Comparison of Deepglider and RAPID-MOCHA Moored Array Observations

大西洋子午线翻转环流(AMOC)是全球气候系统的主要组成部分。在北纬26.5度，AMOC负责携带大约60%的海洋向极地净热通量和大约30%的大气和海洋一起携带的总热通量，在全球范围内进行纬向积分。通过海面温度调制，AMOC与年际到数十年时间尺度上的气候信号联系在一起，这可能会产生广泛的社会影响。气候模型预测，AMOC在下个世纪将大幅减弱，这一变化可能会产生广泛的影响。在过去的十年里，美国和英国的科学家一直保持着一个横跨大西洋的重型仪器系泊阵列，以观测AMOC及其热通量的波动。超过十天的时间尺度上的变化主要是由跨大西洋动态高度差和边界流波动所推断的地转流波动。虽然有效，但系泊阵列的维护成本很高。该项目试图评估超远距离、全海洋深度的水下滑翔机在测量AMOC并排系泊阵列方面的有效性。这些被称为深海滑翔机的自动飞行器，沿着倾斜的轨迹近实时地收集海面到海底的温度、盐度和溶解氧的剖面。它们还返回对全深度平均海流的估计。深度滑翔机在北纬26.5度线上的成功应用将推动将该技术应用于其他感兴趣的断面(如北大西洋副极地环流和南大西洋副热带环流)，以应对全球重复水文测量的挑战，并降低这类项目的总体成本，以便资助机构能够作为一个整体提供这类海洋气候项目。这些都将导致对地球-S气候的更深层次的了解。该项目的总体目标是学习如何在未来几十年内帮助AMOC监测的可持续持续。学习使用深滑器测量AMOC将有助于维持当前阵列在北纬26.5度处的运行数十年，以解决年际和数十年的变化。只有经过几十年的运作，与自然气候变化和人为气候变化相关的信号才会变得明显，并有可能区分开来。在长达18个月的任务中，一架深滑器可以潜入约250米深至6000米的深度，同时使用一套锂电池在海洋中飞行1万公里。它沿着穿过海洋的锯齿状路径对温度、盐度和溶解氧进行采样，并在每次到达海面时通过卫星遥测将它们传送到岸上。双向通信允许将命令传输到深度滑翔机，这样它的自主行为就可以从任何地方的飞行员通过互联网连接进行远程控制。作为一项试点实验，计划在两年内执行四次为期一年的深滑机任务，重叠停泊部署。其中两个将集中在靠近巴哈马阿巴科近海的快速摩卡系泊位置，以解决动态高度的主要变异性，用于估计海洋内部对AMOC变异性的贡献。另外两个将重复一小段旨在捕捉安的列斯群岛和西部边界深海流的时间和空间变化。将对深滑器和系泊设备的测量结果进行比较，以评估相对疗效。

The Atlantic Meridional Overturning Circulation (AMOC) is a principal element of the global climate system. At 26.5 degrees North latitude, the AMOC is responsible for carrying about sixty percent of the net poleward heat flux carried by the oceans and about thirty percent of the total heat flux carried by the atmosphere and ocean together, integrated zonally around the globe. Through sea surface temperature modulation, the AMOC is linked to climate signals on interannual to multi-decadal time scales that can have extensive societal impact. Climate models predict substantial weakening of the AMOC over the next century, a change with potentially wide ramifications. For the past decade, U.S. and U.K. scientists have maintained a transatlantic heavily instrumented moored array to observe fluctuations in the AMOC and its heat flux. Variability on time scales longer than ten days is dominated by geostrophic current fluctuations inferred from transatlantic dynamic height differences and boundary current fluctuations. While effective, the moored array is costly to maintain. This project is an attempt to assess the effectiveness of very long-range full ocean depth underwater gliders in measuring aspects of the AMOC side-by-side the moored array. These autonomous vehicles, named Deepgliders, collect sea-surface to sea-floor profiles of temperature, salinity, and dissolved oxygen along slanting trajectories through the ocean in near-real time. They also return estimates of the full-depth average current. Successful application of Deepgliders to the 26.5 degrees North latitude line will motivate applying the technique to other transects of interest (such as in the North Atlantic subpolar gyre and the South Atlantic subtropical gyre), to address the challenges of repeat hydrography globally, and reduce the overall cost of such programs in order that such ocean climate projects can be afforded as a whole by funding agencies. These together will lead to deeper understanding of earth?s climate.The overall goal of the project is to learn how to assist the sustainable continuation of AMOC monitoring through coming decades. Learning to measure the AMOC using Deepgliders will help sustain operation of the current array at 26.5 degrees North for the many decades required to resolve interannual and multi-decadal variability. Only by operating for several decades will the signals associated with natural climate variability and anthropogenic climate change be evident and potentially distinguishable. A Deepglider is designed to make about 250 dives to as deep as 6000 m in missions lasting as long as 18 months while traveling as much as 10,000 km through the ocean on a single set of lithium batteries. It samples temperature, salinity, and dissolved oxygen along saw tooth paths through the ocean and communicates them to shore each time it reaches the sea surface via satellite telemetry. Two-way communication allows commands to be transmitted to Deepgliders so that its autonomous behavior can be controlled remotely from a pilot anywhere with an internet connection. As a pilot experiment, four one-year Deepglider missions are planned over a 2-year period overlapping moored deployments. Two of these will concentrate on maintaining position close to a RAPID-MOCHA mooring just offshore Abaco, Bahamas to resolve the principal variability in dynamic height for use in estimating the interior ocean contribution to AMOC variability. Two more will repeat a short section intended to capture temporal and spatial variations in Antilles and Deep Western Boundary Current flow. Deepglider and moored measurements will be compared to assess relative efficacy.