ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-14-11611-2014 On direct passive microwave remote sensing of sea spray aerosol production Savelyev I. B. 1 Anguelova M. D. 1 Frick G. M. 1 Dowgiallo D. J. 1 Hwang P. A. 1 Caffrey P. F. 1 Bobak J. P. 1 Remote Sensing Division, Code 7200, US Naval Research Laboratory, 4555 Overlook Ave, SW., Washington, DC 20375, USA 05 11 2014 14 21 11611 11631 Copyright: © 2014 I. B. Savelyev et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/14/11611/2014/acp-14-11611-2014.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/14/11611/2014/acp-14-11611-2014.pdf

This study addresses and attempts to mitigate persistent uncertainty and scatter among existing approaches for determining the rate of sea spray aerosol production by breaking waves in the open ocean. The new approach proposed here utilizes passive microwave emissions from the ocean surface, which are known to be sensitive to surface roughness and foam. Direct, simultaneous, and collocated measurements of the aerosol production and microwave emissions were collected aboard the <i>FLoating Instrument Platform</i> (<i>FLIP</i>) in deep water ~ 150 km off the coast of California over a period of ~ 4 days. Vertical profiles of coarse-mode aerosol (0.25–23.5 μm) concentrations were measured with a forward-scattering spectrometer and converted to surface flux using dry deposition and vertical gradient methods. Back-trajectory analysis of eastern North Pacific meteorology verified the clean marine origin of the sampled air mass over at least 5 days prior to measurements. Vertical and horizontal polarization surface brightness temperature were measured with a microwave radiometer at 10.7 GHz frequency. Data analysis revealed a strong sensitivity of the brightness temperature polarization difference to the rate of aerosol production. An existing model of microwave emission from the ocean surface was used to determine the empirical relationship and to attribute its underlying physical basis to microwave emissions from surface roughness and foam within active and passive phases of breaking waves. A possibility of and initial steps towards satellite retrievals of the sea spray aerosol production are briefly discussed in concluding remarks.

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