## 6 Weddell Sea Anomaly  
The Weddell Sea Anomaly (WSA) appears in the region near the Weddell Sea and Antarctica peninsula and it characterized by the fact that the electron densities recurrently maximize during the local night-time in the austral summer [96]. This event was first detected in ionosonde measurements by [PERSON] and [PERSON], 1958 [97]. However, the satellite observations of the WSA allowed its global structure to be examined more deeply [98; 99]. The major physical mechanisms that have been suggested for the WSA formation are an equatorward neutral wind, an electric field, the photoionization, and the downward diffusion from the plasmasphere. A widely accepted explanation for the mechanism generating the WSA was reported by [PERSON] and [PERSON], 1978 [96], who attributed the WSA to a combination of thermosphere neutral winds and magnetic declination effects in the region of the Weddell Sea. The authors suggested that the summer neutral wind, directed from the higher latitudes to the equator, acts to transport plasma equatorward and upward along the magnetic field lines, where the plasma persists for a longer period of time, due to the reduced loss rate at higher altitudes. The magnetic dip angle around the Weddell Sea region is closer to 45\({}^{\circ}\), and this allows the largest effective wind to be observed there. This leads to the largest amount of plasma drift along the field lines, causing an enhancement in the ionization at this longitudinal zone from plasma transported upward and equatorward from the summer high latitudes. Similar results were obtained by [PERSON] et al., 2009 [100], based on more than two years of F3/C electron density profiles at low solar activities. It has been mentioned before that, although traditionally applied mainly to the dynamics of the neutral middle atmosphere, the recent years have seen a growth in interest of applying the atmospheric tidal analysis to thermospheric and ionospheric parameters suggested for the first time by [PERSON] and [PERSON], 2010 [26]. In the context of tides in the ionosphere and thermosphere [PERSON] et al., 2013 [101], used the SAMI3 model coupled to the TIEGCM neutral winds to reproduce a realistic WSA, including the feature of eastward drift in a constant local time frame that was found in previous observations. Using Fourier analysis, it was found that the salient spatial and temporal features of the simulated WSA, including the eastward zonal drift and nighttime enhancement in the Weddell Sea region, could be attributed to a zonally symmetric diurnal tide, D0, responsible for 35% of the peak electron density anomaly at 300 km. The authors noted that the D0 component was also present in the vertical neutral winds along magnetic field lines in the southern mid to high latitude of the empirical Horizontal Wind Model 93, with phase structure suggesting in situ thermosphere generation. For the first time, however, the WSA has been successfully predicted by the global empirical TEC model established by [PERSON] et al., 2013 [102], thanks to the nonmigrating tides and SPWs involved in it. The basic aim of this sub-section is to establish whether this long-known anomaly, which has so far been studied mostly on time-limited observations, can be observed in this case on a large statistics, and if so, what is its climatology. Only December and January will be considered because these are the months when the WSA most often manifests itself. The first step is to define the main tidal and SPW components which contribute to the WSA production. Having in mind the main features of the WSA, briefly described above, such components among the tides could be only some diurnal tides with amplifications during austral summer and with phases maximizing around local midnight at mid-high southern latitudes; among the SWPs, this apparently could be only the SPW1.