Fig. 1
Parameter space. A map of the Rm-Re parameter space. Note that sodium experiments operate at a magnetic Prandtl number (Pm) of ∼ 7.5×10−6 and therefore fall around a line in this space. The Earth’s quoted values of Rm = 300–1000 in Table 1 are based on the estimates for a range of scales of motion in the outer core (see Olson 2013 for details). Also, the estimate of Pm for the Earth (≤ 10−5) has a large uncertainty, contributing to the spread in possible values for the Earth in this parameter space, represented schematically by a circle. Note that sodium experiments can achieve Earth-like values for these parameters. Simulations are confined to much lower Re (or, equivalently, much larger Pm for similar values of Rm)