Analysis of G-V Aircraft and Complementary SOCRATES Observations to Understand Clouds, Aerosols and their Interactions Over the Southern Ocean

南大洋（SO），意思是高纬度南半球的全球海洋，作为地球上风暴最多的地方，它有着当之无愧的声誉。SO的偏远及其恶劣的条件严重限制了对其上方发生的大气过程的观测，包括沿南极锋移动的气旋中的云过程。然而，由于各种原因，这些过程引起了人们的兴趣，其中包括SO云相对不受大陆和人为气溶胶的影响，因此该地区是研究原始条件下云行为的天然实验室。SO云还通过将射入的阳光反射回太空，在地球的能量平衡中起着重要的冷却作用。有证据表明，这种冷却对与热带辐合带相关的低纬度降雨分布具有长期影响，并且由于全球气候变化导致的SO云量变化将影响南半球急流的位置和强度。我们对SO云过程缺乏了解的一个指标是在气候模式模拟中发现的SO云覆盖不足，这伴随着海洋表面对阳光的过度吸收，这反过来可能导致对气候敏感性估计的误差。模拟云量的不足在沿SO风暴路径行进的锋面天气系统冷、干扇区的边界层和对流层下层云（顶部低于3km）中最为明显。这个项目是名为“南大洋云、辐射、气溶胶、运输实验研究”（SOCRATES）的大型野外活动的一部分。该活动的主要活动是部署一架湾流V （GV）研究飞机，由美国国家大气研究中心地球观测实验室维护。GV将以澳大利亚霍巴特为基地，进行多次飞越南极锋的飞行，收集SO云及其发生的气象条件的数据。GV配备了用于记录环境气象条件的落差探空仪，用于观测云层的雷达和激光雷达，以及安装在机翼上或位于入口后面的仪器，用于对气溶胶和云颗粒（液滴和冰晶）进行取样、收集和分析。苏格拉底活动是对国际和其他美国机构计划的SO活动的补充，包括在船上和在南纬54度的一个无人居住的小岛麦夸里岛进行的水面观测。该奖项支持的工作专门针对在大气边界层顶部发现的相对温暖的浅云，特别关注云滴数浓度，或云中单位体积的液滴数。液滴数浓度是了解云性质和演变的关键参数，在像SO这样的原始区域，它可能受到云凝结核（CCN）的可用性的限制，CCN是气溶胶颗粒，从空气中吸收水蒸气形成液滴。pi试图确定液滴数浓度是否与当地边界层或其上的自由对流层的CCN浓度有关，或者液滴浓度是否更强烈地受到湍流云运动、降水去除或其他气象因素的影响。先前的研究表明，在南极锋以南较冷的空气中的低空云，其平均液滴浓度高于北部较暖的云，这一差异目前尚不清楚。可能的解释包括：在南方较冷的海水中（即更靠近南极的海域）CCN产生增加，以及随着北方CCN去除的增加，降水率增加。与其他苏格拉底项目合作收集的各种观测结果用于检查SO云中液滴数量浓度的时空变化控制：*在边界层以上和边界层内，使用多个飞行水平的GV上的探针和入口，大小分辨气溶胶和CCN浓度；*降水率，云上升气流和下降气流强度，云底和顶高度由机载雷达和激光雷达确定。*来自低空飞行腿的近地表气溶胶和CCN浓度，计划采样至离地表150米；*从飞机上释放的下投式探空仪获得的环境温度、湿度和风的剖面图。将这些数据结合起来形成综合数据集，其中包括一个南北“苏格拉底幕”数据集，便于与数值模式输出进行比较。还计划了基于这些数据集的建模活动。由于SO云在确定全球气候对来自温室气体增加和其他因素的外部强迫的敏感性方面具有潜在的重要作用，因此这项工作具有更广泛的影响。该活动的数据将用于开发用于天气预报和气候影响评估的模型中更好的云表示。这些数据将提供给全世界的科学界，因此，通过为基础科学研究创造一个社区资源，该运动具有更广泛的影响。在活动期间，通过定期通讯和博客以及一个互动的“问苏格拉底”网站，向K-12学生和公众进行宣传。该项目为两名研究生提供支持，从而为该研究领域的未来劳动力提供支持。

The Southern Ocean (SO), meaning the global ocean of the high latitude Southern Hemisphere, has a well-deserved reputation as the stormiest place on earth. The remoteness of the SO and its unforgiving conditions have severely limited observations of atmospheric processes occurring above it, including cloud processes in the cyclones traveling along the South Polar front. Yet these processes are of interest for a variety of reasons, including the fact that SO clouds are relatively free from the effects of continental and anthropogenic aerosols, and the region is thus a natural laboratory for the study of cloud behavior under pristine conditions. SO clouds also play a significant cooling role in the energy balance of the planet by reflecting incoming sunlight back to space. There is evidence to suggest that this cooling has a long-range effect on the distribution of the low-latitude rainfall associated with the intertropical convergence zone, and that changes in SO cloudiness due to global climate change will affect the location and strength of the Southern Hemisphere jet stream. One indicator of our lack of understanding of SO cloud processes is the inadequate SO cloud cover found in climate model simulations, which is accompanied by excessive absorption of sunlight by the ocean surface which may in turn cause errors in estimates of climate sensitivity. The deficiency in simulated cloud cover is most pronounced in boundary layer and lower-tropospheric clouds (tops below 3km) in the cold, dry sectors of frontal weather systems traveling along the SO storm track.This project is part of a larger field campaign titled Southern Ocean Clouds, Radiation, Aerosol, Transport Experimental Study (SOCRATES). The primary activity of the campaign is the deployment of a Gulfstream V (GV) research aircraft maintained by the Earth Observing Laboratory of the National Center for Atmospheric Research. The GV will be based in Hobart, Australia and make multiple flights