## 3 Simulations and Discussion
### Forecasted Results with DVI  
All DA experiments with the DVI were conducted for 5-day forecasts, where either P-match or V-match was chosen for the cycle runs using the analysis at the end of the cycling assimilation. Figure 8 shows the track and intensity for all DVI experiments, which are compared to the CWB best track. Regardless of the selected match for GTS, REF, and BND, the typhoon intensities for the DVI experiments are in better agreement with the best track intensity than the experiments without the DVI (Figure 8g-i). Note that the required cycle runs for P-match are lower than that for V-match. In general, the forecasted tracks are not significantly changed for all the experiments with and without the DVI for GTS, REF, and BND (Figure 8a-c). However, the DVI appears to slightly improve the track prediction for REF and BND, and eliminate the southward deviation for REF. For BND_RV40, REF_RV70, and GTS_RV28, their track errors at 120 h are quite close, nearly 300 km. Here, the number following the experiment (see Table 1) indicates the required cycle runs associated with the match in the DVI. The track forecast with the DVI is still slightly worse for REF and BND, but the noted underprediction in intensity was significantly improved. Apparently, the underestimate of the RO data assimilation on the best track intensity due to the scarcity of RO data in the inner typhoon was largely overcome by the DVI.  
Figure 7: Geometric height (contours at an interval of 10 m), temperature (shaded in K), and horizontal wind (vectors in m s\({}^{-1}\)) at 850 hPa at 0000 UTC 07 July 2016 for (**a**) ERA-Interim, (**b**) GTS, (**c**) REF, and (**d**) BND.  
The daily averaged forecast track errors for all the experiments with and without DVI are summarized in Figure 9. The track errors in all the experiments with the DVI are reduced in the first day, compared to those in the experiments without the DVI. However, the errors are increased for the DVI experiments in days 2 and 3 and remain similar in days 4 and 5, except for REF as shown in Figure 8. These results imply that the DVI can improve the intensity forecast but has no large positive impact on the track forecast. At later stages, the DVI tends to have more positive effects on RO assimilation for BND than REF. The smallest track errors at days 4 and 5 for REF without the DVI are benefited by its more consistent movement but at the cost of the largest underprediction on typhoon intensity.  
To understand the differences in the forecasts after the DVI, their forecasted geometric height, temperature, and wind vector at 850 hPa are shown in Figure 10. With the DVI, the inner typhoon core was significantly enhanced at 0000 UTC 4 July 2016 for BND_RP (Figure 10a) as compared to that without the DVI for BND (Figure 5d). Note that the relocation of the vortex center also shifted the analysis vortex to the best track position that is somewhat east of the typhoon center in BND. Figure 11 shows the differences between the forecasted temperature and specific humidity at 850 hPa at 72 h for BND_RV. At 72 h, the forecasted flow fields for BND_RP are very similar to BND_RV. Indeed, both fields are also similar to that for BND, except for the typhoon circulation (figures not shown). Consequently, all three experimental results exhibit similar differences from the ERA-Interim, with warmer air to the north and east of the outer typhoon and more moistening mainly in the inner typhoon in the lower troposphere. The temperature warming to the  
Figure 8: (**a**) The CWB best track (black line) and the forecasted tracks for BND (pink line), BND_RP (blue line), BND_RV (green line), and NoDA (red line) for Typhoon Neparatak. (**d**) as in (**a**) but for the track errors, and (**g**) as in (**a**) but for the central sea-level pressure error. (**b,e,h**) as in (**a,d,g**), respectively, but for REF. (**c,f,i**) as in (**b,e,h**), respectively, but for GTS. The numbers following the case names indicate the number of cycle runs.