Globally Applicable Whitecap Estimates using Satellite Data

Oceanic whitecap formation is a response to stress imparted by the atmosphere to the ocean. Contributing factors to whitecap formation and variability include wind speed, stability, fetch, sea state, salinity, and surface currents. Over the last four decades, many efforts using in situ and localized remote sensing observations have aided in understanding whitecap formation and characteristics and obtaining whitecap fraction (W). Whitecaps affect air-sea interactions by modifying ocean surface properties such as turbulent fluxes and surface albedo. The nature of these observations provided information on relatively short temporal and spatial scales and cannot capture W variability globally. Recent efforts in satellite-based observations of W on a global scale under a variety of environmental conditions provide new possibilities for understanding whitecap contributions and characteristics.

This study attempts to determine the major contributing factors for W globally using the microwave emissivity-based whitecap retrievals of the Whitecap Database (Anguelova et at. 2010) for one year (2006). This study includes a tentative analysis for W with wind speeds greater than 20 m/s, which are rarely observed in in situ conditions. The major contributing factors from the available parameters--wind speed, stability, and significant wave height are used to determine characteristics of calculating global whitecap fraction. An empirical function for calculating remotely sensed W globally based on available parameters is presented.