Low-Frequency1fNoise in the Interplanetary Magnetic Field

Spacecraft observations of the interplanetary magnetic field at 1 AU (astronomical unit) are shown to have frequency spectra with a $\frac{1}{f}$ dependence in the range 2.7 × ${10}^{-6\mathrm{}}$ to 8.0 × ${10}^{-5\mathrm{}}$ Hz. We suggest that the $\frac{1}{f}$ spectrum results from the superposition of uncorrelated samples of solar surface turbulence that have log-normal distributions of correlation lengths corresponding to a scale-invariant distribution of correlation times over an appropriate range of parameters.