Coherent Frequency Variations in Electron Fluxes at 1 and 5 AU in the Inner Heliosphere

Several years ago we reported evidence for distinct modal structure in the particle flux data from Ulysses and other interplanetary spacecraft, based on detailed time series analyses. Furthermore, we concluded that numerous discrete frequencies could be identified with known solar p-mode frequencies and with several calculated solar g-mode frequencies. This paper continues to explore the nature of the modal structure of the interplanetary medium by investigating the statistics of the coherence in electron fluxes measured at two separate locations in the near-ecliptic heliosphere, at 1 AU and at 5 AU, on the ACE and the Ulysses spacecraft, respectively. We demonstrate, from data taken at different times, that there are coincident frequency peaks at the two locations at high confidence levels, and that, for data acquired at the same time at the two locations, there is multiple frequency coherence across a wide spectral band.