EAGER: Deepglider Pilot Observations of Western Boundary Current Structure Offshore Abaco

该项目是作为早期概念探索性研究赠款资助的。2004年，快速气候变化--子午线翻转环流和热通量阵列(RAPID-MOCHA)开始监测北大西洋从北美到非洲跨大西洋的经向物质输送。它通过对从大西洋盆地两侧的小群系泊设备收集的动态高度廓线的差异，用海流计测量边界流流动，通过电子测量佛罗里达海峡的输送，以及使用卫星风来估计Ekman输送，来估计气候关键的经向翻转环流(MOC)。海底压力计被用来估计随时间变化的正压贡献，而快速MOCHA依靠假设的空间均匀的时间恒定正压气流来估计平均输送。新开发的全海洋深度(水面到6公里)自主水下滑翔机首次科学使用，Deeplider将补充快速MOCHA阵列。深度滑翔机将通过收集巴哈马阿巴科附近延伸的西部边界地区的重复水文断面，独立于RAPID-MOCHA估计绝对运输量。一对车辆将反复穿越快速摩卡动态高度系泊的终端构件之间100和500公里宽的重叠部分。深度滑翔机将分别每周和每月重复这些部分，与系泊提供的空间分辨率相比，提供了相当大的空间分辨率，尽管时间分辨率要粗糙得多。每艘深度滑翔机预计将持续一年以上，可能长达18个月。从剖面中分辨的水平密度梯度推断的综合地转切变将参考从每个滑翔机俯冲周期推断的深度平均海流。航迹推算的滑翔机在水上的位移与GPS在地面上的位移之间的差值被用来估计深度平均海流。深度滑翔机的估计将包括水平变化的时间平均正压对输送贡献的可能性。独立的Deeplider对运输量的估计将与RAPIDMOCHA阵列的估计进行比较。此外，“深滑器”将暂时在“虚拟系泊”模式下使用，以检查系泊设备在测量动态高度时是否足够。同时，重复剖面和系泊时间序列的补充将被用来评估误差并改进对延长的西部边界地区经向输送的估计。智力价值：这项工作的智力价值在于它与全球气候动力学的基本问题有关。MOC的可变性没有得到很好的观察，更不用说理解了。同样的道理也适用于深度流动。对监测MOC的技术进行比较对于确定其可信度和有效性至关重要。深度滑翔机重复水文法将提供对气候关键海洋环流输送的独立测量，即对MOC的西部边界贡献。了解西部边界流的时间/空间结构是了解这一部分气候系统如何运作的先决条件。广泛影响：该项目将展示全深度滑翔机在监测海洋环流方面的有效性和经济性，不仅是沿快速莫查线，而且是沿其他横断面。它将率先使用自动滑翔机不仅监测上层海洋，而且还监测其深海区域。目前，Argo浮标监测全球上层海洋，但深海对气候变化的观测严重不足，这种情况可能会改变。通过使深海访问变得负担得起，深海滑翔机技术开启了观察全球海洋气候变化的全面范围的可能性。

This project is funded as an EArly-concept Grant For Exploratory Research (EAGER).The Rapid Climate Change-Meridional Overturning Circulation and Heat Flux Array (RAPID-MOCHA) began monitoring meridional mass transports in the North Atlantic Ocean along a transatlantic section from North America to Africa in 2004. It estimates the climatically critical meridional overturning circulation (MOC) by differencing dynamic height profiles gathered from small clusters of moorings on either side of the Atlantic basin, measuring boundary current flows with current meters, measuring transport in the Florida Strait electrically, and using satellite winds to estimate Ekman transport. While bottom pressure gauges are used to estimate time-varying barotropic contributions, RAPID-MOCHA relies on an assumed spatially uniform temporally constant barotropic flow to estimate mean transport.The first scientific use of the newly developed full-ocean-depth (surface to 6 km) autonomous underwater glider, Deepglider will complement the RAPID-MOCHA array. Deepgliders will be used to estimate absolute transports independently of RAPID-MOCHA by collecting repeat hydrographic sections of the extended western boundary region off Abaco, Bahamas. A pair of vehicles will repeatedly transit across 100 and 500 km wide overlapping sections between end members of the RAPID-MOCHA dynamic height moorings. These sections will be repeated about weekly and monthly, respectively, by Deepgliders, providing substantial spatial resolution compared to that provided by the moorings, although at considerably coarser temporal resolution. Each Deepglider is expected to last well over 1 year, possibly up to about 18 months. Integrated geostrophic shear inferred from horizontal density gradients resolved in the sections will be referenced to depth-averaged current inferred from each glider dive cycle. The difference between dead-reckoned glider displacement through the water and GPS displacement over the ground is used to estimate depth-averaged current. The Deepglider estimates will include the likely possibility of horizontally varying time-mean barotropic contributions to transport. The independent Deepglider estimates of transports will be compared to those from the RAPIDMOCHA array. In addition, Deepgliders temporarily will be used in 'virtual mooring' mode to check the adequacy of the moorings in measuring dynamic height. Together, the complement of repeat section and moored time series will be used to assess errors and improve estimates of meridional transports in the extended western boundary region.Intellectual Merit: The intellectual merit of this work lies in its connections to basic issues of global climate dynamics. The variability of the MOC is not well observed, let alone understood. The same can be said for the deep flow. Comparison of techniques by which the MOC is monitored is essential to establish their credibility and effectiveness. Deepglider repeat hydrography will provide independent measures of climatically critical ocean circulation transports, the western boundary contributions to MOC. Resolution of the temporal/spatial structure of western boundary currents is prerequisite to understanding how this portion of the climate system operates.Broader Impact: This project will serve as a demonstration of efficacy and economy of full-depth gliders in monitoring ocean circulation not only along the RAPID-MOCHA line, but also along other transects. It will pioneer the use of autonomous gliders to monitor not only the upper ocean, but its deep regions as well. Currently Argo floats monitor the upper ocean globally, but the deep ocean is severely under-observed for climate change, a situation Deepgliders could alter. By making deep ocean access affordable, the Deepglider technology opens the possibility that the complete extent of global ocean climate change may be observed.