J.E. Mazur The Aerospace Corporation, El Segundo, CA 90245-4691
Energetic particles from impulsive solar flares are accelerated in small (<10 degrees) regions near the Sun and have unique elemental and isotopic enhancements. With the instrumentation on board ACE, we are able to measure the energy spectra of a wide range of elements in impulsive flares from supra-thermal energies (~10s of keV/nucleon) to above 10 MeV/nucleon with higher time resolution than previously possible. The wide energy coverage shows the maximum energies that the ions attain as well as the overall distribution of their energy; these are important constraints on acceleration models. The Ultra-Low Energy Isotope Spectrometer (ULEIS) on ACE allows us to observe impulsive flare particle events with high time resolution at low energies where the events last many hours. We have often found that the magnetic flux tubes that convect past ACE during an impulsive flare particle event are alternately filled and devoid of flare ions. The ACE observations show that by the time the solar wind convects them to 1 AU, the field lines near the flare site become mixed, on the scale of ~0.01 AU, with field lines that are not connected to the flare. We will discuss how the field line mixing is not only significant for studies of particle transport, but also how it may complicate measurements of flare particle energy spectra.