## 4 Climatology (2002-2022) of Longitudinal Structures in the Lower Thermosphere
### SABER Temperature WN2 Structure  
According to the authors' knowledge, the WN2 longitudinal structure has not been seriously investigated in the lower thermosphere. Only very recently, based on the neutral wind observations from the Michelson Interferometer for Global High resolution Thermospheric Imaging (MIGHTI) instrument onboard Ionospheric CONnections (ICON), [PERSON] et al., 2023, have studied the longitudinal structures from WN1 to WN4 in the zonal wind [88]. The ICON/MIGHTI zonal wind from version V04 data from December 2019 to January 2022 (about 2 years) were used during the daytime, when the neutral wind data can cover the altitude range of 100-300 km by combining the winds of the red line and green line. Actually, the authors did not report any clear features of the WN2 structure in the IT system, mentioning only that _\"the main wave sources of WN1 and WN2 have complex variations with altitude, latitude, and season\"_.  
Figure 10: (**a**) LT variability of the climatologically mean (2002–2022) SABER WN3 structure at different latitudes, shown in the upper side of each plot, during July; (**b**) latitudinal dependence of the tidal and SPW3 contribution in months when the SABER WN3 structure has large amplitudes: July (**upper left** plot), June (**upper right** plot), December (**bottom left** plot), and February (**bottom right** plot). The present climatological study of the nonmigrating tides based on large statics provides an excellent opportunity for the first time the WN2 longitudinal temperature structure in the lower thermosphere to be examined in detail. The WN2 structure in the lower thermosphere can be generated by DE1, DW3, S0, SW4, TW1, and SPW2 based on  
Figure 11: (**a**) LT variability of the climatologically mean (2002–2022) SABER WN2 structure at different latitudes and during different winter months; the latitudes and months are shown in the upper side of each plot; (**b**) latitudinal dependence of the tidal and SPW2 contribution in months when the SABER WN2 structure has large amplitudes: November (**upper left** plot), February (**upper right** plot), October (**bottom left** plot), and January (**bottom right** plot). \(|\mathbf{s}+k|=2\). The preliminary inspections of the WN2 structure revealed that this structure is strong predominantly during winter months. Figure 11a shows the LT variability of the climatologically mean (2002-2022) SABER WN2 structure at different latitudes and in different winter months; the latter are shown in the upper side of each plot. Similarly to the previous two cases here also the climatologically mean WN2 structure denotes the superposition of the climatologically means DE1 + DW3 + S0 + SW4 + TW1 + SPW2. The main features of the WN2 structure in the lower thermosphere (altitude of 110 km) can be summarized as: (i) unlike the WN4 and WN3 structures, which slope to the east, this WN2 structure slopes to the west; this is most likely due to the predominant influence of the nonmigrating tides propagating westward; (ii) the WN2 structure reveals clear hemispheric asymmetry as it is stronger in the SH than that in the NH; the largest magnitude of the WN2 reaches \(\sim\)13.9 K at latitude of 10\({}^{\circ}\) S making it stronger structure than the WN3 one in the lower thermosphere; (iii) at all latitudes the WN2 structures reveal two or even three enhancements; the main maxima are located between 11-12 and \(\sim\)15 LT; and (iv) at latitudes of \(\pm\)50\({}^{\circ}\), the WN2 structure almost disappears between 2-3 and 6-7 LT. Figure 11b shows the latitudinal dependence of the tidal and SPW2 contribution to the WN2 structure in the winter months when this structure has large amplitudes, as these are November (upper left plot), February (upper right plot), October (bottom left plot), and January (bottom right plot). These results clearly indicated that the SW4 has the largest contribution to the WN2 followed by DW3, S0, DE1, and SPW2; the TW1 has the weakest contribution.