1. n. [Geophysics]
How Earth’s magnetic field varies with time. These time variations, called secular variations, necessitate periodic updating of magnetic field maps and models. Two types of processes in the Earth’s core produce these variations. One process is related to variations in Earth’s main dipole field, which operate on time scales of hundreds or thousands of years. The other process is related to variations in Earth’s nondipole field, which operate on time scales on the order of tens of years.
