The magnetic compass, which operates using the Earth’s magnetic field, is one of the oldest navigation instruments. Even with GPS, the Earth’s magnetic field remains an important navigation tool providing accurate magnetic heading for directional drilling, towed arrays, magnetic compassing, inertial guidance systems, and magnetic anomaly detection. These systems use fluxgate-magnetometer sensors to measure differences in magnetic fields. Similar to your smartphones which have low-cost magnetometers to measure the magnetic field and work out which direction the phones are being held. All rely on the Earth’s magnetic field to tell which direction you are pointing.
The Earth’s magnetic field is primarily caused by the motion of molten iron in the outer core of the Earth. The outer core is composed of liquid iron and nickel, which are good conductors of electricity. The motion of this molten metal generates electrical currents, which in turn create magnetic fields. These magnetic fields interact with each other to create a complex and dynamic system of magnetic fields that surround the Earth.
This process is known as a self-exciting dynamo. The motion of the molten metal in the outer core is thought to be driven by the Earth’s internal heat, which causes convection currents in the liquid metal. As the molten metal flows, it generates electrical currents that create the Earth’s magnetic field.
The magnetic field is not static and changes over time
The changes in the magnetic field are due to fluctuations in the motion of the molten metal in the outer core, changes in the Earth’s rotation, ionosphere, and magnetosphere. The Earth’s magnetic field also undergoes periodic reversals, where the north and south magnetic poles switch places.
What causes variations in the earth’s magnetic field?
There are several factors that cause variations in the Earth’s magnetic field. Some of the main causes of variations in the magnetic field include:
- Core Dynamics: The Earth’s magnetic field is generated by the motion of molten iron in the outer core. Changes in the speed or direction of this motion can cause variations in the magnetic field.
- Reversals: Over time, the polarity of the Earth’s magnetic field has flipped many times. This process, called a magnetic reversal, can cause significant variations in the magnetic field.
- Crustal Changes: Changes in the magnetic properties of rocks in the Earth’s crust can also cause variations in the magnetic field. These changes can be caused by geological processes like plate tectonics, volcanic activity, or changes in the Earth’s climate.
- Solar Wind: The Earth’s magnetic field is constantly interacting with the solar wind, a stream of charged particles emanating from the Sun. This interaction can cause variations in the magnetic field, especially during periods of high solar activity.
- Geomagnetic Storms: During periods of high solar activity, the Earth can experience geomagnetic storms, which are caused by disruptions in the solar wind. These storms can cause significant variations in the magnetic field, which can affect satellite and power grid operations.
- Other Factors: Other factors that can cause variations in the Earth’s magnetic field include earthquakes, lightning, and human activity like mining and drilling.
Overall, the Earth’s magnetic field is a complex and dynamic system that is influenced by many different factors. Understanding these factors is important for mitigating the effects of magnetic field variations on tools.
How do we track variations in the earth’s magnetic field?
Contemporary sea charts, topographical maps, and aeronautical charts do track changes in the Earth’s magnetic field. The magnetic field is an important factor in navigation and map-making, and modern charts and maps are updated regularly to reflect changes in the magnetic field.
For example, sea charts show magnetic declination, which is the difference between magnetic north and true north. This information is used by navigators to determine their position and plot a course. Topographical maps and aeronautical charts also show magnetic declination, as well as other magnetic field parameters such as magnetic inclination and magnetic field strength.
To ensure that these charts and maps are accurate, they are updated regularly using data from a variety of sources, including magnetometers, satellites, and magnetic observatories. This ensures that drillers, navigators and other users of the charts and maps have the most up-to-date information on the Earth’s magnetic field.
What is the current magnetic field of the Earth?
The current state of the Earth’s magnetic field is described by the International Geomagnetic Reference Field (IGRF), which is updated every five years based on measurements from a global network of ground-based and satellite-based instruments. The most recent version of the IGRF is the 13th generation, which was released in 2020.
The IGRF provides a mathematical model of the Earth’s magnetic field that can be used to predict the behavior of the magnetic field at any point on the Earth’s surface. It includes parameters such as magnetic declination, magnetic inclination, and magnetic field strength, which are used in navigation, exploration, and other applications that rely on the Earth’s magnetic field.
The following figures reflect maps of declination, inclination, horizontal intensity, vertical intensity, and total intensity at 2020.0, derived from the 13th Generation IGRF model.
Figure 1. Map of Declination (Degrees East or West of True North) at 2020.0 Image source: http://www.geomag.bgs.ac.uk/education/earthmag.html
Figure 2. Map of Inclination (Angle in Degrees Up or Down that Magnetic Field Vector is from the Horizontal) at 2020.0
Image source: http://www.geomag.bgs.ac.uk/education/earthmag.html
Figure 3. Map of Horizontal Intensity at 2020.0
Image source: http://www.geomag.bgs.ac.uk/education/earthmag.html
Figure 4. Map of Vertical Intensity at 2020.0
Image source: http://www.geomag.bgs.ac.uk/education/earthmag.html
Figure 5. Map of Total Intensity at 2020.0
Image source: http://www.geomag.bgs.ac.uk/education/earthmag.html
THE EARTH’S MAGNETIC FIELD IN APPLICATIONS
It is important to note that the Earth’s magnetic field is constantly changing, and these changes can have significant effects on drilling, navigation and other activities that rely on the magnetic field. As a result, it is important for users of these charts and maps to stay informed about changes in the magnetic field and to update their charts and maps regularly to ensure their accuracy. Tracking these updates is a crucial example of the earth’s magnetic field functioning as a tool.
Further, the earth’s magnetic field serves as a tool with directional drilling, geomagnetically induced currents, satellite operations, and exploration geophysics (can be easily considered a hazard at high altitudes if there is failure to remove daily variations and magnetic storm effects before interpretation.)
About Applied Physics Systems
Applied Physics specializes in the design and manufacture of downhole sensors, electronics and MWD systems. Products manufactured include the AP-250 EM MWD System, AP600 Near Bit Sub, directional sensors, fluxgate magnetometers, gamma sensors, rotation sensors and related equipment.