13 December 1996
Vol 274, Issue 5294

About The Cover

Snapshot of the magnetic field inside Earth's core simulated by a geodynamo model. Magnetic lines of force are gold where they are inside, or blue where they are outside, the solid inner core. The Earth's axis of rotation is vertical in this image. The field is directed inward at the inner core north pole (top) and outward at the south pole (bottom). The maximum magnetic intensity is about 30 millitesla. See 1887 and a related report on 1883. [Image: G. A. Glatzmaier and P. H. Roberts]