A search for evidence of the evolution of rotational discontinuities in the solar wind from nonlinear Alfvén waves

Abstract

The nonlinear theory of the steepening of Alfvén waves into solitons and then into rotational discontinuities (RDs) predicts correlations between the β of the plasma, the sense of polarization of the discontinuity, and changes of magnetic field strength and plasma density across the discontinuity. The predicted correlations have been searched for in ISEE 3 field and plasma data, but no statistically significant evidence for the evolution of RDs from Alfvén solitons could be found. Approximately equal numbers of right‐ and left‐handed discontinuities were observed. Some of the rotations approached 180°, but none exceeded that value. Nearly all the RDs in the 33‐day data set were propagating outward from the Sun, which implies that sunward propagating Alfvénic fluctuations produced by stream interactions in the interplanetary medium seldom steepen into discontinuities before reaching 1 AU. The only unambiguously sunward propagating RD in the data set showed all of the expected relations for a steepened Alfvén soliton. Interplanetary processes, such as changing wave speeds and β and refraction of the discontinuities, may have changed the properties of the RDs created close to the Sun to such an extent that any original correlations are no longer detectable at 1 AU. Another possible explanation of the basically negative result is that some of the RDs produced near the Sun may have steepened from fast or slow Korteweg‐deVries solitons.