Studies of Turbulence and Mixing in the Antarctic Circumpolar Current, a Continuation of DIMES

知识价值：南大洋的深环流和等环流混合实验（DIMES）是对南极环极流（ACC）中海洋混合的研究，该洋流从西向东环绕南极洲大陆，在其他大陆的南部。在遥远的南方和海洋的其他部分之间，目前的系统在某种程度上阻碍了热量、二氧化碳和其他重要的海洋成分的运输，混合过程在这些运输中起着重要的作用。DIMES是一个由美国和英国的物理海洋学家领导的多研究者合作项目。2009年初，在德雷克海峡以西2000多公里处，在亚南极锋和ACC极地锋之间约1500米深的等密度表面上，部署了被动示踪器和一系列水下浮子。2010年初，美国领导的研究巡航对示踪剂、湍流水平、速度和密度剖面进行了采样，并控制了湍流的产生。2011年和2012年，英国领导的研究巡航继续对示踪剂进行采样，因为示踪剂已经穿过德雷克海峡，进入斯科舍海，越过北斯科舍岭，轨迹超过3000公里。初步结果表明，底部相对光滑的德雷克海峡西部的纵向混合并不比其他大部分公海区域大。相比之下，在粗糙地形上存在强烈的速度剪切和强烈的湍流水平，并且在德雷克通道东部和西部，示踪剂的湍动扩散系数比德雷克通道西部大10倍以上。DIMES现场项目继续与美国团队一起在斯科舍海收集新的速度和湍流数据。预计示踪剂将继续通过斯科舍海，至少到2014年初。英国合作伙伴计划于2013年初和2014年初在北斯科舍山脊、东斯科舍海和中斯科舍海进行示踪剂取样。目前的项目将在2012年底和2013年底继续在德雷克海峡进行两次美国领导的巡航。通过对示踪剂观测、中性浮力浮标和数值模型估计的斯科舍海轨迹将用于准确估计示踪剂的混合率，并确定混合集中的位置。在2013年的巡航中，沿着ACC和德雷克海峡山脊的高分辨率横断面的速度和湍流场将被测量，以观察山脊下游的混合增强了多远，并测试湍流在粗糙地形上产生的背风波的破碎增强了混合的假设。更广泛的影响：DIMES（见网站http://dimes.ucsd.edu）涉及许多研究生和博士后研究人员。两名研究生将成为海洋湍流及其产生过程的专家，他们将继续接受这个项目的培训。DIMES的工作的最终动机是需要了解全球海洋的翻转环流。这种循环控制着巨大的海洋水库中热量和二氧化碳的运输和储存，因此在调节地球方面起着重要作用。年代的气候。了解环流及其在外力作用下如何变化，对于了解过去的气候变化以及未来气候可能如何变化是必要的，因此对人类福祉非常重要。DIMES项目收集和分析的数据将在项目结束时汇编并公开提供。DIMES项目是由美国CLIVAR（气候变率和可预测性）项目赞助的一个过程实验。

Intellectual Merit: The Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) is a study of ocean mixing in the Antarctic Circumpolar Current (ACC) which runs west to east all around the continent of Antarctica, south of the other continents. This current system is somewhat of a barrier to transport of heat, carbon dioxide and other important ocean constituents between the far south and the rest of the ocean, and mixing processes play an important role in those transports. DIMES is a multi-investigator cooperative project, led by physical oceanographers in the U.S. and in the U.K. A passive tracer and an array of sub-surface floats were deployed early in 2009 more than 2000 km west of Drake Passage on a surface of constant density about 1500 m deep between the Sub Antarctic Front and the Polar Front of the ACC. In early 2010 a U.S. led research cruise sampled the tracer, turbulence levels, and the velocity and density profiles that govern the generation of that turbulence, and additional U.K. led research cruises in 2011 and 2012 continue this sampling as the tracer has made its way through Drake Passage, into the Scotia Sea, and over the North Scotia Ridge, a track of more than 3000 km. The initial results show that diapycnal, i.e., vertical, mixing west of Drake Passage where the bottom is relatively smooth is no larger than in most other regions of the open ocean. In contrast, there are strong velocity shears and intense turbulence levels over the rough topography in Drake Passage and diapycnal diffusivity of the tracer more than 10 times larger in Drake Passage and to the east than west of Drake Passage.The DIMES field program continues with the U.S. team collecting new velocity and turbulence data in the Scotia Sea. It is anticipated that the tracer will continue passing through the Scotia Sea until at least early 2014. The U.K. partners have scheduled sampling of the tracer on cruises at the North Scotia Ridge and in the eastern and central Scotia Sea in early 2013 and early 2014. The current project will continue the time series of the tracer at Drake Passage on two more U.S. led cruises, in late 2012 and late 2013. Trajectories through the Scotia Sea estimated from the tracer observations, from neutrally buoyant floats, and from numerical models will be used to accurately estimate mixing rates of the tracer and to locate where the mixing is concentrated. During the 2013 cruise the velocity and turbulence fields along high-resolution transects along the ACC and across the ridges of Drake Passage will be measured to see how far downstream of the ridges the mixing is enhanced, and to test the hypothesis that mixing is enhanced by breaking lee waves generated by flow over the rough topography.Broader Impacts: DIMES (see web site at http://dimes.ucsd.edu) involves many graduate students and post-doctoral researchers. Two graduate students, who would become expert in ocean turbulence and the processes generating it, will continue be trained on this project. The work in DIMES is ultimately motivated by the need to understand the overturning circulation of the global ocean. This circulation governs the transport and storage of heat and carbon dioxide within the huge oceanic reservoir, and thus plays a major role in regulating the earth?s climate. Understanding the circulation and how it changes in reaction to external forces is necessary to the understanding of past climate change and of how climate might change in the future, and is therefore of great importance to human well-being. The data collected and analyzed by the DIMES project will be assembled and made publicly available at the end of the project.The DIMES project is a process experiment sponsored by the U.S. CLIVAR (Climate variability and predictability) program.