Britannica Sources used in this answer

What happens to Earth’s dipole magnetic field during a polarity reversal?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

geomagnetic field The magnetic field of a bar magnet has a simple configuration known as a dipole field. Close to Earth's surface this field is a reasonable approximation of the actual field.

During a geomagnetic polarity reversal, the Earth’s dipole magnetic field undergoes a significant transformation. Available data suggest that the strength of the dipole component diminishes toward zero while maintaining its orientation, before eventually re-emerging with the opposite polarity. This process is estimated to take approximately 5,000 years.1

Throughout this transition, while the dipole component is absent or significantly weakened, the non-dipole part of the geomagnetic field is believed to persist.21

The reduction of the dipole field has notable implications for the Earth's magnetosphere. With the dipole component absent, the solar wind can approach much closer to the planet. This allows cosmic-ray particles—which are typically deflected by the magnetic field or trapped in its outer regions—to reach the Earth's surface. While some scientists have hypothesized that this increased radiation could lead to genetic damage or species extinction, evidence from the fossil record regarding such biological impacts remains inconclusive.21