OI 630 nm Airglow Observed From Space as a Diagnostic of Nighttime Low‐Latitude Ionospheric Dynamics

This study investigates the nighttime morphology of the bottomside F region (∼250 km) at low latitudes using 630 nm airglow measurements from the Visible and Infrared Spectral Imager (VISI) aboard the Ionosphere, Mesosphere, Upper Atmosphere, and Plasmasphere (IMAP) mission on the International Space Station. For this purpose, we analyzed IMAP/VISI data collected during the solar maximum period in 2013–2015. The global distribution of 630 nm emission intensity exhibits distinct hemispheric asymmetries, with higher intensities occurring in the winter hemisphere during solstices. This asymmetry varies with longitude, primarily as a function of magnetic declination. The seasonal and longitudinal behavior of the 630 nm emission intensity is inversely related to that of the topside plasma density and total electron content (TEC). Observations of the F region height from an ionosonde, together with ionospheric morphology derived from a model, suggest that this inverse relationship is related to opposing physical dependencies of these parameters on the F region height. Specifically, the 630 nm emission intensity is anti‐correlated with the F region height, whereas the topside plasma density and TEC are positively correlated with it. These behaviors are consistent with the modulation of the F region height by field‐aligned neutral winds. Our results demonstrate that space‐based 630 nm emission measurements serve as an effective diagnostic for global ionospheric morphology at low latitudes and its underlying dynamics.