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 May 10^th and Oct. 10^th, 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 calculated post-scattering wind speeds as the initial wind speeds weighted by both scattered and direct intensities. With fixed initial speeds, the simulation reproduced the temporal characteristics of the atypical winds, demonstrating that scattering causes these intense horizontal differences and downwelling. The simulation also shows that the scattering-induced biases have directional inhomogeneity with characteristics linked to the location and background line-of-sight speed of the brighter airglow region. The commonly used horizontal average wind may experience numerical deviations due to directional inhomogeneity. The accuracy of the simulation is limited by the accuracy of airglow observations and atmospheric optical depth.