JOUR
AU - Takehiro, Shin-ichi
AU - Sasaki, Youhei
PY - 2018
M3 - Original Research
TI - On Destruction of a Thermally Stable Layer by Compositional Convection in the Earth's Outer Core
JO - Frontiers in Earth Science
UR - https://www.frontiersin.org/articles/10.3389/feart.2018.00192
VL - 6
SN - 2296-6463
N2 - We discuss destruction of a thermally stable layer in the upper part of the Earth's outer core by compositional convection excited at the inner core boundary. We propose to use the radial distribution of power induced by thermal and compositional buoyancy (rate of kinetic energy production) as a measure of occurrence of thermal and compositional convection. The power consists of the terms proportional to convective entropy flux and convective compositional flux. In the region with positive power, convection is active because kinetic energy can be produced by buoyancy force, and a stably stratified layer could not be formed there. On the other hand, in the region with negative power, convection is suppressed and a stably stratified layer may be produced. Considering penetration effect of convection, we discuss possible maximum and minimum thicknesses of the stable layer based on the radial distribution of power and its radial integral, respectively. We construct a 1-dimensional thermal and compositional balance model of the Earth's core with a larger value of thermal conductivity recently suggested by high-pressure experiments and first principle calculations, and estimate radial distributions of power for various values of core mantle boundary (CMB) heat flux Q_{CMB}. When Q_{CMB}>Q_{sCMB} no thermally stable layer can exist, where Q_{sCMB} is the conductive heat flux along the adiabat at the CMB. On the other hand, when Q_{CMB}sCMB, formation of an upper thermally stable layer becomes possible, depending on the extent of penetration of compositional convection excited below. When Q_{CMB} is sufficiently lower than Q_{sCMB}, a thermally stable layer survives the maximum penetration of compositional convection. The results show that a thermally stable layer becomes effectively thinner when the effect of compositional convection is considered compared with the results of previous studies where the existence of a stable layer is evaluated based on the convective flux only.
ER -