Investigation of the Causes of Geomagnetic Dipole Moment Change

Johns Hopkins University, Baltimore MD

Investigators

Abstract

This research combines numerical dynamo models and dynamo theory with measurements of the present-day geomagnetic and the ancient paleomagnetic fields to investigate the origins of geomagnetic dipole change in Earth's core. Separate studies of dipole moment variations over short (10-1000 year), intermediate (1-100 thousand year), and long (1-1000 million year) time-scales are being conducted. In collaboration with graduate students, the PI is delineating and interpreting the observed short-term geomagnetic field changes on the core-mantle boundary that are responsible for the present-day rapid decrease of the geomagnetic dipole moment, the even more rapid decrease of the dipole tilt angle, and the relationship between these on-going magnetic field changes and the general circulation in the fluid outer core. Special attention is given to the growth and movement of regions on the core-mantle boundary with reversed magnetic field, including some reversed field regions now developing beneath the North Atlantic and the east coast of North America, which are playing major roles in reducing the present-day dipole moment and the dipole tilt. These magnetic structures provide real-time evidence on the causes of present-day dynamo fluctuations, as well as contemporary evidence on how geomagnetic polarity reversals are initiated. The PI is using numerical dynamo models to investigate the causes of the 1-100 thousand year, intermediate time-scale dipole moment oscillations that are ubiquitous in the paleomagnetic record. This research tests the competing theories for the origin of these paleomagnetic dipole oscillations, including wave, flow vacillation, and precession theories. The connection between geomagnetic field changes on very long time-scales (1-1000 million years) and the energy balance of the Earth's core is being investigated using high-resolution numerical dynamo models to derive scaling relationships between the time-average dipole moment and dynamo energy sources. These scaling relationships are then extrapolated to the extreme conditions of Earth's deep interior to connect the slow change of the geomagnetic dipole moment over geological time-scales to fundamental physical and chemical processes that control the evolution of the core, including the formation and growth of the solid inner core, internal heating by decay of radiogenic isotopes, and the removal of heat from the core by mantle plumes.