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 particle flux data from Ulysses and other interplanetary spacecraft, based on detailed time series analyses (1). 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 that there are highly significant coincident frequency peaks at the two locations in data taken at different times, and that, for data acquired at the same time at the two locations, there are high levels of coherence at multiple frequency pairs across a wide spectral band.