International geomagnetic reference field—Its evolution and the difference in total field intensity between new and old models for 1965–1980

Geophysics ◽  
1983 ◽  
Vol 48 (12) ◽  
pp. 1691-1696 ◽  
Author(s):  
Norman W. Peddie
Keyword(s):  
Magnetic Field ◽  
Field Intensity ◽  
Upper Atmosphere ◽  
Reference Field ◽  
Total Field ◽  
Main Field ◽  
International Geomagnetic Reference Field ◽  
The Earth ◽  
Crustal Field ◽  
The Difference

The total magnetic field near the surface of the Earth is a sum of several constituent fields. Part of the total field consists of fields that are transient or rapidly varying. These fields are caused, either directly or indirectly, by electric currents in the upper atmosphere and beyond. The part of the total field that is more permanent arises from sources that are located inside the Earth. Evidence suggests that this part has two principal constituents: the main field and the crustal field.

scholarly journals Sequential modelling of the Earth’s core magnetic field

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Guillaume Ropp ◽  
Vincent Lesur ◽  
Julien Baerenzung ◽  
Matthias Holschneider
Keyword(s):  
Magnetic Field ◽  
Prior Information ◽  
Spatial Scales ◽  
Model Parameters ◽  
International Geomagnetic Reference Field ◽  
The Earth ◽  
Temporal And Spatial ◽  
Different Sources ◽  
Original Approach ◽  
Modelling Approach

Abstract We describe a new, original approach to the modelling of the Earth’s magnetic field. The overall objective of this study is to reliably render fast variations of the core field and its secular variation. This method combines a sequential modelling approach, a Kalman filter, and a correlation-based modelling step. Sources that most significantly contribute to the field measured at the surface of the Earth are modelled. Their separation is based on strong prior information on their spatial and temporal behaviours. We obtain a time series of model distributions which display behaviours similar to those of recent models based on more classic approaches, particularly at large temporal and spatial scales. Interesting new features and periodicities are visible in our models at smaller time and spatial scales. An important aspect of our method is to yield reliable error bars for all model parameters. These errors, however, are only as reliable as the description of the different sources and the prior information used are realistic. Finally, we used a slightly different version of our method to produce candidate models for the thirteenth edition of the International Geomagnetic Reference Field.

AD HOC COMMITTEE ON MAGNETIC FIELD MODELS

Geophysics ◽  
1976 ◽  
Vol 41 (4) ◽  
pp. 796-797
Keyword(s):  
Magnetic Field ◽  
Working Group ◽  
Ad Hoc ◽  
Field Model ◽  
International Association ◽  
Geological Survey ◽  
Reference Field ◽  
International Geomagnetic Reference Field ◽  
International Geomagnetic Reference ◽  
Purdue University

An SEG ad‐hoc committee on Magnetic Field Models was formed as one result of the Zmuda Memorial Field Model Conference (Regan and Cain, 1975a). The chairman of the committee is Michael S. Reford, Geoterrex Ltd., and committee members are William J. Hinze, Purdue University, Peter J. Hood, Geological Survey of Canada, and Robert D. Regan, U.S. Geological Survey. The main objective of the committee was to produce an SEG resolution on the revision of the International Geomagnetic Reference Field (IGRF) to be submitted to the International Association of Geomagnetism and Aeronomy’s (IAGA) working group 1.1.

