## 3 Results  
### Tropics/Subtropics Analysis  
The results of this study focus on evaluating the specific humidity differences between the C2, ERA5, and MERRA-2 datasets throughout the tropics and subtropics. First, Figure 2 shows the overall C2 specific humidity characteristics on a zonal and latitude/longitude basis to highlight the usefulness of C2 RO profiles in displaying large-scale moisture features and providing context for analyzing the moisture differences observed between datasets in the next sections. Zonal mean moisture contours (Figure 2a) show that lower tropospheric moisture amounts are highest near the surface within the tropics (-15 g/kg) and decrease quickly away from the deep tropics (6-8 g/kg near 40\({}^{\circ}\)) and with height (<1 g/kg into the upper troposphere). More structure is evident when analyzing moisture characteristics on a latitude/longitude basis at different levels, with various moist and dry spots apparent. At 3 km (Figure 2b), moisture amounts are highest throughout the deep tropics, with mean values near 8 g/kg found over the far eastern Pacific and Atlantic Oceans, northern South America, the northern Indian Ocean, and the Pacific Warm Pool. Subtropical SH variations are also observed, with maximums (>4 g/kg) typically occurring over the warm ocean currents (e.g., the Gulf Stream and the Kuroshio Current) and minimums (<2 g/kg) observed above the marine stratocumulus cloud regions, both of which are associated with oceanic subtropical highs. Moisture distributions are similar at 7 km (Figure 2c), although some regional differences are observed. For example, the driest areas at 3 km above the Southern Hemisphere stratocumulus regions occur within the subtropics (between 20\({}^{\circ}\)-30\({}^{\circ}\)) near the coastlines, whereas at 7 km, the driest areas are shifted away from the coastlines and closer to the equator. Figure 2: (a) C2 zonal mean specific humidity (g/kg), along with the C2 specific humidity at (b) 3 km and (c) 7 km within 40\({}^{\circ}\)N–40\({}^{\circ}\)S from September–December 2019. The zonal mean humidity percentage differences between C2 and ERA5 along with C2 and MERRA-2 are analyzed between 40\({}^{\circ}\)N-40\({}^{\circ}\)S in Figure 3. Profile pairs are placed within 2.5\({}^{\circ}\) latitude bands and humidity percentage differences are calculated and averaged to obtain a better idea of which latitudes and tropospheric heights show the largest differences. The C2 and ERA5 comparison (Figure 3a) shows that C2 has a negative specific humidity bias within the boundary layer (-6% to -12%). These differences occur due to well-known issues with RO within the boundary layer, as large refractivity changes associated with a strong inversion layer at the top of the planetary boundary layer (PBL) can lead to super-refraction and various receiver tracking errors which cause negative biases in RO refractivity measurements [18; 20]. Just above the boundary layer, C2 and ERA5 SHs show excellent agreement. As heights increase, the C2 bias becomes positive and the maximum bias (9% to 12%) is observed in the Northern Hemisphere tropics between 8 km and 9 km. C2 and MERRA-2 moisture differences (Figure 3b) within the lower troposphere are similar to those of C2 and ERA5, with negative bias observed in the boundary layer (-9% to -15%) and good agreement just above the boundary layer. However, as heights increase, SH differences increase rapidly and a large negative bias is observed, similar to [PERSON] et al. [34]. Bias is especially large in the tropics (generally between -24% to -30%) and decreases into the subtropics (between -12 to -21%). The most likely explanation for these large differences in the tropical upper troposphere is due to the parameterization of large-scale condensation and evaporation within the atmospheric general circulation model (AGCM) used in MERRA-2.