The Earth's magnetic field has a well-known relatively slow westward drift over the years called the secular variation. The analysis of secular variation and theoretical studies give information on possible fluid flows and dynamo types active in the Earth's liquid core.
The Earth's magnetic field also has a small, regular, daily change, in which the compass needle moves backwards and forwards about a quarter of a degree every day. The compass needle can also exhibit more drastic and rapid changes called magnetic storms. The daily changes are due to electrical currents flowing in the ionosphere and the corresponding eddy currents induced in the Earth. Studies of relationship between these current systems gives information on possible distributions of electrical conductivity within the Earth.
The daily changes are driven by the solar heating of the ozone layer and there are also smaller changes associated with gravitationally-driven lunar tides in the upper atmosphere. Studies of the solar and lunar daily changes give information on the modal structure of movements of the upper atmosphere and electrical conductivity of the ionosphere.
Presently, our research is on the theory of electromagnetic induction in the Earth at long periods of one and two cycles per year. To reconcile differences between the inducing and eddy currents, it is necessary to include a small field which is actually being generated within the Earth. By this means, the electrical conductivity of the lower mantle is reduced by two orders of magnitude from presently accepted values, and well within the upper and lower bounds set by diamond anvil studies.
We are also the Australian principal investigators for the analysis of satellite magnetic data recorded by the Danish Meteorological Office satellited called Oersted. Research here is based on signal processing and spherical harmonic analysis methods to determine crustal anomalies in the magnetic field over the world, and particularly over the Australian region. Results are compared with the low altitude satellite Magsat, which was launched in 1980, remaining in a daw-dusk orbit relative to the Sun. Oersted is moving slowly across local-time zones, which allows us to examine very closely the day-night differences especially in the equatorial electrojet region.
Research in daily magnetic variations and ionospheric dynamo theory is carried out in association with A/Prof Robert Stening of Physics at UNSW. Analysis of satellite magnetic data for the Australian region is carried out in association with Dr. Charles Barton, Dr. Andrew Lewis and Dr Peter Milligan of the Australian Geological Survey Organisation (AGSO). We are also Principal Investigators collaborating with the Danish Meteorological Office on the Oersted project, and will be given access to data recorded by the German satellite Champ, launched by the Geophysikalisches Forschungs Zentrum (GFZ) in Potsdam.
This work is being supported by a large ARC grant from 2001.
See also Magnetic Anomaly Maps From Satellite Observations