中国境内各阶非偶极子磁场的时空变化

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

为了研究中国境内各阶非偶极子(ND)磁场,通过最新的地磁场模型CALS10K.1b计算了10000BC—AD 1990年ND磁场在中国境内的时空及能量变化;22,23和24极子磁场零值线主要呈现出从我国中北部向东南部移动,从北部向东部移动,以及从东南部向西北部移动的趋势;除了26极子磁场,其余ND磁场在1500年以后均有"翘尾"现象,其所占主磁场的比值在10000BC—AD 1500年呈震荡变化,从1500年开始快速上升;除了22极子磁场,其它各阶ND磁场能量随时间变化的趋势基本一致.在5650BC年左右,各阶ND磁场能量值均出现高值并随阶数的增大而衰减,反映了在该时间点通过地核发电机产生的磁场能量随径向距离而近似线性衰减,地磁场能量主要源自地球液态外核.将CALS10K.1b模型结果与IGRF11模型对比后,得出CALS10K.1b模型所计算的ND磁场及能量值较为可靠,而两者差异主要源于数据和建模方法的不同.

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 2 2 ,2 3 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 2 6 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 2 2 pole field.Around the year 5650 BC,the energy reached high value,and then attenuated with the degree increasing,which indi-cates 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.