Summer: Testing Influences and Mechanisms for Europe (SummerTIME)

最近英国一连串潮湿的夏季通过洪水等效应对社会产生了相当大的影响。2013年夏天则逆势而上，天气异常温暖干燥。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，它们引导着个别风暴的路径。但有没有更深层次的根本原因：可能会对喷气式飞机产生影响的远程或外部驱动因素？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内这些高影响事件的预测？这些都是夏季提案将解决的问题。夏季急流的时间变化似乎与大西洋温度有关，在季节和年代际时间尺度上都是如此。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，气候模式通常很难再现这些观察到的关系，而且可操作的季节性预报系统在预测喷流转移方面也没有什么技能。夏季的主要目的是推动对北大西洋-欧洲地区夏季大气环流的季节到年代际预报的科学研究。从历史上看，夏季环流的气象学比冬季环流的气象学研究要少得多，关于其基本性质还有很多需要了解的地方。夏季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一系列不同复杂程度的数值模型进行研究。将围绕新版本的气象局气候模型与非常详细的海洋表层模型相结合，进行一系列敏感性实验。这些实验将被设计来测试可能的驱动因素的作用，如洋流、海冰和气溶胶强迫。最后，该项目将分析广泛的最先进的预报系统，特别是来自气象局的预报系统，以及来自世界各地其他预报中心的预报系统。其目的是找出预测系统中缺失或代表性不佳的流程，并调查如何改进这些流程。夏季团队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，以确保结果成功通过，以帮助业务预报系统的开发。

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.