## 4 Results
### Comparison between F2-Layer Peak Parameters Modeled by IRI and Measured by COSMIC--1  
The accurate specification of the F2-layer peak anchor point has a significant role in topside profile modeling. Since, in our study, this task is assigned to the IRI model, we compared IRI-modeled F2-layer peak parameters with corresponding ones measured by COSMIC--1. We limit the comparison to the nighttime sector when the major discrepancies between modeled \(H_{0}\) values have been found (see Figure 5). Figure 9 reports the IRI-modeled \(hm\)F2 values and those measured by COSMIC-1 for the nighttime sector. Figure 10 shows the corresponding plots for \(Nm\)F2. Figure 9 highlights the good agreement between modeled and measured \(hm\)F2 values, in terms of both magnitude and spatial variations, as noted by other studies [44; 54; 55; 56]. This is somewhat expected because the [PERSON] \(hm\)F2 model [43] is based on COSMIC--1 RO data. Overall, IRI-modeled \(hm\)F2 values vary in a narrower range of magnitude compared to those of COSMIC--1, but they do not show any specific longitudinal variation that could account for the very high \(H_{0}\) values modeled during nighttime.  
Instead, the comparison between modeled and measured \(Nm\)F2 values (Figure 10), albeit showing a general agreement in magnitude, shows differences at specific longitudinal sectors. Focusing on NDJ months (panels g and h in Figure 10), where \(H_{0}\) values calculated through CSES--01 and Swarm B observations maximize, IRI-modeled \(Nm\)F2 values have deep minima in the South Indian Ocean and in two bands at low latitudes in the Asian sector. COSMIC--1 also measures minima in those regions but to a lesser extent than IRI. Moreover, at low latitudes in the Asian sector, COSMIC--1 data do not show the two-band structure modeled by IRI. IRI-modeled nighttime \(Nm\)F2 values often show spatial variations that follow the geomagnetic field lines configuration. This is particularly evident in the already mentioned two minima bands in NDJ months in the Asian sector and also with respect to the relative maximum above the geomagnetic equator in the equinoctial months (panels a and e in Figure 10).  
Figure 9: Geographical representation of median values of _hmF_2 for the nighttime sector (\(\sim\)02:00 LT). First row plots (panels (**a**,**b**)) refer to FMA = (February, March, April) months; second row plots (panels (**c**,**d**)) refer to MJJ = (May, June, July) months; third row plots (panels (**e**,**f**)) refer to ASO = (August, September, October) months; and fourth row plots (panels (**g**,**h**)) refer to NDJ = (November, December, January) months. First column plots (panels (**a**,**c**,**e**,**g**)) are _hm_F_2 values, as modeled by IRI with the Shubin option; second column plots (panels (**b**,**d**,**f**,**h**)) are corresponding values, as obtained with COSMIC—1 radio occultation-measured values. Color bar scale is the same across all panels. The solid black curve in each plot represents the geomagnetic equator.  
Figure 10: Geographical representation of median values of _Nm_F2 values for the nighttime sector (\(\sim\)02:00 LT). First row plots (panels (**a,b**)) refer to FMA = (February, March, April) months; second row plots (panels (**c,d**)) refer to MJJ = (May, June, July) months; third row plots (panels (**e,f**)) refer to ASO = (August, September, October) months; and fourth row plots (panels (**g,h**)) refer to r NDJ = (November, December, January) months. First column plots (panels (**a,c,e,g**)) are _Nm_F2 values, as modeled by IRI with URSI coefficients; second column plots (panels (**b,d,f,h**)) are corresponding values, as obtained with COSMIC—1 radio occultation-measured values. Color bar scale is the same across all panels. The solid black curve in each plot represents the geomagnetic equator.