Progress in the Study of Interplanetary Discontinuities

This paper summarizes some of the recent rebirth of interest in interplanetary discontinuities. Vasquez et al. have developed a new method of searching for discontinuities that allows the study of structures with small angles of rotation. Those discontinuities are consistent with the in situ generation of discontinuities by Alfvenic turbulence. Borovsky has proposed that discontinuities with large rotation angles are the boundaries of flux tubes originating at the Sun. We conclude that both the Sun and turbulence are important sources of interplanetary discontinuities. We also argue that, at least in the slow solar wind, Tsurutani’s in‐situ generation by phase‐steepened Alfven waves may be a manifestation of exhaust fan reconnection. We furthermore suggest that such reconnection may be responsible for the Walen ratio ([4πρ]1/2|Δv|/|ΔB|) across rotational discontinuities being less than the theoretically predicted value of unity. Whether or not the wind consists of discrete flux tubes rather than being sim...