## 3 Results
### Verification of FY3C/GNOS IRO Products in Ionospheric Climatology with COSMIC  
#### 3.2.1 Ionospheric Climatological Characteristics of NmF2 between FY3C/GNOS and COSMIC  
We present the global distribution of season median NmF2 of FY3C/GNOS and COSMIC and their relative differences at daytime(0800-1100 LT) and nighttime (2000 LT-2300 LT) during ME-month, JS-month, SE-month, and DS-month from Figures 6-9, respectively, thus the consistency and inconsistency of NmF2 morphology between FY3C/GNOS and COSMIC can be obtained intuitively. It can be clearly seen from Figure 6a-d, Figure 7a-d, Figures 8a-d and 9a-d that the season median NmF2 of COSMIC are higher than those of FY3C/GNOS regardless of whether it was daytime or nighttime, especially in equinoxes of ME-month and SE-month. Other global ionospheric climatological characteristics of NmF2 presented by FY3C/GNOS and COSMIC are as follows:  
1. It can be clearly seen from Figures 6-9 that the equatorial ionospheric anomalies (EIAs) are reflected in NmF2 of both FY3C/GNOS and COSMIC and are most obvious at daytime, which appears as an electron density trough along the magnetic equator sandwiched by two high electron density strips [57]. Moreover, the EIA exhibited by COSMIC are more pronounced than that of FY3C/GNOS. 2. The daytime NmF2 observed by FY3C/GNOS and COSMIC during equinoxes (ME-month and SE-month) are visibly higher than those in solstices (JS-month and DS-month), which is a typical feature of the semiannual anomaly/asymmetry [46]. The daytime NmF2 of COSMIC are higher than that of FY3C/GNOS, either. 3. The daytime NmF2 of FY3C/GNOS and COSMIC during DS-month shows more evident EIA structures than those in JS-month, and the magnitude of NmF2 observed by FY3C/GNOS and COSMIC in DS-month are about 16% and 20% larger than NmF2 in JS-month, respectively. The phenomenon that NmF2 in December solstice are higher than that in June solstice is known as annual anomaly [58]. 4. The nighttime NmF2 probed by FY3C/GNOS and COSMIC both show peak longitude structures during ME-month, which was also observed in work of [PERSON] et al. [46], and the peak structures of COSMIC NmF2 are more noticeable than that of FY3C/GNOS. 5. Taking into account the NmF2 measurements in both the northern and southern hemisphere, it can be found that at daytime, the NmF2 observed by FY3C/GNOS and COSMIC during ME-month have a more continuous EIA than that in SE-month, at nighttime, the NmF2 during ME-month have more evident peak structures than that in SE-month. Thus, the NmF2 observed in ME-month are higher than that in SE-month regardless of whether it was daytime or nighttime, which is known as equinoctial asymmetry and is most pronounced in the EIA region [59]. 6. The daytime NmF2 measured by FY3C/GNOS and COSMIC in winter are higher than those in summer, which means that the NmF2 observations in the southern hemisphere are higher than those in the northern hemisphere in JS-month, and the NmF2 in northern hemisphere are higher than than those in southern hemisphere in DS-month, this behavior of the ionosphere is the winter anomaly [60]. 7. At nighttime in DS-month, we can see the enhancement of NmF2 of FY3C/GNOS and COSMIC in region of around \(-60^{\circ}\) dip and \(50^{\circ}\)W-\(150^{\circ}\)W, the nighttime NmF2 enhancement can also be observed in area of around \(60^{\circ}\) dip and \(110^{\circ}\)E-\(160^{\circ}\)E in JS-month, which are corresponding to the WSA phenomenon, including the special WSA and the general WSA. The WSA anomaly was first proposed by [PERSON] [61], unlike the typical NmF2 diurnal variation, the NmF2 in Weddell Sea area in summer ionosphere showed anomalous nighttime enhancement as denoted by the black arrows in Figure 9b,d, this is known as the special WSA. We can see that the special WSA of FY3C/GNOS is not as pronounced as that of COSMIC.