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

点击翻译按钮获取中文摘要

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.