Application of a simple coordinate transformation to data from polarity transition and excursion records renders a form of display having strong similarities, yet distinct advantages, over the use of virtual geomagnetic poles. Specifically, the procedure consists of a single rotation about the east-west line so as to align the +z axis of the local Cartesian system with the normal polarity axial dipole field direction associated with the recording site at the time of the event. The method makes possible the redefiniton of concepts relevant to transitional field studies in terms of vector directions, a more meaningful approach than the use of virtual poles when nondipole field components are significant. Visually, polar stereographic plots in (D', I') space present paleodirectional movement as if one were literally peering down the dipole direction. Analysis of individual transition records in this rotated directional space makes easy the determination of (1) the angular distance of a given paleodirection from that of the axial dipole field, (2) the number of strictly transitional directions contained within a given record, and (3) the degree of near-sidedness or far-sidedness of each paleodirection. In addition, the comparison of records from distant sites for the purpose of harmonic analysis can be accomplished without the need for additional normalization. Such comparison plots in (D', I') space display transitional data in a form strongly reminiscent of virtual geomagnetic poles plotted with respect to a common site longitude. Records of polarity transitions and excursions are presented which illustrate the utility of the proposed approach. |