Collaborative Research: Submesoscale-Resolving Large Eddy Simulations Using Reduced Biogeochemical Models

要更好地了解上层海洋生物地球化学，就需要全面研究化学示踪剂与小于一公里尺度(也称为“亚中尺度”)的湍流之间的相互作用，但在这些小尺度上模拟化学示踪物和过程需要大量的计算能力和时间。因此，必须开发新的简化生物地球化学模型，以新的方式求解，以执行在这些尺度上耦合的生物地球化学和物理过程的大涡模拟(LES)。在拟议的项目中，将首次使用燃烧领域采用的减少大型化学动力学机制的技术来缩小大型海洋生物地球化学模型的规模。这项跨学科的研究工作将由一个合作小组开展，该小组由一名反应流和海洋学流动数值模拟专家、一名对海洋生物地球化学有广泛知识的生物海洋学家以及一名化学模型简化和解决专家组成。在这个项目中开发的工具将提供给更广泛的海洋学社区，跨学科博士生的参与将使新一代人接触海洋学和地球科学的计算方法。该项目将通过设计源自和补充拟议研究的项目，为本科生，特别是在STEM中任职人数不足的本科生提供研究经验和指导。最终，该项目将通过改进用于研究气候的地球系统模型(ESM)来造福社会，从而更准确地预测未来气候对人类健康、安全和财产的影响。简化模型的求解将在使用高阶Runge-Kutta-Chebyshev(RKC)时间积分方案的图形处理单元(GPU)上执行。该项目将最终模拟现实的海洋情景，并将与德雷克海峡的观测数据进行比较，以确定次中尺度过程在二氧化碳分压下产生小规模斑块的作用。最终，从大涡模拟中获得的见解将被用来更好地理解小尺度湍流与上层海洋生物地球化学之间的相互作用，包括示踪剂斑块的特征、动力来源和影响。在高保真大涡模拟中集成复杂的生物地球化学模型是非常困难的，但拟议的模型简化，以及GPU和高阶RKC积分器的使用，将使在亚中尺度完全耦合的湍流和生物地球化学过程的高分辨率研究成为可能。这些改进将通过利用燃烧化学动力学建模技术来实现，近十年来，在高保真模拟中减少和集成大型化学机制已经很常见。拟议的模拟工作将深入了解亚中尺度湍流，包括波浪驱动的朗缪尔湍流对上层海洋碳循环的影响，并将为改进的ESM的未来发展提供信息。特别是，次中尺度湍流和生物地球化学示踪剂之间的相互作用被认为是示踪剂斑块的原因，需要进行大量的进一步研究，以开发更准确的次网格尺度的ESM参数。此外，对德雷克航道的模拟将提供对现实条件下示踪剂斑块的具体见解和理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Improved understanding of upper ocean biogeochemistry requires a comprehensive look at the interactions between chemical tracers and turbulence at scales smaller than one kilometer (also termed "submesoscale"), but modeling chemical tracers and processes at these small scales requires a tremendous amount of computing power and time. As a result, new reduced biogeochemical models, solved in novel ways, must be developed to perform large eddy simulations (LES) of coupled biogeochemistry and physical processes at these scales. In the proposed project, techniques adapted from the field of combustion for the reduction of large chemical kinetics mechanisms will, for the first time, be used to reduce the size of large ocean biogeochemical models. This interdisciplinary research effort will be undertaken by a collaborative team consisting of an expert in numerical simulations of both reacting and oceanographic flows, a biological oceanographer with extensive knowledge of ocean biogeochemistry, and an expert in chemical model reduction and solution. The tools developed in this project will be made available to the broader oceanographic community, and involvement of interdisciplinary PhD students will expose a new generation to computational methods in oceanography and the Earth sciences. The project will provide research experience and mentorship to undergraduate students, particularly those under-represented in STEM, by designing projects derived from, and complementary to, the proposed research. Ultimately, this project will benefit society through improvements to Earth system models (ESMs) used to study climate, resulting in more accurate predictions of future climate impacts on human health, safety, and property. Solution of the reduced models will be performed on graphical processing units (GPUs) using a high-order Runge-Kutta-Chebyshev (RKC) time integration scheme. This project will culminate in the simulation of realistic ocean scenarios and comparisons will be made with observational data from the Drake Passage to determine the role of submesoscale processes in generating small-scale patchiness in the partial pressure of carbon dioxide. Ultimately, insights obtained from the LES will be used to develop a better understanding of the interactions between small-scale turbulence and biogeochemistry in the upper ocean, including the characteristics, dynamical origins, and effects of tracer patchiness. Integration of complex biogeochemical models within high-fidelity LES has previously been exceptionally difficult, but the proposed model reduction, as well as the use of GPUs and the high-order RKC integrator, will enable high-resolution studies of fully-coupled turbulent and biogeochemical processes at submesoscales. These improvements will be made possible by leveraging techniques from chemical kinetics modeling for combustion, where reduction and integration of large chemical mechanisms in high-fidelity simulations has been common for nearly a decade. The proposed simulation effort will provide insights into the effects of submesoscale turbulence, including wave-driven Langmuir turbulence, on the upper-ocean carbon cycle, and will inform the future development of improved ESMs. In particular, interactions between submesoscale turbulence and biogeochemical tracers are thought to be the cause of tracer patchiness and require substantial further study to develop more accurate subgrid-scale parameterizations for ESMs. Moreover, simulations of the Drake Passage will provide concrete insights and understanding of tracer patchiness for realistic conditions.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.