Summer: Testing Influences and Mechanisms for Europe (SummerTIME)

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.

The key beneficiaries of SummerTIME are the UK Met Office and the European Centre for Medium-range Weather Forecasts (ECMWF). They will benefit directly from recommendations given by SummerTIME on how to improve their seasonal prediction systems for European summer. By working with both of their operational and development systems we will be able to provide tailored advice for each system.

Direct interaction with, and pull-through by, these key end-users is guaranteed through the depth of collaboration including: 1) project input from jointly-employed staff; 2) the letters of support from parallel projects funded, inter alia, under the EC's 7th framework programme; 3) sub-contracting components of the proposed programme directly from end-users; 4) regularly scheduled collaborative meetings and 5) support from the Met Office Academic Partnership. All these strands will ensure direct operational impact of results by permitting end users to shape the research during the lifetime of the project.

Improved predictive skill for summer climate will have subsequent economic impacts for both government and businesses, who will be better able to prepare for extreme weather and climate conditions. The project team have particularly strong links with the insurance industry, through the Willis and Lighthill networks, which will be invaluable in engaging end-users. In addition, our involvement in the NERC Probability, Uncertainty and Risk in the Environment (PURE) knowledge exchange network will aid in the communication of the important uncertainties surrounding seasonal prediction.

Finally we are keen to expand our existing engagement with wider interest groups such as policy makers, environmental charities, pressure groups, NGOs, student-bodies, and the wider public. This will be achieved through a variety of mechanisms including popular science articles, web content and schools outreach, orchestrated through the Oxford Climate Research Network and the Walker Institute at Reading.