Observations and Modeling of the Transition Layer

GSTDTAP

项目编号	1657676
	Observations and Modeling of the Transition Layer
	Eric D&; 39;Asaro
主持机构	University of Washington
项目开始年	2017
	2017-03-15
项目结束日期	2021-02-28
资助机构	US-NSF
项目类别	Standard Grant
项目经费	1759562(USD)
国家	美国
语种	英语
英文摘要	The upper ocean is a crucial component of the climate system. It mediates the air-sea heat, momentum, gas and nutrient fluxes and plays a large role in ocean biogeochemistry. Current climate models typically have large errors in the depth of the surface mixed layer (ML), likely because their upper ocean parameterizations lack essential physics. Recent efforts have improved representations of the physics near the surface, motivating this look at the other critical yet poorly understood part of the upper ocean? the transition layer (TL) between the turbulent ML and stratified interior. Here, the surface-generated turbulence acts upon the density and tracer gradients below, thereby controlling the depth of the ML and the fluxes of heat, salt, nutrients and other tracers into the ML. This study will combine new theoretical insights with new measurement methods and high-resolution numerical simulations to understand TL dynamics and its role in the new generation of physics-based upper ocean parameterizations. Analyses will describe the TL structure with a focus on the physics of internal waves and instabilities, their forcing and dissipation mechanisms, and their role in setting the upper-ocean mixing and entrainment rates. An improved understanding of these processes is crucial to improving the performance of regional and global models of the ocean and climate. Mixed layer depth and the fluxes of nutrients across the TL play a key role in controlling the rate and character of biological productivity and thus the strength of the biological carbon pump. Improved parameterizations of the TL would thus have direct application to both physical and biogeochemical ocean models. LES is widely used to develop parameterizations of boundary layer mixing; these analyses will assess its accuracy for the TL. A post-doc will be supported for two years and trained in the methods of small-scale Lagrangian oceanography developed by this group over the last 25 years. The measurement program will combine the proven abilities of APL/UW Lagrangian floats with the recent development of highly accurate float-based Acoustic Doppler Current Profilers to accurately target and sample the TL. Two specialized floats will be deployed at Ocean Weather Station P (50N 145W) for100-day missions in fall 2018, the season of rapid wind-driven ML deepening and thus maximum TL activity. The floats will conduct targeted high-resolution measurements of vertical velocity, shear and stratification across the TL. Existing NOAA and OOI moorings at OWS-P will provide high quality surface fluxes and long-term hydrographic context. An existing Waverider buoy will be redeployed to provide reliable surface wave measurements, which will ensure continuation of this valuable climate record for another 2 years. Large Eddy Simulation (LES) will be an integral part of the project, guiding the design of the sampling strategies and interpretation of the data. The central hypothesis of this research is that the waves and instabilities of the TL and their interaction with turbulence in the ML control the mixing and entrainment in the TL. The TL is envisioned as a resonant and often marginally unstable layer forced by the ML from above. Its response to this forcing depends in detail on the mean shear and stratification profiles. Questions that address this hypothesis are: Q1: What are the mean shear and stratification profiles of the TL, and how are these related to its instabilities, waves, turbulence and mixing? What are the theoretical wave and instability modes? Can they be identified in process models or observations. How do they break down to turbulence and mixing? Q2: How are these properties of the TL set by the ML turbulence? Are the TL waves and instabilities directly forced by the ML turbulence or are they internal to the TL? Q3: Do models simulate these physics? How well do existing LES schemes and bulk parameterizations describe the observed structure and evolution? How could they be improved?
来源学科分类	Geosciences - Ocean Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/70904
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Eric D&,39;Asaro.Observations and Modeling of the Transition Layer.2017.