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ACE News #168 - April 23, 2014
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Mean Fe charge states for three impulsive energetic particle events as a
function of energy together with model curves, including acceleration,
stripping, and adiabatic cooling for source temperatures of 1 MK (blue) and 2
MK (red), and transport mean free paths λ = 0.5 AU (solid) and λ = 0.2 AU (dashed)
(Kartavykh et al., ApJ, 671, 947, 2007). Typical coronal temperatures as
derived from ionic charge states in the solar wind are about 1 MK
(ACE News #146).
Earlier studies have shown that impulsive Solar Energetic Particle (SEP) events emit Fe ions with QFe < 14 at the lowest energies (E ≤ 0.1 MeV/nuc) that are consistent with typical corona source material (ACE News #107, DiFabio et al., ApJ, 687, 623, 2008). However, the occasional observation of Fe with QFe > 16 in solar wind associated with active regions (ACE News #52, (ACE News #52, Lepri et al., JGR, 106, 29231, 2001) led to a search for acceleration of high charge state Fe in all SEP events observed with ACE SEPICA.
A total of nine SEP events with QFe ≥ 14 across the entire SEPICA energy range (0.08 - 0.54 MeV/nuc) were identified (Guo et al., ApJ, 785, 26, 2014). Five of these events were CME related events with acceleration of high charge state material, in some cases mixed with the acceleration of a separate component of more normal coronal material. Four of these events are impulsive events with the clear signature of ion velocity dispersion. In comparison with a model that involves acceleration out of a source at equilibrium temperature, further stripping during the acceleration, and adiabatic cooling during transport to 1 AU (shown for three events in the Figure above), all four events are consistent with a source temperature T > 2 MK (Kartavykh et al., ApJ, 671, 947, 2007) and thus the presence of hot solar material in these impulsive events.
This item was contributed by Zhangbo Guo, Eberhard Möbius, and Mark Popecki, University of New Hampshire, and Berndt Klecker, Max-Planck-Institut für exterrestrische Physik. Address questions and comments to
Last modified 23 Apr 2014.