[SEM19-11] Estimating rates of change in the geomagnetic field
Keywords:paleomagnetism, geomagnetic secular variation, extreme geomagnetic variations
For a better understanding of the processes underlying these rapid changes we turn to a suite of numerical dynamo simulations which can provide a complete record of field changes and fluid flow. We find excellent agreement between amplitudes and latitude ranges of extreme directional changes in the geodynamo simulations and GGF100k. Remarkably, maximum rates of simulated directional change reach 10º/year even in times of stable polarity, almost 100 times faster than current changes. Detailed analysis of the dynamo simulations and a simple analogue model indicate that extreme directional changes are associated with movement of reversed flux across the core surface. Our results demonstrate that such rapid variations are compatible with the physics of the dynamo process and suggest that future searches for rapid directional changes should focus on low latitudes. In contrast, the most rapid intensity changes are more prevalent at mid to high latitudes, and may reflect rapid motions of strong normal flux. In the event that anticyclonic gyre-like flow similar to that inferred for the modern field is present, poleward motion of normal (reverse) flux could act to strengthen (weaken) the usually dominant dipole.