Directional Signals in Windsat Observations of Hurricane Ocean Winds

In this paper, wind-direction signals in passive microwave polarimetry for ocean surfaces under hurricane force winds are presented. We performed analysis of Windsat data for several Atlantic hurricanes from 2003 to 2005. The polarimetric third Stokes parameter observations from the Windsat 10-, 18-, and 37-GHz channels were collocated with the ocean-surface winds from the National Oceanic and Atmospheric Administration Hwind analysis. The collocated data were binned as a function of wind speed and wind direction. The 10-GHz data show clear 4-K peak-to-peak directional signals at 50-60-m/s wind speed after correction for atmospheric attenuation. The signals in the 18- and 37-GHz channels were unclear at above 40-m/s wind speeds, probably caused by the impact of clouds and rain. The data were expanded by sinusoidal series of the relative azimuth angles between the Hwind analysis and observation directions. The coefficients of the sinusoidal series suggest decreasing response to wind direction for increasing wind speed, but the 10-GHz data appear to be fairly constant for up to 50-m/s wind speeds.