地球主磁场的能量密度谱及其长期变化

The energy density spectrum and secular variation of the Earth's main magnetic Field

根据BJ地磁场模型和第 8代国际地磁参考场 (IGRF)模型 ,计算并分析了 16 90～ 2 0 0 0年期间地球表面主磁场和分量的能量密度谱及其长期变化 .结果表明 16 90～ 2 0 0 0年期间主磁场的能量密度谱一直在减小 ,其主要原因是由于偶极子磁场的衰减产生的 ,而非偶极子磁场的能量密度谱在 16 90～ 1780年期间减小 ,1780～ 1890年增大 ,1890年以后快速增大 .在地磁场总能谱的变化中 ,Z分量的贡献起主要作用 .能量密度随谐波阶数的变化在半对数坐标中近似线性 ,非偶极子场的等效磁源深度位于核幔边界附近 ,n =1,2谐波项的等效磁源位于地球内核边缘 ,其位置随时间变化 .1780和 1890年前后是地磁场变化的转折时期 .能量密度谱的长期变化存在大约 6 0a的周期规律 .

The energy density spectrum and secular variation of the Earth's main magnetic field on the surface of the earth during 1690～2000 were calculated and analyzed according to the models of Jeremy Bloxham and Andrew Jackson and the eighth generation of International Geomagnetic Reference Field(IGRF). The results show that the energy density spectrum of the main magnetic field is always decrease during 1690～2000. Its main reason is because of the reduction of the dipole magnetic field to produce. But the energy density spectrum of non dipole magnetic field is decrease during 1690～1780, increase during 1780～1890 and quickly enlarge after 1890. Z component rise the main function for contribution of geomagnetic total energy. The energy density spectrum with harmonic degree n is nearly like straight line in the half logarithms coordinate. The apparent source layer of non dipoles field was near CMB. The apparent source layer of harmonics for n =1 and 2 locate the Earth inner core neighborhood, its position is variety with time. The years about 1780 and 1890 is turning period of the geomagnetic field. There are periodic regulation about 60a for secular variation of the energy density spectrum.