Atmospheric Forcing of the Iceland Sea

北大西洋的亚极地地区对全球气候系统至关重要。正是在这种情况下，在各种空间尺度上的耦合大气-海洋过程需要一种综合方法来改进对它们的理解和预测。这个区域加强了大气和海洋之间的“交流”。在这里，大量的地表热量和水分通量使表层海水更冷、更咸、密度更大，导致对流翻转，从而形成大西洋经向翻转环流（AMOC）的下端。AMOC是一种海洋环流，它从热带向北携带温暖的水，并在深处向南返回冷水；它有助于保持欧洲气候相对温和。冰岛海位于冰岛的北部和东部，可以说是北大西洋亚极地海域中研究最少的海域。然而，新的发现正在迫使我们重新设计北大西洋海洋环流的概念模型，该模型将冰岛海置于该系统的中心，并表明它迫切需要科学关注。最近发现的北冰岛急流被认为是稠密水域通过丹麦海峡的两条通道之一。丹麦海峡是冰岛和格陵兰岛之间的一片海域，是稠密水域从北部进入大西洋的主要通道。它的发现为进入北大西洋的稠密水的起源提供了一个新的范例。然而，目前北冰岛喷气机的来源仍然未知。据推测，来自大西洋的相对温暖的水在冰岛海被改造成密度更大的水，尽管目前还不清楚这种情况发生的确切地点、时间和方式。我们将检验这一假设，并研究这种新的海洋环流模式。我们将通过表征其大气强迫来研究冰岛海冬季的大气-海洋过程，即观察该地区地表热、水分和动量通量的空间结构和变异性，以及决定这些通量的天气系统。我们将从多个平台（一架飞机，以及通过项目合作伙伴一架无人驾驶飞行器、一个气象浮标和一艘科考船）对海气相互作用过程进行现场观测，并利用这些平台评估气象分析，以及从业务天气预报中心进行的再分析。这些气象分析和再分析是观测和模式输出的混合，代表了我们所知道的最好的大气。我们将进行数值模拟实验，以调查选定的天气系统的动力学，这些天气系统对该地区有强烈影响，但似乎没有得到很好的代表；例如，在冷空气爆发期间，在海冰和公海之间的过渡过程中形成的边界层；或者冰岛下游的急流和尾流。我们将使用我们独特的观察结果来改进这些系统的模型表示。开展新的高分辨率气候模拟。一系列的实验将涵盖最近的过去和可能的未来情况；以及一些理想化的情况，如冰岛海地区冬季没有海冰。我们将在冰岛海上空使用最先进的高分辨率大气模式来研究大气环流和地表通量的变化。最后，我们将与国际伙伴合作，分析新的海洋观测结果，并确定哪些天气系统对改变该地区的海洋特性很重要。我们将使用一系列海洋和大气模式来确定当前和未来海洋环流路径的功能。简而言之，我们将确定冰岛海的大气-海洋过程在形成流经丹麦海峡并流入AMOC下肢的稠密水域中所起的作用。

The subpolar region of the North Atlantic is crucial for the global climate system. It is where coupled atmosphere-ocean processes, on a variety of spatial scales, require an integrated approach for their improved understanding and prediction. This region has enhanced 'communication' between the atmosphere and ocean. Here large surface fluxes of heat and moisture make the surface waters colder, saltier and denser resulting in a convective overturning that contributes to the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is an ocean circulation that carries warm water from the tropics northward with a return flow of cold water southwards at depth; it is instrumental in keeping Europe's climate relatively mild. The Iceland Sea - to the north and east of Iceland - is arguably the least studied of the North Atlantic's subpolar seas. However new discoveries are forcing a redesign of our conceptual model of the North Atlantic's ocean circulation which places the Iceland Sea at the heart of this system and suggests that it requires urgent scientific focus. The recently discovered North Icelandic Jet is thought to be one of two pathways for dense water to pass through the Denmark Strait - the stretch of ocean between Iceland and Greenland - which is the main route for dense waters from the north to enter the Atlantic. Its discovery suggests a new paradigm for where dense water entering the North Atlantic originates. However at present the source of the North Icelandic Jet remains unknown. It is hypothesized that relatively warm Atlantic-origin water is modified into denser water in the Iceland Sea, although it is unclear precisely where, when or how this happens. We will test this hypothesis and investigate this new ocean circulation paradigm. We will examine wintertime atmosphere-ocean processes in the Iceland Sea by characterising its atmospheric forcing, i.e. observing the spatial structure and variability of surface heat, moisture and momentum fluxes in the region and the weather systems that dictate these fluxes. We will make in situ observations of air-sea interaction processes from several platforms (an aircraft; and via project partners an unmanned airborne vehicle, a meteorological buoy and a research vessel) and use these to evaluate meteorological analyses and reanalyses from operational weather forecasting centres. These meteorological analyses and reanalyses are a blend of observations and model output and represent the atmosphere as best we know it. We will carry out numerical modelling experiments to investigate the dynamics of selected weather systems which strongly influence the region, but appear not to be well represented; for example, the boundary layers that develop over transitions between sea ice and the open ocean during cold-air outbreaks; or the jets and wakes that occur downstream of Iceland. We will use our unique observations to improve model representation of these systems.We will also carry out new high-resolution climate simulations. A series of experiments will cover recent past and likely future situations; as well as some idealised situations such as no wintertime sea ice in the Iceland Sea region. We will use a state-of-the-art atmospheric model with high resolution over the Iceland Sea to investigate changes in the atmospheric circulation and surface fluxes. Finally, in collaboration with our international partners, we will analyse new ocean observations and establish which weather systems are important for changing ocean properties in this region. We will use a range of ocean and atmospheric models to establish how current and future ocean circulation pathways function. In short, we will determine the role that atmosphere-ocean processes in the Iceland Sea play in creating the dense waters that flow through Denmark Strait and feed into the lower limb of the AMOC.