Microturbulence in solar wind streams

Abstract

We present a comparison of spacecraft and IPS measurements of the solar wind velocity for 1973-75, when the large scale velocity structure was very stable. From this comparison we infer a prototype distribution across a high-speed stream for the electron density fluctuations Δn_e in the spatial frequency range 10^-4 - 10^-2 km^-1. This 'microturbulence' is more closely related to the velocity structure in a stream than to the bulk density np. Enhancements of Δn_e occur in the stream interaction region, but they are not as large as those of n_p and they peak 12 hours after the n_p peak. The distribution of Δn_e is similar to that of the large scale (106 km) magnetic field fluctuations α_B, but Δn_e also shows a broad variation not present in sB. Overall, Δn_e is most closely matched to the positive velocity gradient at the leading edge of a stream.