Abstract. Aerosol-cloud-precipitation interactions (ACIs) provide the greatest source of uncertainties in predicting changes in Earth’s energy budget due to poor representation of marine stratocumulus and the associated ACIs in climate models. Using in situ data from 329 cloud profiles across 24 research flights from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign in September 2016, August 2017, and October 2018, it is shown that contact between above-cloud biomass-burning aerosols and marine stratocumulus over the southeast Atlantic Ocean was associated with precipitation suppression and a decrease in the precipitation susceptibility (S_o) to aerosols. The 173 “contact” profiles with aerosol concentration (N_a) greater than 500 cm⁻³ within 100 m above cloud tops had 50 % lower precipitation rate (R_p) and 20 % lower S_o, on average, compared to 156 “separated” profiles with N_a less than 500 cm⁻³ up to at least 100 m above cloud tops. Contact and separated profiles had statistically significant differences in droplet concentration (N_c) and effective radius (R_e) (95 % confidence intervals from a two-sample t-test are reported). Contact profiles had 84 to 90 cm⁻³ higher N_c and 1.4 to 1.6 μm lower R_e compared to separated profiles. In clean boundary layers (below-cloud N_a less than 350 cm⁻³), contact profiles had 25 to 31 cm⁻³ higher N_c and 0.2 to 0.5 μm lower R_e. In polluted boundary layers (below-cloud N_a exceeding 350 cm⁻³), contact profiles had 98 to 108 cm⁻³ higher N_c and 1.6 to 1.8 μm lower R_e. On the other hand, contact and separated profiles had statistically insignificant differences between the average liquid water path, cloud thickness, and meteorological parameters like surface temperature, lower tropospheric stability, and estimated inversion strength. These results suggest the changes in cloud properties were driven by ACIs rather than meteorological effects, and the existing relationships between R_p and N_c must be adjusted to account for the role of ACIs.

中文翻译：

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东南大西洋上空云下气溶胶浓度变化的海洋层积云的降水敏感性

摘要。由于海洋层积云和气候模型中相关 ACI 的代表性较差，气溶胶-云-降水相互作用 (ACI) 为预测地球能量收支变化提供了最大的不确定性来源。使用来自美国宇航局 2016 年 9 月、2017 年 8 月和 2018 年 10 月的云上气溶胶观测及其交互 (ORACLES) 现场活动的 24 次研究飞行的 329 个云剖面的原位数据，表明云上生物量-东南大西洋上空燃烧的气溶胶和海洋层积云与降水抑制和降水对气溶胶的敏感性 ( S _o )降低有关。173 个“接触”剖面与气溶胶浓度 ( N _a)与N _a小于 500 cm ^-3以上的156 个“分离”剖面相比，云顶上方 100 m 内大于 500 cm ^{-3 的}降水率 ( R _p )平均降低50% ，S _o降低 20%到云顶以上至少 100 m。接触和分离的轮廓具有在液滴浓度（统计学差异显著Ñ _Ç）和有效半径（ř _ë）（从双样本t检验95％置信区间被报告）。接触剖面的N _c高84 至 90 cm ^-3，R _e低 1.4 至 1.6 μm与分离的配置文件相比。在清洁边界层（下面云Ñ_一个小于350厘米^-3），联系人简档有25至31厘米^-3更高Ñ _Ç和0.2至0.5μm降低ř _Ë。在受污染的边界层（云下N _a超过 350 cm ^-3），接触剖面的N _c高98 至 108 cm ^-3，R _e低 1.6 至 1.8 μm. 另一方面，接触剖面和分离剖面在平均液态水路径、云层厚度和气象参数（如地表温度、较低的对流层稳定性和估计的逆温强度）之间没有统计学上的显着差异。这些结果表明云特性的变化是由 ACI 驱动的，而不是由气象效应驱动的，并且必须调整R _p和N _c之间的现有关系以考虑 ACI 的作用。