UC Berkeley

Polarity intervals from marine magnetic anomalies exhibit variability that departs from a Poisson process. The deficit of short polarity intervals is well represented by a Weibull distribution with a shape parameter k>1. Polarity intervals from a stochastic model also obey a Weibull distribution, but the shape parameter is controlled by the temporal averaging used to approximate the resolution of the marine record. Reducing the time averaging yields polarity intervals that are well described by a distribution with k<1, suggesting that short polarity intervals are missing from the marine record. All of these missing polarity intervals are expected to occur when the dipole field is weak relative to the time average, often during transition states. We associate many of these short polarity intervals with frequent changes in the sign of the dipole during the transition. These short polarity intervals should be detectable in high-resolution observations of magnetic directions.