Large Amplitude Fluctuations in the Alfvénic Solar Wind

Abstract

Large amplitude fluctuations, often with characteristics reminiscent of large amplitude Alfven waves propagating away from the Sun, are ubiquitous in the solar wind. Such features are most frequently found within fast solar wind streams and most often at solar minimum. The fluctuations found in slow solar wind streams usually have a smaller relative amplitude, are less Alfvenic in character and present more variability. However, intervals of slow wind displaying Alfvenic correlations have been recently identified in different solar cycle phases. In the present paper we report Alfvenic slow solar wind streams seen during the maximum of solar activity that are characterized not only by a very high correlation between velocity and magnetic field fluctuations (as required by outwardly propagating Alfven modes) – comparable to that seen in fast wind streams – but also by higher amplitude relative fluctuations comparable to those seen in fast wind. Our results suggest that the Alfvenic slow wind has a different origin from the slow wind found near the boundary of coronal holes, where the amplitude of the Alfvenic fluctuations decreases together with decreasing the wind speed.