Collaborative Research: Marginal instability and deep cycle turbulence in the equatorial oceans

合作研究：赤道海洋的边缘不稳定和深循环湍流

• 批准号: 1355768
• 负责人: William Smyth
• 金额: $ 48.2万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-03-01 至 2020-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1355768&HistoricalAwards=false
• 关键词: Collaborative; Research; Marginal; instability; deep

Overview: Thirty years after its discovery, the deep cycle of equatorial turbulence remains unexplained. Climate forecast models are unable to represent it accurately, leading to errors in ocean heat uptake. This project brings together two research groups who have made recent progress on the problem to pursue a unified understanding. Combining existing observations and new large-eddy simulations (LES), they will explore deep cycle physics over the range of seasonal and ENSO variability and in all three equatorial oceans. The previously-unexploited deep cycle property of marginal instability will be used together with numerical simulations to (1) document the history of the deep cycle over the past 25 years, (2) describe the mechanics of the deep cycle, and (3) develop improved parameterizations for use in climate models.Intellectual merit: The broad variability of mixing in the upper equatorial Pacific is exemplified by the turbulent diapycnal heat flux sampled at the same location and in the same season, but coinciding with different phases of the El Niño/ Southern Oscillation (ENSO) cycle. Early in the 1991 El Niño, currents were slow and the heat flux was relatively weak. In the 2008 cruise, which coincided with La Niña, currents were much more energetic. The resulting heat flux was stronger by an order of magnitude, and heat was transported to 100 m depth. Despite the extreme difference in magnitude, these mixing regimes exhibited a striking commonality: strong turbulence coincided with a distinct layer in which the gradient Richardson number (Ri) remained within a factor of two of the value of a quarter. Persistent clustering of Ri near 1/4 over a range of depths signifies the state of marginal instability. This near-critical state is maintained in the mean by a balance between large-scale forcing (which reduces Ri) and turbulence (which increases it). Deep cycle mixing is crucial to the climate via its effects on both the zonal current system and the sea surface temperature. In this observational data analyses and large eddy simulations, the investigators will explore the physics of the deep cycle with particular attention to the property of marginal instability. Using marginal instability as a proxy, they will document the history and longitudinal dependence of the deep cycle from existing data. This will lead to both a deeper understanding of the phenomenon and an improved ability to parameterize its effects in large-scale models.Broader Impacts: The causes of long-term Sea Surface Temperature variations will be examined and the results will contribute to ENSO and interdecadal climate prediction. The project will also foster a new collaboration, support a junior researcher, and complement an existing NSF observational project. Two presentations on equatorial oceanography will be developed and presented at high schools and community colleges.

概述：发现后的三十年，等效性湍流的深度循环仍然未知。气候预测模型无法准确表示它，从而导致海洋热吸收错误。该项目汇集了两个研究小组，他们在问题上取得了最新进展，以寻求统一的理解。结合了现有的观察结果和新的大型模拟（LES），他们将在季节性和ENSO变异性范围内以及在所有三个赤道海洋中探索深度循环物理。边际不稳定的先前无法解放的深度周期特性将与数值模拟一起使用，以记录过去25年中深度周期的历史的历史，（（2）描述深度周期的机制，（3）在气候模型中使用改进的参数以在气候模型中使用。在同一季节，但与厄尔尼诺/南部振荡（ENSO）周期的不同阶段相吻合。在1991年的厄尔尼诺现象中，电流慢，热通量相对较弱。在2008年的巡游中，与拉尼娜（LaNiña）相吻合，电流变得更加充满活力。所得的热通量通过一定的数量级强，并将热量传输到100 m的深度。尽管幅度的差异极大，但这些混合状态仍表现出罢工的共同点：强湍流与渐变的理查森数（RI）保持在一个四分之一值的两个倍倍以下。在一定深度的1/4附近的RI持续聚类表示边际不稳定状态。通过大规模强迫（减少RI）和湍流（增加它）之间的平衡来维持这种接近危险的状态。深循环混合对气候对纬向电流系统和海面温度的影响至关重要。在此观察数据分析和大型涡流模拟中，研究人员将特别关注边缘不稳定的特性，探索深层周期的物理。他们将使用边缘不稳定作为代理，将记录来自现有数据的深度周期的历史和纵向依赖性。这将导致对现象的更深入了解，也可以提高参数化在大规模模型中其效果的能力。Boader的影响：将检查长期海面温度变化的原因，结果将有助于ENSO和季节间气候预测。该项目还将促进新的合作，支持初级研究人员，并补充现有的NSF观察项目。将在高中和社区学院开发和介绍两次有关赤道海洋学的演讲。

项目成果

Marginal Instability and the Efficiency of Ocean Mixing

• DOI: 10.1175/jpo-d-20-0083.1
• 发表时间: 2020-08
• 期刊: Journal of Physical Oceanography
• 影响因子: 3.5
• 作者: W. Smyth