## 2 Observations and Method for Data Analysis
### Climatology, Seasonal and Interannual Variability of the Nonmigrating Diurnal Tides  
It is worth noting that the considered nonmigrating diurnal tides DE3 and DE2 are the first and second strongest tides, while DW2 is the fourth one among all diurnal tides for the entire period of 21 years; additionally, DE3 is the strongest nonmigrating tide among all such tides. [PERSON] et al., 2017 [11], clarified that the excitation source of DE3 is the latent heat release associated with the largest wavenumber 4 component of the cumulus convection (because the zonal wavenumber 4 component is the largest in the land-sea distribution at low latitudes, [78] while DE2 is considered to be excited by the cumulus convective activity with zonal wavenumber 3 in the troposphere). [PERSON] et al., 2009 [6], showed that the enhancement of DW2 amplitude occurs during a sudden stratospheric warming (SSW) event in the NH, i.e., the source of DW2 is the nonlinear interaction between the SPW1 and the migrating DW1 tide. Later, [PERSON] et al., 2018 [79], examined the relationship between SPW1 and DW2 waves for 31 winters from 1979 to 2010, with the extended Canadian Middle Atmosphere Model (eCMAM) through correlation and composite analysis. The authors found that although SPW1 is usually very strong during SSW events, especially with displacement, this, however, does not warrant a stronger interaction with DW2. Some evidence that the winter SSW events lead to the generation of DW2 can be found out in the secondary winter maxima at both hemispheres in the climatology of this tide (Figure 1). Additionally, [PERSON] and [PERSON], 2002 [8], by using the GSWM, showed that DW2 is excited by the cumulus convective activity with zonal wavenumber 1, and it has considerable amplitudes in the MLT region. Furthermore, [PERSON] et al., 2014 [31], revealed that the DW2 tidal variability of the MLT follows ElNino-Southern-Oscillation variability, suggesting the importance of interannual variability of cumulus convection in the tropics. Thus, the excitation source of DW2 is not yet clear, and it would be a subject for future study [11]. Figure 1a shows the climatologically mean (2002-2022) latitude-time structures of the DE3 (left plot), DE2 (middle plot), and DW2 (right plot) tidal amplitude (in Kelvin) calculated at altitude of 110 km. It is important to underline that in the present study, all figures will use different color scales for the tides under consideration; this makes it possible to immediately assess the climatologically or monthly mean magnitudes of the tidal amplitude. The DE3 and DE2 tides have been investigated by many authors, and regardless of the different time intervals used, the climatological characteristics of these two tides remained almost unchanged. For example, the largest mean (for full 21 years) tidal DE3 (DE2) amplitude, observed in August-September (June), is \(\sim\)16.5 K (\(\sim\)8.7 K) while that of the secondary amplification in March-April (December) is about 9 K (\(\sim\)8 K). According to [PERSON] et al., 2010 [27], only for 6 full years (2002-2007) are the main and secondary maxima for both tides are observed in the same months with the respective mean amplitudes of \(\sim\)15 K (\(\sim\)8.3 K) and \(\sim\)8 K (\(\sim\)8 K).