## 4 Results
### TC Center Positioning Results
Also indicated are TC intensity categories (symbols), where 0000 UTC from the best track and the satellite observing time closest to 0000 UTC are shown with solid symbols, and other times with open symbols. In order to confirm the existence of vertical tilt in Typhoon Haikui, we need to know the vertical wind shear, which can be calculated using ERA5 reanalysis. To do so, we must first make sure that the typhoon centers in the ERA5 reanalysis are close to the best track. By applying the same center positioning method as we did with microwave scatterometer observations to the 10-m surface wind field in the ERA5 reanalysis, we can obtain the ERA5-derived track, which is very close to the best track (Figure 6a). We then calculated the vertical wind shear and added it to the scatterometer-determined track (Figure 6b). It was found that the observed center shifts between the near-surface and upper-level data match the vertical tilts of Typhoon Haikui. The phenomenon of tilted TC has been reported and intensively studied over the last few decades [42]. The exact reasons for the inconsistencies between the two data types will be further investigated using numerical simulations of Typhoon Haikui [49]. Quantitative measures of the deviations between the scatterometer sea surface wind observation-determined track and the AHI brightness temperature-determined track from the best track are provided in Figure 7 for typhoons Doksuri, Khanun, and Haikui. For typhoons Doksuri (Figure 7a) and Khanun (Figure 7b), whose intensity exceeded category-3 hurricane, the differences between the scatterometer sea surface wind observation-determined track (color symbol) and the best track were smallest (\(\sim\)20 km) during the periods of strongest intensity. This conclusion is also valid for the differences between the best track and the AHI brightness temperature-determined track. Large differences in the scatterometer sea surface wind observations from the best track are found for Typhoon Doksuri when it passed nearby islands on 26 and 27 July 2023 (Figure 7a). The azimuthal spectral TC positioning algorithm does not work for the center positioning of relatively weak tropical storms when their cloud/rainbands are not axisymmetric. For Typhoon Haikui (Figure 7c), the AHI brightness temperature-determined track deviates more from  
Figure 5: The best track (black symbol), the scatterometer 10-m wind-determined track (red symbol), and the AHI channel 13 brightness temperature-determined track (blue symbol) for typhoons (**a**) Doksuri, (**b**) Khanun, and (**c**) Haikui. Also indicated are the typhoon categories (symbol type) and the 0000 UTC in the best track (solid symbol). the best track than the scatterometer sea surface wind observation-determined track, for reasons explained in Figure 6.  
Figure 6: (**a**) The track of Typhoon Haikui determined from the ERA5 reanalysis of the 10-m sea surface wind field and the best track (black symbol). (**b**) Same as Figure 5c, except with vertical wind shear (green arrow) added, calculated from the ERA5 reanalysis. Figure 7: Distances between the best track and the scatterometer sea surface wind observation-determined track (color symbol), and between the best track and the AHI brightness temperature-determined track (blue symbol), as well as the maximum sustained wind (gray symbol) for typhoons (**a**) Doksuri, (**b**) Khanun and (**c**) Haikui.