## 3 Simulations and Discussion
### Initial Analyses after Data Assimilation  
The fractional differences and their standard deviations between the observation (O) and the first guess (B) as well as the observation (O) and the analysis (A) averaged during the DA in the local verification region are shown in Figure 3 for REF and BND. The amounts  
Figure 2: (**a**) The approximate mesh resolution of MPAS-60-15-3 km indicated by the contours at an interval of 3 km, and (**b**) the geometric locations of GPS RO soundings from 0000 UTC 2–4 July 2016 over the global MPAS mesh. The local region indicated by the black box is used for verification. and distributions of the RO profiles assimilated after quality control of GSI are similar for refractivity and bending angle, with about 200 profiles above 10 km impact height and only about 40 profiles near 3 km height during the DA window. At upper levels above 10 km impact height, the magnitudes of both fractional differences and standard deviations for REF and BND are much smaller due to both RO refractivity and bending angle decreasing rapidly with height. The results for BND indicate that the deviation of O from B, i.e., the innovation (O\(-\)B), was reduced in O\(-\)A with smaller magnitudes in the mean fractional differences (from 3% to 2%) and standard deviations (about a maximum reduction of 4% from 13% to 9%) below 5 km height (Figure 3b). Similar reductions are also found for REF but with a slightly larger reduction extending to the upper level near 10 km height. With the extra RO data (bending angle and refractivity), the hybrid assimilation showed an efficient reduction on the analysis difference after the DA period. The fractional differences and their standard deviations of bending angle from FS3/C are similar to that shown in [PERSON] et al. [49] from FS7/C2. Figure 3: (**a**) The vertical profiles of mean fractional differences (red line) in bending angle (i.e., (O\(-\)B)/B in %) and their standard deviations (blue line) between the observation (O) and the first guess (B) at different impact heights in the local verification region during the data assimilation of two days for BND, and (**b**) as in (**a**) but for the observation (O) and the analysis (A), i.e., (O\(-\)A)/A in %. (**c**,**d**) as in (**a**,**b**), respectively, but the fractional differences for REF. The black dashed line indicates the number of all GPS RO soundings (see the top axis) used in the local verification region. Figure 4 shows the horizontal distributions of temperature and specific humidity increments at 850 hPa averaged during DA. The increments are the differences between the DA analysis and the first guess after each cycling (6 h window) and they are averaged during the DA. Larger positive increments are produced near the location of Typhoon Genesis (145\({}^{\circ}\) E, 12\({}^{\circ}\) N) and Japan for BND and REF (Figure 4a-d) than GTS (Figure 4e,f). South of the typhoon center, larger negative increments in both temperature and specific humidity are induced for REF than BND, while both are more intense than GTS. It is noted that considerably negative temperature increments and moderately negative specific humidity increments are produced east of Japan above the typhoon region for REF, which is not found for BND. The results indicate that the impacts of additional RO data give further modification on the model temperature and moisture analysis through the hybrid assimilation. Figure 4: The averaged increments of the (**a**) temperature (shaded in K) and (**b**) specific humidity (shaded in g kg\({}^{-1}\)) at 850 hPa during the data assimilation for the experiment GTS. (**c,d**) as in (**a,b**), respectively, but for REF. (**e,f**) as in (**a,b**), respectively, but for BND. The initial location of Typhoon Nepartak is indicated by the typhoon symbol. The locations of RO profiles used in the entire DA are plotted by solid points in (**a,b**).