基于环向电流场模拟的C-响应值对比研究

Comparative study of C-response based on toroidal current source modelling

磁层和电离层场源模拟是研究地球三维电性结构的重要步骤,本文研究建立场源的方法并对比不同场源计算的C-响应值.本文利用全球地磁参考场模型和格林函数,从时变电磁场推导出环向电流,将其作为地磁测深模拟计算的场源.C-响应值的计算采用积分方程方法,在一维层状地球模型(表层电导随经纬度变化)中验证了其正确性.在准偶极坐标系中,分别计算Y01场源和环向电流计算的C-响应值(CY01和Ctoro),并将它们与地磁台站观测值(Creal)进行对比.结果显示,场源主要由它的1阶球谐分量组成,海洋效应对沿海台站C1d值的虚部的干扰比实部更严重.C-响应值曲线与区域场源形态密切相关,不同频段的场源特征可能不同,在地磁测深反演前应考虑场源形态.

Because magnetospheric and ionospheric current source modelling is a prior step of global mantle conductivity imaging,we research on the current source modelling method and compare the C-responses excited by different sources.The study deduces a toroidal current source from time-varying geomagnetic fields with the IGRF-13 model and Green's function.Then we calculate the C-responses using the integral function method and verify the method on a layered Earth model.In quasi-dipole coordinate system,we compute the C-responses on the surface of the"1D+thin sheet"Earth model separately inspired by the toroidal current and its Y10 degree component,namely Ctoro and CY10 values,and compare them with the real values on the geomagnetic observatories.The outcome shows that ocean effect causes more disturbance on the real part of C1d than its imaginary part and the source is mainly composed of its first-order part.At the GZH,QZH,and SSH observatories along the coastline,real part of Ctoro is closer to Creal in around the period of 1~30 days,and real part of CY10 is nearer in around the period of 30~100 days.Therefore,the local current may have a deep effect on the C-responses,its characteristics change with frequencies and it's influence may be evaluated carefully before GDS inversion.