[1] We report accelerated particles observed by Solar Wind Ion Detectors (SWIDs) on Chang'E-1 spacecraft close to terminator regions of the Moon. As the spacecraft crosses the terminator, a stream of ions with energy of ∼200eV/q are detected. As the spacecraft moves to the anti-subsolar point of the Moon, the energy of these ions increase by 600 ∼ 1500eV. This phenomenon occurs at north/south pole when IMF B y component is dominant and negative/ positive. It is proposed these particles are scattered solar wind protons, accelerated by the convection electric field of the solar wind and E × B drift in the ambipolar electric field at the flank of the lunar wake. This mechanism allows a new portion of solar wind protons to enter the central lunar wake, and provides a possibility to study the property of proton scattering at the dayside of the Moon.

Energetic neutral atoms (ENAs) are produced by the neutralization of energetic ions formed by shock-accelerated gradual solar energetic particle events (SEP). These high-energy ENAs (HENAs) can reach the Earth earlier than the associated SEPs and provide information about the SEPs at the lower corona. The HENA properties observed at Earth depend on the properties of the coronal mass ejection (CME)-driven shocks that accelerate the SEPs. With a model of HENA production in a shock-accelerated SEP event, we semi-quantitatively investigate the energy-time spectrum of HENAs depending on the width, propagation speed, and direction of the shock, as well as the density and ion abundances of the lower corona.Compared to the baseline model parameters, the cases with a wider shock width angle or a higher coronal density would increase the HENA flux observed at the Earth, while the case with an Earth-propagating shock shows a softened HENA spectrum. The comparison of expected HENA fluxes in different cases with a flight-proven ENA instrument suggests that solar HENAs can feasibly be monitored with current technologies, which could provide a lead time of 2-3 hours for SEPs at a few MeV. We propose that monitoring of solar HENAs could provide a new method to forecast shock-driven SEP events that could have significant space weather impacts on the near-Earth environment.