# Comparison of the Heights of Sporadic E Layers and Vertical Ion Convergence Parameters
## 3 Results and Discussion
### The Descending Rates of Es Layers and IVN  
Figure 4 presents the zonal averaged height-local time distributions of EsOR at different latitudes and seasons, derived from the S4 index data of COSMIC-1. The height of the most Es occurrence is from \(\sim\)110 km to \(\sim\)95 km, with local time at mid-latitude. Notably, there is a clear seasonal pattern observed through horizontal comparison. Es layers are predominantly observed in summer, with rare occurrences in winter. Additionally, Figure 4 illustrates the diurnal and semidiurnal variations in EsOR and the corresponding heights. The diurnal variation prevails at lower latitudes, while the semidiurnal variation takes precedence at mid-latitudes. These findings align with prior research, attributing these patterns to the influence of tides on neutral horizontal winds [7; 15; 37; 12]. Simultaneously, Figure 5 illustrates the zonal averaged height-local time distributions of the IVN occurrence rate, calculated from the WACCM-X wind data. The height of the most IVN occurrence is from less than 120 km to \(\sim\)97 km with local time at mid-latitude. IVN tends to occur more frequently in summer compared to other seasons. Similarly, diurnal and semidiurnal variations, along with their latitudinal distributions, can be discerned in the height variation and occurrence rate of IVN. These findings highlight the consistency between the variations in IVN height and Es occurrence. Figure 2: Scatter density diagram of the height of Es and IVN in the low- and mid-latitudes, 2014. The magenta dashed lines display the diagonals. They represent southern mid-latitude (**i**–**l**), low-latitude (**e**–**h**), and northern mid-latitude (**a**–**d**), respectively, from bottom to top, and represent March–May (**a**,**e**,**i**), June–August (**b**,**f**,**j**), September–November (**c**,**g**,**k**), and December–February (**d**,**h**,**l**), respectively, from left to right. The results of this study suggest that Es layers occur at the height of IVN and are dragged down by IVN, aligning with the results reported by [PERSON] [22]. Simulation studies propose that a thin, high-density metal ion layer, generated under the wind shear theory, stabilizes at roughly the height of IVN within thirty minutes [22; 23]. It is worth noting that Es layers will be stationary while Es layers are down below 100 km in Figure 4. However, the descent of IVN is continued in Figure 5. [PERSON] et al. (2023) and [PERSON] et al. (2023) reported a similar phenomenon; they attributed the phenomenon to that of the gradient of the ratio of the ion-neutral collision frequency to the ion gyrofrequency, which plays an important role in the formation of the Es layers at a lower altitude [22; 24]. The height-local time distributions of the southern hemisphere and near-equatorial regions show the same result as above and are displayed in Figures S1-S4 of Supplementary Materials. Furthermore, the descent rates of both IVN and Es layers were estimated based on their height-local time distributions. Figure 6 illustrates the descent rates of Es and IVN at different latitudes. In low- and mid-latitudes, the descent rates of Es layers range from 0.25 to 3 km/h. As latitude increases, the rate of Es descent will gradually increase. This trend is separated into two phases: the descent rate is below 1 km/h at below \(\sim\)30 degrees; the descent rate is 1-3 km/h and increases faster at above 30 degrees than that of below \(\sim\)30 degrees. This pattern aligns with the latitudinal distribution of IVN's descent rate. This is due to the dominance of diurnal and semidiurnal tides at low- and mid-latitudes, respectively [38]. Notably, previous studies considered VICmax as the height of Es layers. However, this paper suggests that IVN can better represent the height variations of Es layers. Figure 3: Scatter density diagram of the height of Es and VICmax in the low- and mid-latitudes, 2014. The magenta dashed lines display the diagonals.