## 4 Climatology (2002-2022) of Longitudinal Structures in the Lower Thermosphere  
It has been already mentioned that, based on the observations made by the SABER and TIDI instruments on the TIMED satellite, even the first climatologies of the most important tidal components in temperature and neutral winds [20; 22; 27; 85] revealed an important result that nonmigrating tides are much larger than hitherto anticipated, and some of them often exceed their migrating counterparts. The nonmigrating tide that has so far attracted most attention is DE3 because it is the largest component during most of the year. The presented in this study climatology based on very long term observations (2002-2022) fully confirms previous climatological reports obtained on much shorter observations. It is important to note that the E3 appears as a zonal wavenumber 4 (wave-4 or WN4) longitudinal structure in the lower thermosphere when observed at constant LT. We consider that [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 in the troposphere; hence, the coupling between the troposphere and lower thermosphere is carried out through this nonmigrating tide. Similarly to the DE3, the DE2 appears as a zonal wavenumber 3 (wave-3 or WN3) longitudinal structure in the lower thermosphere at constant LT. Therefore, these nonmigrating tides, as well as other large nonmigrating ones, can generate longitude structures when they are observed at constant LT [28; 50]. To understand why the nonmigrating tides can produce different longitudinal structures, let us consider the main difference between the migrating and nonmigrating tides. In general, the atmospheric tides can be expressed generally in the form:  
\[\mathrm{C_{ks}}\cos\left[\mathrm{k}(2\pi/24)\mathrm{t}-\mathrm{s}\lambda- \gamma_{\mathrm{ks}}\right] \tag{1}\]  
where \(t\) is universal time in hours, \(\lambda=\) longitude, \(k=\) number of the diurnal harmonic, \(\gamma_{\mathrm{ks}}=\) tidal phase, and \(s\) is zonal wavenumber; the latter is positive when the tide propagates eastward, it is negative at westward propagation and \(\mathrm{s}=0\) at zonally symmetric (or standing) tide. It has been mentioned before that the longitudinal structures are seen at fixed local time. If the general tidal expression (1) is converted from universal time to a local time frame by having in mind that \(\mathrm{t}=\mathrm{t}_{\mathrm{LT}}-24/2\pi\), then we get:  
\[\mathrm{C_{ks}}\cos\left[\mathrm{k}(2\pi/24)\mathrm{t}_{\mathrm{LT}}-(\mathrm{ k}+\mathrm{s})\lambda-\gamma_{\mathrm{ks}}\right] \tag{2}\]  
Migrating tides propagate westward (\(\mathrm{s}<0\)) with the apparent motion of the Sun, and are thus Sun-synchronous and longitude-independent when observed at constant local time. This means that the zonal wavenumber, \(\mathrm{s}\), is equal to the number of the diurnal harmonics, \(\mathrm{k}\), but has a negative sign. Therefore \(\mathrm{k}+\mathrm{s}=0\) indicating that the migrating tides are longitudinally independent. Nonmigrating tides are excited by zonally asymmetries (i.e., longitudinally dependent absorbing species) hence, they are longitudinally dependent and their zonal wavenumber, \(\mathrm{s}\), is not equal to the number of the diurnal harmonics, \(\mathrm{k}\), i.e., \(\mathrm{k}+\mathrm{s}\
eq 0\). The expression (2) indicates that an observed longitudinal structure in satellite data cannot be related unambiguously to a certain tidal component because it is consistent with any values of \(\mathrm{s}\) and \(\mathrm{k}\) for which holds \(|\mathrm{s}+\mathrm{k}|\) is equal to the corresponding structure number. First, WN4 and WN3 longitudinal structures in the lower thermosphere have been reported by [PERSON] and [PERSON], 2008 [86].