A study on variations of non-dipole magnetic field over Chinese mainland during 2000 BC to 1990 AD

作者：Feng Yan; Jiang Yong^*; Sun Han; An ZhenChang; Mao Fei

来源：Science China Earth Sciences, 2014, 57(6): 1229-1244.

DOI：10.1007/s11430-013-4674-6

• non-dipole
• geomagnetic field
• CALS3K.4
• IGRF11

We calculated and analyzed variation of the non-dipole (ND) magnetic field at the millennium scale over the Chinese mainland during 2000 BC-1900 AD using the newest global geomagnetic model, CALS3K.4 (3K.4). The newest-generation IGRF (IGRF11) was used to verify the results. Taking component Z for example, we calculated and analyzed the distribution and annual change rates of the ND field during 1900-1990 AD every 5 yr, using two models. To thoroughly analyze the contributions of field sources, quadrupole and octupole fields, and others within the ND field at the surface and core-mantle boundary (CMB) were investigated. Results show that there were three main variation phases of the field during the period 2000 BC-1900 AD. The mean amplitude roughly reflected the ND field because of the distribution and variation of that field, corresponding somewhat to the mean amplitude change. A magnetic anomaly of the ND field over East Asia (EA) first emerged in 1682 AD, and its extreme intensity had increased a total of 15276.95 nT by 1900 AD. Its location moved continuously southeastward after 1690 AD. The asymmetry between location and intensity of extreme points over EA, particularly during 1740-1760 AD, indicates irregularity of fluid motion inside the outer core. Mean annual changes of Z are generally divided into four phases, which first oscillated between 2000 and 800 BC, then increased, decreased and increased in the periods 800 BC-300 AD, 300-900 AD and 900-1900 AD, respectively. The intensity of mean annual change increased a total of 22.87 nT/yr. Anomaly extreme locations based on 3K.4 and IGRF11 over EA centered around 44A degrees N and 103A degrees E for degree (n) greater than 5, and intensities continuously increased with n. During 2000 BC-1990 AD, ND energy of Z at the surface and CMB had decreased in total by 18.29% and 23.23%, respectively. The field source of 2(6)-2(10) pole fields are more or less affected by the lithospheric field. Energies of higher degree at the surface attenuate by almost 99% compared with CMB, but mean attenuation speeds of the low-degree ND field are faster than high-degree, which implies that the low-degree ND field has a deeper source.

• 出版日期2014-6
• 单位中国科学院地质与地球物理研究所; 中国科学院地质与地球物理研究所兰州油气资源研究中心; 国家卫星气象中心; 中国气象科学研究院; 南京信息工程大学