## 5 Discussion and Conclusions
### Intensity  
In general, annual variations of 557.7 nm emission and mesopause temperature above the south of East Siberia is within the widely accepted understanding of how these parameters behave above mid-latitudes [26]. Variations of 557.7 nm emission from instrument data differ from those obtained from the NRLMSIS model product, which is most noticeable in April. It is probably related to the latitudinal peculiarity of 557.7 nm occurrence, which is not considered in the NRLMSIS model, or climate changes that are not considered in the model.  
In addition, the minimum of I 557.7 nm coincides with the maximum of temperature (Figure 3) and the maximum height of peak intensity (Figure 8) for the entire year. Raising the airglow layer means it is moving into the lower thermosphere where the temperature is higher. In these circumstances, the rate of the triple collision reaction will slow down causing a decrease in airglow intensity, yet the effective temperature will grow, which obvi  
Figure 8: Monthly average altitude of maximum I 557.7 nm and deviations from 2017 to 2021 from SABER (red) and NRLMSIS model (blue) data.  
ously leads to slower seasonal decreases in temperature observed with the interferometer in April, according to Figure 4.  
Temperature and atomic oxygen concentration are the most significant atmospheric parameters in the calculations of I 557.7 nm from SABER data [16]. Evaluation of the temperature contribution to intensity calculations is possible if other input parameters are fixed. The result can be seen in Figure 9, from which it is obvious that the intensity goes down with temperature--the higher the temperature, the lower the intensity.  
The summer airglow maximum from SABER data can be explained by the fact that in the upper atmosphere during summer limb-scanning observations near the terminator, the influence of the sunlit atmosphere remains significant, which cannot be fully eliminated from the height profiles of temperature and atmospheric components using the deconvolution operation. Another possible reason for the discrepancies may be that photochemical processes have no time to come to equilibrium after dawn, and the photochemical model and initial satellite data, which are used in this paper for intensity synthesis, incorrectly represent the real condition of the mesopause airglow layer.  
The presence of the autumn intensity maximum in interferometer data and the absence of it in satellite data, which is clearly seen in Figure 6, is hard to explain. Presumably, there exist the effects of some additional chemical processes in the mesopause region, which cannot be taken into account based on SABER data addressed in this paper. Yet it should be noted that the results of the simulation using the NRLMSIS model imply the existence of the autumn intensity maximum.  
The observed discrepancy of intensities from data by two ground-based instruments in summer and autumn can be explained as follows. Summer and autumn are the seasons with the most frequently occurring fog and cloud cover in the observation point. When preparing time series for interferometer data, we selected time intervals without cloud cover within the region during observations. To do this, we followed the algorithm described in [27]. For the spectrometer time series, such data preparation was not carried out before averaging. As a result, variations from month to month in the summer-autumn period remained similar for the interferometer and spectrometer, but absolute values for the spectrometer got considerably lower (see Figure 7, months 7-12).  
Figure 9: SABER VER (volume emission rate) 557.7 nm, which only depends on temperature (160–260 K) obtained at fixed atmospheric parameters (atomic oxygen concentration \([O]=3.7\cdot 10^{11}\), \([M]=6\cdot 10^{15}\), molecular oxygen concentration \([O_{2}]=1.3\cdot 10^{15}\); used Formula (7) from [16]).