HOW STRONG IS THE MAGNETIC-FIELD IN THE EARTHS LIQUID CORE

A crucial step in the investigation of the energetics of motions in the Earth's core and the generation of the geomagnetic field by the hydromagnetic dynamo process is the estimation of the average strength B of the magnetic field B = Bp + BT in the core. Owing to the probability that the toroidal field BT in the core, which has no radial component, is a good deal stronger than the poloidal field Bp, direct downward extrapolation of the surface field to the core-mantle interface gives no more than an extreme lower limit to B. This paper outlines the indirect methods by which B can be estimated, arguing that B is probably about 10-2 T (100 Γ) but might be as low as 10-3 T (10 Γ) or as high as 5 × 10-2 T (500 Γ). © 1979.