# Mechanisms Underlying the Changes in Sporadic E Layers During Sudden Stratospheric Warming
## 3 Results
### Analysis of Wind Field Fluctuations  
Wind field data were obtained from the TIMED satellite, employing the methodology in reference [33]. This approach involves treating data collected within identical latitude and altitude ranges as observations from the same location. Utilizing this method, 16 data bins were defined, as detailed in Table 1. For each data bin, daily average zonal and meridional winds were computed from 9 January to 28 February 2009. Subsequently, using the methodology previously described, a wavelet analysis was performed on the daily average zonal and meridional winds for this period. The resulting wavelet spectra are presented in Figures 6 and 7. Figure 6a-h demonstrate that following the transition from easterly to westerly winds, both the daily average zonal and meridional winds exhibited fluctuations with a period of approximately 7-8 days. Figure 7a-h show that after the wind shift, both wind components displayed fluctuations with a period of approximately 15-20 days. It is significant to note that, while the fluctuation periods varied among the different data bins, they consistently corresponded to the same category of planetary waves. Recent studies classified 5-8-day and 12-20-day fluctuations as quasi-six-day and quasi-sixteen-day waves, respectively [34; 35; 36; 37]. Following the shift from easterly to westerly winds, a quasi-six-day wave in daily average zonal and meridional wind speeds was observed twice (Figure 6). The occurrence of the first quasi-six-day wave closely aligned with the appearance of approximately six-day fluctuations in the daily average foEs at the three stations, as depicted in Figure 4a-c. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Data Bin Number** & **Latitude Range (\({}^{\circ}\)N)** & **Altitude Range (km)** \\ \hline
1 & 25–35 & 92.5–97.5 \\
2 & 25–35 & 95–100 \\
3 & 25–35 & 97.5–102.5 \\
4 & 25–35 & 100–105 \\
5 & 25–35 & 102.5–107.5 \\
6 & 25–35 & 105–110 \\
7 & 25–35 & 107.5–112.5 \\
8 & 25–35 & 110–115 \\
9 & 30–40 & 92.5–97.5 \\
10 & 30–40 & 95–100 \\
11 & 30–40 & 97.5–102.5 \\
12 & 30–40 & 100–105 \\
13 & 30–40 & 102.5–107.5 \\
14 & 30–40 & 105–110 \\
15 & 30–40 & 107.5–112.5 \\
16 & 30–40 & 110-115 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Information of data bins. Furthermore, the timing of the second quasi-six-day wave corresponded with the six-day fluctuations in daily average foEs observed at the Yamagawa station. Similarly, Figure 7a-h illustrate that, after the wind direction shift, the quasi-sixteen-day fluctuations in both wind components intensified and consistently matched the timing of the approximately sixteen-day fluctuations in daily average foEs at the three stations. Figure 6: Wavelet spectra of daily average wind speeds from 9 January to 28 February 2009 (frequency range: 0.1–1). Panels (**a–d**) show daily average zonal winds, with corresponding latitude ranges of 25–35\({}^{\circ}\) N, 25–35\({}^{\circ}\) N, 25–35\({}^{\circ}\) N, 30–40\({}^{\circ}\) N, and altitude ranges of 95–100 km, 97.5–102.5 km, and 100–105 km, and 100–105 km. Panels (**e–h**) depict daily average meridional winds, with latitude ranges of 25–35\({}^{\circ}\) N, 25–35\({}^{\circ}\) N, 30–40\({}^{\circ}\) N, and 30–40\({}^{\circ}\) N, and altitude ranges of 92.5–97.5 km, and 97.5–102.5 km, 92.5–97.5 km, and 97.5–102.5 km. The vertical white dashed line indicates the time when the winds shifted from easterly to westerly, and the horizontal white dashed line represents the y-coordinate corresponding to the peak value of the enclosed structure in the figure. The y-coordinates corresponding to the horizontal white dashed lines in (**a–h**) are 7.5 days, 7.5 days, 8 days, 7.5 days, 8 days, 7.5 days, and 7.5 days, respectively. Figure 7: Wavelet spectra of daily average zonal wind from 9 January to 28 February 2009 (frequency range: 0.05–0.1).