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During spring and autumn and at low and middle latitudes, the westward winds below HT ht 45 km or above HT ht 70 km surround the eastward winds at HT ht 45-70 km. Among the composite years, the eastward differences with peaks of HT ht 45 m s HT ht occur at HT ht 60-80 km during May-August in the SH. During spring (March, April) and autumn (September, October), the westward winds, which occur at low and middle latitudes and below HT ht 45 km or above HT ht 70 km, are separated by eastward winds at HT ht 45-70 km. 5b and c) vary from HT ht 3 to HT ht 8 m s HT ht with increasing heights. [Extracted from the article]

Tidal and Planetary Wave (PWs) amplitudes are strongly influenced by Sudden Stratospheric Warming (SSW) events. A nonlinear interaction between the tidal winds and planetary waves during the SSW may contribute to the intensification of sporadic-E (Es) layers in the lower thermosphere. This work investigated the relationship between SSW events in the Northern Hemisphere and the Es layer occurrence at low latitudes in the Brazilian sector. We used data from digital ionosondes installed in the observatories of Araguatins (ARA, 5.65° S; 48.12° W; dip lat. −5.44°) and São José dos Campos (SJC, 23.18° S; 45.89° W; dip lat. −21.37°) to analyze the Es layers. Additionally, we used the temperature, zonal wind, and PWs data at high latitudes in the Northern Hemisphere during the major SSW event that occurred in February/2018 and during the events of Dec/2018–Jan/2019 and Dec/2020–Jan/2021. The results showed a maximum frequency peak of 20 MHz (∼5 × 106 electrons.cm−3) at ARA and SJC during these SSW events. The large values of ftEs , fbEs , and electronic densities were observed between 100 and 115 km height in the E s f / l type layers during daytime or nighttime periods. The results also showed that the number of large values of ftEs , fbEs , and electronic density of the Es layer was much higher in ARA than in SJC, in general. The wavelet power spectrum analyses of the ftEs and fbEs showed a periodicity of 2-days before and after the central day of the SSWs events at the station of ARA, with three prominent peaks in the 2018/2019 event. At the SJC station the quasi-2-day periodicity in the wavelet analyses of the ftEs was observed after the central day in all three SSW events, with a peak before the central day during the 2020/2021 event. • Tidal and Planetary Wave (PWs) dynamics are strongly modified during SSW events. • The nonlinear interaction between tides and PWs may contribute to the formation of strong Es layers. • Wavelet analysis of the ftEs and fbEs parameters showed the presence of quasi-2- and quasi-6-day periodicities. [ABSTRACT FROM AUTHOR]