Agulhas Current Time-series (ACT): Towards a multi-decadal index of Agulhas Current transport

在世界西部边界流中，阿古拉斯流具有独特的全球意义。它的变化与热带印度洋偶极子事件有关，而热带印度洋偶极子事件在很大程度上与太平洋风和ENSO(厄尔尼诺-南方涛动)有关。在下游，它向南大西洋输送温暖和咸水，直接影响大西洋经向翻转环流的强度。这使得阿古拉海流成为全球海洋观测系统的印度洋和大西洋热带阵列之间的有效联系。它不仅对印度洋的变化有重要意义，而且对全球气候也有重要意义。智力上的优点：这个项目的目标是建立一个多年代际时间序列的阿古拉海流输送(ACT)。这将以类似于90年代中期开始通过卫星高度计监测黑潮输送的方式进行。ACT的第一阶段需要在阿古拉海流和高度计(TOPEX/JASON)地面轨道上部署一系列仪器，以通过现场测量获得三年的运输时间序列。第二阶段涉及用这些测量的运输量校准沿轨高度计数据，以产生1992年至未来的阿古拉海流运输量的时间序列，只要高度计飞行任务继续沿着这一轨道进行。JASON-2刚刚发射(2008年6月)，确保了持续到2012年的时间序列。这一长达20年的时间序列将为印度洋提供一个重要的气候指数，可以与其他气候指数以及佛罗里达洋流和黑潮时间序列进行比较。在过去十年中，随着需要区分大气/海洋系统的自然变化模式和人为变化，了解十年时间尺度上的气候变化的重要性已成为当务之急。为此，国际海洋学界，特别是通过气候可变性和可预测性计划，为全球海洋观测系统制定了一项合作计划，该系统主要由热带系泊阵列、地下漂浮物、重复的XBT(消耗性水温)剖面和卫星数据组成。CLIVAR印度洋小组认识到，对阿古拉海流进行的西部边界观测是这一观测系统的一个重要组成部分，也是缺失的组成部分。对黑潮和墨西哥湾流的输送都进行了持续监测，为它们的盆地提供了从热带到中纬度变化的联系。然而，对阿古拉海流没有监测能力，它不仅与热带印度洋有联系，而且通过印度尼西亚贯通流和塔斯曼渗漏与太平洋的可变性有关，并通过阿古拉海环与大西洋有联系。非洲科学家和学生将受益于积极参与该项目，特别是通过参加游轮和开普敦大学与迈阿密大学之间的学生交流。这些合作将建立当地的海洋经验和知识。最后，ACT阵列本身以及随后的阿古拉输送的长期时间序列将使人们能够广泛评估阿古拉与其他观测到的气候指数的关系，通过建立长期区域能力，为全球海洋观测系统作出重要贡献。

Among the world's western boundary currents the Agulhas Current has a uniquely global significance. Its variability has been linked upstream to tropical Indian Ocean Dipole events which are largely coupled to Pacific winds and ENSO (El Nino- Southern Oscillation). Downstream, it feeds an inter-ocean transport of warm and saline waters into the South Atlantic which directly impacts the strength of the Atlantic meridional overturning circulation. This makes the Agulhas Current an effective link between the Indian and Atlantic tropical arrays of the Global Ocean Observing System. It is of significance not just to Indian Ocean variability, but to global climate.Intellectual Merit: The goal of this project is to build a multi-decadal time series of Agulhas Current Transport (ACT). This will be done in a manner similar to what was started in the mid nineties for monitoring Kuroshio transport via satellite altimeter. The first phase of ACT requires deployment of an array of instruments across the Agulhas Current and along an altimeter (TOPEX/Jason) ground track, to obtain a three-year time series of transports via in situ measurements. The second phase involves calibrating the along- track altimeter data with these measured transports to produce a time series of Agulhas Current transport from 1992 and into the future, for as long as altimeter missions continue to along this track. Jason-2 has just been launched (June 2008) ensuring a continuing time series through 2012. This twenty-year time series will provide an important climate index for the Indian Ocean, which can be compared to other climate indices and to the Florida Current and Kuroshio time series. The importance of understanding climatic variability on decadal time scales has come to the forefront over the last decade with the need to distinguish natural modes of variability of the atmosphere/ocean system from anthropogenic changes. In response, the international oceanographic community, particularly through the CLIVAR (Climate Variability and Predictability) program, have developed a collaborative plan for a global ocean observing system, consisting largely of tropical moored arrays, sub-surface floats, repeat XBT (eXpendable BathyThermograph) sections, and satellite data. The CLIVAR Indian Ocean Panel recognizes that western boundary observations of the Agulhas Current are an important and missing element to this observing system. Both the Kuroshio and Gulf Stream transports are continuously monitored, providing a link from tropical to mid-latitude variability in their basins. However, there is no monitoring capability for the Agulhas Current, which has links not only to the tropical Indian Ocean, but also to Pacific variability through the Indonesian throughflow and Tasman leakage, and to the Atlantic via Agulhas Rings.The broader impact of the project concerns the societal value of monitoring a current that has climate and marine impacts on Africa, a region lacking the capacity to monitor the current themselves. African scientists and students will benefit from active participation in the project, in particular through participation on cruises and via a student exchange between the University of Cape Town and the University of Miami. These collaborations will build local oceanographic experience and knowledge. Finally, the ACT array itself, and subsequent long-term time series of Agulhas transports, will allow a broad assessment of the relationship of the Agulhas to other observed climate indices, making an important contribution to the Global Ocean Observing System by building long-term regional capacity.