# Mechanisms Underlying the Changes in Sporadic E Layers During Sudden Stratospheric Warming
###### Abstract  
During sudden stratospheric warming (SSW) events, significant modifications occur, not only in the neutral atmosphere, but also in the ionosphere. Specifically, sporadic E layers in the mesosphere and lower thermosphere regions significantly disrupt satellite communication. Although research has frequently focused on ionospheric alterations during SSW events, detailed studies on sporadic E layers remain limited. Examining these variations during SSW events could enhance our understanding of the interaction mechanisms between the ionosphere and the neutral atmosphere, and provide insights into the patterns of sporadic E layer alterations. This study analyzed the behavior of sporadic E layers during the 2008/2009 winter SSW period using data from three Japanese stations and satellite observations. The principal findings included the following: (1) The enhancement in the critical frequency of the sporadic E layers was most notable following the transition from easterly to westerly winds at 60\({}^{\circ}\)N at a 10 hPa altitude, accompanied by quasi 6-day and quasi 16-day oscillations in frequency. (2) The daily average zonal and meridional wind speeds in the MLT region also exhibited quasi 6-day and quasi 16-day oscillations, aligning with the observed periodicities in the critical frequency of the sporadic E layers. (3) Planetary waves were shown to modulate the amplitude of diurnal and semidivantal tides, influencing the sporadic E layers. Furthermore, a wavelet analysis of foEs data with a time resolution of 0.25 h demonstrated that planetary waves also modulate the frequency of diurnal tides, thereby affecting the sporadic E layers. This research contributes to a deeper understanding of the formation mechanisms and prediction of sporadic E layer behavior. sudden stratospheric warming; sporadic E layers; planetary waves 20241512581012581012581012581010 September 202 and the amplitude of the signals, consequently degrading data quality and diminishing the functionality of GNSSs for navigation and measurement purposes. Despite the critical need for forecasting of sporadic E layers, accurately predicting their intensity and geographical distribution remains a formidable challenge in the field. Research has, however, identified some consistent patterns in sporadic E layers. Tidal winds in the mesosphere and lower thermosphere (MLT) region are a major dynamic factor influencing the occurrence of these layers. The intensity of sporadic E layers correlates strongly with distinct tidal wind characteristics, primarily including diurnal [7], semidiurnal [8], terdiurnal [9; 10], and quarter-diurnal tidal features [11; 12], with the diurnal and semidiurnal components being the most pronounced. The latter two features are significantly weaker. Additionally, observational data extensively indicate that sporadic E layers predominantly occur in mid-latitude regions during the summer, with reduced activity in spring and autumn, and minimal occurrences in winter [13]. However, wind shear theory does not account for instances where the intensity of tidal winds and the strength of sporadic E layers are asynchronous [14; 15]. Reference [16] suggested that the concentration of metallic ions in the ionosphere may be a principal factor driving these seasonal variations, demonstrating a strong correlation between daily mean meteor counts and daily mean foEs values. SSW constitutes a major meteorological phenomenon occurring in the polar stratosphere during winter. Throughout these events, the polar stratospheric temperature can surge by tens of degrees within mere days, often surpassing temperatures observed in mid-latitude areas. Simultaneously, significant modifications occur in the wind fields; specifically, the dominant westerlies (or easterlies) may rapidly weaken or even reverse, becoming easterlies (or westerlies) [17]. The consensus in the scientific community is that SSW events arise due to intensified interactions between planetary waves and the zonal mean flow [18].