The Energetic Particle Environment of the Lunar Nearside: Influence of the Energetic Ions from Earth’s Bow Shock

Xiaojun Xu1,2, Qing Chang1, Qi Xu1, Vassilis Angelopoulos3, Yi Wang4, and Pingbing Zuo4
The Astrophysical Journal 863, 80 Link to Article [https://doi.org/10.3847/1538-4357/aad282]
1Space Science Institute, Macau University of Science and Technology, Macao, People’s Republic of China
2Institute of Space Science and Technology, Nanchang University, Nanchang, People’s Republic of China
3Department of Earth, Planetary, and Space Sciences, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
4Institute of Science and Applied Technology, Harbin Institute of Technology, Shenzhen, People’s Republic of China

Energetic particles from Earth’s bow shock can frequently access the lunar orbit. These energetic particles are mainly ions. Since they are mostly field-aligned, they have much greater impacts on the lunar near side than on its far side. We present a statistical study of these upstream energetic ions at the lunar orbit using ARTEMIS observations. During the five-year time interval from 2012 to 2016, 496 energetic ion events with time durations ≥30 minutes were identified. The average duration of an event is about 1.93 hr. Most events occurred at the dawn-looking quadrants of Earth, showing an asymmetric dawn–dusk distribution in space. In 490 of the 496 events, the magnetic field lines directly extend to the bow shock. This is very important in order for energetic ions to arrive at the lunar orbit along field lines. The highest energies of these upstream energetic ions range from 101.5 to 658.5 keV based on the energy channels of ARTEMIS. The spatial distribution of the events depends on the highest energy. Events with higher energies tend to occur near the subsolar region and are related to greater AE indices, indicating stronger disturbances of the geomagnetosphere. By taking into account upstream energetic ions, in addition to galactic cosmic rays and solar energetic particles, our results provide a more comprehensive understanding of the energetic particle environment of the lunar near side.

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