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变速海水运动感应电磁场数值模拟及特征分析
周春,李予国,张宝强
1.中国海洋大学,海洋地球科学学院;2.国家海洋技术中心
摘要:
海水是一种高电导率的流体,根据电磁感应定律,运动的海水切割地磁场会在海水中产生感应电流,从而产生感应电磁场。本文从麦克斯韦方程出发,推导出一维速度场海水运动感应电磁场偏微分方程,利用电磁场水平分量在海水面和海底面上的连续性条件,得到海水运动感应电磁场表达式,并编写了Fortran计算程序。计算了常速度海水运动感应电磁场,并与格林函数法计算结果进行了对比,两种方法的计算结果一致。计算了海水运动速度随深度变化(即变速度)海水运动感应电磁场,并讨论了海水运动周期和海底介质电导率对海水运动感应电磁场的影响。计算结果表明:海水运动周期和海底介质电导率对常速度海水运动和变速度海水运动感应电磁场都有影响,但影响程度不同。在本文所述模型和参数条件下,海水运动感应电场和感应磁场振幅分别可达 6μV/m和10nT ,这与海洋大地电磁响应的量级相当。因而在处理海洋大地电磁数据时,海水运动感应电磁响应是不可忽略的噪音干扰,需要采用必要的压制手段。
关键词:  海水运动  感应电磁场  变速度  周期  海底电导率
DOI:10.11693/hyhz20180700186
分类号:
基金项目:青岛海洋科学与技术实验室“问海计划”项目
Numerical simulation and characteristic analysis of electromagnetic field induced by variable velocity seawater movement
Zhou Chun1, Li YU-Guo2, Zhang Bao-Qiang3
1.College of Marine Geosciences, Ocean University of China;2.College of Marine Geosciences, Ocean University of Chian;3.National Ocean Technology Center
Abstract:
Conductive seawater moving in the earth''s magnetic field generates electromagnetic (EM) field variations. In this paper, the partial differential equations for the induced EM fields from the motion of seawater are derived from the Maxwell equations, in which the continuous condition of tangential component of the electric and magnetic fields on both the air-sea interface and the seafloor is used. The EM fields induced by a constant seawater velocity model are calculated, and compared with the results obtained by using the Green''s function method and they agree very well. The EM fields induced by a variable seawater velocity model are simulated. The numerical calculations show that the EM responses are influenced by both the seawater motion period and the seafloor conductivity, but in different extent. It is shown that the motion of seawater can generate an electric potential difference of 6μV/m and a magnetic field of 10nT on the seafloor, which are almost in the same order of magnitude as the marine magnetotelluric signal. As a result, the induced EM fields from the motion of seawater need to be taken into consideration in the marine MT data processing.
Key words:  seawater motion  electromagnetic field  variable seawater velocity  period  seafloor conductivity
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