Earth's Magnetic Field

The Earth's magnetic field is generated by electric currents deep in the  interior and high above the surface of the planet. The field extends far into space where it encounters the moving plasma of the solar wind. The solar wind flows around the magnetic field, compressing it on the day-side of the planet and stretching it out into a long tail on the night-side.

A representation of the Sun's effect
on the Earth's magnetic field

The geomagnetic field shields the Earth’s surface from the solar wind by deflecting high energy particles emitted by the Sun. During magnetic storms, vast amounts of the Sun’s energy and plasma are dumped into the Earth's upper atmosphere affecting satellites, electricity supplies, radio communication and producing expanded auroral displays.

The Earth's magnetic field is a vector quantity, meaning it has both a magnitude (size) and direction. It can be described by combinations of components or ‘elements’. In geomagnetism the elements most commonly referred to are: X, Y, Z, F, H, D and I as shown in the diagram.

Diagram of seven components
of the magnetic vector

A compass needle points to magnetic north, which is defined by the direction of the horizontal component of the geomagnetic field (H). The geomagnetic declination (D), sometimes called variation, is the angle between true north and magnetic north.

The inclination (I), sometimes called dip, is the angle the field vector is inclined to the horizontal plane.

Geomagnetic observatories in Australia monitor four of the elements of the geomagnetic field, the true north (X) component, true east (Y) component, vertical (Z) component and the total intensity of the magnetic field (F).

The X, Y, Z, F and H elements of the magnetic field are measured in units of nanotesla (nT). Declination (D) and inclination (I) are measured in angular degrees.

All other elements of the magnetic field can be derived from X, Y and Z. For example, F is calculated using the following equation Equation - F equals the square root of the sum of X squared, Y squared and Z squared for magnetic field using F to calculate the derived elements.

More information about the components of the magnetic field.

Topic contact: geomag@ga.gov.au Last updated: May 8, 2013