The Energetic Particle Environment of the Lunar Nearside: SEP Influence

The energetic particle environment of the lunar nearside is quite different from that of the lunar farside. Due to the shielding of the Earth's magnetosphere and the Moon, the lunar nearside may receive much fewer energetic particles from the Sun. It is currently impossible to directly measure the received energetic particle flux of the whole lunar surface. By using the ARTEMIS and Wind observations, we qualitatively studied the shielding effect of the Earth's magnetosphere and the lunar body from solar energetic particles (SEPs). We found that the Earth's magnetosphere can effectively shield SEPs with energies up to 4 Mev during the SEP event. However, in the solar wind, the Moon can provide partial shielding from SEPs with energies ≤100 KeV. SEPs with energies above 150 KeV in the lunar shadow show no difference in flux from in the solar wind, which suggests that the nearside and farside are the same in receiving SEPs with energies above 150 KeV during the SEP event.