scholarly journals Investigation of geomagnetic-field secular variation around the Sverdlovsk magnetic observatory

1978 ◽  
Vol 53 (3) ◽  
pp. 497-502 ◽  
Author(s):  
V. A. Shapiro ◽  
N. A. Ivanov ◽  
L. N. Ivanova
Keyword(s):  
Secular Variation ◽  
Geomagnetic Field ◽  
Magnetic Observatory

scholarly journals Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Sabrina Sanchez ◽  
Johannes Wicht ◽  
Julien Bärenzung
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Wave Number ◽  
Main Magnetic Field ◽  
Candidate Model ◽  
Uncertainty Estimates ◽  
Geomagnetic Field Models ◽  
Dipole Configuration

Abstract The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.

scholarly journals Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellites

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Magnus D. Hammer ◽  
Grace A. Cox ◽  
William J. Brown ◽  
Ciarán D. Beggan ◽  
Christopher C. Finlay
Keyword(s):  
Time Series ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Time Windows ◽  
Low Earth Orbit ◽  
Data Selection ◽  
Spherical Harmonic Analysis ◽  
Core Field ◽  
The Core ◽  
Swarm Satellites

AbstractWe present geomagnetic main field and secular variation time series, at 300 equal-area distributed locations and at 490 km altitude, derived from magnetic field measurements collected by the three Swarm satellites. These Geomagnetic Virtual Observatory (GVO) series provide a convenient means to globally monitor and analyze long-term variations of the geomagnetic field from low-Earth orbit. The series are obtained by robust fits of local Cartesian potential field models to along-track and East–West sums and differences of Swarm satellite data collected within a radius of 700 km of the GVO locations during either 1-monthly or 4-monthly time windows. We describe two GVO data products: (1) ‘Observed Field’ GVO time series, where all observed sources contribute to the estimated values, without any data selection or correction, and (2) ‘Core Field’ GVO time series, where additional data selection is carried out, then de-noising schemes and epoch-by-epoch spherical harmonic analysis are applied to reduce contamination by magnetospheric and ionospheric signals. Secular variation series are provided as annual differences of the Core Field GVOs. We present examples of the resulting Swarm GVO series, assessing their quality through comparisons with ground observatories and geomagnetic field models. In benchmark comparisons with six high-quality mid-to-low latitude ground observatories we find the secular variation of the Core Field GVO field intensities, calculated using annual differences, agrees to an rms of 1.8 nT/yr and 1.2 nT/yr for the 1-monthly and 4-monthly versions, respectively. Regular sampling in space and time, and the availability of data error estimates, makes the GVO series well suited for users wishing to perform data assimilation studies of core dynamics, or to study long-period magnetospheric and ionospheric signals and their induced counterparts. The Swarm GVO time series will be regularly updated, approximately every four months, allowing ready access to the latest secular variation data from the Swarm satellites.

scholarly journals Dependence of the velocity changes of secular variations on the position of observatory and time

2021 ◽  
Vol 43 (3) ◽  
pp. 181-192
Author(s):  
T. P. Sumaruk ◽  
P. V. Sumaruk
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Large Scale ◽  
Magnetic Observatory ◽  
Polar Cap ◽  
Middle Latitudes ◽  
Large Scale Magnetic Field ◽  
Secular Variations ◽  
Geomagnetic Fields ◽  
Velocity Changes

According to the data of world observatories net secular variations of geomagnetic fields from internal and outer sources have been studied. Averaged 3-year data have been used for this purpose. Procedure of calculations of secular variations from internal and outer sources according to observatories data has been submitted. 1979 has been chosen as a zero level for accounting secular variations from outer sources because the sign of the large-scale magnetic field has changed this year. It has been shown that the value of secular variations from outer sources is different for different regions and increases with the growth of the latitude of magnetic observatory. Maximal values of secular variations are observed in the northern polar cap as well as at the longitudes of the eastern focus of secular variation. It has been shown that at the DIK, CSS, TIK observatories secular variations have maximal values. Groups of observatories have been segregated with symmetric and asymmetric changes of secular variation comparing to 1979. Symmetric changes of secular variation during two Hail’s cycles are observed at the observatories in circumpolar area (ALE, NAL, BJN), in auroral and middle latitudes. Maximal asymmetry of secular variation is observed at the observatories GDH, BLC, FCC, as well as at certain subauroral observatories and the regions with raised seismic activity. Secular variation from outer sources depends on the value of the large scale magnetic field of the Sun. The value of secular variation from the inner sources has been modulated by the outer sources and depends on special features of underlying surfaces of the observatories, induction currents in particular.

Thirty-Year Period in Secular Variation of the Main Geomagnetic Field

2006 ◽  
Vol 49 (5) ◽  
pp. 1210-1219 ◽  
Author(s):  
Wen-Yao XU ◽  
Claud Nataf HENRI- ◽  
Zi-Gang WEI ◽  
Ai-Min DU
Keyword(s):  
Secular Variation ◽  
Geomagnetic Field

scholarly journals Bulgarian Geomagnetic Reference Field (BulGRF) for 2015.0 and secular variation prediction model up to 2020

2017 ◽  
Vol 35 (5) ◽  
pp. 1085-1092
Author(s):  
Metodi Metodiev ◽  
Petya Trifonova
Keyword(s):  
Secular Variation ◽  
Geomagnetic Field ◽  
Field Model ◽  
Field Measurements ◽  
Reference Field ◽  
Main Field ◽  
Close Match ◽  
Secular Variation Model ◽  
Geomagnetic Field Models ◽  
Annual Means

Abstract. The Bulgarian Geomagnetic Reference Field (BulGRF) for 2015.0 epoch and its secular variation model prediction up to 2020.0 is produced and presented in this paper. The main field model is based on the well-known polynomial approximation in latitude and longitude of the geomagnetic field elements. The challenge in our modelling strategy was to update the absolute field geomagnetic data from 1980.0 up to 2015.0 using secular measurements unevenly distributed in time and space. As a result, our model gives a set of six coefficients for the horizontal H, vertical Z, total field F, and declination D elements of the geomagnetic field. The extrapolation of BulGRF to 2020 is based on an autoregressive forecasting of the Panagyurishte observatory annual means. Comparison of the field values predicted by the model with Panagyurishte (PAG) observatory annual mean data and two vector field measurements performed in 2015 shows a close match with IGRF-12 values and some difference with the real (measured) values, which is probably due to the influence of crustal sources. BulGRF proves to be a reliable alternative to the global geomagnetic field models which together with its simplicity makes it a useful tool for reducing magnetic surveys to a common epoch carried out over the Bulgarian territory up to 2020.

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