[1] The shape of the particle flux profile in the decay phase of solar energetic particle (SEP) events is of particular importance in understanding the propagation of energetic particles in the interplanetary medium. The majority of few-MeV proton events (>90%) exhibit exponential law declines, suggesting the dominant role of convection transport and adiabatic deceleration. In this case, the characteristic decay time t should depend on the spectral index, the solar wind speed, and the distance from the Sun. More than 600 decays observed in the fluxes of 0.5-48 MeV protons by IMP 8 in 1973-2001 were selected and analyzed in detail. We consider the dependence of t on environmental plasma parameters. The observed decay times, t obs , are compared with those considering convection transport and adiabatic deceleration, t theor , and fair agreement is found (within 25%) in nearly 50% of all declines with constant values of V. Although high-energy proton profiles at various radial distances (Helios, IMP 8, Ulysses) are surprisingly identical, MeV protons in the same events decay more slowly, with increasing r, in agreement with the model. The solar cycle variation and the distribution of the t values as a function of energy are also examined. The dependence on the heliographic longitude suggests that events with significantly different t obs and t theor can be explained by the variation of magnetic connection between the observer and a flare site. The observational results are compared with numerical simulations in the frame of a simple particle propagation model involving scattering, adiabatic cooling, and a propagating shock.

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The relative abundances of thermal and suprathermal C, O, and Fe ions are analyzed and compared in solar wind streams from near-equatorial coronal holes during quiet periods of nearly two solar cycle minima. Ion fluxes with energies of ∼0.04–2 MeV/nucleon are studied using data from the ULEIS instrument aboard the ACE spacecraft together with thermal ions in the fast and slow (Maxwellian) solar wind using data from the SWICS instrument aboard ACE. The analysis was carried out for quiescent periods in 2006–2012 and 2015–17 when solar wind flows from near-equatorial coronal holes (CHs) were detected at 1 AU. Near the minimum of SC23, although they displayed large variability, the C/O and Fe/O ratios of suprathermal ions were, on average, near the corresponding relative abundances of the solar wind. During the decreasing solar activity phase of SC24 suprathermal Fe/O ratios matched those of solar wind ions from CHs. In both cycles the thermal and suprathermal Fe/O ratios exhibited a similar character of dependence on maximum solar wind speed. Our results suggest that the sources of suprathermal ions from CHs in low solar activity periods are accelerated solar wind thermal ions. The thermal and suprathermal Fe/O ratios were found to be higher in 2015–17 in comparison to the ratios measured in 2006–2010. This difference can be attributed to that the second quiet period was selected at times when solar activity has not reached its minimum of SC24 yet.