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Characteristics of the geomagnetic field : comprehensive understanding based on observational data and the dynamo theory

地磁场的特征：基于观测数据和发电机理论的综合认识

基本信息

批准号：
12304024
负责人：
KONO Masaru
金额：
$ 26.78万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2003
项目状态：
已结题

项目摘要

In this research program, we tried to combine the observational (paleomagnetism) and theoretical (dynamo similation) results about the geomagnetic field. In other words, we aimed at understanding how various features of the geomagnetic field (polarity reversals, secular variation, intensity variation) are reproduced by the models, and if so what are the physical causes for these behaviors. We obtained the following results.In Paleomagnetic studies, we dated the basaltic rocks from Inner Mongolia, northeast China, by K-Ar method. The results indicated that these rocks erupted in late Cretaceous, in the so-called Cretaceous Long Normal superchron. Our experiments yielded the paleointensities which are about 1/4 of the present day value.We constructed the field model from the Paleomagnetic data of the last 5 million years. Similar models were already reported by Kelly and Gubbins (1997) and Johnson and Constable (1997), but our model is new in that it considers the effect of the variation of the field at the same time. Consequently our model express both the mean and the fluctuating field at the same time.The 3D, nonlinear dynamo models so far published are compared and reviewed. Our results show that, despite the significant difference between the parameters used in the models and those of the real earth, the numerical models reproduce many of the characteristic behaviors of the geomagnetic field.

在这个研究项目中，我们试图将关于地磁场的观测(古地磁学)和理论(发电机模拟)结果结合起来。换句话说，我们的目的是了解模型如何再现地磁场的各种特征(极性反转、长期变化、强度变化)，如果是这样的话，这些行为的物理原因是什么。在古地磁研究中，我们用K-Ar法测定了中国东北部内蒙古玄武岩的年龄。结果表明，这些岩石喷发于晚白垩世，即所谓的白垩纪长正超时。我们的实验得到的古地磁强度大约是现在的四分之一。我们根据过去500万年的古地磁数据建立了场模型。Kelly和Gubbins(1997)和Johnson和Conable(1997)已经报道了类似的模型，但我们的模型是新的，因为它同时考虑了场的变化的影响。因此，我们的模型同时表达了平均场和脉动场。对迄今发表的三维非线性发电机模型进行了比较和回顾。我们的结果表明，尽管模型中使用的参数与真实地球中使用的参数有显著差异，但数值模式再现了许多地磁场的特征行为。