Geomagnetic Field, Global Pattern

Introduction

The geomagnetic field is generated in the fluid outer core region of the Earth by electrical currents flowing in the slowly moving molten iron. In addition to sources in the Earth’s core, the geomagnetic field observable on the Earth’s surface has sources in the crust and in the ionosphere and magnetosphere. The signal from the core dominates, accounting for over 95% of the field at the Earth’s surface. The geomagnetic field varies on a range of scales, both temporal and spatial; the description of the variations made here concentrates on the recent spatial and temporal variations of the field with origins in the Earth’s core that can be surmised from observations made over the last four centuries.

Observations

The geomagnetic field is a vector quantity, having magnitude as well as direction. The direction of the geomagnetic field has been directly observed and recorded for at least 400 years beginning with observations of the angle in the horizontal plane between true...