Collaborative Research: Using SOCRATES Datasets to Improve Simulations of Clouds, Aerosols and their Climate Impacts

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。本项目是“南大洋云、辐射、气溶胶、运输实验研究”（SOCRATES）的一个组成部分。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总部设在澳大利亚霍巴特，多次飞越南极锋，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。这里支持的工作使用苏格拉底运动收集的数据来改进SO云和云-气溶胶相互作用在气候和天气模式中的表现。讨论了云的缺陷的几个可能的原因，包括云微物理表示的缺陷导致过冷液态水（SLW）云滴过快冻结，来自浅积云的降水过多，小尺度湍流运动表示的错误及其对云水分布的影响。气溶胶及其作为液滴凝结核和云冰成核粒子的作用的不准确表示。该运动的大部分活动都集中在SO云中SLW的丰富程度上，这些云比北半球的云更少被冰川覆盖（即它们含有更多的非常冷的液滴和更少的冰粒），并且在这个项目中使用模型模拟来理解这种差异。采用了两类模式：全球大气模式和大涡模拟模式。全球模式包括社区大气模式第6版（CAM6）和大气模式第4版（AM4），前者由研究界开发，并由国家大气研究中心托管，后者由地球物理流体动力学实验室开发。LES模型是由纽约州立大学石溪分校和科罗拉多州立大学的研究人员开发的大气模拟系统（SAM）。对于全球模式，“微推气象学”策略被用来促进观测和模式模拟之间的比较。在这种策略中，模型受到强迫条件的约束，这些条件约束它保持接近由业务天气预报中心产生的风和温度值。其目标是重现进行战役观测时的大规模气象条件，以便将战役的云和气溶胶观测结果与模拟结果进行合理的比较。该项目利用从这些比较中得到的理解，以及从LES模型中得到的理解，来开发CAM6中冰核粒子的表示。这项工作具有更广泛的影响，因为它对改进用于天气预报和未来气候预测的模式具有潜在价值。由于CAM6和AM4是科学研究中广泛使用的工具，因此对模型改进的工作对科学界也有更广泛的影响。作为该活动收集的长期在线数据档案的一部分，微推气象模拟可供社区使用，此外还有用于微推模型的气象分析以及来自卫星的辅助云和海面观测。除了所开展工作的广泛影响外，该项目还为两名博士后提供了支持和培训，从而为该研究领域的科学劳动力的发展提供了支持。ppi还参与了包括SOCRATES博客在内的竞选活动。

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 a component of the 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 is based in Hobart, Australia and makes 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 here uses data collected in the SOCRATES campaign to improve the representation of SO clouds and cloud-aerosol interactions in climate and weather models. Several possible reasons for the cloud deficiencies are addressed, including deficiencies in the representation of cloud microphysics leading to overly rapid freezing of supercooled liquid water (SLW) cloud droplets, excessive precipitation from shallow cumulus clouds, errors in the representation of small-scale turbulent motions and their effects on the distribution of cloud water, and inaccurate representation of aerosols and their role as condensation nuclei for liquid droplets and nucleating particles for cloud ice. Much of the activity in the campaign is focused on the abundance of SLW in SO clouds, which are less glaciated than their Northern Hemisphere counterparts (i.e. they contain more very cold liquid droplets and fewer ice particles), and work in this project uses model simulations to understand this difference.Two categories of models are used, global atmospheric models and large-eddy simulation (LES) models. Global models include the Community Atmosphere Model version 6 (CAM6), developed by and for the research community and hosted at the National Center for Atmospheric Research, and the Atmospheric Model version 4 (AM4), developed by the Geophysical Fluid Dynamics Laboratory. The LES model is the System for Atmospheric Modeling (SAM), developed by researchers at the State University of New York at Stony Brook and the Colorado State University. For the global models, a "nudged meteorology" strategy is used to facilitate comparisons between observations and model simulations. In this strategy the model is subjected to forcing terms which constrain it to remain close wind and temperature values produced by operational weather forecasting centers. The goal is to reproduce the large-scale meteorological conditions in which campaign observations were made, so that the cloud and aerosol observations from the campaign can be reasonably compared to their simulated counterparts. The project uses the understanding developed from these comparisons, and from the LES modeling, to develop a representation for ice nucleating particles in CAM6. The work has broader impacts due to its potential value for improving models used for weather prediction and future climate projections. The work on model improvement also has broader impacts for the scientific research community, as CAM6 and AM4 are widely used tools for scientific research. The nudged meteorology simulations are available for community use as part of the long-term online archive of data collected in the campaign, along with the meteorological analyses used to nudge the models and ancillary cloud and sea surface observations from satellites. In addition to the broader impacts of the work performed, the project provides support and training for two postdocs, thereby providing for the development of the scientific workforce in this research area. The PIs also contribute to campaign outreach activities including a SOCRATES blog.