Measuring interannual variability of the AMOC and meridional ocean heat transport at 26.5N: The RAPID-MOCHA Array

气候模式表明，大西洋经向翻转环流（AMOC）的变率与海表温度在年际到几十年时间尺度上的变化有关，这可能产生深远的社会影响。此外，气候模式继续预测下个世纪AMOC的显著减弱，这可能通过北大西洋二氧化碳吸收的减少而反馈给气候系统（政府间气候变化专门委员会2007年报告）。由于缺乏对其变率的长期测量，AMOC在气候系统中的具体作用一直难以确定。然而，沿着26.5°N的美英联合海洋观测系统（RAPID-MOCHA）现在提供了近十年来AMOC的连续估计，揭示了其季节到年际变化的本质，这是目前唯一可用的全深度、全流域测量。RAPID-MOCHA项目已经为评估强迫的、数据同化的和耦合的气候模型提供了一个关键的基准，并正在形成一个基本的基石，围绕这个基石，正在制定监测整个大西洋盆地AMOC的国际项目。知识价值：该项目的目标是将该测量系统再维持6年，即从2014年到2020年，以量化AMOC的年际变化及其与北大西洋表面强迫变化的关系。还将监测26.5°N海洋经向热输运（MHT），包括热输运的翻转分量和环流分量的时变贡献。该时间序列的最后几年显示出与前几年相比显著的年际时间尺度变化，这被认为与北大西洋涛动（NAO）强迫的变化有关。北大西洋中纬度地区的海洋热含量和海表温度变化似乎也与最近的AMOC变化有关。迄今为止，RAPID-MOCHA项目的结果主要集中在准确确定AMOC的平均强度和垂直结构，其相关的热输送，以及季节周期和短期变化的动态。今后的重点将是记录和了解年际变化的原因，并将在26.5°N观测到的AMOC变化与大西洋盆地周围发展的AMOC测量计划的其他AMOC指数和结果联系起来。该项目的更广泛影响是为AMOC的长期监测提供基础，以便了解其与观测到的气候波动的关系，并提高我们评估气候模式预测的能力。作为英国RAPID-WATCH计划的一部分，该项目将继续与英国国家海洋学中心的研究人员进行成功的国际合作。美国对这一现场海洋观测系统的贡献包括：(1)使用可操作的海底电缆监测佛罗里达海流，通过使用消耗性温度下降探测仪、船载声学多普勒海流剖面仪（ADCP）和水文测量/低ADCP测量进行定期巡航校准；(2)在巴哈马以东的深西部边界海流和安的列斯海流区域进行连续系泊时间序列测量；包括每隔9个月与美国国家海洋和大气管理局（NOAA）的科学家合作进行的水文/低adcp剖面。佛罗里达洋流的监测是由NOAA独立支持的。英国将为沿26.5°N的扩展系泊阵列提供支持，以完成跨盆地连续时间序列观测系统。该项目是根据美国CLIVAR（气候变率和可预测性）计划对美国AMOC的贡献，该计划将在2014年3月至2020年3月的六年期间内维持要素的系泊部分。

Overview: Climate models suggest that variability of the Atlantic meridional overturning circulation (AMOC) is linked to sea surface temperature changes on inter-annual to multi-decadal time scales that can have far reaching societal impacts. Additionally, climate models continue to project a substantial weakening of the AMOC over the next century that could feed back on the climate system through reduced carbon dioxide uptake in the North Atlantic (2007 Report from the Intergovernmental Panel on Climate Change). The specific role of the AMOC in the climate system has been difficult to determine due to a lack of long term measurements of its variability. However, the joint US-UK ocean observing system along 26.5°N (RAPID-MOCHA) has now provided continuous estimates of the AMOC for nearly a decade that have revealed the nature of its seasonal to inter-annual variability, the only such full-depth, basin-wide measurements currently available. The RAPID-MOCHA program has already provided a critical benchmark for evaluation of forced, data-assimilative, and coupled climate models, and is forming a fundamental building block around which international programs are being developed to monitor the AMOC throughout the Atlantic basin.Intellectual merit: The goal of this project is to maintain this measurement system for an additional 6 years, from 2014 to 2020, to quantify the inter-annual variability of the AMOC and its relationship to changes in surface forcing over the North Atlantic. The ocean meridional heat transport (MHT) at 26.5°N will also be monitored, including the time varying contributions by the overturning and gyre components of the heat transport. The last few years of the time series have shown significant inter-annual time-scale changes with respect to prior years, which are believed to be linked to changes in North Atlantic Oscillation (NAO) forcing. Ocean heat content and Sea Surface Temperature changes in the mid-latitude North Atlantic also appear to be linked to the recent AMOC changes. The results of the RAPID-MOCHA project thus far have been primarily focused on an accurate determination of the mean AMOC strength and vertical structure, its associated heat transport, and the dynamics of the seasonal cycle and shorter-term variations. The focus going forward will be to document and understand the causes of inter-annual variability and to link AMOC changes observed at 26.5°N to other AMOC indices and results from developing AMOC measurement programs around the Atlantic basin.The broader impacts of the project are to provide the basis for long-term monitoring of the AMOC, so that its relationship to observed climate fluctuations can be understood, and our ability to assess climate model predictions can be improved. This project will continue a successful international collaboration with investigators from the U.K. National Oceanography Centre as part of the U.K. RAPID-WATCH program. The U.S. contribution to this in-situ ocean observation system includes: (1) Florida Current monitoring using the operational submarine cable, calibrated by regular cruises with expendable temperature dropsondes, shipboard Acoustic Doppler Current Profiler (ADCP), and hydrographic/lowered-ADCP measurements, and (2) continuous moored time series measurements across the Deep Western Boundary Current and Antilles Current region east of the Bahamas, including hydrographic/lowered-ADCP sections at nine-month intervals in concert with scientists at the National Oceanic and Atmospheric Administration (NOAA. The Florida Current monitoring is independently supported by NOAA. The U.K. will provide support for the extended array of moorings along 26.5°N that completes the trans-basin continuous time series observing system.This project is a contribution to the US AMOC under the US CLIVAR (CLImate VARiability and predictability) program to maintain the moored component of element for a six-year period extending from March 2014 to March 2020.