# Feasibility of Wave Simulation in Typhoon Using WaveWATCH-III Forced by Remote-Sensed Wind
## 1 Introduction  
Typohons frequently occur in the Western Pacific Ocean [1] and play an essential role in the moment and heat exchange. Observations from moored buoys and remote-sensing equipment, i.e., an altimeter [2] and a wave spectrometer (Surface Waves Investigation and Monitoring (SWIM)) based on the Chinese-French Oceanography Satellite (CFOSAT) [3], are valuable sources of data for research on typhoon-induced waves. However, high-precision on-site observations lack continuity on temporal and spatial scales. Moreover, measurements from the abovementioned remote-sensed techniques, which release data with a 1-2-day delay, have coarse spatial resolution, i.e., 10 km for the altimeter and 18 km for SWIM. Moreover, sea surface wind and waves can be simultaneously inverted from synthetic aperture radar (SAR) images, i.e., up to a 1 m pixel size for X-band TerraSAR-X [4] and C-band Gaofen-3 [5]. As an increasing number of satellites are launched, it is vital to cooperatively apply these advanced techniques in oceanic dynamics monitoring, such as in the study of strong-wind-induced waves during typhoons. The sea surface wind field is an essential aspect of typhoon-associated hazard [6], which also determines the drag coefficient and also generates waves [7; 8]. Operational products from atmospheric prediction systems [9; 10], i.e., the European Centre for Medium-Range Weather Forecasts (ECMWFs) and the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS), are usually used as the forcing field in wave hindcasting based on numeric models. However, as revealed in [11], the wind fields from numerical weather prediction systems have significant distortions during typhoons. Hence, wave simulations using these wind products as the forcing field lead to inaccurate forecasting and hindcasting products. Since the 1980s, satellite remote sensing technology has rapidly developed, and operational products can be released daily. Nowadays, scatterometers and radiometers are effective instruments for wind monitoring over the global ocean. The detectable maximum wind speeds from the scatterometer are only up to 25 m/s [12], whereas the radiometer does not suffer this problem. However, the spatial resolution of the scatterometer can reach 12.5 km over the swath with approximately 100 km, which is higher than a typical 0.25\({}^{\circ}\) grid of the radiometer. Although remote-sensed winds are available in descending and ascending directions, the temporary resolution is anticipated to be improved using multiple satellites. Numerical models are widely used methods for hindcasting and predicting sea surface waves over global [13] and regional [14] oceans. Third-generation numerical models, i.e., WAVEWATCH-III (WW3) [15; 16] and Simulation Wave Nearshore (SWAN) [17], are popular for wave hindcasting, with fine spatial resolutions and wide coverage, especially in typhoons [18]. The main difference between the two numerical models is the computational grid, i.e., the rectangle grid for WW3 [19; 20; 21] and the unstructured grid for SWAN [22]. However, the newly updated versions of these models can employ both rectangle and unstructured grids. The acquisition of precisive cyclonic wind data in typhoons is still a challenge, which restricts the accuracy of wave simulations via numerical models due to the strong heat and momentum exchange at the air-sea interface. Although in situ observations from moored buoys are assimilated in a reanalysis system such as ECMWFs, the underestimation of wind speeds needs to be reduced in tropical cyclones (TCs) based on the parametric wind profile model [23]. This leads to the difficulty of wave simulation using numeric models under extreme weather conditions. This difficulty could be solved using real measurements from remote-sensed wind products.