Collaborative Research: Tracing the physics of submesoscale entrainment and subduction

该项目将调查混合良好的海洋表层与所谓亚中尺度分层的海洋内部之间的交换；在数百到数千米的水平长度尺度上，仍然可以感觉到地球的自转，但不像在更大的尺度上那样是主要因素。这种交换被广泛认为是亚中尺度过程影响上层海洋变率和生物地球化学的主要机制之一。然而，尽管大量的工作证明了亚中尺度挟带和俯冲对海洋学领域各种主题的影响，包括例如全球混合层热收支、初级生产力和向内部的碳输出，但基本的物理机制仍然没有得到完整的描述。特别是，由于亚中尺度过程的参数化明确地避免了夹带通量，因此下一步需要包括地面边界层和内部之间的亚中尺度相互作用对大尺度模式的影响。这种回避严重低估了亚中尺度对生物地球化学和气候的影响（例如，长期碳和热吸收）。该小组最近的一些工作进一步表明，亚中尺度流动、地表重力波和湍流之间的跨尺度相互作用也可能显著改变地表混合层底部的交换。然而，这种交流的几种可能机制的平衡尚未确定。该项目将使用新的理论和计算工具量化这些多尺度相互作用的影响，从而产生更完整的海洋内部和表面边界层之间亚中尺度交换的模型。气候尺度和高分辨率大涡模拟模式的进展将与科学界分享。将开发示踪剂诊断和理论的新技术，并用于阐明影响边界层和内部之间交换的多尺度相互作用的作用，为多尺度数值模拟，参数化和海洋观测的新方法提供指导。该项目的大部分资金将用于支持早期职业科学家：一名研究生，一名博士后研究员，一名早期职业研究科学家和一名早期职业教师。reynolds平均数值模拟（RANS）将量化将携带通量纳入广泛使用的亚中尺度混合层不稳定性参数化的影响，包括改进的参数化对纳入南大洋海洋生物地球化学的实际模拟的影响。大涡模拟（LES）将确定亚中尺度不稳定性、表面重力波驱动效应（如Langmuir湍流）和小尺度三维湍流相互作用来改变示踪剂的卷带和俯冲的过程和参数依赖性。边界层能量学、位涡动力学以及作为该项目一部分开发的涡流通量诊断技术的最新发展将使对这些多尺度相互作用的新见解成为可能。这些进展将应用于一组最先进的大域LES，可以解决1米到10公里的尺度，为百亿亿次海洋建模提供新的基准。这些活动将共同模拟和量化亚中尺度夹带和俯冲的基本机制，它们的跨尺度相互作用，以及它们在观测和数值模式中的准确解释。群落海洋和气候模式的改进将通过在两个参数化中纳入经过改进和审查的携带通量表示，包括最广泛使用的亚中尺度混合层不稳定性参数化和较新的过程参数化。将进行的LES将立即供社区使用，为亚中尺度- langmuir -湍流和物理-生物地球化学相互作用的其他研究提供宝贵的新资源。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will investigate the exchange between the well-mixed surface layer of the ocean and the stratified interior at the so-called submesoscales; horizontal length scales of hundreds to thousands of meters, where the rotation of the Earth is still felt but is not the dominant factor like it is at larger scales. This exchange is widely recognized as one of the primary mechanisms through which submesoscale processes affect upper ocean variability and biogeochemistry. However, despite extensive work demonstrating the impacts of submesoscale entrainment and subduction on diverse topics across the field of oceanography— including for example the global mixed-layer heat budget, primary productivity, and the export of carbon to the interior—the essential physical mechanisms remain incompletely described. In particular, next steps need to include the impact of the submesoscale interactions between the surface boundary layer and the interior on large-scale models, as parameterizations of submesoscale processes explicitly avoid entrainment fluxes. This avoidance severely underestimates submesoscale impacts on biogeochemistry and climate (e.g., long-term carbon and heat uptake). Recent work, some from this group, further indicates that cross-scale interactions between submesoscale flows, surface gravity waves, and turbulence may also significantly alter the exchange at the base of the surface mixed layer. However, the balance of several possible mechanisms for this exchange has not been established. This project will quantify the effect of these multiscale interactions using new theoretical and computational tools, resulting in more complete models of submesoscale exchange between the ocean interior and surface boundary layer. Advances for both climate-scale and high-resolution Large Eddy Simulation models will be shared with the science community. New techniques in tracer diagnostics and theory will be developed, and used to clarify the role of multiscale interactions in affecting exchange between the boundary layer and interior, providing guidance towards new approaches in multiscale numerical modeling, parameterization, and ocean observing. The majority of the funds for this project will go towards supporting early career scientists: a graduate student, a postdoctoral researcher, an early career research scientist, and an early career faculty member.Reynolds-averaged numerical simulations (RANS) will quantify the impact of incorporating entrainment fluxes into a widely utilized parameterization of submesoscale mixedlayer instability, including the impact of the improved parameterization on realistic simulations incorporating ocean biogeochemistry in the Southern Ocean. Large-eddy simulations (LES) will determine the processes and parameter dependence through which submesoscale instabilities, surface gravity wave-driven effects such as Langmuir turbulence, and small-scale three-dimensional turbulence interact to modify entrainment and subduction of tracers. New insights into these multiscale interactions will be enabled by recent developments in boundary layer energetics, potential vorticity dynamics, and techniques for eddy-flux diagnostics developed as part of this project. These advances will be applied to a set of state-of-the-art large-domain LES that resolve scales of order 1 m to 10km, providing new benchmarks in exascale ocean modeling. Together these activities will simulate and quantify the essential mechanisms of entrainment and subduction at the submesoscale, their cross-scale interactions, and their accurate interpretation in observations and representation in numerical models. Community ocean and climate model improvements will be furthered through inclusion of improved and vetted representation of entrainment fluxes in two parameterizations, including the most widely used parameterization of submesoscale mixed-layer instability and a newer process parameterization. The LES that will be performed will be made available for immediate community use, providing a valuable new resource supporting other investigations into submesoscale-Langmuir-turbulence, and physical-biogeochemical interactions.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.