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タイトル: | On destruction of a thermally stable layer by compositional convection in the earth’s outer core |
著者: | Takehiro, Shin Ichi Sasaki, Youhei |
著者名の別形: | 竹広, 真一 佐々木, 洋平 |
キーワード: | thermal conductivity heat flux compositional flux power by buoyancy forces kinetic energy production core dynamics core stratification |
発行日: | 2-Nov-2018 |
出版者: | Frontiers Media SA |
誌名: | Frontiers in Earth Science |
巻: | 6 |
論文番号: | 192 |
抄録: | 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 QCMB. When QCMB > QsCMB no thermally stable layer can exist, where QsCMB is the conductive heat flux along the adiabat at the CMB. On the other hand, when QCMB < QsCMB, formation of an upper thermally stable layer becomes possible, depending on the extent of penetration of compositional convection excited below. When QCMB is sufficiently lower than QsCMB, 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. |
著作権等: | © 2018 Takehiro and Sasaki. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. |
URI: | http://hdl.handle.net/2433/235518 |
DOI(出版社版): | 10.3389/feart.2018.00192 |
出現コレクション: | 学術雑誌掲載論文等 |
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