Global Drag-Coefficient Estimates From Scatterometer Wind and Wave Steepness

A neural-network model was developed to retrieve the wave steepness (δ), which was used to represent the sea state (particularly wave state), from the European Remote Sensing (ERS) scatterometer onboard ERS-1/2. Using the retrieved δ and scatterometer wind speed, we calculated and examined the drag coefficient (
CD
) over the global ocean. The results show that
CD
changes significantly when wave steepness is included in the calculation. Combining wave steepness and wind speed increases
CD
by nearly 14% on average. That change is spatially variable, ranging from -18.76% for the tropical Eastern Pacific Ocean to 104% for the Southern Ocean.