## 5 Discussion  
The results reported in Section 4 revealed that, during nighttime, there are remarkable differences between \(H_{0}\) values obtained through calibrated CSES--01 and Swarm B \(N_{\rm e}\) observations and those obtained through COSMIC--1 RO profiles (see Figure 5). On the contrary, during daytime, there is good agreement with differences in magnitude localized around the geomagnetic equator (see Figure 4). We rule out the presence of bias in the \(N_{\rm e}\) topside anchor point because \(H_{0}\) values obtained with both CSES--01 and Swarm B \(N_{\rm e}\)-calibrated observations show the same spatial patterns. In fact, both LPs on CSES--01 and Swarm B should be affected by the same bias. Furthermore, the calibration procedure developed in [34] does not include any spatial variation, meaning that it cannot be the cause of the problem. This is verified by the results obtained with non-calibrated \(N_{\rm e}\) values (Figures 6 and 7), which show similar spatial patterns but with a different magnitude. A possible source of error could lie in the assumption made to apply the scale height linear approximation, i.e., in the modeled \(\mathrm{d}H/\mathrm{d}z\) values, which show large latitudinal variations during nighttime. To rule out this possibility, we re-calculated \(H_{0}\) values by directly using the NeQuick topside effective scale height of Equation (5) in the NeQuick topside representation of Equation (4). The corresponding results have been shown in Figure 8 and compared with Figures 4 and 5. Since Figure 8 was obtained with a constant value of \(\mathrm{d}H/\mathrm{d}z\), this excludes the possibility that the use of \(\mathrm{d}H/\mathrm{d}z\) values modeled through COSMIC--1 RO could bias the analysis during nighttime. This, in turn, attests to the reliability of the linear scale height assumption made in this work. After excluding potential sources of error associated with the \(N_{\rm e}\) topside anchor point and the linear scale height assumption, we looked into the possibility that the analysis may have been impacted by an incorrect representation of the F2-layer peak by the IRI model. To assess the accuracy of the F2-layer peak modeling by IRI, we compared IRI-modeled \(Nm\)F2 and \(lm\)F2 values against those recorded by COSMIC--1 for the same conditions studied in this work. We focused on the nighttime sector, where there are the greatest discrepancies between \(H_{0}\) values calculated through CSES--01 and Swarm B observations and COSMIC--1 RO profiles. Since the topside profile is anchored to the F2-layer peak point, an error in the modeling of \(Nm\)F2 can have a deep impact on modeled scale height values. With a fixed topside anchor point, an increase in \(Nm\)F2 would reduce \(H\) because, to join the topside anchor point, the electron density has to decrease at a faster vertical rate. On the contrary, a decrease in \(Nm\)F2 would increase \(H\) because the electron density has to drop at a slower vertical rate in order to join the topside anchor point. In light of these considerations, an \(Nm\)F2 underestimation by IRI has the effect of overestimating the topside scale height and then \(H_{0}\). This explains the \(H_{0}\) high values during nighttime in the South Indian Ocean and in two bands at low latitudes in the Asian sector (see Figure 5), which are associated with underestimated \(Nm\)F2 values by IRI (see Figure 10). The spatial variations in IRI nighttime \(Nm\)F2 values could be attributed to the spherical harmonics analysis underlying the \(Nm\)F2 modeling. In fact, the IRI \(Nm\)F2 model is based on the spherical harmonics numerical mapping procedure pioneered by the authors of [57; 58; 59] and later extended by the authors of [42]. According to this mapping, the latitudinal dependence is described by the modified dip latitude (modip, [10]), which was introduced by the author of [60] to better describe the ionospheric variations in equatorial and polar regions.