Animation of secular variation in geomagnetic total intensity for the last 400 years.

[desertrose]

http://wdc.kugi.kyoto-u.ac.jp/igrf/anime/index.html

IGRF model field    On geomagnetic data

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Each Panel
1600    1700    1800    1900    2000

[desertrose]

Very  Cool theory Jim,  thank  you  for  sharing.

[Jim Balister]

I talked to a magnetic scientest who worked in an underground facility, who told me that the magnetic lines move yearly from right to left accross the US, at about 1 inch per year.   That was in the 80's when I was doing research for my book.  There are two types of lines!   Isogenics, which are lines of equal declinations and isoclinics which are equal lines of dip.  We talked about magnetic  Zero, which in the US is at Gary, Indiana.  He offered to sell me some government made mapes and said that I could buy several from one of the gov. departments.  A minors compus also know as a spanish dip needle measures the dip in the magnetic field.  I had a theory that if there are dips in the field that iron meteorites might be drawn into the dip and have a trijectory that would lead them to Rosevelt County New Mexico. 

[desertrose]

International Geomagnetic Reference Field (IGRF-11)

Magnetic North, Geomagnetic and Magnetic Poles

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Model field at a point by IGRF

Transformation of Coordinate    [Geographic <-> Geomagnetic (Dipole)]

Coefficients (1900-2010)/IGRF-11:    Html Version   Text Version   MS Excel Version

"Geomagnetic Models and Software" by NGDC, USA

Magnetic Charts (2010.0)

Geomagnetic Element (2005.0/IGRF-10)	Mercator Projection	Northern Hemisphere	Southern Hemisphere
Total Intensity (F)	GIF, PDF	GIF, PDF	GIF, PDF
Declination (D)	GIF, PDF	GIF, PDF	GIF, PDF
Inclination (I)	GIF, PDF	GIF, PDF	GIF, PDF
Horizontal Component (H)	GIF, PDF	GIF, PDF	GIF, PDF
Vertical Component (F)	GIF, PDF	GIF, PDF	GIF, PDF
Northward Component (X)	GIF, PDF	GIF, PDF	GIF, PDF
Eastward Component (Y)	GIF, PDF	GIF, PDF	GIF, PDF

Animation of secular variation in geomagnetic total intensity for t... (392kB)

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[Reference]

IAGA V-MOD Geomagnetic Field Modeling: International Geomagnetic Re...

[desertrose]

High Definition Geomagnetic Model

Directional drillers use the Earth’s magnetic field as a natural reference frame to orient the drill bit. The azimuth of the bottom-hole assembly is inferred by comparing the magnetic field measured while drilling (MWD) with a geomagnetic reference field. Crustal magnetic anomalies constitute a significant source of error in directional drilling, if not accounted for in the geomagnetic reference field. To meet increasing demand for accurate geomagnetic referencing, the U.S. National Geophysical Data Center (NGDC) produces the High Definition Geomagnetic Model (HDGM) which accounts for long-wavelength crustal magnetic anomalies. HDGM significantly reduces geomagnetic referencing errors.

The HDGM model includes:

Main field

Secular variation

Crustal field to degree 720

Basic model for external field

Software

The HDGM model is:

Updated annually (current version is HDGM2012)

Available as an NGDC product at annual charge of $19,997.

Geomagnetic declination maps for two drill sites (red crosses) at the Caspian Sea. The standard approach (left) does not account for crustal anomalies and therefore is unrealistically smooth. The advanced approach (middle) shows the long-wavelength crustal distortion accounted for by the global HDGM model. The best solution (right) makes additional use of an aeromagnetic survey to fully account for local distortion of the geomagnetic field.

