## 1 Introduction  
Atomic oxygen is integral to the photochemistry and energy balance in the mesosphere-lower thermosphere (MLT) region. The maximum concentration of atomic oxygen is observed at altitudes of \(\sim\)100 km. Emission in line 557.7 nm occurs in the recombination of atomic oxygen (is caused by the recombination of atomic oxygen), which is formed due to the photo dissociation of molecular oxygen by solar UV (ultraviolet) emission [1]. Monitoring 557.7 nm atomic oxygen emission is one of the basic ways to investigate MLT thermodynamic conditions. In the entire nighttime airglow spectrum, 557.7 nm emission was the first one revealed at the beginning of the last century [2]. Nowadays, it is the most well-understood nightglow line. However, there are a number of unsolved problems; for example, features of diurnal and seasonal variations in 557.7 nm emission intensity (I 557.7 nm) at different latitudes are not entirely explained. Low latitudes, for which long-term observations from geostationary satellites have been accumulated, are the most well-studied [3, 4]. At middle and high latitudes, I 557.7 nm is mainly monitored at different ground-based stations or using limb-scanning satellites [2, 5]. Long-term studies of I 557.7 nm show the existence of pronounced seasonal dependence and inter-annual variations [6, 7]. The annual component of I 557.7 nm variations is the most significant mode, and its amplitude increases with latitude. The amplitude of the semiannual component of these emission variations is far weaker than the amplitude of the annual component, and it is the strongest over the equator and decreases with latitude [8]. Paper [2] shows that the amplitude of the green line annual component at 7-44\({}^{\circ}\) N is within 10-30%, with smaller amplitudes at low latitudes. The amplitude of semiannual variations also varies with latitude; it decreases with latitude from 37% at low latitudes to \(\sim\)10% at mid-latitudes. Using 557.7 nm photometry data over Kiso for 1979-1994, the authors of [9] showed the existence of two seasonal peaks: one in June and the other one in October. In the tropical region, semiannual variations in 557.7 nm emission were seen from WINDII satellite measurements, in measurements with ground-based photometers and in the TIME-GCM model [10]. However, for mid-latitude regions, the semiannual component was noted in [10] based on satellite data only at 96 km at 20:00 LT; it weakened overnight and almost disappeared by 02:00 LT. Based on long-term data on 1 557.7 nm over the Tory Geophysical Observatory (GPO), paper [11] demonstrates the existence of three I 557.7 nm maxima during equinox periods in February-March and October, and in June, the October maximum has the greatest amplitude. The minimum of I 557.7 nm was observed in April. The following can be referred to as the potential mechanisms determining the features of seasonal variations in I 557.7 nm: variations in global atmospheric circulation at MLT heights that provide the atomic oxygen transfer in the upper atmosphere, oxygen layer vertical motions and temperature variations at the emission level. Due to transition in the excited oxygen atom \(O\big{(}^{1}S-^{1}D\big{)}\), 557.7 nm emission occurs. The 4.2 eV excited oxygen atom \(O\big{(}^{1}S\big{)}\) results from triple collisions with the participation of atomic oxygen (the Barth mechanism) and includes the following stages:  
\[O+O+M\to O_{2}^{*}+M \tag{1}\]  
\[O+O_{2}^{*}\to O\big{(}^{1}S\big{)}+O_{2} \tag{2}\]  
Knowing the atomic oxygen concentration per volumetric unit, and the flow rate (1), (2), we can estimate the number of 557.7 nm photons emanating from a volumetric unit per unit time.