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，被誉为地球上最暴风雨的地方是当之无愧的。SO的偏远及其不可饶恕的条件严重限制了对其上方发生的大气过程的观测，包括沿南极锋面移动的气旋中的云过程。然而，出于各种原因，这些过程是有意义的，包括这样一个事实，即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。因此，云层还通过将入射的阳光反射回太空，在地球的能量平衡中发挥着重要的冷却作用。有证据表明，这种冷却对与热带辐合带有关的低纬降水的分布有长期影响，全球气候变化导致的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气候模型模拟中发现的SO云覆盖不足，伴随而来的是海洋表面对阳光的过度吸收，这可能反过来导致对气候敏感性的估计错误。模拟云层的不足在沿SO风暴路径移动的锋面天气系统的冷干部分的边界层和低对流层云(顶部低于3公里)中最为明显。这项计划是一个名为南大洋云、辐射、气溶胶、输送实验研究(苏格拉底)的更大的实地活动的一部分。该活动的主要活动是部署一架湾流V(GV)研究飞机，该飞机由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，在南极锋面进行多次飞行，收集关于SO云及其出现的气象条件的数据。GV配备了用于记录环境气象条件的投射探测仪，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进气口后面的仪器，用于采样、收集和分析气溶胶和云粒(液滴和冰晶)。苏格拉底活动是对国际上和美国其他机构计划的SO活动的补充，包括在船只上和在南纬54度的无人居住的小岛麦夸里岛上进行的地面观测。该奖项支持的工作专门研究在大气边界层顶部发现的相对温暖的浅层云，特别关注云滴数量浓度，即云中单位体积的水滴数量。液滴数量浓度是了解云的特性和演变的一个关键参数，在像云雾中心这样的原始区域，它可能受到云凝结核(CCN)的可用性的限制，CCN是一种气溶胶粒子，它从空气中吸收水蒸气形成液滴。PIs试图确定液滴数量浓度是否与局部边界层或上覆自由对流层中的CCN浓度有关，或者液滴浓度是否受湍流云运动、通过降水清除或其他气象因素的影响更大。以前的研究表明，南极锋面以南较冷空气中的低云比北极较暖云中的平均水滴浓度高，这一差异目前尚不清楚。可能的解释包括：南方较冷的海水(意思是更靠近南极)的CCN产量增加，以及随着CCN向北移动的增加，降雨率增加。与其他苏格拉底项目合作收集的各种观测被用来检查对SO云中液滴数量浓度的空间和时间变化的控制：*在边界层上方和边界层内使用探测器和GV上的多个飞行水平的进气口，以尺寸分辨的气溶胶和CCN浓度；*降雨率、云上升气流和下沉气流强度、云底和云顶高度由机载雷达和激光雷达确定。*低层飞行支腿的近地表气溶胶和CCN浓度，计划采样至地面以上150米；*从飞机上释放的下沉探测仪所产生的环境温度、湿度和风的轮廓。这些数据结合在一起，产生综合数据集，包括南北“苏格拉底幕”数据集，便于与数值模式输出进行比较。基于这些数据集的建模活动也在计划中。这项工作具有更广泛的影响，因为SO云在确定全球气候对温室气体增加和其他因素造成的外部强迫的敏感性方面具有潜在的重要作用。该活动的数据将用于在用于天气预报和气候影响评估的模型中更好地表示云。这些数据将向全世界科学界提供，因此，这项运动通过为基础科学研究创建社区资源，产生了更广泛的影响。在活动期间，通过定期通讯和博客，以及一个互动的“询问苏格拉底”网站，对K-12学生和普通公众进行了宣传。该项目为两名研究生提供支持，从而为这一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.