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Collaborative Research: Climate Feedbacks in Radiative-Convective Equilibrium--The Role of Self-Aggregation of Convection in A Multi-Model Ensemble of Idealized Simulations

合作研究：辐射对流平衡中的气候反馈——对流自聚集在理想化模拟的多模式系综中的作用

基本信息

批准号：
1830729
负责人：
Kevin Reed
金额：
$ 32.81万
依托单位：
SUNY at Stony Brook
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-09-01 至 2022-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1830729&HistoricalAwards=false
关键词：
Collaborative Research Climate Feedbacks Radiative

项目摘要

The interplay between longwave radiation and the vertical transport of sensible and latent heat by convection is a key ingredient of the weather and climate of the earth. In the absence of convection the cooling effect of longwave radiation produces a vertical temperature profile which is unstable. The instability leads to convection, which transports sensible and latent heat upward and counteracts the longwave cooling, restabilizing the atmosphere. This cooperative interaction between radiative cooling and convective heat transport leads to a state known as radiative-convective equilibrium (RCE), which provides a basic explanation for the dependence of air temperature on altitude. RCE is also fundamental to our understanding of the sensitivity of global temperature to changes in greenhouse gas concentration (referred to as climate sensitivity), the response of the hydrological cycle to changes in global temperature, and the development of large-scale atmospheric circulation.Early simulations of RCE used highly simplified approximations which only captured the bulk effects of convection, but RCE simulations are now performed with more sophisticated models that represent individual convective clouds and their interactions with the surrounding air. Results of such simulations by the PIs and others suggest that the tendency of convective clouds to aggregate into clusters increases with increasing temperature. The temperature dependence of convective aggregation could matter for climate sensitivity, as aggregated clouds are concentrated in relatively small regions, leaving clear skies over a larger portion of the earth than disaggregated convection. Cooling to space is more effective under clear skies, thus an increase in clear sky area due to enhanced aggregation constitutes a negative feedback, counteracting some of the warming that produced increased aggregation. The possibility of a negative feedback due to convective aggregation has clear implications for understanding climate change and its potential societal impacts. But the mechanisms of convective aggregation and its temperature dependence, and the extent to which aggregation affects climate sensitivity are not clear. A further consideration is that the extent of aggregation and its temperature dependence may not be consistent from one model to another, and the PIs have worked to organize an international RCE model intercomparison project (RCEMIP) to address the issue of model dependence.Here the PIs use simulations from RCEMIP to explore the physics and dynamics of aggregation and its temperature dependence using a variety of diagnostics to test hypotheses taken from their own prior work and from their collaborators. Additional simulations are performed using the System for Atmospheric Modeling (SAM), a global cloud resolving model, in specialized configurations designed to promote or suppress aggregation, thereby providing an assessment of its effect on climate sensitivity. The project also includes observational comparisons and the design of a simplified physics package suitable for RCE simulations.The work has broader impacts due to the societal impacts of climate change and the desirability of better estimates of the likely consequences of greenhouse warming. The interaction of clouds, circulation, and climate sensitivity has been identified as a grand challenge by the World Climate Research Program. The project builds international scientific collaboration through the PIs' participation in RCEMIP, as well as the related Cloud Feedback Model Intercomparison Project and the Global Atmospheric System Studies effort. In particular the lead PI has established a data portal for RCEMIP on her campus to provide model output, diagnostic analysis software, and documentation, thereby facilitating community engagement in the project. The project also provides support and training for a student and a postdoc, thereby providing workforce development in this research area.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.

长波辐射与对流引起的感热和潜热的垂直输送之间的相互作用是地球天气和气候的一个关键组成部分。在没有对流的情况下，长波辐射的冷却效应会产生不稳定的垂直温度分布。这种不稳定性导致对流，对流将感热和潜热向上输送，抵消长波冷却，使大气重新稳定。辐射冷却和对流热传输之间的这种合作相互作用导致称为辐射对流平衡（RCE）的状态，这为空气温度对高度的依赖性提供了基本解释。 RCE也是我们理解全球温度对温室气体浓度变化敏感性的基础（称为气候敏感性），水文循环对全球温度变化的响应，以及大尺度大气环流的发展。RCE的早期模拟使用高度简化的近似方法，仅捕获对流的整体效应，但是RCE模拟现在是用更复杂的模型来进行的，这些模型代表了单个对流云及其与周围空气的相互作用。 PI和其他人的模拟结果表明，对流云聚集成团的趋势随着温度的升高而增加。对流聚集的温度依赖性可能对气候敏感性有影响，因为聚集的云集中在相对较小的区域，比分散的对流在地球上留下更大部分的晴朗天空。在晴朗的天空下，冷却到空间更有效，因此，由于聚集增强而增加的晴朗天空面积构成了负反馈，抵消了一些导致聚集增加的变暖。由于对流聚集而产生负反馈的可能性对于理解气候变化及其潜在的社会影响具有明显的意义。但对流聚合的机制及其温度依赖性，以及聚合对气候敏感性的影响程度尚不清楚。另一个考虑是聚集的程度及其温度依赖性可能从一个模型到另一个模型不一致，和PI已经组织了一个国际RCE模型相互比较项目（RCEMIP）在这里，PI使用RCEMIP的模拟来探索聚集的物理和动力学及其温度依赖性，使用各种诊断来测试假设从他们之前的工作和他们的合作者那里。使用大气建模系统（SAM）进行额外的模拟，这是一个全球云解析模型，采用专门的配置，旨在促进或抑制聚集，从而评估其对气候敏感性的影响。该项目还包括观测比较和适合RCE模拟的简化物理包的设计。由于气候变化的社会影响和更好地估计温室效应的可能后果的可取性，这项工作具有更广泛的影响。云、环流和气候敏感性的相互作用被世界气候研究计划确定为一个重大挑战。该项目通过参与RCEMIP以及相关的云反馈模型相互比较项目和全球大气系统研究工作，建立国际科学合作。特别是首席PI在她的校园里为RCEMIP建立了一个数据门户，提供模型输出，诊断分析软件和文档，从而促进社区参与该项目。该项目还为一名学生和一名博士后提供支持和培训，从而在这一研究领域提供劳动力发展。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。