Geomagnetic vertical transfer function revealed from multi-interval geomagnetic data

The geomagnetic vertical transfer functions (VTFs) are useful to constrain the conductivity structure in the deep Earth. In this study, we propose an approach of estimating the geomagnetic VTFs in the wide period range from the multi-interval geomagnetic data. Applying the above method to the different interval (such as one-second, one-minute, one-hour) data from some geomagnetic observatories in China, we obtain the corresponding VTFs in the wide period range from 64 s to 9,830,400 s. In order to evaluate the possible ocean effect on different observatories, we make close investigations of the real geomagnetic induction vectors at QZH, SYG and XIC observatories. The results indicate that the ocean effect is clear at the coastal observatory like QZH. However, the ocean effect tends to decrease for the inland observatories (such as SYG and XIC) with the increasing distance from the coast.