ARTEMIS Observations of Electron Cyclotron Harmonic Waves in the Lunar Plasma Environment

We report Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) observations of electron cyclotron harmonic (ECH) emissions in the lunar plasma environment. ECH emissions are correlated with electron loss‐cone distributions and electron beams during periods of magnetic connection to the lunar surface. Intermittent connection to lunar crustal magnetic anomalies correlates with a reduction or cessation in the ECH waves. In one case, ECH waves diminish in the presence of an additional cold (10 eV) electron population despite the presence of an electron beam and loss‐cone distribution. The spatial occurrence distributions show that ECH waves occur predominantly (97%) within the terrestrial magnetotail and within 1.5 lunar radii of the Moon‐Sun line. This is consistent with magnetic connection to the lunar surface and the formation of electron loss cones and/or electron beams while within the terrestrial magnetotail lobe. The full data set of ARTEMIS ECH observations represents a robust data set with which to test ECH wave formation theories.