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 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ to 8.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$ 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.