Air-Sea Aerosol Flux and Sea State Measurements During HiWinGS

The High Wind Gas exchange Study (HiWinGS) field program took place in the autumn of 2013 to the South-West of Greenland. A team of US and UK scientists onboard the R/V Knorr directly measured air-sea fluxes of aerosol, momentum, heat, moisture, CO₂, DMS, acetone, methanol and monoterpenes. The project aims to investigate the influence of forcings such as sea state on turbulent fluxes at high latitude and in high wind speed conditions. Comprehensive sea state measurements were obtained using a Waverider buoy, a laser wave profiler, whitecap cameras and spar-buoys equipped with wave wires, bubble resonators and wave cameras. Seawater concentration measurements enabled computation of transfer velocities for several gases.

Measurements were successfully obtained under a wide variety of wind speeds and sea states and during the passage of several storms. Average H_s during HiWinGS was 4.8 m and maximum 10-minute average U₁₀ and H_s were 27.7 m s^-1 and 11.4 m respectively. Winds were consistently high, with U₁₀ continuously sustained above 15 m s^-1 for 34 hours (165 hours total above 15 m s^-1).

Here we focus on the direct eddy-covariance sea-spray aerosol flux measurements obtained during HiWinGS using a Compact Lightweight Aerosol Spectrometer Probe (CLASP). The CLASP provides a 16-channel aerosol size spectrum in the range 0.18 < R < 7.5 mm at 10 Hz, enabling fully size segregated aerosol fluxes to be determined. The unique measurements and conditions from HiWinGS are used for an analysis of the influence of sea state and an evaluation of existing Reynolds number-based aerosol flux parameterisations.