## 5 Climatology (2002-2022) of Longitudinal Structures in the Ionosphere
### TEC WN4 Structure  
The climatology of the TEC WN4 structure is calculated by the superposition of the same climatologically mean nonmigrating tides (and SPW4) as those in the lower thermosphere, i.e., DE3, SE2, and TE1. Figure 12a displays the LT variability of the climatologically mean (2002-2022) TEC WN4 structure at different latitudes, shown in the upper side of each plot, during August. Similarly to the climatology of WN4 in the lower thermosphere (Figure 9a) here, also, the largest magnitudes are seen in August and September. However, while in August, the WN4 largest magnitudes are seen at latitudes of \(\pm\)(20-30\({}^{\circ}\)), and those in September are at latitudes of \(\pm\)(40-50\({}^{\circ}\)). Keeping in mind that the EIA in modify latitude is located around \(\pm 30^{\circ}\) then the largest WN4 structures occur in August, and this is the reason this month to be chosen for Figure 12a. The main features of the climatologically mean TEC WN4 structure can be summarized as: (i) although in this study we work with absolute tidal amplitudes, the seasonal dependence of the TEC WN4 structure is the same as that of the SABER temperature one in the lower thermosphere; this is mainly due to the similar seasonal variation of the SABER DE3 to the TEC semiannual one; (ii) there is a clear hemispheric asymmetry, as the SH structure (with the largest magnitude of 3.7 TECU) is stronger than the NH one (\(\sim\)1.8 TECU); this feature is similar to the SABER temperature one, but at latitudes of \(\pm 30^{\circ}\); (iii) at all latitudes, the WN4 structures disappeared or significantly weaken (as at 40\({}^{\circ}\) N) around 4-6 LT; this may be due to a change of the production mechanism; (iv) the strong WN4 structures are seen between 8-9 and 22-23 LT, and at all latitudes their maxima are centered around the longitudes: \(-180^{\circ}\), \(-90^{\circ}\), \(0^{\circ}\), \(90^{\circ}\), and \(180^{\circ}\); and (v) there are WN4 structures between 00 and 04 LT as well, but their maxima are centered \(-20\)-\(30^{\circ}\) eastward of those observed during the daytime; these structures are stronger in the NH than those in the SH. It is worth noting that besides August and September, large magnitudes are seen in June (over the equator) and May (at 10\({}^{\circ}\) N). Figure 12b presents the latitudinal dependence of the tidal and SPW4 contribution to the TEC WN4 structure in the months when it has large amplitudes; these are August (upper left plot), September (upper right plot), March (bottom left plot), and June (bottom right plot). These results confirm the already known features that the DE3 also has the largest contribution to the ionospheric WN4 structure, but in this case it is followed by the SPW4; the latter contributes the most in March and June. The third contributor is the SE2 while the TE1 is the weakest one. Figure 12c demonstrates the latitude-time climatological structure of the TEC SPW4 amplitude (left plot) and the TEC SE2 amplitude (right plot); both plots reveal clear hemispheric asymmetry, indicating that both waves SPW4 and SE2 are stronger in the SH. Keeping in mind that the same asymmetry exists in the DE3 electron density response at an altitude of 400 km [56] and in the TEC DE3 climatology in this study, the reason for the observed hemispheric WN4 asymmetry can be clarified. According to [PERSON] et al., 2014 [91], the DE3 and SE2 are nonmigrating tides which can propagate from the lower thermosphere (110 km) up to the upper thermosphere at ~400 km. [PERSON] and [PERSON], 2012 [55], show that the DE3 and SE2 responses in the F3/C electron density at altitude of 400 km.