| 13 Jul 2026
A Fast Spectral Line-Ratio Algorithm for Mesospheric Airglow Rotational Temperature Retrieval and Validation
Abstract. Airglow rotational temperatures are effective tracers of variability in the mesopause region. To enable efficient processing of long-duration, high-temporal-resolution observations from the Mesospheric Airglow Spectrum Photometer (MASP), a Fast Airglow Spectral Line-Ratio algorithm (FASLR) is developed for rotational temperature retrieval. FASLR uses forward-modeled synthetic spectra to establish ratio–temperature relationships, derives independent temperature estimates from multiple line-intensity ratios, and combines them with weights based on the relative sensitivity of each ratio to instrumental perturbations. By avoiding computationally intensive multi-parameter iterative optimization, the algorithm substantially improves computational efficiency and remains robust to occasional anomalies in individual spectral lines. FASLR is validated using two nights of co-located MASP and sodium fluorescence Doppler lidar observations, showing good consistency with the corresponding lidar temperatures. The algorithm is then applied to six nights of dual-channel MASP observations of the O₂ (0–1) and OH (6–2) emissions and compared with independent temperatures from SABER, Aura/MLS, SD-WACCMX, and NRLMSIS 2.1. Overall, these comparisons indicate general consistency in the background temperature level, the relative offset between the O₂ and OH emission layers, and the range of nocturnal variability. Near representative emission-layer altitudes, the O₂ rotational temperatures reproduce the nocturnal background evolution reasonably well, whereas the OH temperatures show a more evident early-night high bias but better agreement during the latter half of the night. Case studies further demonstrate that the FASLR-derived temperatures are suitable for quantitative analyses of both longer-period nocturnal variability and shorter-period disturbances. On 2 February 2024, temperature and intensity perturbations in the O₂ and OH layers exhibit a common dominant period band and stable phase relationships. On 7 February 2024, both layers show concurrent power enhancements within a similar period band, and simultaneous observations from the Mesospheric Airglow Wide-angle Imager (MAWI) independently support the identified disturbance. Overall, FASLR provides an efficient and robust approach for dual-channel airglow temperature retrieval and supports investigations of multi-scale wave processes in the mesopause region.
This manuscript presents the FASLR method for MASP observations by calculating the relationship between spectral line intensity ratio and temperature. The proposed approach provides a potential solution for processing long-duration and high-temporal-resolution observations of MASP datasets in the future. The retrieved temperatures are compared with those derived from the MPII method, lidar observations, satellite measurements, and model simulations, demonstrating the reliability of the proposed retrieval method. In particular, comparisons with the MPII method and co-located lidar observations indicate that, although the absolute temperature values retrieved by the FASLR method show some differences, the temporal variations are generally consistent with those observed by lidar. In addition, spectral analysis is applied to the retrieved temperatures, and atmospheric wave signatures are successfully identified, suggesting that FASLR-retrieved temperatures can be potentially used for atmospheric wave studies.
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