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Current  Earth‐like  numerical dynamo simulations are able to reproduce many characteristics of the observed geomagnetic field. One notable exception is the geomagnetic octupolar component. Here we investigate whether a stably stratified layer at the top of the core, a missing ingredient in standard dynamo simulations, can explain the observed geomagnetic octupole. Through numerical simulations, we find that the existence of a stable layer has significant influence on the octupolar‐to‐dipolar ratio of the magnetic field. Particularly, we find that a 60‐km stable layer with relatively strong stability or a 130‐km layer with relatively weak stability are compatible with the observations, but a 350‐km stable layer, as suggested by recent seismological evidence, is not compatible with Earth's octupole field over the past 10,000 years.

Sensitivity of the Geomagnetic Octupole to a Stably Stratified Layer in the Earth's Core