From Boundary Layer to Deep Convection: The Multi-Plume Eddy-Diffusivity/Mass-Flux (EDMF) Fully Unified Parameterization

云在调节地球气候方面发挥着关键但微妙的作用。 它们通过将大约四分之一的入射阳光反射回太空来冷却地球，但它们也通过捕获传出的红外辐射来温暖地球。 鉴于在气候模型中表示云的困难，气候对云量和性质的敏感性对气候建模提出了重大挑战。 事实上，云非常难以模拟，气候模型通常使用单独的云参数化方案（本质上是计算机子程序）来表示不同类型的云。在对流云的情况下，模型通常使用两种方案，一种用于在行星边界层（PBL，通常是地表上方一公里或两公里）内部和顶部形成的浅积云，另一种用于可延伸穿过对流层深度（可能达到 10 公里或更高的高度）的深层积云。 深对流和浅对流的分离是出于实际原因，但实际上云有各种大小，并且无论大小如何，最终都适用相同的物理定律。 此外，浅层和深层对流方案的独立性可能会巧妙地歪曲浅层和深层对流云之间的相互作用。 一个统一的方案，代表从 PBL 中的小规模对流到深层积云的一切，显然是可取的，但实施起来也具有挑战性。该奖项支持一个气候过程团队，致力于在社区地球系统模型 (CESM) 中开发和实施这种统一的对流方案。该方案被称为涡扩散率/质量通量 (EDMF) 参数化，其中使用扩散近似处理最小的对流羽流以及 PBL 湍流空气运动，并结合质量通量方法来表示与 PBL 深度一样高或更高的云。 该方案的涡流扩散率和质量通量分量经过仔细协调，以便它们能够代表干 PBL 湍流和 PBL 云之间的相互作用以及从浅层对流到深层对流的过渡。这里开发和实施的 EDMF 方案建立在主要 PI 和其他人开发的先前 EDMF 方案的基础上，增加了一些功能，包括模拟质量通量羽流集合的能力，从而允许在单个网格框中存在多个对流状态，以及有组织的对流和冷池的影响。这项工作的主要更广泛的影响是，它寻求提高气候模型的性能及其作为科学研究工具的有用性，并为关心气候变率和变化的决策者提供指导。 CESM 是一个开源模型，由国家大气研究中心托管和支持，拥有全球用户社区。 该计划还将由未受该奖项资助的合作者在地球物理流体动力学实验室（GFDL）的气候模型中实施。 此外，该奖项还支持举办关于气候模型中的湍流、对流和云的年度研讨会，该研讨会为从事云和 PBL 参数化研究的研究人员提供了互动的场所。 该项目支持三名博士后，从而为气候模型开发培养未来的劳动力。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。

Clouds play a critical but delicate role in regulating Earth's climate. They cool the Earth by reflecting about a quarter of the incoming sunlight back into space, but they also warm the Earth by trapping outgoing infrared radiation. The sensitivity of climate to cloud amount and properties poses a substantial challenge to climate modeling given the difficulty of representing clouds in climate models. In fact clouds are so difficult to simulate that climate models typically use separate cloud parameterization schemes (essentially computer subroutines) to represent different kinds of clouds. In the case of convective clouds models typically use two schemes, one for the shallow cumulus clouds which form within and on top of the of the planetary boundary layer (PBL, commonly the first kilometer or two above the surface), and another for the deep cumulus clouds which can extend through the depth of the troposphere (to heights of perhaps 10km or more). The separation of deep and shallow convection is done for practical reasons but in reality clouds come in all sizes and ultimately the same laws of physics apply regardless of size. Also, the independence of the shallow and deep convection schemes can subtly misrepresent the interaction between shallow and deep convective clouds. A unified scheme, which represents everything from small-scale convection in the PBL to deep cumulus clouds, is clearly preferable but also challenging to implement.This award supports a Climate Process Team engaged in the development and implementation of such a unified convection scheme in the Community Earth System Model (CESM). The scheme is known as as an Eddy Diffusivity/Mass Flux (EDMF) parameterization, in which the smallest convective plumes are treated along with PBL turbulent air motions using a diffusive approximation, combined with a mass flux methodology for representing clouds which are as tall or taller than the depth of the PBL. The eddy diffusivity and mass flux components of the scheme are carefully coordinated so that they can represent the interactions between dry PBL turbulence and PBL clouds and the transition from shallow to deep convection. The EDMF scheme developed and implemented here builds on previous EDMF schemes developed by the lead PI and others, adding features including the ability to simulate an ensemble of mass flux plumes, thus allowing multiple convective regimes to exist in a single grid box, and the effects of organized convection and cold pools.The primary broader impact of the work is that it seeks to improve the performance of climate models and their usefulness as tools for scientific research and for providing guidance for decision makers concerned with climate variability and change. CESM is an open-source model which is hosted and supported by the National Center for Atmospheric Research and has a worldwide user community. The scheme will also be implemented in the climate model of the Geophysical Fluid Dynamics Laboratory (GFDL) by collaborators not funded under this award. In addition, the award supports an annual workshop on turbulence, convection and clouds in climate models, which serves as a venue for interactions among researchers working on cloud and PBL parameterization. The project supports three postdocs, thereby developing the future workforce for climate model development.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.