Ocean Dynamics as Driver of Seasonal to Decadal European Atmospheric variability (ODYSEA)

ODYSEA将在长达十年的时间尺度上评估海洋如何、何时、何地影响欧洲特别是英国的大气变化和天气。将特别强调查明海洋先兆，这些先兆预示着在几个月或几年之前，特别是与极端天气事件有关的异常温暖、寒冷、干燥或潮湿情况的发展。这些前兆包括海洋表面温度的变化或主要洋流（如墨西哥湾流）位置的变化。在气候学的层面上，大西洋巨大的热容缓和了西欧的季节温度循环。大西洋也为欧洲提供了大量的降水，包括2013年底至2014年初英国的大范围洪水。海洋和大气的环流共同作用，通过将热量从热带带到极地，缩小了低纬度和高纬度之间的温差。在大西洋，经向翻转环流（MOC）以超过1000太瓦（TW）的速率向北输送热量——相当于100万个平均规模的核电站产生的能量。这种热量输送导致西欧全年额外变暖，西欧的平均温度高于美国西北部类似纬度的海洋性气候。理论论证和GCM模拟都表明，海洋向极地的热输送能够对大气风暴路径产生非常深远的影响，而大气风暴路径是造成欧洲天气日常变化的主要原因。这种变化还可能影响拟议的将偏远地区的大气变率与欧洲大陆联系起来的“遥相关”的途径。因此，在ODYSEA中，我们将研究海洋环流的变化如何调节大气环流及其对欧洲的影响。研究表明，墨西哥湾暖流的蜿蜒影响了北大西洋风暴形成的关键区域的大气。MOC也被证明是高度可变的，可能对海洋表面温度产生影响。这影响了释放到海洋上方大气的热量，也影响了海洋热量和水分被带到大陆的大气环流。国家海洋局最近进行的一项研究表明，海洋表面温度的异常是导致2010年12月极端寒冷的大气条件发展的关键。在这些异常的海洋表面温度之前，2009年出现了一个特别弱的MOC。在ODYSEA中，我们将确定以前影响欧洲和英国的极端天气（例如，2005年、2007年和2012年的潮湿夏季，2003年夏季和2006年7月的热浪）是否可以确定类似的海洋影响。重点将放在更好地了解海洋如何影响大气，进而影响我们的天气和气候。目前的知识有力地表明，海洋在数月至数年的时间尺度上影响着欧洲天气和气候的变化，但其潜在机制还远未完全了解。这阻碍了对这些事件的预测和归因。ODYSEA将通过使用英国现有的最先进的海洋和大气模型，以及分析英国气象局运行的最新季节到十年预测系统的数据，缩小我们对英国/欧洲天气和气候变化的理解差距。

ODYSEA will assess how, when, and where the ocean affects atmospheric variability and weather in Europe and in particular in the UK on timescales up to a decade. Particular emphasis will be on the identification of oceanic precursors that indicate the development of unusually warm, cold, dry or wet conditions several months or years in advance, especially related to extreme weather events. Such precursors can include changes in the ocean surface temperature or in the position of major ocean currents such as the Gulf Stream.On a climatological level, the large heat capacity of the Atlantic ocean acts to moderate the seasonal cycle of temperature over Western Europe. The Atlantic also provides much of the moisture precipitating over Europe, including the recent widespread flooding in the UK in late 2013/early 2014. Together, the circulation of the ocean and the atmosphere act to reduce the temperature difference between low and high latitudes by carrying heat polewards from the tropics. In the Atlantic, the meridional overturning circulation (MOC) transports heat northward at a rate of more than 1000 Terawatts (TW) - equivalent to the energy produced by 1,000,000 average sized nuclear power stations. This heat transport leads to an additional warming of Western Europe that is present throughout the year and temperatures in Western Europe are on average higher than at similar latitudes in the maritime climate of Northwest America. Both theoretical arguments and GCM simulations suggest that ocean poleward heat transports are capable of having very profound impacts on the atmospheric storm tracks which are responsible for much of the day-to-day variability in European weather. Such changes may also influence the pathways of the proposed "teleconnections" that link atmospheric variability in remote regions to the European continent. In ODYSEA we will therefore investigate how variability in the ocean circulation modulates the atmospheric circulation and its impact on Europe. Research suggests that meanders of the Gulf Stream affect the atmosphere in a region that is key to the formation of North Atlantic Storms. The MOC has also been shown to be highly variable with likely impacts on ocean surface temperatures. This affects the amount of heat released to the atmosphere overlying the ocean, but also the atmospheric circulation through which oceanic heat and moisture is carried towards the continents. A recent study performed at NOC suggests that anomalies of surface ocean temperatures were key to the development of the atmospheric conditions that led to the extremely cold December of 2010. These anomalous ocean surface temperatures were preceded by a particularly weak MOC in 2009. In ODYSEA we will establish if similar oceanic impacts can be identified for previous weather extremes that have affected Europe and the UK (e.g. wet summers of 2005, 2007 and 2012, the heat waves in the summer of 2003 and of July 2006). Emphasis will be on acquiring a better understanding of the mechanisms through which the ocean can impact the atmosphere and therefore our weather and climate. Current knowledge strongly suggests that the ocean affects variability of European weather and climate on timescales of months to years, but the underlying mechanisms are far from fully understood. This hampers prediction and attribution of those events. ODYSEA will reduce this gap in our understanding of the variability of UK/European weather and climate by using cutting edge ocean and atmosphere models available in the UK as well as by analysing data from the latest seasonal to decadal forecasting systems run by the UK Met Office.