Abstract

This presentation will provide an overview of observations of the geomagnetic field, highlighting those that could be considered sufficiently reliable to inform what might be considered Earth-like numerical dynamo simulation.  Modern high-quality direct geomagnetic observations have contributed greatly to our knowledge of Earth’s field and short-term secular variation.  However, they only touch a tiny fraction (400 of about 4 billion years) of the full spectrum of field behavior, providing some illusion of stability, while the longer view is revealed by paleomagnetic studies.  With appropriate chronological constraints paleomagnetic data provide information about the field’s longevity, the rates of occurrence and some broad inferences concerning polarity reversals, excursions, rapid changes in field strength, and other less spectacular features collectively known as paleosecular variation. The past three decades have seen considerable effort devoted to developing both stochastic and deterministic descriptions of paleofield observations and some attempts to reconcile the two approaches will be described.