Accuracy of 10 m winds from satellites and NWP products near land-sea boundaries

Through a comprehensive analysis, reliability of 10 m wind speeds is presented near the land-sea boundaries over the global ocean. Winds from three numerical weather prediction (NWP) centers and two satellite-based products are analyzed. NWP products are 1.875 degrees x 1.875 degrees National Center Environmental Prediction reanalyses, 1.125 degrees x 1.125 degrees European Centre for Medium-Range Weather Forecasts 40-year Reanalysis (ERA-40), and 1.0 degrees x 1.0 degrees Navy Operational Global Atmospheric Prediction System (NOGAPS) operational product. These are compared to much finer resolution (0.25 degrees x 0.25 degrees) satellite winds, Quick Scatterometer (QSCAT) and Special Sensor Microwave/Imager. Large biases (e. g., >3 m s(-1)) may exist in NWP products near the land-sea boundaries, because wind speeds from the uniformly gridded global fields are generally at a spatial scale too coarse to appropriately define the contrast between water and land grid points. This so-called land contamination of ocean-only winds varies, and typically depends on the extent of the land-sea mask. A creeping sea-fill methodology is introduced to reduce errors in winds. It is based on the elimination of land-corrupted NWP grid points and replacement by adjacent, purely over-ocean values. In comparison to winds from many moored buoys, the methodology diminishes RMS errors (from >4 m s(-1) to <1 m s(-1)) for NOGAPS and ERA-40. The creeping sea-fill is not advised for NCEP winds which have low contrast between land and sea points, thereby resulting in little impact from the land contamination.