Andrew Jackson
Department of Earth Sciences, University of Leeds, Leeds, UK.
The Earth's dynamo lies in the fluid outer core of the Earth. Whilst considerable progress has been, and is being made on understanding the dynamo mechanism from numerical simulations, it is likely that we can be guided by observations of the field from the recent and historical past (i.e. the last 4-5 centuries) and from the ``geological past'' (i.e. palaeomagnetic data). The highest resolution images of the field at the edge of the dynamo region, namely the core-mantle boundary, come from direct observations of the field, with satellite data providing the most complete geographical coverage possible. At this moment in time no less than three satellites are making measurements of the magnetic field: the satellites Oersted, Champ and SAC-C. I will give examples of some of the features in the field that arise from analyses of Oersted and Magsat data and that are supported by historical data: they appear to be long-lived features. I will also describe a new methodology for creating maps of the magnetic field at the core mantle interface based on the Maximum Entropy method that is perhaps more suited to delineating features of interest in the field. In particular I will show intense equatorial flux spots whose amplitude appears to be higher than perhaps previously thought. The presence of one such spot in both the historical field and in some authors' images of the time averaged palaeomagnetic field is particularly striking.