美国加州大学圣地亚哥分校Lynn M. Russell团队发现云过饱和度的竞争响应解释了热带大西洋烟雾气溶胶的Twomey效应减弱。这一研究成果发表在2025年3月24日出版的《美国科学院院刊》上。

Twomey效应通过增加气溶胶浓度来增亮云层，这会激活更多的液滴并降低云层的过饱和度，以应对更多的水蒸气竞争。为了量化这种竞争反应，研究组在分层气溶胶-烟雾与云相互作用（LASIC）活动期间，在热带南大西洋阿森松岛的清洁和烟雾条件下使用了海洋低云观测。这些观测结果表明，基于地表和卫星云的反演中，随着累积模式粒子的增加，液滴数量也有类似的增加，这表明了云下气溶胶测量对于在清洁和烟雾气溶胶条件下反演气溶胶-云相互作用（ACI）的重要性。

研究组比较了从气溶胶-云测量中估算云过饱和度的四种方法，基于云场景和基于包裹的方法显示出足够的可变性，对气溶胶累积数浓度和云基上升气流速度都有很强的依赖性。分解云反照率和光学深度中与气溶胶相关的变化表明，计算出的竞争响应将激活响应抑制了12%至35%，这解释了LASIC和以前世界各地烟雾条件下观测到的高气溶胶浓度下Twomey效应减弱的原因。

这一结果与基于云场景的液滴数和云凝结核以及基于包裹的多模尺寸分辨拉格朗日方法的独立过饱和度反演结果是一致的。将气溶胶效应转化为局部辐射强迫，将清洁条件作为当今工业化前和烟雾条件的替代，表明竞争反应将Twomey辐射强迫的冷却减少了12%至35%，为改善间接气溶胶强迫气候模型模拟中气溶胶竞争的表示提供了一个重要的过程特定约束。

附：英文原文

Title: Competition response of cloud supersaturation explains diminished Twomey effect for smoky aerosol in the tropical Atlantic

Author: Dedrick, Jeramy L., Pelayo, Christian N., Russell, Lynn M., Lubin, Dan, Mülmenstdt, Johannes, Miller, Mark

Issue&Volume: 2025-3-24

Abstract: The Twomey effect brightens clouds by increasing aerosol concentrations, which activates more droplets and decreases cloud supersaturation in response to more competition for water vapor. To quantify this competition response, we used marine low cloud observations in clean and smoky conditions at Ascension Island in the tropical South Atlantic during the Layered Aerosol Smoke Interactions with Cloud (LASIC) campaign. These observations show similar increases in droplet number for increased accumulation-mode particles from surface-based and satellite cloud retrievals, demonstrating the importance of below-cloud aerosol measurements for retrieving aerosol–cloud interactions (ACI) in clean and smoky aerosol conditions. Four methods for estimating cloud supersaturation from aerosol–cloud measurements were compared, with cloud scene-based and parcel-based methods showing sufficient variability for a strong dependence on both aerosol accumulation number concentration and cloud-base updraft velocities. Decomposing aerosol-related changes in cloud albedo and optical depth shows the calculated competition response accounts for dampening the activation response by 12 to 35%, explaining the diminished Twomey effect at high aerosol concentrations observed for smoky conditions at LASIC and previously around the world. This result was consistent for independent supersaturation retrievals by cloud scene-based droplet number and cloud condensation nuclei and parcel-based multimode size-resolving Lagrangian methods. Translating aerosol effects to local radiative forcing with clean conditions as a proxy for preindustrial and smoky conditions for present-day showed that the competition response reduces cooling from the Twomey radiative forcing by 12 to 35%, providing an essential process-specific constraint for improving the representation of aerosol competition in climate model simulation of indirect aerosol forcing.

DOI: 10.1073/pnas.2412247122

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2412247122