Study On The Long-term Variation Of The Geomagnetic Field From 2010 To 2021 Based On The Time Mean And Covariance Matrix Of Geomagnetic Station

As one of the conditions essential for human survival,the secular variation in the geomagnetic field have been of great interest.Scientists have demonstrated that geomagnetic jerks originate from the Earth’s interior and have found periodic variations in the geomagnetic field,but there are few studies on the recent new geomagnetic jerks and the global trends,and there is a lack of studies on the periodic variations of the geomagnetic field in China.Therefore,in this paper,we focus on the new geomagnetic jerks and the geomagnetic field periodicity in China during 2010-2021.In order to investigate the secular variation in the geomagnetic field during the period of 2010-2021,especially the geomagnetic jerks and periodic in the secular variation,by using the hourly mean data from 18 foreign(outside China)observatories of the World Data Center(WDC)for Geomagnetism from January 2010 to January 2020 as well as 9 observatories in the Geomagnetic Network of China from January 2015 to April 2021.In addition,according to the correlation of noisy components from the observatories,a covariance matrix was constructed to remove external contamination.To analyze the denoising effect and geomagnetic field sharp variation.The hourly mean of geomagnetic observatories in China from 2010 to 2021 and the fast Fourier transform were used to analyze the geomagnetic field periodic variation in China.The related results are as follows:(1)The covariance matrix was constructed to calculate the external contamination (magnetospheric ring current).Results showed the correlation coefficient between external noise(mainly the magnetosphere ring current)and the Dst index was 0.82,and the correlation coefficient between external noise and the Ring Current(RC)index reached 0.94.The clarity improvement is the largest,with 53.8%for foreign observatories and 50.8%for Chinese observatories.(2)A new geomagnetic jerk was discovered on the geomagnetic eastward component Y.The jerk timing in China was around 2020,with the earliest one was in 2018.75 and the latest in 2020.08.The jerk timing in foreign was around 2018,the earliest is the KDU observatory located in Australia,which in 2017.67;the latest is the European HAD observatory,in 2018.75.This 2-year lag may have been caused by the higher electrical conductivity of the deep mantle.The strength of the jerk is the most intense at the KDU observatory in the foreign,reaching–12.32 nT/yr~2;the most at the YON observatory in the Chinese observatories,reaching 22.20 nT/yr~2.After more data were added,this jerk event was found to occur in an orderly manner in the northern hemisphere as the longitude increased and the intensity gradually increased as well.(3)The variations in location of the jerk center were analyzed according to the CHAOS-7.4 model.Results revealed six extreme points distributed nearby the equator.The strongest was near the equator,at 170°E,and the strength gradually decreased as it extended to the northern and southern hemispheres.Another extreme point with the opposite sign was located at the equator,at 20°W,in the south-central part of the Atlantic,and the strength gradually decreased as it extended into Europe.(4)By fast Fourier transform analysis,it is found that the long-term acceleration variation of the geomagnetic field has two periods of 10.8 and 18 months,and the amplitude of the X component is the largest,reaching 10.98 nT/yr~2 and 14.98 nT/yr~2,respectively,on average for the 16 observatories.This study was based on the hourly mean data of Chinese and foreign geomagnetic observatories,and the covariance matrix method is used to simulate the magnetospheric ring current to denoise the data,and the denoising process no longer depends on the geomagnetic index,which improves the data reliability significantly.Based on the de-noised data,a new geomagnetic jerk was discovered,and the characteristics of this jerk were studied and analyzed.Preliminary analysis of the periodic variation of the geomagnetic field using data from regional stations in China.This study is of reference value for analyzing the geomagnetic field secular variation in China and the studying global geomagnetic jerk.