## 7 Summary
The climatology of the ionospheric structures clearly indicates that the TEC WN3 (Figure 13) is the strongest one, with a maximum magnitude of 5.9 TECU located on the Southern crest of the EIA (at \(-\)30\({}^{\circ}\) modify latitude); it also shows a hemispheric asymmetry, as the SH structure is stronger than the NH one, but only at latitudes of \(\pm\)(30-50\({}^{\circ}\)). The main contributors to this TEC structure turns out to be first the TEC SPW3 followed by the TEC DE2. The second strongest TEC structure is the WN2 one (Figure 14), with the largest magnitude of 5.4 TECU seen on the Northern ridge of the EIA (at 30\({}^{\circ}\) modify latitude). Generally, this structure also reveals a hemispheric asymmetry, but in this case, the NH structure is stronger than the SH one, with an exceptionat \(\pm\)20\({}^{\circ}\). In this case, the TEC SPW2 is the strongest contributor, followed by the TEC DE1. The weakest TEC structure is the WN4 one (Figure 12) that has the largest amplitude of 3.7 TECU observed on the Southern crest of the EIA. It displays a clear hemispheric asymmetry at all latitudes, as the SH structure is stronger than the NH one. In general, the TEC DE3 is the main contributor, while the TEC SPW4 is the second one, to the production of the TEC WN4 structure. The last result of this paper is presented in Section 6, and it is related to the well-known Weddell Sea Anomaly. Its detailed investigation revealed that not all wave components leading to the WSA production are in situ generated; the non-migrating DW2 tide is a propagating from below tide. This study demonstrates, for the first time, the climatology of the WSA based on the full 21 years, as well as its very good reconstruction (Figure 18). This result is also supplemented by the assessment of the contribution of each climatologically mean wave component in building up this anomaly. In conclusion, we note that, by means of a detailed analysis with the same method of two long-term data sets representing the wave forcing from the MLT region and the respective ionospheric TEC response, we present valuable climatological evidence for recognizing regular TEC structures generated by lower atmospheric weather systems. It is worth noting that the longitudinal TEC structures considered in this paper are weaker than geomagnetic anomalies, but, in contrast, they are almost constantly present in the ionosphere and have well-defined seasonal and latitudinal dependences; the latter make them predictable. Additionally, the MLT tidal diagnostics, based on the large statistics presented in this overview paper, provides the necessary observational constraints for the numerical simulations. Conceptualization, D.P. and P.M.; methodology, D.P. ; software, P.M.; validation, D.P. and P.M.; formal analysis, D.P. ; investigation, D.P. ; resources, P.M.; writing--original draft preparation, D.P. ; writing--review and editing, D.P. and R.B. ; visualization, D.P., P.M. and R.B. ; supervision, D.P. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Science Fund under Competition for financial support of basic research projects--2020, grant No KP-06-H44/2 from 27 November 2020 \"Space weather over a period of the century solar activity descending\". Not applicable. The SABER temperature data version 2.0, level 2A, are downloaded from: [[https://saber.gats-inc.com/data.php](https://saber.gats-inc.com/data.php)]([https://saber.gats-inc.com/data.php](https://saber.gats-inc.com/data.php)) (accessed on 10 April 2024). The vertical TEC maps generated with the NASA JPL (Jet Propulsion Laboratory, California Institute of Technology, USA) IGS Ionosphere Center are provided by: [[https://sideshow.jpl.nasa.gov/pub/iono_daily/IONEX_rapid](https://sideshow.jpl.nasa.gov/pub/iono_daily/IONEX_rapid)]([https://sideshow.jpl.nasa.gov/pub/iono_daily/IONEX_rapid](https://sideshow.jpl.nasa.gov/pub/iono_daily/IONEX_rapid)) (accessed on 10 April 2024).