## 3 Results
### Regional Analysis  
In this section, we shift focus from larger-scale moisture comparisons to smaller-scale regional analysis in places that see either frequent deep convection or recurring sharp moisture gradients to better understand what causes large humidity differences between profile pairs. First, the northern Pacific Warm Pool is studied as this region  
Figure 7: (**a,c**) C2 and ERA5 standard deviation of specific humidity differences (g/kg, color contours) at 3 km and 7 km, and (**b,d**) C2 and MERRA-2 standard deviation of specific humidity differences (g/kg, color contours) at 3 km and 7 km along with the mean outgoing longwave radiation (OLR, solid black contours) from ERA5 within 40\({}^{\circ}\)N–40\({}^{\circ}\)S from September–December 2019.  
has frequent occurrences of extremely dry air intrusions in the low-to-mid troposphere (3-9 km) in the winter months along with sharp moisture gradients [44]. Figure 8 shows the regional specific humidity over the Pacific Warm Pool (in g/kg) from both ERA5 (top) and MERRA-2 (bottom) at 3 km on 21 December 2019 at 12:00 UTC. A C2 profile was also observed at this time and the profile tangent points are shown by the solid white and black line. Both reanalyses show a combination of moist air (SH > 10 g/kg) and extremely dry air (SH < 1 g/kg) separated by a very sharp gradient at roughly 10\({}^{\circ}\)N. The lower tropospheric portion of the C2 profile is located within the sharp moisture gradient in both reanalyses, which results in large SH differences between the profile pairs. Of course, inherent differences within the model physics can generate some of the larger SH differences between profile pairs, especially in regions with sharp moisture gradients such as these. Thus, a shift in the location of either reanalysis maximum SH gradients of just 100 km can result in the C2 moisture being slightly smaller or much larger than the corresponding reanalysis SH (as shown here for ERA5). The presence of sharp gradients can also cause errors in the retrieved moisture from C2. The derivation of accurate atmospheric refractivity profiles requires precise bending angle measurements, which are only valid assuming local spherical symmetry [45]. However, as the horizontal resolution of GNSS RO is \(\sim\)200 km on average, sharp lower tropospheric moisture gradients result in departures from spherical symmetry. [PERSON] [46] produced simulations where bending angle errors near the surface exceeded 10% dependent on the horizontal gradient of the bending angle profile, which would then produce large errors in retrieved moisture. Therefore, differences in underlying model physics within the reanalyses and errors due to departures from spherical symmetry within the retrieved RO moisture profiles could result in many of the large SH differences observed. Figure 8: (**Top**) ERA5 regional specific humidity at 3 km and (**Bottom**) MERRA-2 regional specific humidity at 3 km on 21 December 2019 at 12:00 UTC, with a large moisture gradient present and large specific humidity differences relative to the collocated C2 profile. The collocated C2 profile tangent points are indicated by the solid white and black line, with the black line indicating tangent points below 5 km. Next, we investigate the relationship between profile pair SH differences and the maximum local reanalysis SH gradients per 100 km near each pair in Figure 9. The profiles are obtained within 10\({}^{\circ}\)-15\({}^{\circ}\)N and 150\({}^{\circ}\)-155\({}^{\circ}\)E, which is within the same region shown in Figure 8. The local SH gradient is obtained over a roughly 300 km transect (transect lengths are slightly different due to differing reanalysis resolutions) in all directions, with only the maximum gradient saved for analysis. This transect length was chosen as it is slightly larger than the native horizontal resolution of C2. The observed SH differences are generally larger as humidity gradients become larger at both altitudes and for both ERA5 and MERRA-2.