Verification of the geomagnetic secular variation models based on laboratory experiments and numerical simulations.

本研究的目的是在实验室实验和数值模拟的基础上验证几种地磁长期变化模型。该项目包括（1）观测地磁场在不同时间尺度上的变化，（2）液态金属热对流湍流特性的实验室实验，（3）导电流体壳层中磁场产生的数值模拟。(1)In对日本伊豆大岛火山和富士山历史熔岩流、日本中海和埃及喀伦湖沉积物进行了地磁场观测和古地磁研究，估算了几千年来地磁场的长期变化。(2)In通过实验室实验，研制了一种利用超声测速技术观测液态金属层中流体运动的新装置。用新研制的装置继续观测了高瑞利数下液态镓层中的湍流对流运动。在现有实验的基础上，我们发现在一定的瑞利数范围内，对流模式存在准周期性的涨落。图案的振荡频率作为瑞利数的函数而变化，其中在较高的瑞利数处观察到较高的频率。（3）对使用地球模拟器进行的高分辨率地球发电机模拟结果的研究表明，可以从地磁场的时间变化推断流体壳层中的湍流状态。在地球表面观察。综合观测、实验和数值模拟的结果，可以推断地磁场的起源及其变化。

Purpose of the present research is to verify several models for the geomagnetic secular variations based on laboratory experiments and the numerical simulations. This project consists of (1)observation of the variations of the geomagnetic fields in various time scales, (2)laboratory experiments on the turbulent properties of thermal convection in liquid metal, and (3)numerical simulations of generation of the magnetic field in a conducting fluid shell. (1)In the geomagnetic field observations, paleomagnetic studies on the historical lava flows from Izu-Oshima volcano and Mt.Fuji, and the lake sediments from Nakaumi, Japan and Lake Qarun, Egypt, were performed and the geomagnetic secular variations during the past several thousand years were estimated. (2)In the laboratory experiments, a new apparatus was developed for observing fluid motions in liquid metal layer by using the ultrasonic velocimetry technique. Observations of turbulent convective motions in liquid Gallium layer at high Rayleigh numbers have been continued by using the newly developed apparatus. Based of the present experiments, we found the quasi periodic fluctuation of convection patterns at a certain range of the Rayleigh number. The oscillation frequency of the patterns varies as a function of the Rayleigh numbers, where the higher frequency was observed at the higher Rayleigh number. (3)Examination of the results of the high resolution geodynamo simulations using the Earth Simulator revealed that the turbulent state in the fluid shell can be inferred from the temporal variation of geomagnetic fields. observed at the earth's surface. The results of the observations, laboratory experiments, and the numerical simulations can be integrated to infer the origin of the geomagnetic field and its variations.