Surface Mixed Layer at Submesoscales (SMILES)

我们目前对地球气候的了解主要是基于模拟大气和海洋的行为及其相互作用的数值模型的预测。然而，这些模式的分辨率非常有限，因此，海洋中水平尺度小于约10公里的过程无法明确表示，需要对其影响进行参数化，才能将其纳入模式。该项目的目的是确定这些未解决的过程中的一种（称为亚中尺度）在影响上层海洋的结构和性质方面可能发挥的关键作用，从而影响南大洋内表面水团的转变。亚中尺度流动是指在海洋上层发生的空间尺度为1-10公里的流动，海洋和大气之间的交流和交换发生在海洋上层。以前认为不重要的气候尺度的研究，由于其规模小，并假定其动力学的重要性，最近从高分辨率区域模式和观测研究中得到的证据表明，亚中尺度实际上在整个上层海洋中广泛分布，并在气候动力学中起着关键作用，因为它们能够迅速限制上层海洋，减少从海洋到海洋的浮力损失。气氛这种过程的影响对于亚季风模式水（SAMW）等水团的表面转化特别重要，SAMW是经向翻转环流（MOC）的重要组成部分，它在地球仪周围重新分配热量、淡水和示踪剂。在MOC内，SAMW等密集水团在高纬度形成并通过表面过程转化，然后俯冲到海洋内部。俯冲水团的性质和示踪剂和溶解的气体，如其中所含的二氧化碳，是至关重要的全球气候和地球化学循环，因为这些水团保持了十年至百年的时间尺度与表面接触。鉴于最近的发现有关的能力submesoscales大幅影响上层海洋的属性，我们将直接研究的影响submesoscales的SAMW属性内的斯科舍海。使用综合的方法，我们将在一系列的空间和时间尺度上观察和模拟上层海洋中的亚中尺度，从湍流到模式水的形成。这项研究的主要目标是诊断中尺度下的水团转换中所发挥的作用，使我们能够准确地将这些影响纳入气候尺度模型，不能明确解决这些问题。我们的方法将需要在福克兰群岛以南约200英里的亚南极洲前沿（SAF）进行巡航，SAMW在其以北发生变化，并使用最先进的全球环流模型进行同步建模研究。在航行期间，我们将使用拖曳式仪器测量整个海洋上层300米的温度、盐度和相关领域的变化幅度。这些数据将使我们能够确定SAF附近的中尺度下的强度和分布，并确定产生它们的强迫机制。结合该项目的建模部分，其中将包括高分辨率和粗尺度模拟与MITgcm和大涡模拟（LES），我们将评估如何submesoscales最终影响SAMW的属性在该地区和最终的影响，这对SAMW的形成。

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.