## 3 Assimilation and Impact of GNSS RO Data
### Impact of GNSS RO Data
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Observation**} & & & & & & & & & & & \\ \cline{3-14}  & & \multicolumn{1}{c}{**Developing**} & \multicolumn{1}{c}{**Non-Developing**} & \multicolumn{1}{c}{**Total**} & \multicolumn{1}{c}{**Hit Rate**} & \multicolumn{1}{c}{**Specificity**} & \multicolumn{1}{c}{**False Alarm**} & \multicolumn{1}{c}{**False Alarm**} & \multicolumn{1}{c}{**Bias Score**} & \multicolumn{1}{c}{**Accuracy**} & \multicolumn{1}{c}{**Threat Score**} \\ \cline{3-14}  & & & & & & & & & & & & \\ \hline \multirow{2}{*}{
\begin{tabular}{c} GTS \\ Forecast \\ \end{tabular} } & Detected & 4 (hits) & 11 (false & \multirow{2}{*}{0.44 \({}^{*}\)} & \multirow{2}{*}{0.52 \({}^{*}\)} & \multirow{2}{*}{0.73 \({}^{*}\)} & \multirow{2}{*}{0.48 \({}^{*}\)} & \multirow{2}{*}{1.67} & \multirow{2}{*}{0.50 \({}^{*}\)} & \multirow{2}{*}{0.20 \({}^{*}\)} \\  & Non-detected & 5 (misses) & 12 (correct & negatives) & & & & & & \\ EPH & Detected & 7 (hits) & 8 (false & \multirow{2}{*}{0.78 \({}^{*}\)} & \multirow{2}{*}{0.65 \({}^{*}\)} & \multirow{2}{*}{0.53 \({}^{*}\)} & \multirow{2}{*}{0.35 \({}^{*}\)} & \multirow{2}{*}{1.67} & \multirow{2}{*}{0.69 \({}^{*}\)} & \multirow{2}{*}{0.41 \({}^{*}\)} \\ Forecast & Non-detected & 2 (misses) & 15 (correct & negatives) & & & & & & \\ Total & 9 & 23 & 32 & / & / & / & / & / & / \\ Sensitivity to RO & 0.33 & 0.13 & 0.19 & / & / & / & / & / & / & / \\ \hline \hline \end{tabular}
\end{table} 
Table 2: 2 \(\times\) 2 contingency tables and various skill scores of TC forecasts formation for GTS (assimilating conventional data) and EPH (GNSS RO data in addition to GTS). Hit rate: hits/(hits + misses). Specificity: correct negatives/(false alarms + correct negatives). False alarm ratio: false alarms/(hits + false alarms). False alarm rate: false alarms/(false alarms + correct negatives). Bias score: (hits + false alarms)/(hits + misses). Accuracy rate: (hits + correct negatives)/(hits + misses + false alarms + correct negatives). Threat score: hits/(hits + misses + false alarms). Sensitivity to RO: proportion of GNSS RO data assimilation improved performance cases in total categories [74]. Figure 8: **(a–c)** The Control Hurricane Zeta forecasts initialized at 1200 UTC 26 Oct, respectively, at 12, 24, and 30 h. (**d–f**) The C2 (Control with RO bending angle) Hurricane Zeta 12, 24, and 30 h forecasts initialized at 1200 UTC 26 Oct, respectively. **(a–f**)** figures have horizontal wind vectors on the forecasts. **(g–i)** SSMIS 91-GHz color composite imagery, at 2225 UTC 26 Oct, 1058 UTC 27 Oct, and 0030 UTC 28 Oct, respectively. In **(h)**, the NHC best track center is marked by a white triangle at 1200 UTC 27 Oct (21.38N, 89.08W) [76]. Figure 11: Time series of the central pressure predicted by NHM of typhoon Usagi, for GA, MA, MA_RO, and Bestrack data [78]. Figure 10: (**a–c**) is for GA (the JMA global analysis), MA (analysis by the Meso 4D-Var system), and MA_RO (the same as MA but RO data were assimilated additionally), the distributions of sea-level pressure (hPa), surface wind vectors (m/s), and accumulated precipitation (shade, mm) in a 3 h period at 0000 UTC 31 July 2007 from NHM forecasts using different background fields [78]. Figure 9: (**a**) The HWRF Control Hurricane Zeta horizontal wind vectors (m/s) at 750 mbar with layer-averaged RH (shade, %) at 700–800 mbar from the cycled analysis initialized at 1200 UTC 26 Oct. (**b**,**c**) As in (**a**), but for the 12 and 18 h verification times, respectively. (**d–f**) As in (**a–c**), but for the HWRF C2 forecast. The dry tongue is highlighted by the black rectangular boxes [76]. Figure 12: **(a)** The black dot is the best track from observations, and others are the simulated tracks for NODA (the initial condition from NCEP), GTS (assimilating conventional and satellite radiance data), REF (GTS along with RO refractivity), and BND (GTS along with RO bending angle), respectively. The area in the dashed square is zoomed as shown at the upper-right corner with the details of the tracks.