Surface Mixed Layer at Submesoscales (SMILES)

我们目前对地球气候的了解很大程度上是基于数值模型的预测，这些模型模拟了大气和海洋的行为以及它们之间的相互作用。然而，这些模式的分辨率非常有限，以至于水平尺度小于大约10公里的海洋过程不能明确表示，需要参数化，以便将其影响包括在模式中。“亚中尺度表面混合演化”（SMILES）项目的目的是确定这些未解决的过程（称为亚中尺度）中的一种，在影响上层海洋的结构和性质，从而影响南大洋表面水团的转变方面所发挥的潜在关键作用。亚中尺度是空间尺度为1-10公里的流动，发生在海洋上层，在那里海洋和大气之间发生通信和交换。由于亚中尺度尺度小，其动力学被认为是不重要的，因此以前被认为对气候尺度研究不重要，现在出现了来自高分辨率区域模式和观测研究的最新证据，这些证据表明，亚中尺度尺度实际上在整个上层海洋中广泛存在，并在气候动力学中发挥关键作用，因为它们能够迅速重新调整上层海洋并减少从海洋到大气的浮力损失。这一过程的影响对像亚南极模态水（SAMW）这样的水团的表面转化尤其重要，它是经向翻转环流（MOC）的重要组成部分，在全球范围内重新分配热量、淡水和示踪剂。在MOC内，像SAMW这样的致密水团是在高纬度地区通过表面作用形成和转化的，然后才俯冲到海洋内部。俯冲水团及其所含的示踪剂和溶解气体（如二氧化碳）的性质对全球气候和地球化学循环至关重要，因为这些水团在十年至百年的时间尺度上与地表保持不接触。鉴于最近关于亚中尺度对上层海洋性质有实质性影响的能力的发现，我们将直接研究亚中尺度对斯科舍海内SAMW性质的影响。采用综合方法，我们将在空间和时间尺度范围内观察和模拟海洋上层的亚中尺度，从湍流到模态水的形成。这项研究的主要目的是诊断亚中尺度在水团转变中所起的作用，以便我们能够准确地将这些影响纳入不能明确解决它们的气候尺度模式中。我们的方法包括在亚南极前沿（SAF）的福克兰群岛以南约200英里处进行巡航，SAMW向北转变，并使用最先进的全球环流模型进行同步建模研究。在巡航期间，我们将使用拖曳仪器测量整个海洋300米以上的温度、盐度和相关领域变化的长度尺度。这些数据将使我们能够确定南亚风区附近亚中尺度的强度和分布，并确定产生它们的强迫机制。结合该项目的建模部分，将包括使用MITgcm和大涡模拟（LES）的高分辨率和粗尺度模拟，我们将评估亚中尺度最终如何影响该区域内SAMW的性质，以及这对SAMW形成的最终影响。

Our current understanding of the Earth's climate is largely based on the predictions of numerical models that simulate the behaviour of, and interaction between, the atmosphere and the ocean. These models are crucially limited in their resolution, however, such that processes within the ocean that have horizontal scales of less than approximately 10 km cannot be explicitly represented and need to be parameterised for their effects to be included within the models. The purpose of this project, Surface Mixed Evolution at Submesoscales (SMILES), is to identify the potentially crucial role played by one variety of these unresolved processes, referred to as submesoscales, in influencing the structure and properties of the upper ocean, and thereby the transformation of surface water masses, within the Southern Ocean. Submesoscales are flows with spatial scales of 1-10 km that occur within the upper ocean where communication and exchange between the ocean and the atmosphere occurs. Previously considered unimportant to climate-scale studies due to their small scale and the presumed insignificance of their dynamics, recent evidence from high resolution regional models and observational studies is now emerging which suggests that submesoscales are actually widespread throughout the upper ocean and play a key role within climate dynamics due to their ability to rapidly restratify the upper ocean and reduce buoyancy loss from the ocean to the atmosphere. The impact of such a process is particularly important to the surface transformation of water masses such as Subantarctic Mode Water (SAMW), which is an important component of the Meridional Overturning Circulation (MOC) that redistributes heat, freshwater and tracers around the globe. Within the MOC, dense water masses such as SAMW are formed and transformed at high latitudes by surface processes before being subducted into the ocean interior. The properties of the subducted water masses and the tracers and dissolved gases such as carbon dioxide contained within them are vitally important to the global climate and geochemical cycles as these water masses remain out of contact with the surface over decennial to centennial timescales. In the light of the recent discoveries concerning the ability of submesoscales to substantially influence the properties of the upper ocean, we will directly study the impacts of submesoscales on SAMW properties within the Scotia Sea. Using an integrated approach, we will both observe and simulate submesoscales within the upper ocean at a range of spatial and temporal scales, spanning from turbulence up to mode water formation. The principal goal of the study is the diagnosis of the role played by submesoscales in water mass transformation so that we can accurately incorporate these effects into climate-scale models which cannot explicitly resolve them. Our methods will entail a cruise approximately 200 miles south of the Falklands Islands at the Subantarctic Front (SAF), to the north of which SAMW is transformed, and a concurrent modelling study using a state-of-the-art global circulation model. During the cruise, we will use towed instruments to measure the length scales of variability in the temperature, salinity and related fields throughout the upper 300 m of the ocean. The data will enable us to identify the intensity and distribution of submesoscales within the vicinity of the SAF, and to ascertain the forcing mechanisms that generate them. In conjunction with the modelling component of the project, which will include both high resolution and coarse-scale simulations with the MITgcm and large eddy simulations (LES), we will assess how submesoscales ultimately impact on the properties of SAMW within the region and the ultimate effect this has on the formation of SAMW.