A test of the frozen-flux approximation using a new geodynamo model

The physics underlying the frozen-flux approximation is reviewed. Recent high-resolution geodynamo simulations, described here for the first time, afford opportunities of testing the approximation, and the results from a very simple test are reported. This consists in evaluating the unsigned flux of magnetic field from the core at three successive epochs separated by about 150 years, and in showing that this changes by only ca.3% in the intervals between the epochs. Because of the smallness of this change, which is created by the electromagnetic diffusion excluded in the frozen-flux approximation but present in the simulations, we argue that the approximation is useful in analogous analyses of the geomagnetic field over similar time-scales.