Palaeomagnetic interpretation of dynamo simulations

Abstract

SUMMARY The properties of geomagnetic field excursions and reversals are commonly inferred from one palaeomagnetic site only. However, dynamo simulations suggest that the relative dipole contribution is lower during transitional times than in stable periods. Local field properties thus become more important and cause increased local differences in virtual dipole signatures. These differences in turn account for a larger site dependence of inferred excursion and reversal properties. A self-consistent numerical dynamo simulation is used to test and quantify this effect. Estimates of reversal durations are found to vary by an order of magnitude depending on the site location. The same is true for excursions. Moreover, not all excursions are global phenomena. A larger number of smaller excursions are present at higher latitudes. This can be attributed to a latitudinal increase in secular variation that is also found in palaeomagnetic data. Larger excursions are more likely to be observed globally, but the particular signature may vary significantly from site to site. It is speculated that these excursions have a different dynamical origin from secular variation.