Marine stratocumulus clouds cover nearly one-quarter of the ocean surface and thus play an extremely important role in determining the global radiative balance. The semipermanent marine stratocumulus deck over the southeastern Atlantic Ocean is of particular interest, because of its interactions with seasonal biomass burning aerosols that are emitted in southern Africa. Understanding the impacts of biomass burning aerosols on stratocumulus clouds and the implications for regional and global radiative balance is still very limited. Previous studies have focused on assessing the magnitude of the warming caused by solar scattering and absorption by biomass burning aerosols over stratocumulus (the direct radiative effect) or cloud adjustments to the direct radiative effect (the semidirect effect). Here, using a nested modeling approach in conjunction with observations from multiple satellites, we demonstrate that cloud condensation nuclei activated from biomass burning aerosols entrained into the stratocumulus (the microphysical effect) can play a dominant role in determining the total radiative forcing at the top of the atmosphere, compared with their direct and semidirect radiative effects. Biomass burning aerosols over the region and period with heavy loadings can cause a substantial cooling (daily mean −8.05 W m⁻²), primarily as a result of clouds brightening by reducing the cloud droplet size (the Twomey effect) and secondarily through modulating the diurnal cycle of cloud liquid water path and coverage (the cloud lifetime effect). Our results highlight the importance of realistically representing the interactions of stratocumulus with biomass burning aerosols in global climate models in this region.

海洋层积云覆盖了近四分之一的海洋表面，因此在确定全球辐射平衡方面发挥着极其重要的作用。东南大西洋上空的半永久性海洋层积云甲板特别令人感兴趣，因为它与南部非洲排放的季节性生物质燃烧气溶胶相互作用。了解生物质燃烧气溶胶对层积云的影响以及对区域和全球辐射平衡的影响仍然非常有限。先前的研究重点是评估层积云上的太阳散射和生物质燃烧气溶胶吸收（直接辐射效应）或云对直接辐射效应（半直接效应）的吸收所引起的变暖程度。在这里，使用嵌套建模方法结合多个卫星的观测，我们证明了由夹带到层积云中的生物质燃烧气溶胶激活的云凝结核（微物理效应）可以在确定云层顶部的总辐射强迫方面发挥主导作用。大气层及其直接和半直接辐射效应的比较。在负荷重的地区和时期，生物质燃烧气溶胶会导致大幅降温（日均值 -8.05 W m ^-2 ），这主要是由于云滴尺寸减小（图梅效应）而使云变亮，其次是通过调节云液态水路径和覆盖范围的日循环（云寿命效应）。我们的结果强调了在该地区的全球气候模型中真实地表示层积云与生物质燃烧气溶胶的相互作用的重要性。