# Mechanisms Underlying the Changes in Sporadic E Layers During Sudden Stratospheric Warming
## 4 Conclusions and Discussion  
Sporadic E layers, existing as ionospheric irregularities within the mesosphere-lower thermosphere (MLT) region, significantly impact the quality of satellite communications. Consequently, further research into sporadic E layers holds practical significance. During SSW events, both the neutral atmosphere and the ionosphere undergo substantial changes. While ionospheric changes during SSW events have long been a focus of research, studies specifically addressing sporadic E layers remain limited. Investigating variations in sporadic E layers during SSW events not only aids in understanding the coupling mechanisms between the ionosphere and the neutral atmosphere, but also contributes positively to discerning patterns of change in these layers. This paper utilized data from three stations in Japan, along with satellite data, to explore the changes in and causes of sporadic E layers during the winter of 2008/2009. The main conclusions are as follows:  
(1) During the winter SSW event of 2008/2009, enhancement in the critical frequency of sporadic E layers primarily occurred following the transition from easterly to westerly winds at 60\({}^{\circ}\) N at the 10 hPa altitude. Following this shift, the critical frequency of the sporadic E layers exhibited quasi-six-day and quasi-sixteen-day fluctuations. (2) Concurrently, the daily average zonal and meridional wind speeds in the MLT region displayed quasi-six-day and quasi-sixteen-day fluctuations, which corresponded in timing with the fluctuations observed in the critical frequency of the sporadic E layers. (3) The amplitudes of the diurnal and semidiurnal tidal components of the sporadic E layers also showed fluctuations similar to the quasi-six-day and quasi-sixteen-day oscillations, influenced by planetary waves modulating the amplitudes of diurnal and semidiurnal tides. Furthermore, the wavelet spectra of the foEs data, with a time resolution of 0.25 h, indicated that planetary waves modulate the frequency of diurnal tides, thus impacting the sporadic E layers. This paper highlights the critical juncture of wind direction reversal at 10 hPa and 60\({}^{\circ}\) N for changes in the critical frequency of sporadic E layers, the MLT region wind field, and the amplitudes of diurnal and semidiurnal tidal components. This instance underscores the interconnectedness of stratospheric conditions and ionospheric phenomena. Moreover, other studies, such as those by the authors of reference [43], using artificial neural networks (SELF-ANN) to predict sporadic E layers incorporating stratospheric and tropospheric conditions as model inputs, and the authors of reference [44], utilizing COSMIC occultation data to explore the correlation between the El Nino-Southern Oscillation (ENSO) and ionospheric E region scintillations, further elucidated the impact of atmospheric conditions on sporadic E layers. Their findings showed a clear link between tropospheric ENSO changes and the mid-latitude E region S4 index, with similar spectral periods especially pronounced in the Southern Hemisphere mid-latitudes. In conclusion, the research presented in this paper significantly advances our understanding of the mechanisms behind the occurrence and forecasting of sporadic E layers. Conceptualization, H.Z. and H.F.; methodology, H.Z. and H.F.; software, H.Z. and C.X. ; validation, H.H., D.D., and G.R. ; formal analysis, H.Z. and C.X. ; investigation, H.H. and D.D. ; resources, H.Z. and G.R. ; data curation, H.Z. and H.F.; writing--original draft preparation, H.Z. ; writing--review and editing, C.X. and H.H. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding authors.