An investigation of the rock magnetic properties using stepwise isothermal remanence (IRM) acquisition, thermomagnetic analysis and temperature-dependent susceptibility history, identifies magnetite as the carrier of ...An investigation of the rock magnetic properties using stepwise isothermal remanence (IRM) acquisition, thermomagnetic analysis and temperature-dependent susceptibility history, identifies magnetite as the carrier of the main fraction of the remanence, associated with maghemite and hematite in Malan loess (L1), Holocene soil (SO) and last-glacial paleosol (S1). The presence of short-lived direction fluctuations indicates that no significant smoothing occurs in L1 when its remanence is locked, and thus L1 is capable of recording the geomagnetic secular variation (PSV), while the PSV has been severely smoothed or wiped out by pedogenic processes during S1 formation. It has been suggested that the Mono Lake and Laschamp excursions are two independent geomagnetic events based on this study.展开更多
Earth’s magnetic field,which is generated in the liquid outer core through the dynamo action,undergoes changes on timescales of a few years to several million years,yet the underlying mechanisms responsible for the f...Earth’s magnetic field,which is generated in the liquid outer core through the dynamo action,undergoes changes on timescales of a few years to several million years,yet the underlying mechanisms responsible for the field variations remain to be elucidated.In this study,we apply a novel data analysis technique developed in fluid dynamics,namely the dynamic mode decomposition,to analyze the geomagnetic variations over the last two decades when continuous satellite observations are available.The dominant dynamic modes are extracted by solving an eigen-value problem,so one can identify modes with periods longer than the time span of data.Our analysis show that similar dynamic modes are extracted from the geomagnetic secular variation and secular acceleration,justifying the validity of applying the dynamic mode decomposition method to geomagnetic field.We reveal that the geomagnetic field variations are characterized by a global mode with period of 58 years,a localized mode with period of 16 years and an equatorially trapped mode with period of 8.5 years.These modes are possibly related to magnetohydrodynamic waves in the Earth’s outer core.展开更多
The secular variation in the global geomagnetic field was analyzed in terms of the annual differences in monthly means by using the hourly mean data from 18 foreign(outside China)observatories of the World Data Center...The secular variation in the global geomagnetic field was analyzed in terms of the annual differences in monthly means 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 based on residuals between observations and the CHAOS-7.4 model to remove external contamination.Through a comparison before and after denoising,we found that the overall average standard deviations were reduced by 29.97%in China and by 41.4%outside China.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.A geomagnetic jerk was globally discovered around 2018.0 on the geomagnetic eastward component Y.The jerk timing in China was around 2020.0,and the earliest one was in2018.75,whereas the timing outside China was around 2018.0,and the earliest one was in 2017.67.This 2-year lag may have been caused by the higher electrical conductivity of the deep mantle.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.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.The covariance matrix method can be used to analyze data from the Macao Science Satellite-1 mission in the future,and this method is expected to play a positive role in modeling and separating the large-scale external field.展开更多
A sediment sequence,from Fangshan in the Beijing Basin,has been sampled for paleomag-netic studies.The 1430 paleomagnetic samples possess a strong and stable magnetic remanence.A high-res-olution record of secular var...A sediment sequence,from Fangshan in the Beijing Basin,has been sampled for paleomag-netic studies.The 1430 paleomagnetic samples possess a strong and stable magnetic remanence.A high-res-olution record of secular variation in North China over the past 15 ka B.P.has been provided.Spectral anal-yses have shown that main periods of inclination,declination and relative intensity are about 1000,2000 and4000 a;800,1640 and 3300 a;and 820,1200,2200 and 3300 a;respectively.Two excursions have beendiscovered,and the correlation between the geomagnetic intensity variations and the climatic changes hasbeen discussed.展开更多
文摘An investigation of the rock magnetic properties using stepwise isothermal remanence (IRM) acquisition, thermomagnetic analysis and temperature-dependent susceptibility history, identifies magnetite as the carrier of the main fraction of the remanence, associated with maghemite and hematite in Malan loess (L1), Holocene soil (SO) and last-glacial paleosol (S1). The presence of short-lived direction fluctuations indicates that no significant smoothing occurs in L1 when its remanence is locked, and thus L1 is capable of recording the geomagnetic secular variation (PSV), while the PSV has been severely smoothed or wiped out by pedogenic processes during S1 formation. It has been suggested that the Mono Lake and Laschamp excursions are two independent geomagnetic events based on this study.
