Improved calculations of interplanetary magnetic field phase front angles and propagation time delays

Abstract

It has been known that the variations in the interplanetary magnetic field (IMF) occur within surfaces that are tilted with respect to the solar wind velocity vector. This tilting of the IMF phase fronts may cause the propagation from a point of observation to another location to have delay times that vary substantially. Therefore for accurate delay calculations in real time, or for the creation of scientific data sets, it is necessary to be able to determine the phase surface orientation angles using the magnetic field measurements on one spacecraft only. Methods for calculating these tilt angles have been tested for accuracy by a comparison using IMF measurements on multiple satellites. One method is a variation of the minimum variance of the magnetic field, where it is constrained by the condition that the average field along the phase front's normal vector is zero. This method is referred to as MVAB‐0. Another technique is to simply calculate the vector cross product between magnetic fields measured at two different sample times. The choices of the different parameters for the calculation and error discrimination are important. An optimization of parameters was done by testing how well the propagation delays from one spacecraft to others are predicted. The tests have indicated that, when optimized, both procedures work comparably well. It had also been found that further improvements to time delay predictions are obtained by combining together both the MVAB‐0 and cross‐product techniques, where the results of both methods must be in near agreement.