## 5 Climatology (2002-2022) of Longitudinal Structures in the Ionosphere
### TEC WN3 Structure  
In this sub-section, again the climatology of the TEC WN3 structure is calculated by the superposition of the same climatologically mean nonmigrating tides (and SPW3) as those in the lower thermosphere, i.e., DE2, DW4, SE1, and T0. Figure 13a shows the LT variability of the climatologically mean (2002-2022) TEC WN3 structure at different latitudes, shown in the upper side of each plot, during March. We underline that, in this case, the seasonal dependence of the TEC WN3 structure is different from that of the SABER temperature WN3 one. The reason is that the seasonal behavior of the SABER DE2 tide is very different from the semiannual TEC variability, and the latter has strong impact on the TEC DE2 response. We consider that the TEC semiannual variability is consistent with the known seasonal variation of the neutral thermosphere connected to changes in composition [93; 94]. Similarly to the TEC WN4, here, also, March is chosen because the largest peak of the TEC WN3 with magnitude of 5.9 TECU is located at the EIA. The main features of the climatologically mean TEC WN3 structure can be summarized as: (i) there is a clear hemispheric asymmetry as the SH structure is stronger than the NH one; this asymmetry, however, is well-seen mainly in March; (ii) if we consider the strongest TEC WN3 at all latitudes, then, such as in March, asymmetry is observed at latitudes of \(\pm\)(30-50\({}^{\circ}\)), while at \(\pm\)(10-20\({}^{\circ}\)) it is reversed; we consider the fact that the SABER WN3 structure does not reveal a clear asymmetry; (iii) at all latitudes, strong WN3 structures can be distinguished predominantly between 08 LT and ~20 LT, as their maxima are seen at ~16 LT, with an exception at latitude of 40\({}^{\circ}\) N where it is at ~14 LT; (iv) while in the SH, the WN3 maxima are centered at longitudes of \(-\)120\({}^{\circ}\), 0\({}^{\circ}\), 120\({}^{\circ}\) those in the NH are on the average 30\({}^{\circ}\) westward, i.e., \(-\)150\({}^{\circ}\), \(-\)30\({}^{\circ}\), 90\({}^{\circ}\); and (v) there are WN3 structures between 00 LT and 03-04 LT as well, but in general they are weak. Besides March, large TEC WN3 magnitudes are seen in April, September, and October. Figure 13b presents the latitudinal dependence of the tidal and SPW3 contribution to the TEC WN3 structure in the months when it has large amplitudes; these are March (upper left plot), April (upper right plot), October (bottom left plot), and September (bottom right plot). These results show that both the DE2 and SPW3 are the main contributors for the production of this structure. However, the SPW3 is larger than the DE2 contributor. The third contributor is DW4 followed by SE1; their basic effect is in October and partly in September. Figure 13c demonstrates the latitude-time climatological structure of the TEC SPW3 amplitude (left plot) and the TEC DW4 amplitude (right plot); both plots reveal opposite hemispheric asymmetry. The TEC SPW3 has largest amplitude of 2.9 TECU, while the climatology of TEC DE2 tide is 2.1 TECU, and this is the reason for the larger contribution of the TEC SPW3. [PERSON] et al., 2014 [91], reported that the DE2 and SE1 are nonmigrating tides which can propagate from the lower thermosphere (110 km) up to the upper thermosphere at \(\sim\)400 km. [PERSON] and [PERSON], 2010 [21], showed strong evidence that the F3/C DE2 seen in the \(h_{m}F2\) is a response of the SABER temperature DE2 at altitude of 110 km, while the SABER temperature is 110 km, which is consistent with the SABER temperature at 110 km.