Summer: Testing Influences and Mechanisms for Europe (SummerTIME)

最近英国连续多雨的夏季通过洪水等影响对社会产生了相当大的影响。然而，2013年夏天却出现了反常的温暖和干燥天气。造成这些不寻常季节的直接原因是大西洋急流和风暴路径的变化，它们控制着单个风暴的路径。但是，是否存在更深层次的潜在原因：远程或“外部”驱动因素可能对急流产生影响？如果是这样的话，我们能否利用这些驱动因素来改进我们对未来几个月到几年的高影响事件的预测？这些都是SummerTIME提案将要解决的问题。在季节和年代际尺度上，夏季急流的变化似乎与大西洋温度有关。其他潜在的驱动因素包括海冰变化、人为气溶胶排放和热带环流模式。然而，气候模式一般难以再现这些观测到的关系，而可操作的季节预报系统在预测急流变化方面几乎没有技巧。SummerTIME的主要目的是推进北大西洋-欧洲地区夏季大气环流的季节至年代际预测科学。历史上对夏季环流的气象学的研究远远少于对冬季环流的研究，对其基本性质仍有许多有待了解。SummerTIME的第二个目的是提高我们对夏季环流基本原理的理解，例如为什么风暴路径在不列颠群岛以西分成两条截然不同的路径。这将使用最新的观测数据集和不同复杂程度的数值模型进行研究。一系列的敏感性实验将围绕英国气象局气候模型的一个新版本进行，该模型与海洋表层的一个非常详细的模型相结合。这些实验将用于测试洋流、海冰和气溶胶强迫等可能驱动因素的作用。最后，该项目将分析一系列最先进的预测系统，尤其是来自英国气象局的，也包括来自世界各地其他预测中心的。其目的是确定预报系统中缺失的或代表性差的过程，并调查如何改进这些过程。“夏日时光”小组将与英国气象局和欧洲中期天气预报中心的科学家密切合作，以确保这些结果能够成功地用于开发可操作的预报系统。

The recent string of wet UK summers had considerable impact on society via effects such as flooding. The summer of 2013 then bucked the trend, with unusually warm and dry conditions prevailing. The proximate causes of these unusual seasons were shifts of the Atlantic jet and storm track, which steers the path of individual storms. But are there deeper underlying causes: remote or 'external' drivers that can have an influence on the jet stream? If so, can we use these drivers to improve our forecasts of these high-impact events from months to years ahead? These are the questions that will be addressed by the SummerTIME proposal. Summertime shifts of the jet stream appear to be related to Atlantic Ocean temperatures, both on seasonal and decadal timescales. Other potential drivers include sea ice variations, anthropogenic aerosol emissions and tropical circulation patterns. However, climate models in general have difficulty in reproducing these observed relationships, and operational seasonal forecast systems have little skill in predicting jet shifts. The primary aim of SummerTIME is to advance the science of seasonal to decadal prediction of summertime atmospheric circulation over the North Atlantic-European region. The meteorology of summertime circulation has historically been much less studied than its wintertime counterpart, and much remains to be understood of its fundamental nature. A secondary aim of SummerTIME is to improve our understanding of the fundamentals of summer circulation, for example why the storm track splits into two distinct paths just west of the British Isles. This will be investigated using the latest observational datasets and a hierarchy of numerical models of different complexities. A series of sensitivity experiments will be performed centred around a new version of the Met Office climate model coupled to a very detailed model of the ocean surface layer. These experiments will be designed to test the roles of possible drivers such as ocean currents, sea ice and aerosol forcing. Finally, the project will analyse a wide range of state of the art forecast systems, particularly from the Met Office but also from other forecasting centres around the world. The aim is to identify missing or poorly represented processes in the forecast systems and investigate how these may be improved. The SummerTIME team will work closely with scientists from the Met Office and the European Centre for Medium-range Weather Forecasting, to ensure that the results are successfully pulled through to aid the development of operational forecast systems.