JpGU-AGU Joint Meeting 2020

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-EM Earth's Electromagnetism

[S-EM22] Geomagnetism, paleomagnetism and rock magnetism

convener:Masahiko Sato(Department of Earth and Planetary Science, The University of Tokyo), Chie Kato(Faculty of Social and Cultural Studies, Kyushu University)

[SEM22-P03] Statistical property of the polarity reversals in numerical dynamo models with implications for the geomagnetic field reversals

*Futoshi Takahashi1, Yuhji Yamamoto2 (1.Faculty of Sciences, Kyushu University, 2.Center for Advanced Marine Core Research, Kochi University)

Keywords:dynamo, reversal, core

Geomagnetic secular variation provides a way to characterize dynamo processes in the Earth’s outer core. Among them, polarity reversals of the Earth’s dipole have been one of the least understood phenomena. Recent advances in numerical dynamo simulation have enabled us to examine secular variation in both short- and long-period. Here we use numerical dynamo modeling to have general statistical property of the reversals occurred in numerical dynamos. Since we primarily focus on statistical behavior, long-term (typically longer than 1 Myrs) dynamo simulations are required to have a large number of reversals. However, it is tough and enormously time-consuming to perform a long-term dynamo simulation at state-of-the-art parameters. To handle the circumstances, we have to choose a higher value of E (Ekman number) by compromise. Some of the parameters adopted in the present study are fixed at E = 3.25 x 10-3 and 2 x 10-3, Pr (Prandtl number) = 1, Pm (magnetic Prandtl number) = 20, whereas Ra (Rayleigh number) is varied to see effects of the buoyancy on time variation of the dynamos. Time-integration is carried out for 30 – 40 non-dimensional time unit, which is scaled by the magnetic diffusion time. In each run, we have observed tens to hundreds of reversals during the above intervals. Based on the results, we calculate some statistics and examine their behavior. Preliminary results will be reported.