Lognormal distributions and spectra of solar wind plasma fluctuations: Wind 1995–1998

The fluctuations in the hour averages of the speedV, densityN, and proton temperatureTat 1 AU are large, intermittent, and spiky on a scale of a year. The lognormal distribution is a good model for the distribution of measurements of these variables made at 1 AU during 1996, 1997, and 1998, near solar minimum, and during the rising phase of the solar cycle. The lognormal distribution is less satisfactory as a model for the data obtained during 1995, when corotating streams were present. For that year the distributions ofV,N, andTwere double‐peaked; nevertheless, the number of observations associated with the fast wind distribution was only 12–17%. Shocks, corotating streams, interaction regions, signatures of the sources of the streams, and the heliospheric plasma sheet are present in the data, but each of these features has its own variability. Taken together, these components and their interactions result in episodic signals and distribution functions with large tails. There remains a need for dynamical models of the solar wind that incorporate and describe both deterministic and statistical properties of the solar wind.