Abstract
Atmospheric-chemical coupled models usually parameterize sea-salt aerosol (SSA) emissions using whitecap fraction estimated considering only wind speed and ignoring sea state. This approach may introduce inaccuracies in SSA simulation. This study aims to assess the impact of sea state on SSA modeling, applying a new parameterization for whitecap fraction estimation based on wave age, calculated by the ratio between wave phase velocity and wind speed. To this end, the new parameterization was incorporated in the coupled Chemical Hydrological Atmospheric Ocean wave modeling System (CHAOS). CHAOS encompasses the wave model (WAM) two-way coupled through the OASIS3-MCT coupler with the Advanced Weather Research and Forecasting model coupled with Chemistry (WRF-ARW-Chem) and, thus, enabling the concurrent simulation of SSAs, wind speed and wave phase velocity. The simulation results were evaluated against in-situ and lidar measurements at 2 stations in Greece (Finokalia on 4 and 15 July 2014 and Antikythera-PANGEA on 15 September 2018). The results reveal significant differences between the parameterizations with the new one offering a more realistic representation of SSA levels in some layers of the lower atmosphere. This is attributed to the enhancement of the bubble-bursting mechanism representation with air-sea processes controlling whitecap fraction. Our findings also highlight the contribution of fresh wind-generated waves to SSA modeling.
Highlights
Sea-salt aerosols (SSAs) are released from sea-spray droplets directly produced at the air-sea interface and constitute a major component of the natural aerosol mass
The implementation of the new whitecap fraction parameterization in Chemical Hydrological Atmospheric Ocean wave modeling System (CHAOS) was tested on three cases studies: 4 July 2014, 15
CHAOS was set up to simulate the three cases initializing on 3 July at 00:00 UTC, on 14 July 2014 at 00:00 UTC and on 13 September 2018 at 00:00 UTC, respectively
Summary
Sea-salt aerosols (SSAs) are released from sea-spray droplets directly produced at the air-sea interface and constitute a major component of the natural aerosol mass. The wind-wave interaction leads to air bubbles entrapment beneath the sea surface. These air bubbles, due to their buoyancy, reach the sea surface bursting and forming droplets as a result of two processes [4]. Depending on the temperature and the relative humidity of the air, sea-spray droplets evaporate as they enter a dryer environment forming SSAs which either circulate in the atmosphere or drop back to the sea surface [3,6]. The circulating SSAs, usually with radius ranging from 0.1 μm to
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