# Feasibility of Wave Simulation in Typhoon Using WaveWATCH-III Forced by Remote-Sensed Wind
## 2 Data and Method
### Remote-Sensed Products and Assembling Method  
During the typhoon season in 2021-2022, scatterometer and radiometer wind products were acquired in the Western Pacific Ocean. Figure 1 shows the tracks and maximum wind speeds \(V_{max}\) in 30 typhoons during the 2021-2022 typhoon season from the National Hurricane Center (NHC). The area marked by the black rectangle is the modeling region (100\({}^{\circ}\) E-180\({}^{\circ}\) E, 0\({}^{\circ}\) N-60\({}^{\circ}\) N). Some scatterometer and radiometer wind products were acquired for the Western Pacific Ocean region in this period. In this study, the scatterometers include ASCAT-A/B/C and HY-2B/C/D constellations. The radiometers consist of Soil Moisture Active-Passive (SMAP), Advanced Microwave Scanning Radiometer-2 (AMSR-2), and HY-2B. It is necessary to clarify that wind direction data are not available from the radiometer. These products were calibrated and are useful for the study of atmosphere and oceanography in tropical cyclones [27,28]. The wind vectors measured from the HY-2B scatterometer and radiometer [29] on 26 September 2021 are presented in Figure 2a and Figure 2b, respectively. At present, the wave spectrum can be inferred from SAR [30] and SWIM, especially in tropical cyclones [31,32]. Unfortunately, the accuracy of wave retrieval from typhoon SAR images necessitates further improvements [33], and there are few SAR images of the above typhoons. Here, the SWIM-measured wave spectra of 30 typhoons are used for  
Figure 1: Information on typhoons obtained from the National Hurricane Center (NHC), in which the black rectangle represents the modeling region and the color lines correspond the best tracks of typhoons. validating the simulations from WW3. Note that the SWIM-measured wave spectrum has 180\({}^{\circ}\) ambiguity; therefore, a comparison of the wave directions between SWIM and WW3 is not conducted in our work. Moreover, the SWIM-measured wave spectrum is transformed to the wave number space and then compared with WW3 simulations. Figure 2: _Cont_. In 1978, SEASAT carrying an altimeter demonstrated the feasibility of SWH measurements when using an altimeter. From then on, spaceborne radar altimeters have been rapidly developed worldwide, e.g., the Jason-2/3 working with the Ocean Surface Topography Mission (OSTM) and the HY-2 satellite constellation. The footprint-following altimeter-measured SWHs have a spatial coverage of 10 km with highly detailed data of the sea surface. The cooperative satellite Jason-3, launched in 2016 by international agencies (NOAA, CNES, and EUMETSAT), provides well-calibrated wave products such as SWHs. In this study, the monthly averaged SWHs from Jason-3 altimeter products from January 2021 to December 2022 were used for conducting the error analysis of the wave simulations from the WW3 model. The Cressman interpolation method based on the distance is used for assembling remote-sensed winds, which is expressed as  
\[\overset{\rightarrow}{u}_{f}=\overset{\rightarrow}{u}_{0}+\frac{1}{n}{\sum }_{i=1}^{n}\,W_{i}\Delta\overset{\rightarrow}{u}_{i} \tag{1}\]  
where \(\overset{\rightarrow}{u}_{0}\) is the wind velocity vector from the initial HY-2B scatterometer (<25 m/s) or radiometer (\(\geq\)25 m/s) nearest to the assembling point; \(n\) represents the numbers of available wind vectors within the spatial resolution of assembling wind (\(R\)) assumed to be a 0.125\({}^{\circ}\) grid; \(\Delta\overset{\rightarrow}{u}_{i}\) is the difference between individual referred wind and the initial wind vector; and \(W_{i}\) is the distance-dependant weight, stated as  
\[W_{i}=\frac{D_{i}^{2}-R^{2}}{D_{i}^{2}+R^{2}} \tag{2}\]  
Figure 2: Wind maps from (**a**) Haiyang-2B (HY-2B) scatterometer and (**b**) radiometer. (**c**) The wind map from assembling data during Typhoon Mindulle at 18:00 UTC on 26 September 2021. European Centre for Medium-Range Weather Forecasts (ECMWFs) reanalysis (ERA-5) maps during Typhoon Mindulle at 18:00 UTC on 26 September 2021: (**d**) wind and (**e**) significant wave height (SWH).