Global distribution of electrostatic electron cyclotron harmonic waves observed on THEMIS

A global, statistical analysis of electrostatic electron cyclotron harmonic (ECH) waves is performed using THEMIS wave data. Our results confirm the high occurrence of <1 mV/m ECH emissions throughout the outer magnetosphere (L > 5). The strongest (≥1 mV/m) ECH waves are enhanced during geomagnetically disturbed periods, and are mainly confined close to the magnetic equator (∣ λ ∣ < 3°) over the region L ≤ 10 in the night and dawn MLT sector. ECH wave intensities within 3° ≤ ∣ λ ∣ < 6° are generally much weaker but not negligible especially for L < ∼12 on the midnight side. Furthermore, the occurrence rates and variability of moderately intense (≥0.1 mV/m) ECH emissions suggest that ECH wave scattering could contribute to diffuse auroral precipitation in the outer (L > 8) magnetosphere where chorus emissions are statistically weak.