Magnetic field of the earth

The Earth's magnetic field resembles that of a bar magnet placed along an axis passing through the Earth's center. This axis is tilted by about 11.3° from the Earth's rotation axis. The Earth's magnetic poles (located near the geographic North and South poles) are called the South magnetic pole and the North magnetic pole, respectively. The magnetic field behaves like that of a dipole, with field lines emerging from the South magnetic pole and entering the North magnetic pole.

The Earth's magnetic field is a vector field, meaning it has both magnitude and direction at every point. At any point on the Earth's surface, the field can be described using three components:

• Horizontal component (H): The part of the magnetic field in the horizontal plane.
• Vertical component (Z): The part of the magnetic field in the vertical direction.
• Inclination (I): The angle the magnetic field vector makes with the horizontal plane.
• Declination (D): The angle between the magnetic meridian and the geographic meridian.

The relationship between these components can be described by the following equations:

Where X, Y, and Z are the Cartesian components of the magnetic field, and B_E is the magnitude of the total magnetic field. In Cartesian coordinates:

Given the horizontal component of the Earth's magnetic field $H = 4 \times 10^{-5} \, \text{T}$ and the angle of dip $I = 60^\circ$, we can calculate the vertical component $Z$ and the total intensity of the Earth's magnetic field $B_E$:

1. Vertical component:

2. Total intensity:

The Earth's magnetic field exhibits both spatial and temporal variations:

• Spatial variations occur due to differences in the Earth's magnetic field across different locations on the surface.
• Temporal variations can be:
  • Short-term variations (due to currents in the magnetosphere and ionosphere)
  • Long-term variations (called secular variations caused by the dynamics of the Earth's interior)

One key feature of long-term variations is the phenomenon of magnetic pole reversal, where the Earth's magnetic poles switch places. This has occurred numerous times in Earth's history, with the last reversal occurring approximately 780,000 years ago. The transition between poles takes thousands of years. Paleomagnetism is the study of the record of Earth's magnetic field in rocks and sediments, which has been instrumental in understanding past geomagnetic field behavior.