日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 S (固体地球科学) » S-EM 固体地球電磁気学

[S-EM18] 地磁気・古地磁気・岩石磁気

2019年5月26日(日) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:清水 久芳(東京大学地震研究所)、佐藤 雅彦(東京大学地球惑星科学専攻学専攻)

[SEM18-P02] Forecasting geomagnetic secular variation based on magnetic diffusion at the core-mantle boundary

*松島 政貴1清水 久芳2高橋 太3南 拓人2中野 慎也4藤 浩明5 (1.東京工業大学理学院地球惑星科学系、2.東京大学地震研究所、3.九州大学大学院理学研究院、4.統計数理研究所、5.京都大学大学院理学研究科附属地磁気世界資料解析センター)

キーワード:国際標準地球磁場、地磁気永年変化、磁気拡散

The International Geomagnetic Reference Field (IGRF) is a standard mathematical description in terms of spherical harmonic coefficients, known as the Gauss coefficients, for the Earth's main magnetic field and its secular variation, updated every five years. In the next IGRF revision, the 13th generation of IGRF (IGRF-13), the Definitive Geomagnetic Reference Field for 2015 (DGRF-2015), the IGRF for 2020 (IGRF-2020), and the Secular Variation (SV) from 2020 to 2025 (SV-2020-2025) are to be released. We are planning to submit a model of SV-2020-2025 using our strong points, such as geodynamo numerical simulations, data assimilation, and core surface flow modeling.

Forecasts of geomagnetic SV are likely to require geomagnetic secular acceleration (SA), which can be expressed in terms of core fluid velocity and acceleration in the first time derivative of induction equation. In fact, Whaler and Beggan (2015) pointed out that forecasts of the Earth's main magnetic field and its temporal changes are improved for a model in which fluid velocity and acceleration are included. They also suggested that the quality of forecasts might be lowered for a period during which a geomagnetic jerk, a sudden temporal change in the geomagnetic acceleration, occurs. On the other hand, however, Fournier et al. (2015) pointed out that core flow acceleration could be neglected to forecast SV through data assimilation. Thus it is important to clarify the necessity of employing core flow acceleration.

In this presentation, we investigate whether or not geomagnetic SA is of importance to forecast geomagnetic SV, taking into account geomagnetic jerks occurred in 2003 and 2007 (e.g. Olsen and Mandea 2007; Chulliat et al. 2010). We assume that geomagnetic SV is caused only by magnetic diffusion at the core-mantle boundary, because core flow should vanish at the core surface on the no-slip boundary condition. We also show that the present method of forecasting the Earth's main magnetic field and its SV is consistent with simple analytical extrapolation of geomagnetic field. In other words, such simple extrapolation is based on a physical phenomenon of magnetic diffusion.