## 3 Results
### Average Electron Density Profile Comparison  
The average EDPs were calculated by first finding the average \(N_{e}\) in one-kilometer increments from 90 to 120 km for the ionograms and 60 to 120 km for the GNSS-RO profiles. The lower thresholds were chosen in order to encompass the minimum altitude for each profile, generally 90 km for ionograms and 55-60 km for the GNSS-RO profiles. The upper threshold of 120 km was selected due to the fact that some of the GNSS-RO profiles have a maximum altitude slightly lower than 130 km. This 120 km encompasses all GNSS-RO profiles and is well above the average \(hmE\). The average \(N_{e}\) for each altitude value was calculated using \(N_{e}\) measurements from each profile corresponding to that altitude. Due to the relatively small number of profiles for each site, the average EDP could not be calculated separately for season, time-of-day, etc., and here we show the overall average for all conditions. However, the standard deviation of these values was calculated for each altitude in the same range to estimate variability and uncertainty. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Site** & **Hermanus** & **I-Cheon** & **Gakona** & **Fortaleza** & **Combined** \\ \hline \(\Delta\)alt avg (km) & 2.8 & 4.5 & 3.9 & 3.3 & 3.5 \\ \(\Delta\)alt stdev (km) & 5.4 & 3.5 & 1.8 & 2.7 & 4.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The average and standard deviation of the altitude difference (\(\Delta\)alt) at \(fmin\) for each site and for the combined results. The altitude difference at \(fmin\) was calculated for each profile and was used to shift the entire ionosonde profile. Positive values indicate the ionosonde profile was shifted up in altitude. Figure 5 shows the average GNSS-RO and ionosonde derived EDPs for Hermanus. For the unshifted profiles, the ionogram \(N_{e}\) is larger than the GNSS-RO profiles in the primary area of interest between \(fmin\) and \(hmE\). The ionosonde estimates have more variability, as seen by the width of the error bars, but have a clear average E-region peak at 106 km, above which the \(N_{e}\) is almost constant with altitude. In contrast, the RO profiles show a steady increase in electron density with respect to altitude above \(hmE\), which is due to the large number of profiles without a clear E-region peak. In the shifted average EDP, the profiles align better. However, the RO profile remains slightly higher in altitude in most of the region of interest. In both cases, it is clear to see the ionosonde profile \(N_{e}\) rapidly decreases to zero below \(fmin\), while the GNSS-RO profile measures the D- to E-region transition. Figure 6 shows the average EDPs for I-Cheon. There is less variability in both the average ionosonde and GNSS-RO EDPs due to the fact that there were significantly fewer profiles used for the comparison (the fewest of all the sites). There is a clear average E-region peak at 105 km for the ionosonde, with a nearly vertical density profile above \(hmE\). Of note, the \(N_{e}\) at the average \(hmE\) is higher for I-Cheon than it is for Hermanus, both of which are mid-latitude sites. Once the profiles are shifted, the average profiles align closely from \(fmin\) throughout most of the E-region, but they begin to diverge near \(hmE\). The GNSS-RO average EDP does not have a clear E-region peak, and density steadily increases in altitude whereas the ionosonde profile begins to increase slowly with altitude up to \(hmE\). This is due to the fact that the E-region peak was not evident in the majority of the GNSS-RO profiles for this site. The shifted ionosonde EDP also appears to be better aligned with the GNSS-RO below \(fmin\); however, this comes from only a few of the profiles having \(N_{e}\) measurements below 90 km. Once the profile is shifted, these are now above 90 km, thus they appear in the calculation for average density. Figure 4: Shifted individual electron density profile comparison examples.