Atmospheric Forcing of the Iceland Sea (AFIS)

北大西洋的亚极地地区对全球气候系统至关重要。在不同空间尺度上的大气-海洋耦合过程需要一种综合办法来改进对它们的理解和预测。这一地区加强了大气和海洋之间的“交流”。在这里，巨大的地表热量和水汽通量使地表水域变得更冷、更咸、更稠密，导致对流翻转，从而促成了大西洋子午线翻转环流(AMOC)的下端。AMOC是一种海洋环流，将热带地区的暖水带到北方，并在深处向南回流冷水；它有助于保持欧洲的气候相对温和。冰岛海位于冰岛以北和以东，可以说是北大西洋次极地海域中研究最少的。然而，新的发现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这个系统的核心，并表明它需要迫切的科学关注。最近发现的北冰岛喷流被认为是密水通过丹麦海峡的两条路径之一。丹麦海峡是冰岛和格陵兰岛之间的一片海洋，是来自北部的密水进入大西洋的主要路径。这一发现为进入北大西洋的致密水的起源提供了一个新的范例。然而，目前这架北冰岛喷气式飞机的来源仍然不明。据推测，来自大西洋的相对温暖的水在冰岛海被改造成更稠密的水，尽管目前还不清楚这是在哪里、何时或如何发生的。我们将检验这一假说，并研究这一新的海洋环流模式。我们将通过描述冰岛海大气强迫的特征来研究冬季大气-海洋过程，即观测该区域地表热量、水汽和动量通量的空间结构和变化，以及决定这些通量的天气系统。我们将从几个平台(一架飞机；并通过项目伙伴一架无人驾驶飞行器、一个气象浮标和一艘考察船)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和业务天气预报中心的再分析。这些气象分析和再分析是观测和模式输出的混合，代表了我们所知的大气。我们将进行数值模拟实验，以调查对该区域有强烈影响但似乎没有得到很好反映的选定天气系统的动力学；例如，在冷空气爆发期间在海冰和开阔海洋之间过渡时形成的边界层；或发生在冰岛下游的急流和尾流。我们将使用我们独特的观测结果来改进这些系统的模型表示。我们还将进行新的高分辨率气候模拟。一系列实验将涵盖最近的过去和可能的未来情况；以及一些理想的情况，如冰岛海地区冬季没有海冰。我们将使用冰岛海上空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，我们将与我们的国际伙伴合作，分析新的海洋观测结果，并确定哪些天气系统对改变该区域的海洋性质很重要。我们将使用一系列海洋和大气模型来确定当前和未来的海洋循环路径是如何发挥作用的。简而言之，我们将确定冰岛海的大气-海洋过程在创造流经丹麦海峡并流入AMOC下端的密集水域中所起的作用。

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.