[Physics Class Notes] on Geomagnetic Field Pdf for Exam

Geomagnetism is the property of the Earth to exhibit magnetic characteristics such that it acts like a magnet. 

Geomagnetism is one of the oldest studies of the science behind the magnetic field on the earth. It was discovered in Ancient Greece and China during the period when the properties of the natural magnet or the lodestone were discovered for the first time.

Geomagnetism has always been a great help for scientists; in today’s time, we find the use of geomagnetic data in navigation and mineral exploration. 

On this page, you will understand the geomagnetic field of the earth, geomagnetic force, and geomagnetic energy.

What is the Geomagnetic Field?

The geomagnetic field is also referred to as the earth’s magnetic field. A geomagnetic field is dipolar, also called geomagnetic poles. They are geomagnetic North and South poles on the earth’s surface. 

It is the magnetic field that emerges from the Earth’s interior out into space, where it interacts with the solar wind, a freshet of charged particles disgorging from the Sun. 

A geomagnetic field is produced by the convection currents movement, which is a mixture of molten iron and nickel in the Earth’s outer core; these convection currents are generated by escaping heat from the earth’s core; it is a natural process known as geodynamo. 

The magnitude of the geomagnetic a.k.a earth’s magnetic field at its surface ranges from 25 to 65 μT, i.e., 0.25 to 0.65 gauss.

Geomagnetic Force Diagram

Below is the diagram of the earth’s magnetic field:

From this diagram, we can see that near to the earth’s surface, a geomagnetic force of lines follow the property of magnetism, i.e., they initiate from the North pole and terminate at the South pole; thereby forming a continuous loop; however, away from the earth’s surface, the dipole gets distorted. 

Geomagnetic Force

Geomagnetic lines of force are the lines of the force of the geomagnetic field at various latitudes and longitudes in the northern hemisphere. These lines are traced approximately to their intersections with the earth’s surface in the southern hemisphere, using devices like an electronic computer and the first nine Gauss coefficients.

Do You Know?

• During the 1830s, a German mathematician and astronomer named Carl Friedrich Gauss studied and analyzed Earth’s magnetic field. Hr concluded that the principal dipolar component had its origin inside the earth. For this, he showcased the dipolar component was a decreasing function varying inversely with the square of Earth’s radius.

This conclusion led scientists to surmise the origin of Earth’s magnetic field in terms of ferromagnetism, various rotation theories, and various dynamo theories.

Significance of Geomagnetic Field

The earth’s magnetic field acts both as an umbrella, protecting us from harmful cosmic radiation, and as a window for offering us a few glimpses of the inner workings of the earth. 

Old data of the geomagnetic field inform us of the geodynamics of the ancient earth and changes in boundary conditions across time.

Also, the geomagnetic field has acted as a guide that points to the direction of the axis of rotation and provides latitudinal information for both explorers and geologists. 

IGRF Geomagnetic Field

In October 2019, BGS (British Geological Survey) made contributions in the creation of the 13th generation of the International Geomagnetic Reference Field (IGRF). 

The IGRF is a joint model produced by geomagnetism from around the world and endorsed (declared publicly with approval) by the International Association of Geomagnetism and Aeronomy or IAGA. 

The IGRF is a fundamental tool of survey for geophysicists and space scientists, as it is a good quality reference model. 

The IGRF dates back to sometime around 1970 and grew out (emanated) of discussions that took place within IAGA in the 1960s as a result of the World Magnetic Survey and International Geophysical Year of 1957-1958.

The International Geomagnetic Reference Field (IGRF) Geomagnetic field model is the first-hand/verifiable representation of the Earth’s magnetic field suggested for scientific use by a special working group of IAGA. 

The IGRF model represents the core (main) of the field without external sources. The model accepts the customary spherical harmonics expansion of the scalar potential in geocentric coordinates. 

The IGRF model coefficients are all empirical available data sources including geomagnetic measurements from observatories, like ships, aircraft, and satellites.

Fun Fact

• The dipole of the earth’s magnetic field is not exactly aligned with the earth’s rotation axis. The poles of the dipole are positioned approximately in northern Canada and on the coast of Antarctica rather than at the geographic poles, which implies that the dipole is shifted from the rotation axis in a geographic meridian crossing the eastern US.