基金supported by Macao Science and Technology Development Fund grant 0001/2019/A1Macao Foundation+1 种基金the preresearch Project on Civil Aerospace Technologies of CNSA(Grants No.D020303 and D020308)the National Natural Science Foundation of China(41904066,42142034)。
文摘Earth’s magnetic field,which is generated in the liquid outer core through the dynamo action,undergoes changes on timescales of a few years to several million years,yet the underlying mechanisms responsible for the field variations remain to be elucidated.In this study,we apply a novel data analysis technique developed in fluid dynamics,namely the dynamic mode decomposition,to analyze the geomagnetic variations over the last two decades when continuous satellite observations are available.The dominant dynamic modes are extracted by solving an eigen-value problem,so one can identify modes with periods longer than the time span of data.Our analysis show that similar dynamic modes are extracted from the geomagnetic secular variation and secular acceleration,justifying the validity of applying the dynamic mode decomposition method to geomagnetic field.We reveal that the geomagnetic field variations are characterized by a global mode with period of 58 years,a localized mode with period of 16 years and an equatorially trapped mode with period of 8.5 years.These modes are possibly related to magnetohydrodynamic waves in the Earth’s outer core.
基金the support of the National Natural Science Foundation of China(Nos.42030203,41974073,41404053)the Macao Foundation and the pre-research project of Civil Aerospace Technologies(Nos.D020308 and D020303)+3 种基金which is funded by the China National Space Administrationsupport from the opening fund of the State Key Laboratory of Lunar and Planetary Sciences(Macao University of Science and Technology,Macao Science and Technology Development Fund[FDCT]No.119/2017/A3)the Specialized Research Fund for State Key Laboratoriesthe NUIST-Uo R International Research Institute。
文摘The secular variation in the global geomagnetic field was analyzed in terms of the annual differences in monthly means 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 based on residuals between observations and the CHAOS-7.4 model to remove external contamination.Through a comparison before and after denoising,we found that the overall average standard deviations were reduced by 29.97%in China and by 41.4%outside China.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.A geomagnetic jerk was globally discovered around 2018.0 on the geomagnetic eastward component Y.The jerk timing in China was around 2020.0,and the earliest one was in2018.75,whereas the timing outside China was around 2018.0,and the earliest one was in 2017.67.This 2-year lag may have been caused by the higher electrical conductivity of the deep mantle.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.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.The covariance matrix method can be used to analyze data from the Macao Science Satellite-1 mission in the future,and this method is expected to play a positive role in modeling and separating the large-scale external field.
基金funded by two of the Hebei Province Spark Program of Earthquake Sciences (DZ2021121400007 and DZ2024112200008)the China Earthquake Administration and Hebei Earthquake Agency for their support.
基金the Xi'an Laboratory of Loess and Quaternary Geology,Academia Sinica.
文摘A sediment sequence,from Fangshan in the Beijing Basin,has been sampled for paleomag-netic studies.The 1430 paleomagnetic samples possess a strong and stable magnetic remanence.A high-res-olution record of secular variation in North China over the past 15 ka B.P.has been provided.Spectral anal-yses have shown that main periods of inclination,declination and relative intensity are about 1000,2000 and4000 a;800,1640 and 3300 a;and 820,1200,2200 and 3300 a;respectively.Two excursions have beendiscovered,and the correlation between the geomagnetic intensity variations and the climatic changes hasbeen discussed.
