A new interpretation of Weimer et al.'s solar wind propagation delay technique

[1] We present an evaluation of the Weimer et al. (2003) scheme designed to model interplanetary magnetic field ( IMF) phase front propagation in the solar wind. The new method is based on the fact that IMF fluctuations tend to be rotations contained within planes. Weimer et al. ( 2003) report that phase front orientations can be found via minimum variance analysis (MVA) with planar normals defined by the minimum variance direction. The phase plane tilt angle results they present appear to be accurate as they vary in a similar fashion to those found utilizing phase front coplanarity analysis using multipoint interplanetary observations ( Weimer et al., 2002). Here we report on an attempt to reproduce their results, an effort that failed since Weimer et al. ( 2003) adopted a nonstandard form of the equation used to calculate the magnetic field variance matrix that composes the basis of MVA. Use of the modified variance matrix forces a reevaluation of the physics underlying their new propagation model. The revised interpretation suggests that phase plane orientations are organized in a coordinate system whose axes are defined by the mean IMF direction and the minimum and maximum perturbation directions perpendicular to the mean field vector. The phase plane normal is found to be the minimum perturbation direction in this coordinate system. Given that the new technique appears to improve the accuracy of estimating solar wind propagation delays and that it requires IMF data from only one interplanetary monitor, testing it as a space weather forecasting tool is clearly motivated.