CYGNSS Data Impact on Global Analyses of Ocean Surface Winds

The CYclone Global Navigation Satellite System (CYGNSS) has been providing new estimates of 10-meter ocean surface winds in the tropics since March 2017. Due to the low-inclination-angle orbit of the eight CYGNSS spacecraft, temporal and spatial sampling of the global tropics is much improved over traditional polar-orbiting low earth orbit (LEO) satellites. Through the calibration/validation work of the NASA CYGNSS Science Team and partners, winds in the 0-15 m/s range have become very reliable observations of topical ocean surface wind speed. As a new information source, these are combined with existing global analyses of ocean surface winds using a 2-dimensional Variational Analysis Method (VAM) in 6-hourly analyses to assess their impact, both statistical and phenomenological. The impact of CYGNSS winds on global analyses of 10-meter ocean surface winds will be shown for a range of existing analyses, including GFS operational analyses, ECMWF global operational analyses, ECMWF reanalysis (ERA5) and NASA's MERRA-2 reanalyses. These existing global ocean surface wind analyses are created by a wide variety of analysis systems for widely varying purposes at a range of spatial resolutions from ~ 9 km horizontal resolution (ECMWF operational analyses) to ~ 60 km (MERRA-2 reanalyses). Because these global analyses are quite different from one another, resolving different ranges of spatial and temporal scales in the atmosphere, CYGNSS wind speed data impacts each in different ways. Using the statistics of analysis innovations (o-b) and residual fit (o-a), as well as phenomenological evaluation of features in the 10-meter tropical global ocean winds, the impacts of CYGNSS data are demonstrated in these global analyses.