Observations of the Earth's magnetic field made in Edinburgh from 1670 to the present day

1994 ◽  
Vol 85 (4) ◽  
pp. 239-252 ◽  
Author(s):  
D. R. Barraclough
Keyword(s):  
Magnetic Field ◽  
Mathematical Models ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Upper Atmosphere ◽  
The Difference ◽  
Time Changes ◽  
Relative Measurements ◽  
Magnetic North ◽  
Made In

AbstractMagnetic observations made at the same site give valuable information about the time changes (the secular variation) of the geomagnetic field. This paper gives details of all known measurements of the geomagnetic field in and around Edinburgh since the earliest observation of magnetic declination (the difference between true and magnetic north) by George Sinclair in 1670. Early observations of the strength of the field were only relative measurements. Approximate conversion factors are derived to enable these data to be expressed in modern absolute units (nanoteslas). Observed values of declination, inclination and the horizontal intensity of the geomagnetic field are plotted and compared with values computed from mathematical models of the field covering the interval 1690 to 1990, inclusive. The earlier observations were not corrected for the effects of the rapidly varying magnetic fields caused by electric currents in the upper atmosphere. The consequences of this are estimated.

Some archaeomagnetic results from Greece

1963 ◽  
Vol 58 ◽  
pp. 8-13 ◽  
Author(s):  
J. C. Belshé ◽  
K. Cook ◽  
R. M. Cook
Keyword(s):  
Magnetic Field ◽  
The Other ◽  
Secular Change ◽  
Magnetic Oxides ◽  
Archaeological Remains ◽  
Main Field ◽  
Thermoremanent Magnetization ◽  
The Past ◽  
The Earth ◽  
The Magnetic Field

Many clays and stones contain particles of magnetic oxides of iron. These particles, if heated above their Curie points, which range up to 670° C., lose whatever magnetism they have; and when they cool back through their Curie points, they acquire a new ‘thermoremanent’ magnetization under the influence of the surrounding magnetic field, which generally is the magnetic field of the earth. That field is changing continuously, both in direction and intensity, and the course of its secular change is not yet understood; the change is compound, one factor being the main field, which may be fairly stationary over long periods, and the other being the numerous minor regional fields, which move and alter relatively quickly and largely determine the local variations in the magnetic field. So it is dangerous to extrapolate values for local variations either for more than a century or two in time or for more than five to ten degrees in space. At present the best hope for discovering past changes in the earth's field is from the thermoremanent magnetization of burnt clays and stones, where the date of the burning is reasonably closely fixed from other evidence. Such knowledge is obviously of interest to geophysicists, but for periods and places where the past course of the earth's field has been ascertained, archaeomagnetism—that is the study of the thermoremanent magnetization of archaeological remains—can help archaeologists too. It should be evident on reflection that if an archaeomagnetic specimen is to be useful certain requirements are necessary. First, the locality where it was magnetized must be known. Secondly, for the study of direction, the sample's orientation at the time when it was magnetized must be recorded, so that the inclination [or dip] and declination [or compass bearing] of its own thermoremanent magnetism can be related to the horizontal and to true North respectively.

scholarly journals Geomagnetic core field models and secular variation forecasts for the 13th International Geomagnetic Reference Field (IGRF-13)

2020 ◽  
Author(s):  
Ingo Wardinski ◽  
Diana Saturnino ◽  
Hagay Amit ◽  
Aude Chambodut ◽  
Benoit Langlais ◽  
...  
Keyword(s):  
Secular Variation ◽  
Geomagnetic Field ◽  
Singular Spectrum Analysis ◽  
Reference Field ◽  
Candidate Model ◽  
Main Field ◽  
International Geomagnetic Reference Field ◽  
Core Field ◽  
International Geomagnetic Reference ◽  
Continuous Models

Abstract Observations of the geomagnetic field taken at Earth's surface and at satellite altitude were combined to construct continuous models of the geomagnetic field and its secular variation from 1957 to 2020. From these parent models, we derive candidate main field models for the epochs 2015 and 2020 to the 13th generation of the International Geomagnetic Reference Field (IGRF). The secular variation candidate model for the period 2020 - 2025 is derived from a forecast of the secular variation in 2022.5, which results from a multi-variate singular spectrum analysis of the secular variation from 1957 to 2020.

scholarly journals Changes with Height of Longitudinal Magnetic Field in Active Regions

