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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 21 | Copyright
Atmos. Chem. Phys., 16, 13725-13751, 2016
https://doi.org/10.5194/acp-16-13725-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Nov 2016

Research article | 07 Nov 2016

Parameterization of oceanic whitecap fraction based on satellite observations

Monique F. M. A. Albert1, Magdalena D. Anguelova2, Astrid M. M. Manders1, Martijn Schaap1, and Gerrit de Leeuw1,3,4 Monique F. M. A. Albert et al.
  • 1TNO, P.O. Box 80015, 3508 TA Utrecht, the Netherlands
  • 2Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375, USA
  • 3Climate Research Unit, Finnish Meteorological Institute, Helsinki, Finland
  • 4Department of Physics, University of Helsinki, Helsinki, Finland

Abstract. In this study, the utility of satellite-based whitecap fraction (W) data for the prediction of sea spray aerosol (SSA) emission rates is explored. More specifically, the study aims at evaluating 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 discrete whitecap method. The starting point is a data set containing W data for 2006 together with matching wind speed U10 and sea surface temperature (SST) T. Whitecap fraction W was estimated from observations of the ocean surface brightness temperature TB by satellite-borne radiometers at two frequencies (10 and 37GHz). A global-scale assessment of the data set yielded approximately quadratic correlation between W and U10. A new global W(U10) parameterization was developed and used to evaluate an intrinsic correlation between W and U10 that could have been introduced while estimating W from TB. A regional-scale analysis over different seasons indicated significant differences of the coefficients of regional W(U10) relationships. The effect of SST on W is explicitly accounted for in a new W(U10, T) parameterization. The analysis of W values obtained with the new W(U10) and W(U10, 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(U10, T) parameterization is able to partially model the spread (or variability) of the satellite-based W data. The satellite-based parameterization W(U10, T) was applied in an SSSF to estimate the global SSA emission rate. The thus obtained SSA production rate for 2006 of 4.4 × 1012kgyear−1 is within previously reported estimates, however with distinctly different spatial distribution.

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Sea spray source functions (SSSFs) predict production of sea salt aerosol, important for climate. Sea spray originates from bubble bursting within whitecaps, mainly formed by wind speed (U). Using satellite-based whitecap fraction (W) data analyzed on global and regional scale and explicitly accounting for sea surface temperature (T) we derive a new W(U, T) parameterization. We use it to evaluate influence of secondary factors on a SSSF via W.
Sea spray source functions (SSSFs) predict production of sea salt aerosol, important for...
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