The primary research objective for this project is to obtain new constraints on the profile of deep mantle electrical conductivity, plus the toroidal field and its vertical growth rate in both the lower mantle and the upper core. Two different geophysical data sets, the geomagnetic field and decade variations in the length-of-day, will be combined with several concepts from geodynamo theory, especially electromagnetic core- mantle coupling, self-excitation, and the strong-field dynamo. A secondary objective is to implement a new theory of fluid motion near the top of the core which relaxes the much used "frozen-flux assumption." The new method has been developed in the preceding NSF award, but has not yet been submitted for publication, nor has it been fully implemented. Moreover, there is a remaining source of ambiguity in the model which requires new work to resolve. Work on these two objectives are expected to contribute importantly to the "second generation" of studies aimed a mapping the fluid motion of the uppermost parts of the liquid outer core.