1993 ◽  
Vol 141 ◽  
pp. 24-31
Author(s):  
S.I. Gopasyuk
Keyword(s):  
Magnetic Field ◽  
Field Intensity ◽  
Longitudinal Magnetic Field ◽  
Magnetic Field Intensity ◽  
Transverse Electric ◽  
Active Regions ◽  
Line Profiles ◽  
Current Value ◽  
The Difference ◽  
The Magnetic Field

Results of a study of longitudinal magnetic fields in active regions are presented. The observed magnetic field strength increases with height in the photosphere. The maximum of the magnetic field intensity coincides with the level where the central parts of λ5324,2 Å FeI and λ5269,5 FeI line profiles are formed. On the Hβ formation level the observed magnetic field intensity is smaller as compared with the potential one calculated on the basis of the observed field in FeI λ5253, 5Å line. The difference between the observed magnetic field and potential one is explained in terms of transverse electric currents. The current value can mount to 3×1011 A.

Implications of magnetic secular variation for interpretation of crustal field anomalies

2020 ◽  
Author(s):  
Rick Saltus ◽  
Aaron Canciani ◽  
Brian Meyer ◽  
Arnaud Chulliat
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomalies ◽  
Source Inversion ◽  
Magnetic Minerals ◽  
The Earth ◽  
Crustal Field ◽  
Data Compilation ◽  
Initial Work ◽  
Navigation Accuracy ◽  
Changes Over Time

<p>We usually think of crustal magnetic anomalies as static (barring some major seismic or thermal disruption).  But a significant portion of the crustal magnetic field is caused by the interaction of magnetic minerals with the Earth’s magnetic field.  This induced magnetic effect is dependent on the direction and magnitude of the ambient field.  So, of course, as the Earth’s magnetic field changes over time, the form and magnitude of induced magnetic anomalies will vary as well.  These changes will often be negligible for interpretation when compared with measurement and other interpretational uncertainties.  However, with the reduction of various sources of measurement noise and increased fidelity of interpretation, these temporal anomaly changes may need to be considered.</p><p>In addition to considerations relating to interpretation uncertainty, these temporal anomaly changes, if they are measured in multiple magnetic epochs, can theoretically provide valuable information for use in source inversion.  For example, since crustal magnetic anomalies arise from a combination of induced (dependent the ambient field) and remanent (not dependent on ambient field) magnetic sources, measurements of secular magnetic variation can assist in separating these two sources during inversion.</p><p>We will report modeling of the expected form and magnitude of predicted induced anomaly variations, the possible implications of these variations for data compilation and interpretation, and on the availability of relevant data for measuring them.  Recent research into the use of high-resolution magnetic anomaly maps for airborne magnetic navigation has also brought the issue of changing magnetic fields into focus.  Initial work indicates that changes in induced anomalies could affect navigation accuracy in certain situations.</p>

International Geomagnetic Reference Field 1980 A Report by IAGA Division I, Working Group I

Geophysics ◽  
1982 ◽  
Vol 47 (5) ◽  
pp. 841-842 ◽  
Author(s):  
Norman W. Peddie
Keyword(s):  
Secular Variation ◽  
Working Group ◽  
Field Model ◽  
International Association ◽  
Division I ◽  
Reference Field ◽  
Main Field ◽  
International Geomagnetic Reference Field ◽  
International Geomagnetic Reference ◽  
Group I

IGRF 1965, the first international geomagnetic reference field, was adopted by the International Association of Geomagnetism and Aeronomy (IAGA) in 1968 (IAGA Commission 2, Working Group 4, 1969). It consists of a model of the main field at 1965.0, along with a model of secular variation for use in extending the main field model in time, both backward (not earlier than 1955.0) and forward (not later than 1975.0). IGRF 1975, adopted later, consists of IGRF 1965 extended to 1975.0, along with a revised model of secular variation for use in extending the main field model up to 1980.0 (IAGA Division I Study Group, 1976).

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