Mechanisms Responsible for Mesoscale Eddy Energy Dissipation (MeRMEED)

在过去的几十年里，海洋学家一直在寻找海洋中缺失的混合，以完成海洋能量预算。回答能量在哪里被添加到海洋，又在哪里被移除的问题，有助于我们理解海洋环流的驱动因素。20世纪90年代，随着高分辨率卫星测量地表洋流的出现，科学家们可以看到，海洋中充满了被称为中尺度漩涡的水漩涡。虽然在所有的海洋盆地中都存在漩涡，漩涡内的水流有时超过每秒1米，但它们在卫星测量中优先在西部边界消失。涡旋在西部边界消失的原因有几种可能：它们可能将能量辐射出去，为大规模的海洋环流提供能量，或者通过湍流和消散在局部损失能量。在这些候选条件中，先前的工作表明，局部耗散足够强，可以解释涡旋消失的大部分原因。我们的目的是确定漩涡是如何以及为什么在西部边界失去能量的。这些结果和我们的测量结果将提供给参与海洋数值模拟的科学家。作为一个长期目标，我们的研究结果可能有助于指导如何在海洋模型中表示涡流，这是气候模拟中需要改进的关键领域之一。然而，由于这一领域的科学刚刚起步，最终的目标仍有几步之遥。基础物理学表明，大多数涡旋缓慢地向西移动，这些涡旋在到达边界前几个月的海面高度卫星测量中是可见的。在MeRMEED项目中，我们将在接近实时的卫星数据中观察涡旋，当一个合适的涡旋接近北美东海岸时，我们将部署一个小的研究小组，配备先进的仪器，在涡旋到达时迎接它。在那里，我们将使用部署在小船和名为“滑翔机”的自主水下航行器上的高分辨率剖面仪来调查涡流。在船基调查完成后，滑翔机将继续观察几个月的漩涡，因为漩涡正在慢慢消失。这些滑翔机通过卫星通信将测量结果传回我们在英国的基站。我们还计划利用英国和美国联合资助的RAPID项目的现有观测数据，测量北纬26度的海洋环流。我们将在其中一个系泊处安装额外的高分辨率速度和温度计，以便在18个月内连续观测漩涡。从调查、滑翔机和系泊测量中，我们将能够评估局部耗散对漩涡消失的重要性。我们将利用我们的发现来阐明导致海洋涡旋消失的过程，以及这些过程如何随时间变化。

Over the last decades, oceanographers have been searching for the missing mixing in the ocean to complete the ocean energy budget. Answering questions of where energy is added to the oceans, and where it is removed, helps us to understand the drivers of ocean circulation. With the advent of high-resolution satellite measurements of surface currents in the 1990s, scientists could see that the oceans were filled with swirling vortices of water called mesoscale eddies. While eddies are present in all ocean basins, with currents inside the eddies sometimes exceeding 1 m/s, they disappear from satellite measurements preferentially at western boundaries. There are several possibilities for why eddies disappear at western boundaries: they may radiate energy away, contribute energy to large scale ocean circulation, or lose energy locally through turbulence and dissipation. Of these candidate terms, previous work has suggested that local dissipation is strong enough to explain a substantial part of the eddy disappearance. Our aim is to determine how and why eddies are losing energy at the western boundaries. These results and our measurements will then be made available to scientists involved in numerical simulations of the ocean. As a longer-term goal, the results of our research may help guide how eddies are represented in ocean models, which is one of the critical areas needing improvement in climate simulations. However, due to the fledgling nature of the science in this field, that eventual goal is still several steps away.Fundamental physics dictate that most eddies move slowly westward, and these eddies are visible in satellite measurements of sea surface height a few months before they arrive at the boundary. In the project MeRMEED, we will watch the eddies in near real-time satellite data, and when an appropriate eddy approaches the east coast of North America, we will deploy a small team of researchers, with advanced instruments, to meet the eddy upon arrival. There, we will survey the eddy using high-resolution profilers deployed from small boats and autonomous underwater vehicles called Seagliders. After the ship-based survey is completed, the gliders will continue to observe the eddies for several months, as the eddies are slowly disappearing. These gliders transmit their measurements via satellite communications back to our base station in England. We also plan to use the existing observations from the joint UK/US-funded RAPID programme, measuring ocean circulation at 26N. We will install additional high-resolution velocity and temperature meters on one of these moorings, to make continuous observations of the eddies over 18 months. From the survey, glider and moored measurements, we will be able to assess how important local dissipation is to the disappearance of eddies. We will use our findings to shed light on the processes responsible for eddy disappearance from the oceans, and how those processes change in time.