CAREER: Understanding Low-cloud Feedbacks Using Large-eddy Simulation of Spatially Developing Cloud Transitions

职业：利用空间发展云转变的大涡模拟来理解低云反馈

• 批准号: 2143276
• 负责人: Georgios Matheou
• 金额: $ 42.54万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-02-15 至 2027-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2143276&HistoricalAwards=false
• 关键词: CAREER; Understanding; Low; cloud; Feedbacks

A traveler flying from California to Australia might take off through a flat, unbroken cloud layer and watch as the layer gets lumpy, with stratocumulus clouds protruding from the stratus layer as the flight tracks over warmer water. Eventually the cloud deck breaks up and the ocean appears between puffy cumulus clouds, which start out small but grow into towers over the warm equatorial Pacific. The breakup of the cloud deck, referred to as the stratocumulus to cumulus transition, matters for climate as a cloud deck cools the earth by reflecting sunlight to space while the ocean absorbs most of the sunlight that falls on it. One concern here is that the stratus to cumulus transition is tied to sea surface temperature (SST), thus the warming of SSTs by greenhouse gas increases could lead to additional warming by favoring well-separated cumulus clouds over a continuous stratocumulus cloud deck. Concern over this feedback, in which warming begets further warming, has prompted intense interest in the stratocumulus to cumulus transition.Researchers studying stratocumulus clouds have found a powerful tool in Large Eddy Simulation (LES) models, in which the cloudy atmosphere is simulated on a grid mesh with flow variables like wind speed, temperature, moisture, and cloud amount defined on a lattice of gridpoints spaced perhaps a few tens of meters apart. LES models produce surprisingly realistic simulations of clouds, but they require considerable computing power and the cloud fields they simulate are not more than a few tens of kilometers wide. The small domain is a severe limitation in studies of the cloud transition, which takes place over hundreds of kilometers. A further limitation is that cloud behavior is strongly influenced by the large-scale atmospheric circulation, particularly the planetary-scale overturning of the Hadley cells (one each for the Northern and Southern Hemispheres). The Hadley cells feature rising motion in the towering cumulus clouds over the warmest SSTs balanced by subsidence over the subtropics. The overturning motion and accompanying large-scale atmopsheric characteristics have to be externally imposed in LES simulations, which is unfortunate as changes in the cloud transition may influence the overturning circulation in ways that could feed back on the cloud transition.Reseach under this award addresses the mismatch between the accessible domain sizes for LES models and the much larger areas covered by the stratocumulus to cumulus transition and the even larger Hadley cells. The strategy involves the development and use of a hierarchy of three LES model configurations, the first of which is a small-domain LES domain with periodic boundaries (clouds flowing out of the western side of the domain reenter on the eastern side). The small domain can be slowly moved over progressively warmer SSTs to induce the cloud transition. The second configuration is a long channel with inflow at the northern end (representing conditions near California) and outflow at the southern end (the "Australian" end). The domain is narrow but periodic in the longitudinal direction to save on computational expense, and not as long as an actual Pacific transect. Nevertheless preliminary work shows that the domain is capable of producing the stratocumulus to cumulus transition if an SST contrast is imposed between the northern and southern ends, along with appropriate subsidence. The third configuration is similar to the second only much deeper and closed at the ends so that it generates its own overturning circulation, smaller than but analogous to a Hadley cell.Several experiments are planned, for instance with varying carbon dioxide concentration to study changes in the cloud transition as climate warms. Analysis of model results is guided in part by the theory of horizontal convection, meaning the behavior of convection generated by temperature contrasts along the top or bottom boundary of a domain. Horizontal convection has been extensively studied in oceanography but is not a common framework for understanding clouds and large-scale atmospheric overturning.The education and outreach component of this CAREER award takes advantage of the realism of clouds simulated by LES models. The project works with the Visualization Services and Research Lab (VisLab) at the National Center for Atmospheric Research (NCAR) to create a collection of cloud images and animations that will be offered to the public as an online Cloud Gallery. A version of the Cloud Gallery will be exhibited at the William Benton Museum of Art (WBMA), a public museum in Connecticut. The project also involves efforts to incorporate art into science teaching, acknowledging the perceptive portrayal of clouds and turbulence found in artworks such as Da Vinci's sketches of waterfalls. One such effort is conducted through the Joule Fellows program, a six week summer program for K-12 teachers. Joule Fellows work with the project team to develop visual materials for their classroom teaching.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

