 Geomagnetic secular variation

Geomagnetic secular variation refers to the long-term changes in the Earth's magnetic field, which occur over periods of years to centuries. Unlike the daily and seasonal fluctuations in the magnetic field, secular variation encompasses changes in the strength, structure, and orientation of the magnetic field over much longer timescales. These changes can be caused by various factors, including: 1. **Movement of the Earth's molten outer core**: The Earth's magnetic field is generated by the motion of electrically conducting fluids in its outer core.