Comparative study of C-response based on toroidal current source modelling
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 Y01 degree component,namely Ctoro and CY01 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 CY01 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.
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