Intermittent turbulence in large‐scale velocity fluctuations at 1 AU near solar maximum

The large‐scale fluctuations of the bulk speed at 1 AU near solar maximum, from day 1 through day 365, 1979 exhibit multifractal scaling over the range from 8 hours to 2.7 days. The observations are consistent with the binomial cascade model of intermittent turbulence proposed by Meneveau and Sreenivasan (1987a). The intermittency exponent computed from these observations is µ, = 0.19 ± 0.02, which is consistent with the best estimate µ = 0.025 ± 0.05 obtained from earth‐based measurements of intermittent turbulence (Sreenivasan and Kailasnath, 1993). Thus the complicated speed fluctuations observed over this range of periods at 1 AU near solar maximum are described by a simple relation for the inertial range of intermittent turbulence. The multifractal structure of these fluctuations differs from that associated with the large‐scale fluctuations observed during 1974 when corotating streams were dominant. In both cases the distribution of speed differences was exponential. There appears to be a solar cycle variation in the spectral exponent describing the large‐scale speed fluctuations.