Wind stress retrieval in tropical cyclones from collocated GPS-dropsonde data and cross-polarization Sentinel-1 IW mode

Abstract

The preliminary attempts to develop of the geophysical model function (GMF) for the retrieval of wind speed and wind stress in hurricanes, based on a dependency between the cross-polarized satellite SAR data from Sentinel-1 and wind speed or turbulent stress obtained from collocated NOAA GPS-dropsondes data array. Field measurements in the Atlantic Ocean during hurricane season in the period 2001-2018 were analyzed. Using the data measured by GPSdropsondes, due to the ensemble averaging, mean wind velocity profiles were obtained, and the atmospheric boundary layer parameters drag coefficient and turbulent stress (or friction velocity) were retrieved from the “wake” part of the velocity profiles taking into account a self-similarity property of the velocity profile “defect”. The parameters were retrieved for 25 major hurricanes of categories 4 and 5. The collocation of Sentinel-1 images and GPS-dropsonde data was made for the hurricanes Irma 2017/09/07, Maria 2017/09/21 and 2017/09/23, taking into account the assumption that turbulent boundary layer parameters in the hurricanes remain quasistationary. The dependencies of the cross-polarized normalized radar cross-section (NRCS) on the wind speed and wind friction velocity were obtained, the results were compared to the data for small and moderate winds, represented in [1], a good agreement is demonstrated. In the region of high wind speeds the relation between NRCS and the wind friction velocity becomes ambiguous, it may be explained by the dependency on the hurricane sector.