# Mechanisms Underlying the Changes in Sporadic E Layers During Sudden Stratospheric Warming
## 3 Results
### Analysis of Wind Field Fluctuations
Panels (**a–d**) show the daily average zonal winds, with corresponding latitude ranges of 25–35\({}^{\circ}\) N, 25–35\({}^{\circ}\) N, 30–40\({}^{\circ}\) N, and 30–40\({}^{\circ}\) N, and altitude ranges of 107.5–112.5 km, 110–115 km, 107.5–112.5 km, and 110-115 km. Panels (**e–h**) depict the 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 97.5–102.5 km, 100–105 km, 97.5–102.5 km, and 100–105 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 18 days, 19 days, 18 days, 20 days, 20 days, 15 days, 15 days, and 15 days, respectively. Furthermore, it is apparent that, for daily average zonal wind speeds, the altitude of the quasi-six-day wave was lower than that of the quasi-sixteen-day wave. However, this clear distinction was not observed for the average meridional wind speeds. Moreover, a comparative analysis of Figures 6 and 7 indicates that the intensity of the quasi-sixteen-day waves surpassed that of the quasi-six-day waves, which aligns with the intensity patterns of the fluctuations in daily average foEs at the three stations. To further investigate the relationship between wind fluctuations and variations in foEs, the relative daily mean vertical motion velocity of Fe+ at 30\({}^{\circ}\) N at the 110-115 km altitude was calculated. This velocity was determined by the ratio of the daily mean vertical motion velocity of Fe+ for each day following 9 January to that on 1 January (with positive values indicating upward motion and negative values indicating downward motion), denoted as RV, as illustrated in Figure 6a. The calculation method is presented in Equations (5)-(8), using the method referenced in Reference [38]. \(\omega\) is the vertical motion velocity of iron ions. \(n_{\rm N_{2}}\), \(n_{\rm O_{2}}\), \(n_{\rm O}\), and \(m_{i}\) are, respectively, the number density of \(N_{2}\), the number density of \(O_{2}\), the number density of the oxygen atom, and the mass of the iron atom. The number densities of three neutral gases were derived from the empirical model NRLMSISE-00. The significance of the parameters I, V, U, B, and q is as follows: the magnetic dip angle, zonal wind, merdional wind, horizontal magnetic intensity, and elementary charge. I and B were sourced from the model International Geomagnetic Reference Field (the version was IGRF-12). \[w=\frac{rcosI}{1+r^{2}}V+\frac{sinIcosI}{1+r^{2}}U \tag{5}\]  
\[r=v_{in}/\omega_{i} \tag{6}\]  
\[v_{in}=\left[\frac{1.8106}{\sqrt{A(A+28)}}n_{N_{2}}+\frac{1.8398}{\sqrt{A(A+3 2)}}n_{O_{2}+}\frac{0.017}{\sqrt{A(A+30)}}n_{O}\right]*10^{-14} \tag{7}\]  
\[\omega_{i}=\frac{qB}{m_{i}} \tag{8}\]  
A comparison with Figure 3 reveals that a greater absolute value of the vertical motion velocity for downward-moving Fe+ correlated with intensified Es layers. Furthermore, it is evident from Figure 8b that the RV at 30\({}^{\circ}\) N at the 110-115 km altitude displayed fluctuations with a period of over 17 days, which aligned with fluctuations in the wind and Es layers. Consequently, it is posited that the quasi-six-day and quasi-sixteen-day fluctuations in daily average foEs at these stations were influenced by planetary waves. However, this does not suggest that planetary waves directly modulate sporadic E layer changes through a wind-shear mechanism. The specific mechanisms underlying this relationship will be explored in the subsequent section. Figure 8: The relative daily mean vertical motion velocity of Fe+ (RV) at 30\({}^{\circ}\) N at 110–115 km altitude and its wavelet spectra. The blue and white dotted lines indicate the time when the winds shifted from easterly to westerly at 60\({}^{\circ}\) N at 10 hPa altitude.