月球均匀模型阶跃感应磁场模拟计算

Simulation of Induced Step-transient Magnetic Field with a Lunar Homogeneous Model

针对月球均匀模型,利用电磁感应理论,对行星际磁场阶跃扰动产生的感应磁场进行了模拟计算.设磁导率恒为μ_0,对于一些特定的电导率值,给出了月表磁场分量和总场从跃变到重新达到稳态的变化过程;在一条经线上的赤道附近、中纬地区和极区各选取一个测点,利用Laplace逆变换的数值公式给出了磁场瞬变响应函数和磁场分量及总场在不同电导率情况下的变化趋势.计算结果表明,此研究方法可行,结果合理.经过足够长的时间,与外磁场跃变方向垂直的磁场分量将会消失,而与之平行的磁场分量将与外场趋于一致.在外场发生跃变的时刻,赤道附近能够测到的最大磁场分量值约为13.65 nT,极区附近能测到约2.7l nT;在中低纬度和极区,平行分量变化的过程显著不同,反映出实际探测中,选取在月表不同位置的磁强计将可能监测到完全不同的磁场变化曲线形态.

With a homogeneous model of the Moon,the induced magnetic field caused by steptransient disturbation of interplanetary magnetic field is simulated by the electromagnetic induction theory.As the range of conductivity assigned,the variation from step to calm of both the vectors and magnitudes can be obtained with a fixed permeability μ_0.Then the magnetic characteristic transient response function,the field components and total field at 3 different points selected in a longitude line can all be given in different conductivities by numerical inverse Laplace transformation.The calculation provides a reasonable result that components perpendicular to the external step-transient field will disappear in a long-enough time,whereas the parallel component will become unity with it.When the external field step varies,the maximum field value which can be detected in the vicinity of the equator and the polar region are 13.65 nT and 2.71 nT,respectively.The processes of parallel component change are remarkably different in low latitude and polar region.This phenomenon reflects that magnetometers in different sites of lunar surface may lead to different field curves.