## 6 Conclusions, Discussions, and Potential Applications
The comparison of COSMIC and COSMIC-2 shows that their mean fractional refractivity differences between 5 km and 35 km range from \(-\)0.5% (at 5 km) to 0.4% (at 35 km). This is very consistent with the comparison results for the collocated COSMIC-2-KOMPSAT-5 pairs. This result demonstrates the consistent data quality between COSMIC-2 and COSMIC (and KOMPSAT-5). COSMIC-2 data are consistent with other RO missions, mainly over both the troposphere and the lower stratosphere below 40 km. 5. Tracking uncertainty from receivers. Although L1 SNR for COSMIC-2 varies with different satellite systems (GPS with the mean L1 SNR of 1250 \(\forall\psi\) and GLONASS with the mean L1 SNR of 1100 \(\forall\psi\)), we did not find significant quality change for COSMIC-2/GPS and COSMIC-2/GLONASS retrievals. The mean difference and uncertainty of the COSMIC-2/GPS-RS41 pairs are very close to those of the COSMIC-2/GLONASS-RS41 collocated pairs. However, we find that the COSMIC-2 retrievals under the beamforming period are slightly less biased and uncertain than those of the non-beamforming period. 6. The accuracy of COSMIC-2 temperature in the lower stratosphere. Studies have demonstrated that COSMIC-2 temperature profiles in the lower stratosphere are very accurate. The mean COSMIC-2 and RS41 temperature difference from 8 km to 30 km altitude range is equal to \(-\)0.04 K with a std of 1.34 K. In this study, we also compare COSMIC-2 and RS41 collocated pairs during the day and night. The mean COSMIC-2-RS41 temperature differences in the lower stratosphere is equal to zero for both the day time and the night time. This result gives us confidence in the quality of temperature measurement for both RS41 and COSMIC-2 in the low stratosphere. The mean difference and uncertainty of COSMIC-2 temperature are very compatible with those from COSMIC. Ref. [46] confirmed that for the COSMIC-RS92 pairs, the mean bias and the deviation in this height range were equal to \(-\)0.01 K and 2.09 K, respectively. 7. COSMIC-2 refractivity and water vapor retrievals for different SNR groups in the troposphere. In general, the COSMIC-2-RS41 refractivity differences vary in different latitudinal zones. The mean fractional refractivity difference from 45\({}^{\circ}\) N to 45\({}^{\circ}\) S near the surface is equal to \(-\)4% with a std of 5%. The more substantial mean difference in the tropical regions below 2 km altitudes may be owing to a more considerable tracking uncertainty from COSMIC-2, mostly below SR. Comparison results show that the mean fractional refractivity difference for COSMIC-2 minus those from RS41 is slightly larger for the 0-500 \(\forall\psi\) group compared to other groups. Except for the \(>\) 2000 \(\forall\psi\) group, the high SNR measurements from COSMIC-2 measurements seem to improve the mean water vapor difference for the higher SNR group slightly (especially for the 1500-2000 \(\forall\psi\) group) comparing with those from lower SNR groups. The COSMIC-2 and RS41 comparison pairs are mainly collected either over lands or islands. We will compare the COSMIC-2 water vapor and refractivity comparisons over oceans, where the larger horizontal water vapor variation will be more significant than those over lands. That will be for a future study. Ref. [42] has demonstrated that because COSMIC data are of exceptionally high precision and accuracy and have no significant mission-dependent biases above 5 km, they are very suitable for climate monitoring. With similar precision and stability, COSMIC-2 shall also be used as an anchor reference to calibrate other satellite data (see [42]) and in situ RAOB data (see [34; 32]). With a deeper penetration, high density, and similar accuracy with those from COSMIC, COSMIC-2 data in the tropical lower troposphere are extremely useful for studying hydrological processes over the tropics (see COSMIC applications in [50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61]), and global and regional planetary boundary layer (PBL) structures (see [62]).