Origin of Quiet-Time Suprathermal Tails Near 1 AU

摘要

We have surveyed the spectral and compositional properties of suprathermal (-40-320 keV nucleon~(-1)) heavy ions during quiet times from 1995 January 1 to 2008 December 31 using instruments on board ACE and Wind spacecraft in the interplanetary (IP) medium near 1 AU. We find that the composition of the quiet-time suprathermal heavy ion population (3He and C-Fe) depends on the level of solar activity: the ions exhibit SEP-like composition signatures during solar maximum and CIR or solar-wind like composition during solar minimum. In addition, we find that during quietest times in the IP medium, all ion species exhibit suprathermal tails with power-law spectral indices ranging from 1.27 to 2.29, i.e., significantly different from recent observations and theoretical predictions of a unique 1.5 index. We discuss the implications of these new observations for the origin of the suprathermal ion population near 1 AU.