Abstract. Quantification of the radiative adjustment of marine low-clouds to aerosol perturbations, regionally and globally, remains the largest source of uncertainty in assessing current and future climate. An important step towards quantifying the role of aerosol in modifying cloud radiative properties is to quantify the susceptibility of cloud albedo and liquid water path (LWP) to perturbations in cloud droplet number concentration (Nd). We use 10 years of space-borne observations from the polar-orbiting Aqua satellite, to quantify the albedo susceptibility of marine low-clouds over the northeast (NE) Pacific stratocumulus region to Nd perturbations. Overall, we find a low-cloud brightening potential of 20.8 ± 0.96 W m⁻² ln(N_d)⁻¹, despite an overall negative LWP adjustment for non-precipitating marine stratocumulus, owing to the high occurrence (37% of the time) of thin non-precipitating clouds (LWP < 55 g m⁻²) that exhibit brightening. In addition, we identify two more susceptibility regimes, the entrainment-darkening regime (36% of the time), corresponding to negative LWP adjustment, and the precipitating-brightening regime (22% of the time), corresponding to precipitation suppression. The influence of large-scale meteorological conditions, obtained from the ERA5 reanalysis, on the albedo susceptibility is also examined. Over the NE Pacific, clear seasonal covariabilities among meteorological factors related to the large-scale circulation are found to play an important role in grouping favorable conditions for each susceptibility regime. Our results indicate that, for the NE Pacific stratocumulus deck, the strongest positively susceptible cloud states occur most frequently for low cloud top height (CTH), the highest lower-tropospheric stability (LTS), low sea-surface temperature (SST), and the lowest free-tropospheric relative humidity (RHft) conditions, whereas cloud states that exhibit negative LWP adjustment occur most frequently under high CTH and intermediate LTS, SST, and RHft conditions. The warm rain suppression driven cloud brightening is found to preferably occur either under unstable atmospheric conditions (low LTS) or high RHft conditions that co-occur with warm SST. Mutual information analyses reveal a dominating control of LWP, Nd and CTH (cloud state indicators) on low-cloud albedo susceptibility, rather than of the meteorological factors that drive these cloud states.

中文翻译：

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东北太平洋层积云的反照率敏感性：共变气象条件的作用

摘要。在区域和全球范围内，对海洋低云对气溶胶扰动的辐射调整进行量化，仍然是评估当前和未来气候的最大不确定性来源。量化气溶胶在改变云辐射特性中的作用的一个重要步骤是量化云反照率和液态水路径 (LWP) 对云滴数浓度 (Nd) 扰动的敏感性。我们使用极轨 Aqua 卫星 10 年的星载观测来量化东北 (NE) 太平洋层积云区域上的海洋低云对 Nd 扰动的反照率敏感性。总体而言，我们发现低云增亮潜力为 20.8 ± 0.96 W m ^-2 ln(N _d ) ^-1，尽管非降水海洋层积云的 LWP 总体为负调整，但由于薄的非降水云（LWP < 55 g m ^-2) 表现出增亮。此外，我们还确定了另外两种易感性状态，夹带-变暗状态（36% 的时间），对应于负 LWP 调整，以及沉淀-变亮状态（22% 的时间），对应于降水抑制。还研究了从 ERA5 再分析获得的大尺度气象条件对反照率敏感性的影响。在太平洋东北部，发现与大尺度环流相关的气象因素之间明显的季节性协变在为每个易感性制度分组有利条件方面发挥着重要作用。我们的结果表明，对于东北太平洋层积云甲板，最强烈的正易感云状态最常出现在低云顶高度（CTH）、最高的低对流层稳定性（LTS）、低海面温度 (SST) 和最低的自由对流层相对湿度 (RHft) 条件，而在高 CTH 和中等 LTS、SST 和 RHft 条件下，表现出负 LWP 调整的云状态最常发生。发现暖雨抑制驱动的云增亮优选发生在不稳定的大气条件（低 LTS）或高 RHft 条件下，这些条件与温暖的 SST 共同发生。互信息分析揭示了 LWP、Nd 和 CTH（云状态指标）对低云反照率敏感性的主导控制，而不是驱动这些云状态的气象因素。而表现出负 LWP 调整的云状态最常出现在高 CTH 和中等 LTS、SST 和 RHft 条件下。发现暖雨抑制驱动的云增亮优选发生在不稳定的大气条件（低 LTS）或高 RHft 条件下，这些条件与温暖的 SST 共同发生。互信息分析揭示了 LWP、Nd 和 CTH（云状态指标）对低云反照率敏感性的主导控制，而不是驱动这些云状态的气象因素。而表现出负 LWP 调整的云状态最常出现在高 CTH 和中等 LTS、SST 和 RHft 条件下。发现暖雨抑制驱动的云增亮优选发生在不稳定的大气条件（低 LTS）或高 RHft 条件下，这些条件与温暖的 SST 共同发生。互信息分析揭示了 LWP、Nd 和 CTH（云状态指标）对低云反照率敏感性的主导控制，而不是驱动这些云状态的气象因素。