Spatio-temporal variation of non-dipole magnetic fields with different degree in China

In order to systematically study all non-dipole (ND) magnetic fields (truncation level N=2—10) in China, we studied the spatio-temporal variation of ND magnetic fields with different degree and their energies during the period of 10000 BC—1990 AD based on the newest time-based global model CALS10K.1b. The latest version of IGRF, i.e., IGRF11, was also adopted to compare and verify. Results show that the zero lines of 2², 2³ and 2⁴ pole fields mainly moved from middle-northern region to southeastern region of China, from northern to eastern China, and moved from southeastern to northwestern region of China. Except the 2⁶ pole field, all ND fields exhibited “tail raise”. The percentage of ND field accounting for main field oscillated during 10000 BC—1500 AD, and then rapidly increased. The energies of all ND fields changed following almost same trend except the 2² pole field. Around the year 5650 BC, the energy reached high value, and then attenuated with the degree increasing, which indicates that the energy resulting from the Earth core’s dynamo attenuates linearly alone with radial distance. The energy of geomagnetic field mainly originates from the Earth’s fluid outer core. Comparison of the result based on CALS10K.1b with that from IGRF11 showed that CALS10K.1b’s results in this study are more reliable, and their differences mainly result from different data used and modeling methods.