Language：Japanese   Book type：Scholarly book

コアの歴史と地球磁場変動の関連の解説

Responsible for pages：pp.63-77 本全体の編者は春日直樹（一橋大学）。本全体としては１７名の著者による。   Language：Japanese   Book type：Scholarly book

Connecting Science and Culture: Analogical Thinking (Naoki Kasuga, ed.) Chapter 3 "Analogy as inference through similar phenomena -- an example in a scientific research on the modelling of the Earth's inner core anisotropy" (Shigeo Yoshida and Hisashi Nakao)

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Magnetohydrodynamic (MHD) shallow water linear waves are investigated over a rotating sphere with an imposed equatorially antisymmetric toroidal magnetic field: B0Φ=B0sinθcosθ, where B0 is a constant, θ is the colatitude and Φ is the azimuth. This system can imitatively represent the dynamics of a liquid metal within a stably stratified layer at the top of the Earth's core, which was detected through seismological surveys (e.g. Helffrich & Kaneshima, 2010[1]) and also has been deduced from geophysical and geochemical knowledge (e.g. Buffett & Seagle, 2010[2]; Pozzo et al., 2012[3]; Gubbins & Davies, 2013[4]; Brodholt & Badro, 2017[5]). Because slowly propagating waves in the liquid core can result in geomagnetic secular variations, comparison between exhaustive studies of MHD waves in a rotating stratified fluid and observations of geomagnetic fluctuations should provide constraints on the obscure stratified layer in the outermost core (e.g. Braginsky, 1993[6]; Buffett, 2014[7]).

The adopted configuration of the background field complicates solving the eigenvalue problem of linear waves due to the emergence of an Alfvén continuum and critical latitudes unless dissipation effects are taken into account. These result from non-dissipative Alfvén resonance, which occurs only when B0Φ/sinθ depends on θ, that is, regular singular points appear in the differential equation of linear problems. The solutions of the continuum are required to express the transient evolution of an arbitrary initial disturbance (e.g. Case, 1960[8]; Goedbloed & Poedts, 2004[9]). We can confirm numerically and analytically that introducing magnetic diffusion eliminates these Alfvén continuous modes and their singular structures around critical latitudes (Nakashima, Ph.D. thesis, 2020[10]).

For the Earth's core-like parameter (B0≃0.5—5mT and magnetic diffusivity η≃1m2/s), westward polar trapped modes are obtained as eigenmodes, which have a period of around from several to 1000 years. We may be able to observe these modes as geomagnetic secular variations in high latitude regions, if the strength of stratification in the stratified layer is close to the estimate of Buffett (2014)[7]. The analyses of recent geomagnetic models and paleomagnetic data in terms of such waves could confirm the robustness of previous estimates of the properties of the layer.

[ Reference ]
[1] Helffrich, G., Kaneshima, S. (2010) Nature, 468, 807. doi: 10.1038/nature09636
[2] Buffett, B. A., Seagle, C. T. (2010) J. Geophys. Res., 115, B04407. doi: 10.1029/2009JB006751
[3] Pozzo, M., Davies, C., Gubbins, D., Alfè, D. (2012) Nature, 485, 355. doi: 10.1038/nature11031
[4] Gubbins, D., Davies, C. J. (2013) Phys. Earth Planet. Inter., 215, 21. doi: 10.1016/j.pepi.2012.11.001
[5] Brodholt, J., Badro, J. (2017) Geophys. Res. Lett., 44, 8303. doi: 10.1002/2017GL074261
[6] Braginsky, S. I. (1993) J. Geomag. Geoelectr., 45, 1517. doi: 10.5636/jgg.45.1517
[7] Buffett, B. (2014) Nature, 507, 484. doi: 10.1038/nature13122
[8] Case, K. M. (1960) Phys. Fluids, 3, 143. doi: 10.1063/1.1706010
[9] Goedbloed, J. P., Poedts, S. (2004) Principles of magnetohydrodynamics: with applications to laboratory and astrophysical plasmas, Cambridge Univ. Press, Cambridge.
[10] Nakashima, R. (2020) Ph.D. thesis, Kyushu University. http://dyna.geo.kyushu-u.ac.jp/HomePage/nakashima/pdf/doctoral_thesis.pdf

Event date： 2019.10

Language：Japanese  

Venue：熊本市国際交流会館（熊本市）   Country：Japan  

Shallow water MHD waves trapped in the polar regions on a rotating sphere with an imposed azimuthal magnetic field

