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Extended lunar precursor regions: Electron‐wave interaction
Journal article   Open access   Peer reviewed

Extended lunar precursor regions: Electron‐wave interaction

Y Harada, J. S Halekas, A. R Poppe, S Kurita and J. P McFadden
Journal of geophysical research. Space physics, Vol.119(11), pp.9160-9173
11/2014
DOI: 10.1002/2014JA020618
url
https://doi.org/10.1002/2014JA020618View
Published (Version of record) Open Access

Abstract

We present Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) observations of electron‐wave interactions which extend to quite large distances upstream from the Moon. We first study electron velocity distributions and wave spectra on an event basis. In both the solar wind and terrestrial plasma sheet, we observe strong whistler wave activity on the magnetic field lines connected to the dayside lunar surface. These whistlers are most likely driven by the anisotropy of upward electrons caused by surface absorption. The whistler growth rates computed from the measured electron distributions successfully reproduced the spectral characteristics of the observed ∼100 Hz narrowband oscillations and those reaching lower frequencies. Meanwhile, the incoming solar wind strahl beam is occasionally isotropized near the Moon, and broadband electrostatic waves are observed simultaneously, suggesting streaming instabilities between the incoming and outgoing beams. Based on the case study, we statistically survey the spatial variations of the characteristic quantities of the upstream electron‐wave interactions. Both the electron anisotropy and electromagnetic wave intensity decay with increasing field line distances but remain higher than the ambient level at 6 lunar radii (∼10,000 km) or more. The strahl electron isotropization and electrostatic waves are found mainly at lower altitudes below 1 lunar radius. The electron anisotropy and whistler intensity exhibit clear anticorrelation with crustal magnetic fields, indicating that the magnetic anomalies suppress the whistler wave growth. The ARTEMIS observations convincingly illustrate that the lunar influence on electrons reaches out to 6 lunar radii or more upstream from the Moon. Key PointsSurface absorption causes electron anisotropy and whistler‐mode wave growthLunar influence on electrons extends out to 10,000 km or more above the surfaceLunar magnetic anomalies suppress the electron anisotropy and whistlers
 electron‐wave interaction magnetic anomaly magnetosphere Moon solar wind whistler

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