Characteristics of Wind Field Observed by Synthetic Aperture Radar and Microwave Radiometer in Tropical Cyclone

Wind field structure of tropical cyclone (TC) can be resolved by remotely sensed sensors operated at microwave frequency, i.e. synthetic aperture radar (SAR) and microwave radiometer. The main purpose of this study is to investigate the characteristics of TC wind observed by Sentinel-1 (S-1) and soil moisture active passive (SMAP) during over 100 TCs from 2016 to 2023. The swath coverage of CyclObs winds inverted from S-1 images is about 500 km with a spatial resolution of about 500 m, while the SMAP wind products have a swath coverage of 1000 km with spatial resolution of 0.25° grids. Three TC parameters, geographic location of eye, maximum wind speed and radius of maximum wind speed, 34, 50, and 64 knot (kt) wind radii are estimated from CyclObs and SMAP winds. It is found that the distance between TC eyes derived from these two remote-sensed products and those from International Best Track Archive for Climate Stewardship (IBTrACS) reanalysis increases with central pressure increasing. Compared with IBTrACS data, the Root Mean Squared Error (RMSE) and Correlation Coefficient (COR) of maximum wind speed by CyclObs are 9.94 m s–1 and 0.63, whereas those by SMAP are 12.34 m s^–1 and 0.51. In contrast, about 23 m RMSE of radius of maximum wind speed and about 0.7 COR is achieved from both CyclObs and SMAP winds. Here, the angle is defined as follows: 0°−135° clockwise relative with TC movement represents the right side, 135°−225° represents the back side, and 0°−135° counterclockwise represents the left side. The angle between the maximum wind velocity direction relative to TC translation direction (forward direction) is not correlated well with NHC maximum wind speed or NHC radius of maximum wind speed. Interestingly, as the radius of maximum wind speed increases, the angle in CyclObs wind increases at the back and left sides of TC centre, whereas the angle decreases at the right side. This behaviour is only observed at the left side in SMAP wind.