science

World Magnetic Model

World Magnetic Model is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand World Magnetic Model rather than just read about it. In short: The World Magnetic Model (WMM) is a large spatial-scale representation of the Earth's magnetic field. It was developed jointly by the US National Geophysical Data Center and the British Geological Survey.

Key takeaways

World Magnetic Model belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect World Magnetic Model to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of World Magnetic Model from memory before moving on to harder problems.

Reference excerpt

The World Magnetic Model (WMM) is a large spatial-scale representation of the Earth's magnetic field. It was developed jointly by the US National Geophysical Data Center and the British Geological Survey. The data and updates are issued by the US National Geospatial-Intelligence Agency and the UK Defence Geographic Centre. The model consists of a degree and order 12 spherical harmonic expansion of the magnetic scalar potential of the geomagnetic main field generated in the Earth's core. Apart from the 168 spherical-harmonic "Gauss" coefficients, the model also has an equal number of spherical-harmonic secular variation coefficients predicting the temporal evolution of the field over the upcoming five-year epoch. WMM is the standard geomagnetic model of the United States Department of Defense (DoD), the Ministry of Defence (United Kingdom), the North Atlantic Treaty Organization (NATO), the International Hydrographic Organization (IHO) navigation and attitude/heading reference, and the Federal Aviation Administration (FAA). It is also used widely in civilian navigation systems as the magnetic model of the World Geodetic System. For example, WMM is pre-installed in Android and iOS devices to correct for the magnetic declination. The WMM is produced by the U.S. National Geophysical Data Center (NGDC) in collaboration with the British Geological Survey (BGS). The model, associated software, and documentation are distributed by the NGDC on behalf of National Geospatial-Intelligence Agency (NGA). Updated model coefficients are released at 5-year intervals, with WMM2015 (released Dec 15, 2014) supposed to last until December 31, 2019. However, due to extraordinarily large and erratic movements of the north magnetic pole, an out-of-cycle update (WMM2015v2) was released in February 2019 (delayed by a few weeks due to the U.S. federal government shutdown) to accurately model the magnetic field above 55° north latitude until the end of 2019. The next regular update (WMM2020) occurred in December 2019. The latest update (WMM2025) occurred in December 2024 and will remain valid until late 2029.

Enhanced Magnetic Model (EMM) The Enhanced Magnetic Model (EMM) is a sister product of the NGDC featuring a much higher amount of data to degree and order 790, giving a wavelength of 51 km as opposed to the 3000 km of WMM. At this resolution, it is not only able to model the Earth's magnetic field at the core-mantle boundary ("main field"), but also take into account magnetic anomalies caused by the minerals in the Earth's crust.

See also International Geomagnetic Reference Field: another model, of similar quality, which models past years as well Runway numbering

References

External links WMM model and software can be downloaded from the National Geophysical Data Center's WMM page World Magnetic Model method in the Android operating system World Magnetic Model 2015 NOAA press release

Illustrations

World Magnetic Model: Magnetic declination map at sea-level for the year 2010 derived from WMM2010. — Magnetic declination map at sea-level for the year 2010 derived from WMM2010.

Worked examples

Example 1 — a first encounter with World Magnetic Model

Start with the simplest possible case. Write down what World Magnetic Model claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to World Magnetic Model before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about World Magnetic Model ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of World Magnetic Model

In research: World Magnetic Model appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses World Magnetic Model in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: World Magnetic Model is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geomagnetism, so understanding it makes those chapters shorter.
In everyday life: Look for World Magnetic Model outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study World Magnetic Model in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what World Magnetic Model means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain World Magnetic Model out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is World Magnetic Model in simple terms?

Why does World Magnetic Model matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study World Magnetic Model?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on World Magnetic Model.