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<p>Cloud droplet number concentration (N<sub>d</sub>) is modulated by aerosols and subsequently influences low-level cloud radiative effects. Using two decades of satellite and reanalysis data, we quantified N<sub>d</sub> responses to aerosol perturbations over the Southern Ocean (south of 60°S). Significant temporal increases over 2003–2022 in sulfate (47.6%), coarse sea salt (CSS, 76.5%), and fine sea salt (FSS, 80.6%) align with shifting environmental drivers. Despite these trends, summertime N<sub>d</sub> rose by only 6.6%. This muted response is primarily associated with opposing microphysical effects: FSS enhances N<sub>d</sub> by acting as cloud condensation nuclei in low-sulfate regimes, whereas large, hygroscopic CSS tends to suppress N<sub>d</sub> through water vapor competition. A neural network attributes ~60% of the N<sub>d</sub> trend to sulfate, while the counteracting effects of FSS and CSS result in a negligible net sea-salt contribution. These results reveal a buffering mechanism, necessitating size-resolved sea-salt in climate models to better constrain cloud–radiative feedbacks.</p>

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Opposing effects of sea salt aerosols constrain cloud droplet responses over the Southern Ocean

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年6月26日

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  • Jun Shi,
  • Minghuai Wang,
  • Yannian Zhu,
  • Daniel Rosenfeld,
  • Yang Cao,
  • Jihu Liu,
  • Yichuan Wang,
  • Boyang Zheng

摘要

Cloud droplet number concentration (Nd) is modulated by aerosols and subsequently influences low-level cloud radiative effects. Using two decades of satellite and reanalysis data, we quantified Nd responses to aerosol perturbations over the Southern Ocean (south of 60°S). Significant temporal increases over 2003–2022 in sulfate (47.6%), coarse sea salt (CSS, 76.5%), and fine sea salt (FSS, 80.6%) align with shifting environmental drivers. Despite these trends, summertime Nd rose by only 6.6%. This muted response is primarily associated with opposing microphysical effects: FSS enhances Nd by acting as cloud condensation nuclei in low-sulfate regimes, whereas large, hygroscopic CSS tends to suppress Nd through water vapor competition. A neural network attributes ~60% of the Nd trend to sulfate, while the counteracting effects of FSS and CSS result in a negligible net sea-salt contribution. These results reveal a buffering mechanism, necessitating size-resolved sea-salt in climate models to better constrain cloud–radiative feedbacks.