## 1 Introduction
For example, if we consider only diurnal and semidiurnal tides, the WN4 structure can be forced by DE3, DW5, SW6, SE2, and SPW4 (according to the standard nomenclature S corresponds to semidiurnal tide, while W/E to westward/eastward propagation; SPW means the stationary planetary wave), and the WN3 structure by DW4, DE2, SW5, SE1, and SPW3 [50]; any of these waves could, in principal, contribute to the ionosphere WN4/WN3 variability. The relative importance of each tide depends on its magnitude in the E-region, as well as its latitudinal shape and vertical wavelength [28]. The formation mechanism of the WN3 structure, observed mainly during the Northern hemisphere (NH) winter [26; 63], has not yet been clarified. [PERSON] et al., 2008 [64], have already underlined that the WN3 is mainly due to the DE2, but the contribution of the other above-mentioned tides and SPW3 cannot be excluded. The significant advantage of the used by [PERSON] and [PERSON], 2010 [26], data analysis approach is that it allows assessing the possible contributions of all waves that can force the WN4/WN3 structures, and this has been done in [PERSON] and [PERSON], 2011 [21]. The authors showed that the ionospheric response from the superposition of all the above-mentioned waves, having contribution to the WN4 (WN3) longitudinal structure, forms the same longitudinal structure as that of the nonmigrating DE3 (DE2) tide, but with double (1.5 time stronger) amplitude. Later, this result was supported by using the GAIA model [57], and, in this way, provides evidence that the ionospheric WN4 (WN3) longitudinal structure is not generated only by the DE3 (DE2) tide, as it has been often assumed. It is worth underlying that all the above-mentioned observational evidence illustrating the MLT wave impacts on the ionosphere and its response are based predominantly on case studies or quite limited time periods of observations. The basic tasks of the present study are: (i) to investigate the climatology, seasonal, and interannual variability of those nonmigrating tides in the MLT region which are largely responsible for the global longitudinal structures in the ionosphere; the mentioned tidal features to be obtained by using long-term observations; (ii) to clarify the main features of the climatologically mean longitudinal structures seen in the lower thermospheric temperature field; and (iii) to elucidate the basic features (seasonal, latitudinal, asymmetry according to the equator) of the climatologically mean longitudinal structures observed in the ionospheric total electron content (TEC). For this purpose, the following data sets are used: (i) the wave forcing from below (e.g., the lower thermospheric waves) is defined by using the SABER/TIMED temperatures for the period of time January 2002-December 2022, i.e., the full 21 years; this period covers almost two solar cycles; and (ii) the ionospheric response is considered by the global TEC data for the same time interval of 21 years. In addition to the climatology of the ionospheric longitudinal structures, this paper also presents the climatology of the well-known Weddell Sea Anomaly (WSA); by analyzing the F3/C electron density profile data for December 2008, some evidence is found that not all tidal components contributing to the production of the WSA anomaly are in situ generated.