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Title: Backscattered energetic neutral atoms from the Moon in the Earth's plasma sheet observed by Chandarayaan-1/Sub-keV Atom Reflecting Analyzer instrument
Authors: Harada, Yuki  kyouindb  KAKEN_id  orcid (unconfirmed)
Futaana, Yoshifumi
Barabash, Stas
Wieser, Martin
Wurz, Peter
Bhardwaj, Anil
Asamura, Kazushi
Saito, Yoshifumi
Yokota, Shoichiro
Tsunakawa, Hideo
Machida, Shinobu
Author's alias: 原田, 裕己
Issue Date: 20-May-2014
Publisher: American Geophysical Union
Journal title: Journal of Geophysical Research: Space Physics
Volume: 119
Issue: 5
Start page: 3573
End page: 3584
Abstract: We present the observations of energetic neutral atoms (ENAs) produced at the lunar surface in the Earth's magnetotail. When the Moon was located in the terrestrial plasma sheet, Chandrayaan-1 Energetic Neutrals Analyzer (CENA) detected hydrogen ENAs from the Moon. Analysis of the data from CENA together with the Solar Wind Monitor (SWIM) onboard Chandrayaan-1 reveals the characteristic energy of the observed ENA energy spectrum (the e-folding energy of the distribution function) ∼100 eV and the ENA backscattering ratio (defined as the ratio of upward ENA flux to downward proton flux) <∼0.1. These characteristics are similar to those of the backscattered ENAs in the solar wind, suggesting that CENA detected plasma sheet particles backscattered as ENAs from the lunar surface. The observed ENA backscattering ratio in the plasma sheet exhibits no significant difference in the Southern Hemisphere, where a large and strong magnetized region exists, compared with that in the Northern Hemisphere. This is contrary to the CENA observations in the solar wind, when the backscattering ratio drops by ∼50% in the Southern Hemisphere. Our analysis and test particle simulations suggest that magnetic shielding of the lunar surface in the plasma sheet is less effective than in the solar wind due to the broad velocity distributions of the plasma sheet protons.
Rights: ©2014. American Geophysical Union.
DOI(Published Version): 10.1002/2013JA019682
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