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

南大洋（SO），意思是南半球高纬度的全球海洋，作为地球上风暴最多的地方，有着当之无愧的声誉。SO的遥远和它的恶劣条件严重限制了对它上面发生的大气过程的观测，包括沿着南极锋行进的气旋中的云过程。然而，这些过程由于各种原因而令人感兴趣，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，这种冷却有一个长期的影响，低纬度降水的分布与热带辐合带，和SO云量的变化，由于全球气候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，这反过来可能导致气候敏感性估计的错误。模拟云量的不足在边界层和低对流层云（顶部低于3公里）中最为明显，这些云位于沿着SO风暴路径行进的锋面天气系统的寒冷干燥区域，该项目是南大洋云、辐射、气溶胶、输送实验研究的一个组成部分。该运动的主要活动是部署一架由国家大气研究中心地球观测实验室维护的湾流V（GV）研究飞机。GV的基地设在澳大利亚的霍巴特，并在南极锋面进行多次飞行，收集SO云的数据及其发生的气象条件。GV配备了用于记录环境气象条件的下投式探空仪，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进气道后面的仪器，用于采样，收集和分析气溶胶和云粒子（液滴和冰晶）。SOCRATES活动是对国际上和美国其他机构计划的SO活动的补充，包括在船上和MacQuarie岛上进行的表面观测，MacQuarie岛是南纬54度的一个无人居住的小岛。这里支持的工作使用SOCRATES活动中收集的数据，以提高SO云和云-气溶胶相互作用在气候和天气模式中的代表性。云缺陷的几个可能的原因，包括云微物理的代表性的不足，导致过冷液态水（SLW）云滴的过快冻结，从浅积云降水过多，在小尺度湍流运动的代表性及其对云水分布的影响的错误，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。 活动中的大部分活动都集中在SO云中SLW的丰富性上，SO云比北方半球的对应云少冰川化（即它们包含更多的非常冷的液滴和更少的冰粒），并且在这个项目中的工作使用模型模拟来理解这种差异。使用了两类模型，全球大气模型和大涡模拟（LES）模型。 全球模型包括社区大气模型第6版（CAM 6），由研究界开发并为研究界开发，由国家大气研究中心托管，以及地球物理流体动力学实验室开发的大气模型第4版（AM4）。 LES模型是大气模拟系统（SAM），由纽约州立大学州立大学和科罗拉多州立大学州立大学的研究人员开发。 对于全球模式，采用“微推气象学”战略，以便利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，使其保持接近业务天气预报中心产生的风和温度值。 其目标是再现大规模的气象条件下，活动的观测，使云和气溶胶观测活动可以合理地比较，他们的模拟同行。 该项目使用从这些比较和LES建模中获得的理解，在CAM 6中开发冰成核粒子的表示。这项工作具有更广泛的影响，因为它对改进用于天气预测和未来气候预测的模型具有潜在价值。 模型改进工作对科学研究界也有更广泛的影响，因为CAM 6和AM4是广泛使用的科学研究工具。 推动气象学模拟可供社区使用，作为活动中收集的数据的长期在线档案的一部分，沿着用于推动模型的气象分析和卫星辅助云和海面观测。除了所做工作的广泛影响外，该项目还为两名博士后提供支持和培训，从而为该研究领域的科学工作者提供发展。 PI还为运动的外联活动做出贡献，包括SOCRATES博客。

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.