Agulhas System Climate Array (ASCA)

阿古拉斯流是南印度洋副热带涡旋的西边界流，控制着印度洋海盆的热量收支。海洋表面温度和热含量的变化对印度洋盆地气候的许多方面至关重要，例如东非降雨、热带气旋活动和海平面上升。印度洋海表温度年代际变化的50%以上可以用均匀的、盆地范围的变暖或变冷来解释，并推测这可能与经向翻转环流的变化有关。目前，由于缺乏观测，对印度洋翻转、经向热量输送和海洋表面温度之间的联系的了解受到阻碍。在过去的50年里，对印度洋经向翻转环流的估计不到几次。然而，人们可以预计，它的短期变化将超过这几个估计的范围，就像它在大西洋所做的那样。通过阿古拉斯流离开印度洋的极地热量输送既向北输送到大西洋，在那里它被认为影响了经向颠覆，从而影响了该盆地的气候，又向南输送到南大洋。测量阿古拉斯变率并调查其与风强迫和阿古拉斯泄漏指标的关系将有助于更好地理解这些现象在真实海洋中是如何联系起来的。该项目的一个组成部分是向南非科学家和技术人员提供技能转让，以便他们能够领导和维持长期的阿古拉阵列。资源共享、能力建设、开放数据政策和协作分析将促进西印度洋海洋学界更高的生产力和更高质量的研究。作为该项目的一部分，首席研究员将在2015年和2018年担任开普敦大学的客座教授，教授为期两周的大型动力海洋学荣誉模块。一名美国研究生、一名博士后研究员和一名早期职业科学家将接受培训。阿古拉斯系统气候阵列(ASCA)项目是南非、荷兰和美国科学家之间的合作，作为全球海洋观测系统的一部分，实施对阿古拉海流的持续观测。ASCA的这一五年阶段将建立对海流中速度、温度和盐度变化的测量，包括其对沿海水域的影响。这些测量将与卫星和ARGO数据合成，以实现以下主要科学目标：(1)表征阿古拉斯流的体积和温度输送之间的关系。(2)通过将ASCA测量与ARGO和海洋内部的卫星数据综合起来，量化整个盆地范围的印度洋翻转和热量输送的季节变化。(3)在风强迫以及反向反射和泄漏的背景下调查阿古拉斯流的年度和年际变化。ASCA将在南非考察船上进行三次研究巡航(2016、2018和2019年)，在此期间，国际团队将部署和维护一个由七个全深度海流计系泊设备组成的线性阵列，并配备额外的温度和盐度传感器，以及四个底部安装的电流和压力传感倒置回声探测仪。最后，三个沿海系泊设施将在陆架断裂处和近岸添加到阵列中，全部在不到200米的水中。这些研究由南非合作伙伴牵头，他们的动机是研究阿古拉斯海流变化对沿海洋流、上升流和年度沙丁鱼捕捞的区域影响。在部署和回收系泊设备期间，将收集横跨阿古拉斯流的S附近的水文断面。采样计划是基于以前在该地点成功收集的系泊速度观测，该实验由美国国家科学基金会资助的阿古尔哈斯当前时间序列实验。该项目是对美国气候可变性和可预测性(CLIVAR)计划的贡献。

The Agulhas Current is the western boundary current of the South Indian Ocean subtropical gyre and, as such, it dominates the heat budget of the Indian Ocean basin. Variability in sea surface temperature and heat content is central to many aspects of climate over the Indian Ocean basin, such as East African rainfall, tropical cyclone activity, and sea level rise. More than 50% of decadal Sea Surface Temperature variability over the Indian Ocean is explained by uniform, basinwide warming or cooling and it is hypothesized that this could be linked to changes in the meridional overturning circulation. Understanding the links between Indian Ocean overturning, meridional heat transport and sea surface temperature is currently hampered by lack of observations. Estimates of the Indian Ocean meridional overturning circulation have been made less than a handful of times over the past 50 years. Yet, one can expect its short-term variability to exceed the span of these few estimates, just as it does in the Atlantic. The poleward heat transport that exits the Indian Ocean via the Agulhas Current feeds both northward into the Atlantic, where it is believed to influence meridional overturning and hence climate in that basin, and southward into the Southern Ocean. Measuring Agulhas variability and investigating its relationship to wind forcing and Agulhas leakage proxies will lead to a better understanding of how these phenomena are linked in the real ocean. An integral component of this project is to provide skills-transfer to South African scientists and technicians so that they can lead and sustain an Agulhas array in the longer term. Resource sharing, capacity building, an open data policy, and collaborative analyses will promote greater productivity and better quality research from the western Indian Ocean oceanographic community in general. The principal investigator will be a visiting Professor at the University of Cape Town in 2015 and 2018 and teach a 2-week Honors module on large-scale dynamical oceanography, as part of this project. A U.S. graduate student, a postdoctoral researcher and an early career scientist will be trained. The Agulhas System Climate Array (ASCA) project is a collaboration between South African, Dutch, and US scientists to implement sustained observations of the Agulhas Current, as part of the Global Ocean Observing System. This five-year phase for ASCA will establish measurements of velocity, temperature, and salinity variability in the Current, including its influence on coastal waters. These measurements will be synthesized with satellite and Argo data to achieve the following major scientific objectives:(1) Characterize the relationship between volume and temperature transport in the Agulhas Current.(2) Quantify the seasonal variability in basin-wide overturning and heat transports of the Indian Ocean, by synthesizing ASCA measurements with Argo and satellite data over the ocean interior.(3) Investigate the annual and interannual variability of the Agulhas Current in the context of wind forcing and changes in retroflection and leakage.Three ASCA research cruises (2016, 2018 and 2019) will take place aboard South African research vessels, during which the international team will deploy and maintain a linear array of seven full-depth current meter moorings with additional temperature and salinity sensors interspersed with four bottom-mounted Current and Pressure-sensing Inverted Echo Sounders. Finally, three coastal moorings will be added to the array at the shelf break and inshore, all in less than 200 m of water. These are led by the South African partners, whose motivation is to study the regional impact of Agulhas Current variability on coastal currents, upwelling, and the annual sardine run. During deployment and recovery of the mooring, hydrographic sections across the Agulhas Current near 34◦S will be collected. The sampling plan is based on moored velocity observations that have been successfully collected before in this location under the Agulhas Current Time-series experiment funded by NSF. This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) program.