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.

Potential Impact:
Beneficiaries

The UK Met Office is the main beneficiary of the results obtained in ODYSEA is the UK Met Office. However, the results developed in this project will be relevant to broader consumers of weather/climate information over the UK region. These include:

- (Re)insurance industry (hazards such as flooding and wind-storms)

- The energy-sector (particularly energy-trading and risk management),

- Water (blocking, droughts, floods)

How will the potential beneficiaries benefit from our research?

The new forecasting systems GloSea5 and DePreSys3 show significantly improved forecasting skills for the North Atlantic region compared with their predecessors. The reasons for this improvement are far from fully understood yet. However, a mechanistic understanding of why forecasts are improved is crucial if we want to make best use of the new systems, and if we want to improve them further. ODYSEA will provide a detailed assessment of the performance of GloSea5 and DePreSys3 and of their skill for different seasons, and for chosen case studies of weather events that are known to have had significant socio-economic impacts. A particular emphasis of ODYSEA will be on improving the understanding of oceanic (but also other) physical processes affecting atmospheric variability. These results will help the Met Office to gain a deeper understanding their new forecasting system and increase the confidence in the use of GloSea5 and DePreSys3 as it will provide new insight into the strengths and weaknesses of these cutting edge tools.

Key improvements of the NEMO ocean component will be channeled to the Met Office via the existing collaboration in the framework of the Joint Ocean Modelling Programme (JOMP) and will benefit the development of the next generation coupled model currently underway (coupling of ORCA12 with N1024 atmosphere) at the Met Office and NCAS.

Case studies of recent extreme European weather events, and enhanced capabilities for simulating and predicting them, will also be of particular interest to a wider community. ODYSEA has a strong link to several of these sectors through Brayshaw's role in the Willis Research Network (insurance/reinsurance) and his work with the energy-sector in particular (recent or current research projects with three of the "big six" UK energy companies, as well as the UK transmission system operator and major consultancy companies).