CYGNSS Ocean Surface Wind Validation in the Tropics

Surface wind plays a crucial role in many local/regional weather and climate processes,26 especially through the exchanges of energy, mass and momentum across the Earth’s surface.27 However, there is a lack of consistent observations with continuous coverage over the global28 tropical ocean. To fill this gap, the NASA Cyclone Global Navigation Satellite System29 (CYGNSS) mission was launched in December 2016, consisting of a constellation of eight small30 spacecrafts that remotely sense near surface wind speed over the tropical and sub-tropical oceans31 with relatively high sampling rates both temporally and spatially. This current study uses data32 obtained from the Tropical Moored Buoy Arrays to quantitatively characterize and validate the33 CYGNSS derived winds over the tropical Indian, Pacific, and Atlantic Oceans. The validation34 results show that the uncertainty in CYGNSS wind speed, as compared with these tropical buoy35 data, is less than 2 m s-1 root mean squared difference, meeting the NASA science mission36 Level-1 uncertainty requirement for wind speeds below 20 m s-1. The quality of the CYGNSS wind is further assessed under different precipitation conditions, and in convective cold-pool38 events, identified using buoy rain and temperature data. Results show that CYGNSS winds39 compare fairly well with buoy observations in the presence of rain, though at low wind speeds40 the presence of rain appears to cause a slight positive wind speed bias in the CYGNSS data. The41 comparison indicates the potential utility of the CYGNSS surface wind product, which in turn42 may help to unravel the complexities of air-sea interaction in regions that are relatively under43sampled by other observing platforms.