Atmosphere‐Ocean Feedback From Wind‐Driven Sea Spray Aerosol Production

• Published in: Geophysical Research Letters
• Main Authors: Wotherspoon NE, Jones OJ, Bhatti YA, Williams JHT, Mackie SL, Mulcahy JP, Revell, Laura
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2021
• Subjects: Fields of Research::37 - Earth sciences::3701 - Atmospheric sciences::370103 - Atmospheric aerosols; Fields of Research::37 - Earth sciences::3701 - Atmospheric sciences::370105 - Atmospheric dynamics; Fields of Research::37 - Earth sciences::3702 - Climate change science::370202 - Climatology; Southern Ocean
• Online Access: https://hdl.handle.net/10092/102104; https://doi.org/10.1029/2020gl091900

Marine aerosol production is influenced by wind speed, particularly over the Southern Ocean which is the windiest region on Earth year-round. Using climate model simulations with artificially enhanced sea spray aerosol (SSA), we show that Southern Ocean wind speeds are sensitive to SSA via surface cooling resulting from enhanced aerosol concentrations. The near-surface westerly jet weakens, therefore reducing SSA production. Comparing coupled and atmosphere-only simulations indicates that SSA partially regulates its own production via a feedback between the atmosphere and ocean. The decrease in radiative forcing in the coupled model is approximately one-quarter of that simulated by the atmosphere-only model, and the extent of the feedback also depends on the SSA source function used. Our results highlight the importance of understanding SSA emissions and their parameterization in climate models. Including a temperature dependence in SSA parameterizations can play a large role in the climate feedback, but further investigation is needed. Plain Language Summary Atmospheric aerosols can have a cooling influence on Earth's climate by scattering sunlight and seeding cloud formation. Over oceans, aerosols often contain a high fraction of sea spray, and their abundance is strongly dependent on wind speed. High wind speeds cause wave breaking and bubble bursting, which emit sea spray aerosol (SSA). Previously SSA has been shown to have a cooling influence on surface climate. We show that when we artificially enhance SSA emissions in a coupled Earth system model that about half of the cooling influence is offset by the ocean response; more SSA emitted from the ocean leads to surface cooling, and therefore wind speeds weaken and produce less SSA. This is particularly important over the Southern Ocean which is the windiest region on Earth year-round. We show that, in a climate model, the strength of the feedback depends on how SSA emission is represented by the model. Therefore in a warmer, windier climate, simulating SSA ...