Event date： 2019.5

Language：Japanese  

Venue：幕張メッセ（千葉市）   Country：Japan  

Magnetohydrodynamic (MHD) waves in a thin layer on a rotating sphere with an imposed toroidal magnetic field are investigated. The system is often considered as a model of the stably stratified outermost Earth's outer core or the tachocline of the Sun. The stratification of the outermost core is suggested on the basis of seismological evidence (e.g. Helffrich and Kaneshima, 2010; Kaneshima, 2018) and interpretations of the geomagnetic variations with MHD waves (e.g. Braginsky, 1993; Buffett, 2014; Chulliat et al., 2015). In order to provide constraints on the obscure stratified layer by comparing with wavy variations in the geomagnetic field, we studied the linear waves of the two-dimensional MHD and the MHD shallow water system over a rotating sphere.
We adopt an azimuthal equatorially antisymmetric field (BΦ(θ) = B0 sinθcosθ, where θ is colatitude, Φ is azimuth) as a background magnetic field. On the other hand, an equatorially symmetric field (BΦ(θ) = B0sinθ) was assumed in Márquez-Artavia et al.(2017), whose results we replicated and reported in JpGU 2018.
Compared with previous results, the dispersion diagrams obtained with the toroidal equatorially antisymmetric field show that some fast magnetic Rossby branches remain, while slow magnetic Rossby waves disappear. Besides, a continuous spectrum is found in the range where an azimuthal phase velocity is coincident with a local Alfvén velocity divided by sinθ. Similar continuous spectra are also seen in
various physical situations, including inviscid shear flow (e.g. Case, 1960; Balmforth and Morrison, 1995; Iga, 2013) and plasma oscillations (e.g. Van Kampen, 1955; Case, 1959; Barston, 1964; Sedláček, 1971). The continuous spectra are accompanied by a singular eigenfunction, which is physically meaningful only when they are integrated over the continuous spectra. Its integrated solutions generally decay with time, which is referred to as phase mixing. Unlike exponentially damped discrete modes, this decaying is proportional to negative powers of time.
In the case of the shallow water system with the antisymmetric field, discrete eigenvalues buried in the continuous spectrum is found, which include unstable modes. For the Earth-like parameters, polar trapped modes with decadal period and equatorial trapped Rossby waves with a few years period are found when the stratification is weak.

Event date： 2018.5

Language：English  

Venue：幕張メッセ（千葉市）   Country：Japan  

We investigated waves in a stably stratified thin layer in a rotating sphere with an imposed magnetic field. This represents the stably stratified outermost Earth's core or the tachocline of the Sun. Recently, many geophysicists focus on the stratification of the outermost outer core evidenced through seismological studies (e.g. Helffrich and Kaneshima, 2010) and an interpretation of the 60-year geomagnetic secular
variations with Magnetic-Archimedes-Coriolis (MAC) waves (Buffett, 2014).
Márquez-Artavia et al.(2017) studied the effect of a toroidal magnetic field on shallow water waves over a rotating sphere as the model of this stratified layer. On the other hand, MAC waves are strongly affected by a radial field (e.g. Knezek and Buffett, 2018). We added a non-zero radial magnetic perturbation and magnetic diffusion to Márquez-Artavia et al.(2017)'s equations. Unlike their paper's formulation, we applied velocity potential and stream function for both fluid motion and magnetic perturbation, which is similar to the first method of Longuet-Higgins(1968). In the non-diffusive case, the dispersion relation obtained with the azimuthal equatorially symmetric field (Bφ(θ) ∝sinθ, where θis colatitude) is almost the same as Márquez-Artavia et al.(2017)'s result, which includes magneto-inertia gravity (MIG) waves, fast magnetic Rossby waves, slow MC Rossby waves and an unexpected instability. In particular, we replicate the transition of the propagation direcition of zonal wavenumber m=1 slow MC Rossby waves from eastward to westward with increasing Lamb parameter (ε=4Ω^2 a^2/gh, where Ω, a, g and h is the rotation rate, the sphere radius, the acceleration of gravity and an equivalent depth, respectively) and Lehnert number (α=v_A/2Ωa, where v_A is Alfvén wave speed). As a consequence, fast magnetic Rossby waves and slow MC Rossby waves interact, and the non-diffusive instability occur.
Next, we are examining the case with an equatorially antisymmetric background field, which is more realistic in the Earth's core. In this case, if the magnetic diffusion is ignored, the continuous spectrums appear owing to Alfvén waves resonance (similar to the continuous spectrums in inviscid shear flow, e.g. Balmforth and Morrison, 1995). To solve this difficulty, our numerical model includes the magnetic diffusion term.