For further details and case studies see: http://geomag.us/models/HDGM.html

[desertrose]

Enhanced Magnetic Model (EMM2010)

Declination Comparison of WMM and EMM (larger image)

The Earth's internal magnetic field is a superposition of the field generated by the geodynamo in the liquid outer core (main field) and the field of magnetized rocks in the crust and upper mantle. The main field dominates the long wavelengths, whereas the crustal field dominates at wavelengths smaller than 2500 km. Geomagnetic field models are conveniently represented as spherical harmonic expansions of a scalar magnetic potential. Such a model can then be evaluated at any desired location to provide the magnetic field vector, its direction, and strength. The standard World Magnetic Model uses a spherical harmonic representation to degree and order 12, resolving the magnetic field at 3000 km wavelength. In contrast, the Enhanced Magnetic Model (EMM) extends to degree and order 720, resolving magnetic anomalies down to 56 km wavelength (see comparison in the figure). The higher resolution of the EMM results in significantly improved pointing accuracy. The EMM model was compiled from satellite, marine, aeromagnetic and ground magnetic surveys (see our acknowledgement of data providers and collaborators). Why is this important? Many different applications utilize Earth's magnetic field,whether for navigation, resource evaluation, or research. The magnetic field experienced at or near the Earth's surface is a combination of the main magnetic field, the relatively static crustal magnetic field, and the rapidly time-varying external magnetic field (solar origin). The better we are able to define these fields, the more accurate the results. Acknowledgments Changes to the code The Enhanced Magnetic Model is now expanded to years 2000 through 2015. To extend the model from 2010 back to 2000 the EMM's main field coefficients are replaced with the first 15 degrees of the Pomme 7 model.

[desertrose]

These links will help explain the basis behind the graphs.

"Geomagnetic Models and Software" by NGDC, USA

Online Calculators
Checkout our new online calculators!
The old calculators will be phased out December 2012.

NGDC hosts online calculators to compute the geomagnetic field at any location on the Earth. The geomagnetic models behind these calculators are regularly updated to maintain their accuracy. We are currently hosting revised on-line calculators for the IGRF (1900-2015), DoD WMM (2010-2015), Declination only (1900-2015), and US Historic Declination (1750-2015).

Maps

The world maps of all the components of the geomagnetic field, calculated from the latest WMM model (WMM2010) are available for at the WMM home page (click the map on the lower left). Use the IAGA Web Image Spreadsheet Tool (Wist) to display and download IGRF magnetic field maps and data from 1900 - 2015. The Wist allows the user to select the number of rows (years) and columns (magnetic elements) to display. Each "cell" of the Wist displays the appropriate map for the selected year and element and links to the PDF for a higher resolution version of the map and to the data used to create the map.

Geomagnetic main-field models

Because the Earth's magnetic field is constantly changing, it is impossible to accurately predict what the field will be at any point in the very distant future. By constantly measuring the magnetic field, we can observe how the field is changing over a period of years. Using this information, it is possible to create a mathematical representation of the Earth's main magnetic field and how it is changing. Since the field changes the way it is changing, new observations must continually be made and models generated to accurately represent the magnetic field as it is. NGDC participates in the development and distribution of two global main-field models, the World Magnetic Model and the International Geomagnetic Reference Field Model. The WMM is the standard navigation model for the U.S. and U.K. Departments of Defense and NATO. The IGRF is the international research reference model. To learn more about these models, visit the home Web sites for the US / UK World Magnetic Model (WMM) 2010 and IAGA IGRF-11. You can download the models for use on your own machine, or compute magnetic field values online from the current IGRF model. Before using the IGRF please look at the 'Health Warning'.

High Resolution Models

NGDC also provides geomagnetic models with higher spatial resolution than the above models. These models include the magnetic field contribuions from the Earth's crust. These models are suitable for applications where higher navigational accuracy is required.

The EMM2010 is an epoch 2010 release of the Enhanced Magnetic Model, intended to calculate the magnetic field for both the Earth's internal magnetic field as well as the crustal field. It extends to degree and order 720, resolving magnetic anomalies down to 56 km wavelength. It is updated along the same schedule as the standard World Magnetic Model.

The HDGM is a product of NGDC which is updated annually. The annual charge for the model is $19,997. It includes the internally generated Main Field, the secular variation of the field, the crustal field to degree and order 720, and a basic model for the external field. To purchase the model contact us. For more details and case studies see: http://geomag.us/models/HDGM.html.

[Tammy Fielder]

Please forgive my ignorance, but what do the colors represent?  I see there is a drastic change but am unsure from where to what.  :)