[P-EM11] Coupling Processes in the Atmosphere-Ionosphere System

[PEM11-12] EUV signals associated with O+ ions observed from ISS-IMAP/EUVI in the nightside ionosphere

*Shin ya Nakano^1,2, Yuta Hozumi³, Akinori Saito⁴ (1.The Institute of Statistical Mathematics, 2.Center for Data Assimilation Research and Applications, Joint-Support Center for Data Science Research, 3.University of Electro-Communications, 4.Graduate School of Science, Kyoto University)

Keywords:O+ ions in the ionosphere, resonant scattering, ion recombination

The extreme ultraviolet (EUV) imager, EUVI-B, on board International Space Station (ISS) under the ISS-IMAP mission was designed for observing EUV emission at 83.4 nm scattered by O+ ions. During the mission, EUVI-B sometimes detected evident EUV signals in the umbra of the Earth. These nightside signals were expected to be resulted from multiple scattering of EUV by O+ ions and their source was attributed to EUV emitted by O+ ions excited by solar radiation on the dayside. However, the effect of the multiple scattering has not been assessed in the existing studies.

We simulated the nightside EUV flux at 83.4 nm using with the Monte Carlo method to compute EUV scattering process due to O+ ions. In this Monte Carlo computation, the scattering cross section was estimated from the O+ density and temperature distribution given by the IRI model. However, the simulation suggested that the multiple scattering does not explain the features of the observations from EUVI-B of ISS. We also modeled the nightside EUV at 91.1 nm as a result of recombination between O+ ions and electrons. The result showed that the recombination well explain the observations from EUVI-B morphologically and quantitatively. We therefore conclude that the EUV signals observed from EUVI-B in the umbra of the Earth were mainly attributed to 91.1 nm emission due to recombination. This result suggests that the spatial distribution of ionospheric O+ density can be estimated from the EUVI-B data.