across the South Polar front collecting data on SO clouds and the meteorological conditions in which they occur. The GV is equipped with dropsondes to record ambient meteorological conditions, radar and lidar to observe the clouds, and instruments mounted on the wings or positioned behind inlets to to sample, collect and analyze aerosols and cloud particles (liquid droplets and ice crystals). The SOCRATES campaign is complementary to SO activities planned internationally and by other US agencies, including surface observations taken on ships and on MacQuarie Island, a small uninhabited island at 54 degrees South.Work supported under this award specifically addresses the relatively warm, shallow clouds found at the top of the atmospheric boundary layer, with a specific focus on cloud droplet number concentration, or the number of droplets per unit volume in a cloud. Droplet number concentration is a key parameter for understanding cloud properties and evolution, and in a pristine region like the SO it can be limited by the availability of cloud condensation nuclei (CCN), aerosol particles which absorb water vapor from the air to form droplets. The PIs seek to determine if droplet number concentration can be related to CCN concentration in the local boundary layer or the overlying free troposphere, or if droplet concentrations are more strongly influenced by turbulent cloud motions, removal through precipitation, or other meteorological factors. Previous studies suggest that low clouds in the colder air to the south of the South Polar front have higher mean droplet concentrations than the warmer clouds to the north, a difference which is not presently understood. Possible explanations include increased CCN production in the colder ocean waters to the south (meaning closer to the South Pole), and higher precipitation rates with increased CCN removal to the north.A variety of observations, collected in collaboration with other SOCRATES projects, are used to examine the controls on space and time variability of droplet number concentration in SO clouds:* size-resolved aerosol and CCN concentrations, both above and within the boundary layer, using probes and inlets on the GV at multiple flight levels;* precipitation rates, cloud updraft and downdraft strength, and cloud base and top heights determined from onboard radar and lidar.* near-surface aerosol and CCN concentrations from low-level flight legs, planned to sample as low as 150m above surface;* profiles of ambient temperature, moisture, and wind from dropsondes released from the aircraft.These data are combined to produce integrated datasets including a north-south "SOCRATES curtain" dataset which facilitates comparison with numerical model output. Modeling activities based on these datasets are also planned.The work has broader impacts due to the potentially significant role of SO clouds in determining the sensitivity of global climate to external forcing from greenhouse gas increases and other factors. Data from the campaign will be used to develop better representations of clouds in models used for weather prediction and climate impacts assessments. The data will be made available to the worldwide scientific community, thus the campaign has broader impacts by creating a community resource for basic science research. Outreach to K-12 students and the general public is conducted during the campaign through regular newsletters and blogs, and an interactive "Ask SOCRATES" website. This project provides support to two graduate students, thereby providing for the future workforce in this research area.