A new phenomenon in impulsive-flare-associated energetic particles

We present ACE/ULEIS and Wind/STEP observations of a new and unusual feature of energetic ions between 0.02 and 3 MeV nucleon(-1) associated with impulsive solar flares. In addition to the usual velocity dispersion associated with the transit in the heliospheric magnetic field of energetic particles from a small localized source on the Sun, these events also show intermittent behavior that may be related to the magnetic flux tube structure of the solar wind. These are anomalous bursts of low-energy particles, which we call ``tassels.'' Tassels are enhancements of ions extending to much lower energies than those associated with the main event. In one year of data from 2000 June to 2001 July, we have identified two events with tassels, both of which occur simultaneously with interplanetary coronal mass ejections ( ICMEs). The tassels may be a superposition of two events, either gradual and impulsive or two impulsive events. Since the tassels could be interpreted as ions arriving earlier than those with the same energy in the main velocity dispersion, we suggest that the tassels occur when the spacecraft intercepts a flux tube with a relatively shorter path length. The decrease in path length may be caused by a decrease in scattering or a shorter travel distance, since flux tubes may be distorted by the passage of the ICME. These tassel events may allow us to infer some of the structure of the ICME.