scholarly journals GEODYNAMICS

GEODYNAMICS ◽  
2011 ◽  
pp. 67-76
Author(s):  
V. Yu. Maksymchuk ◽  
◽  
Yu.M. Horodyskyy ◽  
D. O. Marchenko ◽  
◽  
...  
Keyword(s):  
Spatial Structure ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Secular Variations ◽  
Geomagnetic Models

The spatial structure of geomagnetic field secular variations in Europe was examined. Using the data of geomagnetic observatories the new maps of this secular variation (SV) for X, Y, Z, D – components for 5-years intervals 1995-2000 and 2000-2005 were constructed. Their comparison with the IGRM global geomagnetic models was done. The global anomalies – SV-focuses in the structure of the secular variations in Europe were discovered and their kinematics was studied.

scholarly journals Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

1997 ◽  
Vol 15 (6) ◽  
pp. 734-739 ◽  
Author(s):  
A. Bhattacharyya ◽  
B. Mitra
Keyword(s):  
Secular Variation ◽  
Geomagnetic Field ◽  
Electric Circuit ◽  
Cosmic Ray ◽  
Computer Time ◽  
Transmission Factor ◽  
Field Variation ◽  
Quadrupole Field ◽  
Secular Variations ◽  
Time Required

Abstract. An analytical expression is derived for the cutoff rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic field is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cutoffs due to secular variation of the geomagnetic field since 1835. Effects of westward drift of the quadrupole field and decrease in the effective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cutoff rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic field in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic field variation to long term changes in climate through cosmic ray related modulation of the current flow in the global electric circuit.

scholarly journals Review of Long-Term Trends in the Equatorial Ionosphere Due the Geomagnetic Field Secular Variations and Its Relevance to Space Weather

Atmosphere ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 40
Author(s):  
Ana G. Elias ◽  
Blas F. de Haro Barbas ◽  
Bruno S. Zossi ◽  
Franco D. Medina ◽  
Mariano Fagre ◽  
...  
Keyword(s):  
Space Weather ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Upper Atmosphere ◽  
Anthropogenic Activity ◽  
Weather Forecasts ◽  
Term Change ◽  
Secular Variations ◽  
Long Term Trends

The Earth’s ionosphere presents long-term trends that have been of interest since a pioneering study in 1989 suggesting that greenhouse gases increasing due to anthropogenic activity will produce not only a troposphere global warming, but a cooling in the upper atmosphere as well. Since then, long-term changes in the upper atmosphere, and particularly in the ionosphere, have become a significant topic in global change studies with many results already published. There are also other ionospheric long-term change forcings of natural origin, such as the Earth’s magnetic field secular variation with very special characteristics at equatorial and low latitudes. The ionosphere, as a part of the space weather environment, plays a crucial role to the point that it could certainly be said that space weather cannot be understood without reference to it. In this work, theoretical and experimental results on equatorial and low-latitude ionospheric trends linked to the geomagnetic field secular variation are reviewed and analyzed. Controversies and gaps in existing knowledge are identified together with important areas for future study. These trends, although weak when compared to other ionospheric variations, are steady and may become significant in the future and important even now for long-term space weather forecasts.

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

Analysis of Secular Variations of Geomagnetic Field in Lithuania Based on the Survey in 2016

2017 ◽  
Author(s):  
Arunas Buga ◽  
Simona Einorytė ◽  
Romuald Obuchovski ◽  
Vytautas Puškorius ◽  
Petras Petroškevicius
Keyword(s):  
Geomagnetic Field ◽  
Field Research ◽  
Field Measurements ◽  
Geomagnetic Observatory ◽  
Research Activities ◽  
Secular Variations ◽  
Geomagnetic Data ◽  
The Mean ◽  
Using Data ◽  
Magnetic Field Variations

Lithuania is successfully integrated in the European geomagnetic field research activities. Six secular variation research stations were established in 1999 and precise geomagnetic field measurements were performed there in 1999, 2001, 2004, 2007 and 2016. Obtained diurnal magnetic field variations at measuring station and neighbouring observatories were analysed. All measurements are reduced to the mean of the year using data from geomagnetic observatory of Belsk. Based on the measured data the analysis of geomagnetic field parameter secular changes was performed. Results of the presented research are useful for updating the old geomagnetic data as well as for estimation of accuracy of declination model.

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