EUV signals associated with O+ ions observed from ISS-IMAP/EUVI in the nightside ionosphere

Abstract The extreme ultraviolet (EUV) imager, EUVI-B, on board the International Space Station (ISS) under Station–ionosphere-mesosphere-atmosphere plasmasphere cameras (ISS-IMAP) mission was originally intended to observe EUV emissions at 83.4 nm scattered by $${\mathrm O}^+$$ O + ions. During mission, EUVI-B occasionally detected evident signals in umbra of Earth. However, source has not been verified. To evaluate effect EUV, we conduct a Monte Carlo simulation which considers multiple scattering In addition, modeled contribution 91.1 emission, is due recombination O}^{+}$$ ions and electrons, because might affect measurement from wavelength range covered. results suggest that likely be negligible while explains observations morphologically quantitatively. We therefore conclude observed Earth can largely attributed emission recombination. This conclusion would facilitate use data for reconstructing density.