中国地磁台观测的2014年地磁急变

The 2014 geomagnetic jerk observed by geomagnetic observatories in China

地磁急变(jerk)是起源于地球外核并在导电地幔过滤效应后在地球表面观测到的一种地磁现象,其反映了地核内部某些动力学过程.Jerks在空间范围上既可以是区域性的,也可以是全球性的.中国地区地磁台能否检测到2014年jerk?针对这一问题,利用中国大陆10个地磁台的磁静日月均值和CHAOS-6全球磁场模型,分析了X、Y和Z分量2008—2018年期间的长期变化,估算了2014年前、后的长期加速度值,确定了2014年地磁jerk的时间和强度.研究表明中国地磁台Y分量的长期变化为“Λ”型,Z分量存在明显的“V”型,具有典型的jerk特点.Y分量jerk出现的时间大约在2014年6月,比非洲大陆的Algeria TAM台和南美洲French Guiana KOU台时间滞后大约4个月.这暗示着产生jerks的地核流体波动的时序特点.中国西部和东北部地磁台的长期变化形态有明显的差别,主要由非偶极磁场引起.CHAOS-6模型与地面台站的长期变化形态并非始终一致.本文结果有助于更好地理解和解释长期变化的时间演变和地理分布,并为深入探讨jerks的地核起源和驱动机制提供新的观测约束.

As a geomagnetic phenomenon,the geomagnetic jerk originates from the Earth′s outer core,which is observed on the Earth′s surface after the filtering of the conductive mantle.It reflects some dynamic processes inside the core of the earth.Jerks can be either regional or global in their spatial extent.Could China′s geomagnetic observatories detect the jerks in 2014?To answer this question,using the monthly mean values of quiet days at ten geomagnetic observatories in China's Mainland and the CHAOS-6 global magnetic field model,we analyzed the secular variations(SVs)of the X,Y and Z components of the geomagnetic field from 2008 to 2018,respectively.We also estimated the secular accelerations before and after 2014 and determined the time and intensity of the geomagnetic jerk in 2014.The results show that the SVs from the geomagnetic observatories have typical jerk features,which exhibited a“Λ”shape for the Y component and an obvious“V”shape for the Z component.The jerk of the Y component occurred in June 2014,lagging approximately 4 months behind the jerk occurred at the TAM Observatory in Algeria,Africa and the KOU Observatory in French Guiana,South America.This implies the temporal characteristics of the fluid fluctuations in the core that produce jerk.The patterns of secular variation of the geomagnetic observatories in western and northeastern China show significant differences,which is mainly caused by the non-dipole magnetic field.The patterns of secular variation of the CHAOS-6 model and the ground stations are not always consistent.The results of this paper are anticipated to improve the understanding and interpretation of the secular variation in temporal evolution and geographical distribution.This may also provide new observational constraints on further exploration of the origin and driving mechanism of the core.