SOCRATES: Microphysical Processes in Southern Ocean Clouds

苏格拉底：南大洋云层的微物理过程

• 批准号: 1660594
• 负责人: Greg McFarquhar
• 金额: $ 82.15万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-06-01 至 2017-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1660594&HistoricalAwards=false
• 关键词: SOCRATES; Microphysical; Processes; Southern; Ocean

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.The work funded under this award 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. A key issue addressed here is the relative abundance of supercooled liquid water (SLW) droplets and ice particles in SO clouds, as SLW is more prevalent in SO clouds than their Northern Hemisphere counterparts. When ice crystals form in clouds they tend to grow at the expense of liquid droplets, as water preferentially evaporates from droplets and condenses onto ice particles through the Wegener-Bergeron-Findeisen process. The PIs hypothesize that the persistence of SLW in SO clouds is due in part to a lack of ice nucleating particles (INPs), particles which trigger freezing within liquid droplets. INPs are much less common than cloud condensation nuclei (CCN), the particles onto which water vapor condenses to produce liquid droplets, as ice nucleation can only occur on particles which have a conducive crystalline structure. Lack of INPs is a reasonable conjecture as many ice nucleating materials such as soil minerals and plant matter come from land and might thus be unavailable over the SO. But ice nucleation can also be driven by fragments and splinters of ice from the breakup of graupel and other frozen precipitation particles, and the PIs hypothesize that this sort of "secondary nucleation" is hampered by factors including limited cloud depth, weak cloud updrafts, and low precipitation rates.The examination of controls on the depth, amount, and longevity of SLW in SO clouds is conducted using several wing-mounted probes to characterize raindrops, cloud droplets, and ice particles. Instruments including a Cloud Droplet Probe (CDP), a two-dimensional cloud probe (2DC), and a 2-D stereo probe (2DS), are used to generate size distributions for particles from 25 microns to 2mm. A Particle Habit Imaging and polar Scattering probe (PHIPS) is used to determine the shape of ice particles, and two additional probes are used to determine cloud SLW content. The wing-mounted probes are used along with data from inlet-based instruments to assess the relative importance of secondary ice formation compared with primary nucleation. Data collected by airborne radar and lidar provides information on cloud ice particles and droplets on larger spatial scales as well as information on cloud updraft and downdraft strength. Further work is performed using numerical models.The campaign 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. In addition, the pristine conditions of the SO are the closest available analog to the pre-industrial atmosphere and thus campaign observations could be helpful in understanding the anthropogenic contribution to aerosols and aerosol-cloud interactions. 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. Educational broader impacts include the participation of three graduate students in campaign and post-campaign activities. Several outreach activities are planned for the deployment, involving public speaking and tours of the aircraft. Social media outreach is also planned, through blog postings, twitter, and a Facebook page.

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。这项由该奖项资助的工作是名为“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。这里讨论的一个关键问题是SO云中相对丰富的过冷液态水（SLW）液滴和冰粒，因为SLW在SO云中比北半球的同类云更普遍。当冰晶在云中形成时，它们倾向于以液滴为代价而增长，因为水优先从液滴蒸发，并通过韦格纳-伯格龙-芬德森过程凝结成冰粒。PIs假设，在SO云中持续存在的慢冷天气部分是由于缺乏冰核粒子（INPs），这些粒子会触发液滴内的冻结。INPs远不如云凝结核（CCN）常见，因为冰核只能发生在具有有利结晶结构的粒子上。云凝结核是水蒸气凝结在其上产生液滴的粒子。缺乏INPs是一个合理的推测，因为许多冰核物质，如土壤矿物质和植物物质来自陆地，因此在SO上可能无法获得。但是，霰和其他冰冻降水颗粒破碎产生的冰块碎片也可能驱动冰的成核。pi假设，这种“二次成核”受到云层深度有限、云层上升气流弱和降水率低等因素的阻碍。使用几个安装在机翼上的探针来表征雨滴、云滴和冰粒，对SO云中SLW的深度、数量和寿命的控制进行了检查。包括云滴探针（CDP）、二维云探针（2DC）和二维立体探针（2DS）在内的仪器用于生成25微米至2mm的颗粒尺寸分布。粒子习惯成像和极性散射探针（PHIPS）用于确定冰颗粒的形状，另外两个探针用于确定云的SLW含量。安装在机翼上的探测器与基于入口的仪器的数据一起使用，以评估与初级成核相比，二次冰形成的相对重要性。机载雷达和激光雷达收集的数据提供了更大空间尺度上云冰颗粒和液滴的信息，以及云上升气流和下降气流强度的信息。进一步的工作是使用数值模型进行的。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，因此该活动具有更广泛的影响。此外，SO的原始条件与工业化前的大气最接近，因此活动观测有助于理解人为对气溶胶和气溶胶-云相互作用的贡献。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。更广泛的教育影响包括三名研究生参与竞选和竞选后的活动。为部署计划了几项外联活动，包括公开演讲和参观飞机。此外，还计划通过博客、twitter和Facebook页面向社会媒体推广。