## 3 Approaches for Quantifying the Precision, Stability, Accuracy, and Uncertainty of COSMIC-2 Data  
Like [32], we first collect all available RS41 measurements within 300 km and 2 h with the locations and time of COSMIC-2 data. The COSMIC-2 geo-location is defined at the tangent point from 4 km to 5 km altitudes. If there is more than one RS41 profile within 2 h and 300 km of one COSMIC-2 profile, the closest RS41 in location is selected. We use the hydrostatic equation to convert the RAOB pressure level to the geometric height. Then we interpolate the COSMIC-2 data to the radiosondes' geometric height at radiosondes' mandatory pressure level (i.e., surface, 850, 700, 500, 200, 150, 100, 50, and 20 hPa).  
As shown in Figure 1, COSMIC-2 SNR ranges from 200 \(\psi\)\(\psi\) to 2800 \(\psi\)\(\psi\) which covers the SNR range for other RO missions (i.e., COSMIC, KOMPSAT-5, etc.). In this study, COSMIC-2 profiles are grouped into five SNR ranges: (i) SNR \(<\) 500 \(\psi\)(i.e., 0-500 \(\psi\)(\(\psi\) group), (ii) 500 \(\psi\)(\  
procedures, the retrieval stops at a height when significant retrieval uncertainties occur. In this study, the COSMIC-2 penetration depth is defined as the lowest mean sea level height with valid refractivity from UCAR processed atmospheric profiles (atmPrf). Ref. [40] showed that with a better tracking system and higher SNR signals, COSMIC-2 data penetrate lower than other RO missions. We further examine how the penetration depth varies with the atmosphere moisture distribution, which is usually a function of latitude. Figure 4 depicts the COSMIC-2 penetration depth over mid-latitude in North Hemisphere (45\({}^{\circ}\) N-30\({}^{\circ}\) N and 30\({}^{\circ}\) N-10\({}^{\circ}\) N), tropical region (10\({}^{\circ}\) N-10\({}^{\circ}\) S), and mid-latitude Southern Hemisphere (10\({}^{\circ}\) S-30\({}^{\circ}\) S and 30\({}^{\circ}\) S-45\({}^{\circ}\) S) over oceans during the period from June to October 2019. The mean penetration height is computed from the average of 100 _v/v_ intervals. We also calculate the standard error of the mean (SEM) and plot it in the vertical line superimposed to the mean. Figure 4 shows that, in general, COSMIC-2 occultations penetrate deeper with higher SNR over oceans. With a higher mean SNR than all other RO missions, more than 85% of COSMIC-2 data penetrate deeper than 1 km altitude. COSMIC-2 occultations penetrate deeper when the atmosphere is drier. The reason that the dark blue line (45\({}^{\circ}\) N-30\({}^{\circ}\) N) is higher than the red line (the tropical region, 10\({}^{\circ}\) N-10\({}^{\circ}\) S) is that during this period, the Intertropical Convergence Zone (ITCZ) moves to the Northern mid-latitude region (mid-latitude summer) in September and October, and the Northern mid-latitude region may be moister than that of the other area.  
To compare COSMIC-2 penetration with different SNR groups and other RO missions, we also calculate the corresponding penetration heights for 80% accumulated sample number for individual COSMIC-2 SNR groups and those for COSMIC, KOMPSAT5, and MetOp series over the oceans (Table 1). Table 1 shows that with the improved SNR, the COSMIC-2 accumulated penetration depth for the >2000 _v/v_ group is, in general, about 300 m to 900 m deeper than that for the 0-500 _v/v_ group. More than 85% of COSMIC-2 data penetrate deeper than 1 km altitude, where about 80% of COSMIC penetrate deeper than that height [1]. Although MetOp Series also use open-loop tracking, the average penetration depth at 80% accumulated level is about at 3 km altitude (see Table 1). Note that the penetration depth for COSMIC is very close to that of the COSMIC-2 500-1000 _v/v_ group. The mean COSMIC-2 penetration depths for different latitudinal zones are very close to those for the 1000-1500 _v/v_ group.