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市、ホテルポートヒルズ福岡   Country：Japan  

A possible stably stratified layer at the top of the outer core --the compositional evolution of the outer core

Event date： 2017.5

Language：Japanese  

Venue：幕張メッセ（千葉市）   Country：Japan  

Equatorial waves modified by the presence of a toroidal magnetic field within the stably stratified layer at the top of the Earth’s outer core

Event date： 2016.5

Language：Japanese  

Venue：幕張メッセ（千葉市）   Country：Japan  

Empirical mode decomposition of the decadal variation of the Gauss coefficients

Event date： 2015.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ（千葉市）   Country：Japan  

The boundary mode of axially symmetric MAC waves can exist in the stratified layer at　the top of the Earth’s outer core

Event date： 2015.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ（千葉市）   Country：Japan  

Spontaneous rotation of a block ice melting on metal surface

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京大学大気海洋研究所講堂（柏市）   Country：Japan  

Spontaneous rotation of a melting ice block

Event date： 2014.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡国際会議場（福岡市）   Country：Japan  

Spontaneous rotation of a melting ice block

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学川内北キャンパス講義棟（仙台市）   Country：Japan  

Spontaneous rotation of a block of ice on a flat surface of a warm metal column

Event date： 2013.10

Language：English  

Venue：新潟大学（新潟市）   Country：Japan  

Linear stability analysis of two-layer thermal convection and the generation of surface flow of gas giants

Event date： 2013.10

Language：English   Presentation type：Oral presentation (general)  

Venue：新潟大学（新潟市）   Country：Japan  

Introduction to the geodynamo theory and the alpha effect

Event date： 2013.5

Language：Japanese  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

A model of modern science and its working: Dual Feedback-Loop Operator

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

The history of the study on the Earth’s inner core with the aid of a scientometric method

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

How to write the history of geoscience -right and wrong of Whig interpretation of history-

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

The evolution of behavioral modernity and the evolution of science

Event date： 2013.4 - 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：パシフィコ横浜（横浜市）   Country：Japan  

Spontaneous rotation of a block of ice on a flat surface of a warm metal column

Event date： 2012.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京外国語大学（東京都府中市）   Country：Japan  

Event date： 2012.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福島県・くつろぎ宿千代滝   Country：Japan  

Event date： 2012.5

Venue：幕張メッセ国際会議場（千葉県千葉市）   Country：Japan  

Models and Simulations in Geosciences

Event date： 2012.5

Presentation type：Oral presentation (general)  

Venue：幕張メッセ国際会議場（千葉県千葉市）   Country：Japan  

Historical reconstruction in science

Event date： 2012.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

From philosophy of science to science of science - A casestudy on earth science

Event date： 2012.5

Language：Japanese  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

Model, where earth science and the philosophy of science meets

Event date： 2012.5

Language：Japanese  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

How to launch the Science of Science

Event date： 2012.5

Language：Japanese  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

A natural view of the World in philosophy of science provided by interpretation of the Earth’s evolution history

Event date： 2012.5

Language：Japanese  

Venue：幕張メッセ国際会議場（千葉市）   Country：Japan  

Where and how did science come from? A cognitive approach.

Event date： 2011.11

Presentation type：Symposium, workshop panel (public)  

Venue：日本大学文理学部（東京都世田谷区）   Country：Japan  

Methodology of science studies and the science of future

Event date： 2011.11

Presentation type：Symposium, workshop panel (public)  

Venue：日本大学文理学部（東京都世田谷区）   Country：Japan  

The reason we began to study the philosophy of science -- as an extension of the project "Decoding the Earth's Evolution"

Event date： 2011.9

Presentation type：Oral presentation (general)  

Venue：阿蘇白雲山荘（熊本県阿蘇市）   Country：Japan  

The alpha effect in the dynamo theory

Event date： 2010.5

Presentation type：Oral presentation (general)  

Venue：幕張メッセ　国際会議場   Country：Japan  

Evaluating Akiho Miyashiro's philosophy of science

Event date： 2010.4

Presentation type：Symposium, workshop panel (public)  

Venue：北海道大学　人文・社会科学総合教育研究棟   Country：Japan  

Usage of the term "model" in science

Event date： 1998.7

Language：English  

Venue：Seattle, WA, USA   Country：Other  

A method to examine the shifts in individual surface features in multi-temporal SAR images has been proposed. First, line-like and boundary-like features were extracted from SAR imagery using the pixel swapping method. The extracted feature images were then tied to observe an overall shift in individual features. We applied this method to two JERS-1 SAR images of the same path-row observed on different dates. We observed that the shift in flat areas was simple, but that in mountainous regions, there was a clear difference in the direction of the shift in ridges and valleys caused by the slightly different orbital characteristics of the satellite between the two images. In addition, care in choosing appropriate tie points was found to be important. The method used in this investigation is expected to be useful in planning an appropriate strategy for the coregistration of images, such as in SAR images used for change detection in environmental monitoring, and InSAR.

Type：Competition, symposium, etc. 

Number of participants：30

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：1

Type：Scientific advice/Review 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Academic society, research group, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Scientific advice/Review 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

打ち上げ自体は悪天候のため延期になったので、講演会、ビデオ上映、ジバニャン撮影会、学生による関連研究展示などが行われた。

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Other

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Other