The transition at a periodT∼ 1 Day in solar wind spectra

Abstract

The sharp change in behavior at periods above and below approximately 1 day in the solar wind spectra, reported by Goldstein and Siscoe, is discussed in terms of a damping‐growth transition for ion acoustic waves in a density gradient recently observed in laboratory experiments. The region immediately surrounding the sun (∼ 10 RS radial extent) is envisaged as a low‐pass filter for compressional perturbations, with a sharply defined upper frequency of ∼ 10−5 s−1.