Two spacecraft observations of magnetic discontinuities in the solar wind with STEREO

Directional discontinuities in the solar wind magnetic field are often explored by either single-spacecraft studies with tens of thousands of events or multiple-spacecraft studies with between ten and a few hundred events. The unique orbits of the twin STEREO spacecraft afford the opportunity for a multiple-spacecraft study of tens of thousands of directional discontinuities at variable spacecraft separation. Automated algorithms are developed both for identifying magnetic directional discontinuities at a single spacecraft and for matching discontinuities between spacecraft. Four months of data yield tens of thousands of discontinuities per spacecraft and several thousand discontinuities identified at both spacecraft. Rates of occurrence, minimum lengths, and aspect ratios are determined for discontinuities identified at both spacecraft. Distributions of directional discontinuity properties, including thickness, normal vector orientation, waiting times between successive discontinuities, and the angle through which the magnetic field rotates while crossing the discontinuity (shear angle), are determined for directional discontinuities observed at both spacecraft as well as those observed at only a single spacecraft. It is found that the distributions of many of these properties are different between directional discontinuities observed by both spacecraft and those observed by only a single spacecraft. Based on the nature of these differences, the population of discontinuities observed by both spacecraft is most consistently interpreted as the walls of solar wind flux tubes.