## 3 Results
### Verification of FY3C/GNOS IRO Products in Ionospheric Climatology with COSMIC
#### 3.2.2 Ionospheric Climatological Characteristics of hmF2 between FY3C/GNOS and COSMIC  
The global distribution of season median hmF2 of FY3C/GNOS and COSMIC and their absolute differences at daytime (0800-1100 LT) and nighttime (2000 LT-2300 LT) during ME-month, JS-month, SE-month, and DS-month are presented from Figures 10-13, respectively, to depict the hmF2 morphology of FY3C/GNOS and COSMIC intuitively. As can be seen in Figure 10a-d, Figure 11a-d, Figures 12a-d and 13a-d, the season median hmF2 of FY3C/GNOS and COSMIC show good consistency on morphology trend, but there are still some magnitude discrepancies, for example, at daytime, the smaller magnitude of COSMIC hmF2 makes it less continuous in African longitude sector in JS-month and SE-month. At nighttime in the ME-month, FY3C/GNOS exhibits a significant hmF2 peak in the Atlantic region compared to hmF2 of COSMIC. Besides, higher hmF2 of both FY3C/GNOS and COSMIC are most concentrated in low latitude regions at daytime but expand to mid-high latitudes at nighttime, especially in the south Pacific Ocean, showing the global nighttime enhancement of hmF2. One interesting thing is that during daytime when the highest value hmF2 are assembled along the magnetic equator, another relatively high hmF2 appears near the African longitude sector and extends to mid-high latitudes in the southeast direction, and when global hmF2 goes up at nighttime, the aforementioned area is filled by the low value hmF2 again, which are most obvious in ME-month and DS-month. This was also observed in work of [PERSON] et al. (2017). Other hmF2 climatological characteristics are presented as below:  
Figure 9: Ionospheric climatological characteristics of season median NmF2 observed by FY3C/GNOS and COSMIC and their differences at 0800–1100 LT and 2000–2300 LT during DS-month (\(\pm\)45 days to December solstice of 2016) from 2016.311 to 2017.035. The regions denoted by red and black arrows indicate diurnal variation of NmF2, in which the general WSA and special WSA can be observed at nighttime, respectively. Refer to Figure 6 for more detailed descriptions. 1. hmF2 of FY3C/GNOS and COSMIC are higher in summer hemisphere than that in the winter hemisphere regardless of whether it was daytime or nighttime, that is, the hmF2 in northern ionosphere is higher than that in southern ionosphere in JS-month, and higher in southern ionosphere than that in northern ionosphere in DS-month, which is a typical embodiment of hemispheric asymmetry of hmF2 [65]. 2. Generally speaking, the enhancement of NmF2 is usually accompanied by an increasement of hmF2 [35], thus we can observe the WSA phenomenon of hmF2 in either solstice. However, different from NmF2, hmF2 WSA also appeared in winter hemisphere and equinoxes, and the hmF2 of FY3C/GNOS and COSMIC show a more significant WSA characteristics than that of NmF2. From Figure 10e,f, Figure 11e,f, Figure 12e,f and Figure 13e,f we can see that at nighttime, the hmF2 of FY3C/GNOS are significantly higher than those of COSMIC in low latitudes but lower in mid-high latitudes, which is exactly opposite to NmF2 differences between FY3C/GNOS and COSMIC mentioned before. Additionally, the white area (absolute error within \(\pm\)10 km) occupies the majority of the mid-latitude region, indicating the better consistency of hmF2 morphology between FY3C/GNOS and COSMIC in mid-latitudes. Figure 10: Ionospheric climatological characteristics of season median hmF2 observed by FY3C/GNOS and COSMIC and their differences at 0800–1100 LT and 2000–2300 LT during ME-month (2016.035-2016.125). (**a,b**) The climatological characteristics of season median hmF2 observed by FY3C/GNOS at 0800–1100 LT and 2000–2300 LT, respectively. (**c,d**) The climatological characteristics of season median hmF2 probed by COSMIC at 0800–1100 LT and 2000–2300 LT, respectively. The dip contours in (**a–d**) are represented by white curves, which are 60\({}^{\circ}\) dip, 0\({}^{\circ}\) dip, \(-\)60\({}^{\circ}\) dip from top to bottom, respectively.