Parameterization of oceanic whitecap fraction based on satellite observations

Satellite-based whitecap fraction (W) data have been used to predict sea spray aerosol (SSA) emission rates. This allows to evaluate how an account for natural variability of whitecaps in the W parameterization would affect SSA mass flux predictions when using a sea spray source function (SSSF) based on the whitecap method. Data set containing W data for 2006 together with matching wind speed U 10 and sea surface temperature (SST) T has been used. Whitecap fraction W was estimated from observations of the ocean surface brightness temperature T B by satellite-borne radiometers at two frequencies (10 and 37 GHz). A global scale assessment of the data set yielded approximately quadratic correlation between W and U 10 . A regional scale analysis yielded a new W(U 10 , T) parameterization which explicitly accounted for the effect of SST on W. The analysis of W values obtained with the new W(U 10 ) and W(U 10 , T) parameterizations indicates that the influence of secondary factors on W is for the largest part embedded in the exponent of the wind speed dependence. In addition, the W(U 10 , T) parameterization is capable to model the spread (or variability) of the satellite-based W data. The satellite-based parameterization W(U 10 , T) was applied in an SSSF to estimate the global SSA emission rate. The thus obtained SSA production rate is within previously reported estimates, however with distinctly different spatial distribution.