Cuddy Decay: Observation of Subthermocline Eddy Spindown and Property Exchange

这是一个研究亚温跃层涡旋的项目，当它从加利福尼亚暗流（CU）的产生地点附近穿过大陆斜坡进入近海水域时。CU是加利福尼亚洋流系统（CCS）的重要组成部分，它沿着北美西海岸向北输送相对温暖、含盐、缺氧的太平洋赤道水。在极地和近海，温度和盐度普遍下降，而溶解氧增加，因为CU旋转出长期存在的涡流，将其水特性从CCS转移到东太平洋。这些漩涡，因其起源而被称为cuddies，已经被孤立的浮标追踪了好几个月，偶尔也会进行水文调查，但它们在衰变过程中的结构演变尚未被观察到。它们以亚中尺度相干涡的形式存在，由于其体积小且在地下增强，遥感技术在很大程度上是不可见的。cuddy对CCS及其他地区的大尺度性质梯度的贡献程度与它们的径向垂直结构的演变有关。这项研究将使用一对扩展范围的滑翔机，在几个月的时间里，对一只cuddy进行频繁的调查。由美国国家海洋和大气管理局（NOAA）单独支持、华盛顿大学（University of Washington）同事维护的正在进行的“滑翔机重复样带”（slilider repeat样带）将确定和定位一个cuda。随着性能效率的提高，预计滑翔机可以运行长达一年的时间，同时几乎实时地传输上层海洋结构的倾斜剖面。在10个月的时间里，以4-6公里的分辨率沿着几乎垂直的路径同时进行采样，每周或更少地重复一次，似乎是可行的，另外两个月的任务时间用于从沿海地区到达并返回，进行发射和回收。对cuddy进行大约50次三维调查，以观察其衰减率，相关的细尺度分层特征的频率和强度，以及垂直径向结构的变化。观察到的地下涡流的结构演变将被用来推断与周围水域的物理、化学和生物特性的交换率。虽然人们普遍认为cuddy是CCS中财产交换的重要代理人，但提出的观察将是第一个在其生命的相当一部分时间内从四个维度描述cuddy的观察。这项研究将有助于了解涡旋输送的一般情况，特别是亚中尺度相干涡在向海洋内部传递东部边界区域特性方面的作用。涡旋输送的影响不仅对海洋的物理分布很重要，而且对化学和生物分布也很重要。该项目将培养一名研究生成为一项新兴观测技术以及漩涡在海洋环流中的作用方面的专家。

This is a project to study the decay of a subthermocline eddy as it travels from near its generation site in the California Undercurrent (CU) over the continental slope into offshore waters. The CU, a prominent element of the California Current System (CCS), transports relatively warm, saline, anoxic Pacific Equatorial Water north along the North American west coast. Temperature and salinity generally decrease both poleward and offshore, while dissolved oxygen increases, as the CU spins off long lived eddies transporting its water properties away from the CCS into the eastern Pacific. These eddies, nicknamed cuddies for their origin, have been tracked by solitary floats for many months and surveyed hydrographically on occasion, but their structural evolution as they decay has yet to be observed. They take the form of submesoscale coherent vorticies and are largely invisible to remote sensing techniques due both to their small size and subsurface intensification. The extent to which cuddies contribute to broad scale property gradients in the CCS and beyond is tied to the evolution of their radial-vertical structure.This study will use a pair of extended-range Seagliders to frequently survey a cuddy over many months as it travels. A cuddy will be identified and located for study by an ongoing Seaglider repeat transect, separately supported by NOAA and maintained by University of Washington colleagues. With improvements to performance efficiency, Seagliders are projected to be capable of operating as long as a year while transmitting slanting profiles of upper-ocean structure ashore in near real time. Simultaneous transects at 4-6 km resolution along nearly perpendicular paths repeated every week or less over the course of ten months appear feasible, with an additional two months of mission time devoted to reaching from and returning to the coastal region for launch and recovery. The sequence of approximately 50 three-dimensional surveys of a cuddy will be used to observe its decay rate, associated frequency and intensity of fine scale stratification features, and changes in vertical-radial structure.The observed structural evolution of a subsurface eddy will be used to infer the exchange rates of physical, chemical, and biological properties with the surrounding waters. While cuddies are widely suspected to be important agents of property exchange in the CCS, the observations proposed will be the first to describe a cuddy in four dimensions over an appreciable portion of its lifetime.This study will contribute to understanding of eddy transport in general and the role of submesoscale coherent vorticies in particular in transmitting eastern boundary region properties to the ocean interior. Implications of eddy transport are important not only to physical distributions in the ocean, but to chemical and biological ones as well. The project will train a graduate student to be expert in an emerging observational technique as well as in the role of eddies in ocean circulation.