# Analysis and Interpretation of the Main Geomagnetic Field: The Magnetic Field at the Core-Mantle Boundary: Some Topological Speculations

Tuesday, October 9, 2001 - 9:30am - 10:30am

Keller 3-180

Raymond Hide (NONE)

The determination of the main geomagnetic field at the core-mantle boundary (CMB) from observations made at nearly twice the distance from the geocentre, i.e. at and near the Earth's surface, is a crucial first step in the use of such observations in the study of core motions and the testing of geodynamo models. Important details of CMB field patterns remain controversial,so it is of interest to investigate whether they can be elucidated by considering topological characteristics of the patterns associated with the intersection of lines of force of any solenoidal vector field V with a general spherical surface S. Such patterns are characterised by (a) patches bounded by null flux lines where the component of V normal to S vanishes and (b) dip poles where V is normal to S, and,when V is sufficiently complex, by (c) touch points on null flux lines where the component of V that is tangential to S is also tangential to the null flux line. At the Earth's surface there is at present just one pair of dip poles and one null flux line, but no touch points. The more complex CMB field has several pairs of dip poles and several null flux lines, not all of which are nested and upon some of which there are pairs of touch points.