Submesoscale frontal dynamics

在不同温度和盐度的海水交汇的地方形成海锋。锋面，包括大规模的洋流系统，如墨西哥湾流和较小的短暂特征，在上层海洋中无处不在。锋面是极具活力和动态的环境，对当地生物和全球碳循环具有重要影响。根据定义，锋面是密度面或等斜线从海洋分层的内部露出来的地方。最近的证据表明，这些露头等平线提供了一条途径，使重要的示踪剂，如溶解的碳、氧和营养物质，能够在海洋表面和内部之间直接而快速地转移。海洋表面和内部的水交换速率反过来又影响着海洋调节地球气候变化的能力。尽管它们具有全球意义，但关于前线的许多基本问题仍未得到解答。为什么前线的生物生产力通常比周边地区高得多？锋面如何改变湍流混合的强度？是什么物理过程平衡了锋面的辐合气流，最终决定了锋面的宽度和强度？在这个项目中，学生将结合数值模拟、数学理论和现场数据来回答这些重要问题。根据几个海洋锋的水文剖面，我们将确定重要的参数，包括密度对比、混合层深度和锋的垂直范围。然后，我们将建立和分析一套数值模拟来研究锋面在不同参数范围内的演变。线性稳定性分析将使我们能够识别最终发展成锋面涡流的扰动。最后，我们将把我们的结果与现有的和新的观测数据进行比较。我们将根据结果和学生的兴趣调整方法，项目将有开放探索主题的空间。

Ocean fronts develop where waters with different temperature and salinity meet. Fronts, which include large-scale current systems such as the Gulf Stream and smaller ephemeral features, are ubiquitous in the upper ocean. Fronts are extremely energetic and dynamic environments with important influences on the local biology and the global carbon cycle. By definition, fronts are places where density surfaces, or isopycnals, outcrop from the ocean's stratified interior. Recent evidence indicates that these outcropping isopycnals provide a pathway that allows direct and rapid transfer of important tracers such as dissolved carbon, oxygen, and nutrients between the ocean surface and interior. The rate of exchange of water between the ocean surface and interior in turn affects the ability of the ocean to mediate changes in the earth's climate. Despite their global significance, many fundamental questions about fronts remain unanswered. Why are fronts often much more biologically productive than surrounding areas? How do fronts modify the intensity of turbulent mixing? What physical processes balance the convergent surface flow at fronts, ultimately determining their width and strength?For this project, the student will use a combination of numerical simulations, mathematical theory, and field data to answer these important problems. Based on available hydrographic sections taken across several ocean fronts, we will identify important parameters including the density contrast, mixed layer depth, and vertical extent of the front. We will then build and analyse a suite of numerical simulations to study the evolution of fronts in different parameter ranges. A linear stability analysis will allow us to identify the disturbances that eventually develop into frontal eddies. Finally, we will compare our results with existing and new observational data. We will adapt the approach based on the results and the interests of the student and the project will have scope for open exploration of the topic.