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arXiv 2407.00124physics.ao-ph
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基于嵌入式对流可分辨模拟学习的综合大气模式中次网格过程的稳定机器学习参数化

Stable Machine-Learning Parameterization of Subgrid Processes in a Comprehensive Atmospheric Model Learned From Embedded Convection-Permitting Simulations

Zeyuan Hu, Akshay Subramaniam, Zhiming Kuang, Jerry Lin, Sungduk Yu, Walter M. Hannah, Noah D. Brenowitz, Josh Romero, Michael S. Pritchard

AI总结:

研究提出一种基于U-Net和物理热力学约束的稳定机器学习混合气候模式,通过模拟嵌入式云分辨模式实现至少5年真实地理与云耦合积分,显著降低了温度、水汽和降水偏差。

摘要:

现代气候预测常因计算限制而空间和时间分辨率不足,导致次网格过程表征不准确。解决此问题的一项有前景的技术是多尺度建模框架(MMF),它在主体气候模式的每个大气柱中嵌入一个千米分辨率的云分辨模式,以取代传统的对流和云参数化。机器学习(ML)提供了一个独特的机会,通过模拟嵌入式云分辨模式并降低其大量计算成本,使MMF更易于使用。尽管许多研究已证明实现稳定混合模拟的概念验证成功,但在真实地理条件和包含显式云凝结物耦合的综合变量模拟下实现近业务级成功仍是一项挑战。在本研究中,我们提出了一个具有近业务级复杂度的稳定混合模式,能够积分至少5年,包括粗网格地理、季节性、显式云凝结物和风预测以及陆地耦合。我们的模式表现出良好的在线性能,5年纬向平均对流层温度偏差在2K以内,水汽偏差在1 g/kg以内,降水均方根误差为0.96 mm/day。促成我们在线性能的关键因素包括富有表达力的U-Net架构和微物理的物理热力学约束。通过微物理约束缓解不切实际的云形成,我们的工作是首个在MMF框架下展示真实多年云凝结物气候态的研究。尽管取得了这些进展,在线诊断揭示了某些区域存在持续偏差,突出了进一步优化在线性能的创新策略的需求。

英文摘要:

Modern climate projections often suffer from inadequate spatial and temporal resolution due to computational limitations, resulting in inaccurate representations of sub-grid processes. A promising technique to address this is the Multiscale Modeling Framework (MMF), which embeds a kilometer-resolution cloud-resolving model within each atmospheric column of a host climate model to replace traditional convection and cloud parameterizations. Machine learning (ML) offers a unique opportunity to make MMF more accessible by emulating the embedded cloud-resolving model and reducing its substantial computational cost. Although many studies have demonstrated proof-of-concept success of achieving stable hybrid simulations, it remains a challenge to achieve near operational-level success with real geography and comprehensive variable emulation that includes, for example, explicit cloud condensate coupling. In this study, we present a stable hybrid model capable of integrating for at least 5 years with near operational-level complexity, including coarse-grid geography, seasonality, explicit cloud condensate and wind predictions, and land coupling. Our model demonstrates skillful online performance, achieving a 5-year zonal mean tropospheric temperature bias within 2K, water vapor bias within 1 g/kg, and a precipitation RMSE of 0.96 mm/day. Key factors contributing to our online performance include an expressive U-Net architecture and physical thermodynamic constraints for microphysics. With microphysical constraints mitigating unrealistic cloud formation, our work is the first to demonstrate realistic multi-year cloud condensate climatology under the MMF framework. Despite these advances, online diagnostics reveal persistent biases in certain regions, highlighting the need for innovative strategies to further optimize online performance.

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