从加利福尼亚飞往澳大利亚的旅行者可能会从平坦的，不间断的云层开始，并观察层的块状，而随着飞行轨道在较温暖的水上轨道，地层云从Stratus层伸出。 最终，云层甲板分解，海洋出现在蓬松的积云云之间，这些云云开始很小，但在温暖的赤道太平洋上生长成塔。 云甲板的破裂，被称为积云过渡的层状层，作为云甲板的气候至关重要，通过将阳光反射到太空时，而海洋吸收了大部分阳光。 这里的一个问题是，到积云过渡的地层与海面温度（SST）相关，因此，通过增强温室气体对SST的变暖可以通过在连续的层状云层上偏爱良好分离的积云云，从而导致额外的变暖。 Concern over this feedback, in which warming begets further warming, has prompted intense interest in the stratocumulus to cumulus transition.Researchers studying stratocumulus clouds have found a powerful tool in Large Eddy Simulation (LES) models, in which the cloudy atmosphere is simulated on a grid mesh with flow variables like wind speed, temperature, moisture, and cloud amount defined on a lattice of gridpoints spaced perhaps a few tens分开的米。 LES模型对云产生了令人惊讶的现实模拟，但是它们需要相当大的计算能力，并且它们模拟的云场不超过几十公里宽。 小域是对云转变的研究的严重限制，该研究发生在数百公里。 另一个限制是，云行为受到大规模大气循环的强烈影响，尤其是哈德利细胞的行星尺度倾覆（北半球和南半球都有一个。 哈德利细胞的高耸的积云中的运动在最温暖的SST上与亚热带的沉降平衡。 在LES模拟中必须强加于外部的倾覆运动和随附的大规模大型大型特征，这是不幸的，这是不幸的，因为云过渡的变化可能会影响颠覆的循环，以反馈在云下过渡下的方式。在该奖项下进行回避，这是在LES模型和较大较大的区域中覆盖的可访问域之间的不匹配范围，该区域由较大的型号和较大的型号覆盖了较大的型号和均匀的型号。 该策略涉及三种LES模型配置的层次结构的开发和使用，其中第一个是带有周期性边界的小域LES域（从东侧的域的西侧流出云）。 可以在逐渐变暖的SST上缓慢移动小域以诱导云转变。 第二个配置是一个长通道，在北端（代表加利福尼亚附近的条件）和南端流出（“澳大利亚”端）。 该域是狭窄的，但沿纵向方向进行周期性，以节省计算费用，而不是实际的太平洋样带。 然而，初步工作表明，如果北端和南部末端之间施加了SST对比，则该域能够产生层状量为积云过渡，并有适当的沉降。 第三个配置类似于第二个末端仅在末端更深且封闭的配置，因此它会产生自己的倾覆循环，比与哈德利细胞相似的循环。计划进行角色实验，例如，二氧化碳浓度变化，以研究云的变化变化，因为气候温暖。 模型结果的分析部分是由水平对流理论指导的，这意味着沿域的顶部或底部边界所产生的对流的行为。 水平对流已经在海洋学中进行了广泛的研究，但并不是理解云和大规模大气推翻的常见框架。该职业奖的教育和外展部分利用了LES模型模拟的云现实主义的优势。 该项目与国家大气研究中心（NCAR）的可视化服务和研究实验室（VISLAB）合作，创建了一系列云图像和动画，这些图像和动画将作为在线云画廊提供给公众。 云画廊的版本将在康涅狄格州的公共博物馆威廉·本顿艺术博物馆（WBMA）展出。 该项目还涉及将艺术纳入科学教学的努力，承认在达芬奇（Da Vinci）的瀑布素描等艺术品中发现的云和动荡的刻画。 通过焦耳研究员计划（Joule Fellows Program）进行了一项这样的努力，这是一个为K-12老师的六周夏季计划。 焦耳研究员与项目团队合作，为其课堂教学开发视觉材料。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛影响的评论标准来评估值得支持的。

项目成果

Computational Domain Size Effects on Large-Eddy Simulations of Precipitating Shallow Cumulus Convection

• DOI: 10.3390/atmos14071186
• 发表时间: 2023-07
• 期刊: Atmosphere
• 影响因子: 2.9
• 作者: Oumaima Lamaakel;R. Venters;João Paulo Ramos Teixeira;G. Matheou

The texture of atmospheric humidity: Near-surface turbulence in precipitating cumulus convection

大气湿度的结构：降水积云对流中的近地表湍流

• DOI: 10.1103/aps.dfd.2022.gfm.p0007
• 发表时间: 2022
• 期刊: 75th Annual Meeting of the American Physical Society’s Division of Fluid Dynamics (APS DFD
• 作者: Matheou, Georgios;Venters, Ravon;Lamaakel, Oumaima;Teixeira, Joao
• 通讯作者: Teixeira, Joao

Large-eddy simulation of cumulus clouds

积云大涡模拟

• DOI: 10.1103/physrevfluids.7.110507
• 发表时间: 2022
• 期刊: Physical Review Fluids
• 影响因子: 2.7
• 作者: Matheou, Georgios