Impact of lower atmospheric scattering on ground-based optical thermospheric wind observations with spatially uneven airglow

Abstract. Scattered airglow emissions in the lower atmosphere can bias ground-based interferometer observations of thermospheric winds, particularly when airglow brightness becomes spatially uneven due to auroras. During two geomagnetic storms with visible auroras on 10 May and 10 October 2024, the Doppler Asymmetric Spatial Heterodyne (DASH) and Fabry-Perot (FP) interferometers concurrently detected atypical winds at Siziwang (SIZW, 41.83° N, 111.93° E), suspected to be caused by scattering. These atypical winds, characterized by horizontal differences exceeding 400 m s−1 between opposite cardinal directions (N-S or E-W) and downwelling exceeding 100 m s−1, showed a strong temporal association with airglow brightness. By modelling the transmission of scattered airglow emissions, we calculate post-scattering wind speeds as the initial wind speeds weighted by both scattered and direct intensities. With fixed initial winds (100 m s−1 westward, 400 m s−1 southward, zero vertical wind), the simulation reproduces horizontal differences of approximately 400 m s−1 on 10 May and 100 m s−1 on 10 October, both capturing the temporal characteristics of the atypical winds. The simulation shows that scattering-induced biases on line-of-sight speed take their sign from the brighter region, while their magnitude varies directionally with the angle to that region: at 45° elevation, biases 135–180° azimuth away exceed those in the brighter region by more than 10 times. Limited by uncertainties in airglow images and optical depth of model inputs, the simulation incurs numerical errors of roughly 75 % during some periods. Effective correction of the scattering impact will require improved accuracy of model inputs in the future.