Ocean Surface Wave Impacts on SFMR Measurements in Tropical Cyclones

This study will investigate the impacts of ocean surface waves on Stepped-Frequency Microwave Radiometer (SFMR) measurements in tropical cyclones. Over the past several years, the Wide-Swath Radar Altimeter (WSRA) has been collecting surface wave spectra data in coincidence with the SFMR on one of NOAA’s WP-3D hurricane hunter aircraft in tropical cyclones. The wave spectra data from the WSRA will be analyzed to gain a better understanding of the surface wave field in different regions of tropical cyclones. There is still much to learn about the surface wave field in tropical cyclones and how the surface wind speed retrievals from the SFMR are impacted by changes in the wave field. Different combinations of wind and wave directions will impart different magnitudes of wind stress on the ocean surface for a given wind speed. Changes to the surface wind stress on the surface will modify the wave breaking and thus the white-water coverage on the surface. The SFMR measures the brightness temperature of the ocean surface, which varies based on the amount of white-water on the surface, and a wind speed is obtained through the use of a radiative transfer model and inversion algorithm. Therefore, any changes in the brightness temperature of the surface related to varying combinations of wind and wave direction for a given wind speed will lead to biases in the SFMR wind speed measurements. In order to quantify these biases, results of the wave spectra analysis will be compared to collocated SFMR and dropwindsonde data.