Authors: Klecker, B.
Reference: Workshop on "Solar Terrestrial Interactions from Microscale to Global Models", Invited Paper, September 2005, Sinaia, Romania.
The ionic charge of solar energetic particles (SEP) is an important parameter for the understanding of the plasma conditions at the source region in the solar corona. Furthermore, acceleration, transport in interplanetary space, and access to the near-Earth environment depend significantly on velocity and rigidity, i.e. on the mass, M, and ionic charge, Q, of the ions. Previous measurements were limited to a small energy range at ~1MeV/nuc and showed significant differences of the mean ionic charge of heavy ions in events related to interplanetary shocks (gradual SEP events, Q_Fe~10-14) and flares (impulsive SEP events, Q_Fe~20). With advanced instrumentation onboard the SAMPEX, SOHO and ACE spacecraft the determination of heavy ion ionic charge states has been extended over the last ~10 years to the large energy range of ~0.01 - 80 MeV/nuc. The new measurements show a surprisingly large variability of Q with energy. In impulsive events Q is increasing significantly with energy from ~12 to 20 at ~0.01 \u2013 0.55 MeV/nuc (for Fe) in all events analyzed so far. In gradual events Q_Fe is increasing with energy in many events, in particular at energies >10MeV/nuc. Of particular importance are therefore the measurements at high energies (~0.3-70 MeV/nuc) with SAMPEX, that use the Earth's magnetic field as a magnetic spectrometer. The increase of the ionic charge with energy can be explained by stripping effects in the low corona and thus provides information on the source region of these ions. In this paper we (i) summarize recent ionic charge measurement techniques, with emphasis on the method based on the determination of the rigidity cutoff of the magnetic field of the Earth, (ii) discuss the effect of cutoff variations during SEP events, (iii) review the new results on ionic charge states in impulsive and gradual events, and (iv) discuss the results in the context of models that include charge stripping in the low corona.