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

Lead Research Organisation: National Oceanography Centre
Department Name: Science and Technology

Abstract

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.

Planned 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).
 
Description Using observations as well as output from climate models we have studied oceanic reemergence in the North Atlantic and its impact on the atmosphere. Oceanic reemergence refers to anomalous ocean temperatures persisting persisting subsurface from one winter to the next when the anomalies can reemerge and become visible in the sea surface temperatures. Our results show that 11 such events occurred since the late 19th Century and that they can be preceded by both negative and positive states of the North Atlantic Oscillation. Analysis of climate models (CMIP5) reveals that these models cannot simulate the observed links between ocean reemergence and atmospheric conditions, thereby revealing shortcomings in the models' ability to realistically simulate winter climate over the North Atlantic.

We have also identified a hitherto unreported link between temperature anomalies in the North Atlantic Ocean and the development of summer heat waves over central Europe. Our results show that several of the major European heat waves of the last 35 years were preceded by a cold anomaly in the Northeast Atlantic several months before the onset of the heat wave. In an additional study we have also shown that winters with persistent (i.e 4 months or longer) positive phases of the North Atlantic Oscillation (NAO) are often followed by anomalously warm summers over Europe (central Europe in particular) the following summer. The persistent NAO+ conditions in winter precondition both the sea surface temperature over the North Atlantic as well as the soil moisture over Europe in ways that favour the development of warm conditions.

We have undertaken research to understand how the ocean may have affected the very active hurricane seasons of 2005, 2010 and 2017. These three seasons were characterised by the highest recorded sea surface temperatures (SSTs) in the main hurricane development region (MDR). Our results show that in 2005 and 2010 the ocean circulation (more specifically the Atlantic meridional overturning circulation (AMOC)) was the main contributor to the anomalously warm SSTs in the MDR. Weak AMOC values during the winter seasons 2004/2005 and 2009/2010 led to the development of warm SST anomalies in the MDR by the end of winter which then persisted until the start of the hurricane season in August. In contrast, the anomalous SST anomalies in 2017 resulted from anomalous exchanges of heat between the ocean and the atmosphere between spring and summer.
Exploitation Route The findings described above have implications for seasonal winter and summer forecasts for the North Atlantic region. In particular our results suggest that extreme conditions in both summer and winter can be preceded by potential oceanic precursors for both seasons which can potentially increase the lead time for seasonal forecasts.
Sectors Environment

URL https://www.nature.com/articles/s41467-019-08496-4
 
Title Reemergence 
Description Using observational data from the ocean and the atmosphere we have developed a methodology to determine the frequency of reemergence events in the ocean and if reemergence is linked to preferred atmospheric conditions. 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact Key paper describing the links between reemergence of temperature anomalies in the North Atlantic and atmospheric conditions. New knowledge about the predictability of North Atlantic winter weather. 
 
Title Stationary waves 
Description Development of a method to automatically identify quasi-stationary waves in the atmosphere. 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact One of the key goals of ODYSEA is to assess how strongly the Atlantic influences the atmosphere. The method will allow us to identify where quasi-stationary waves occur spatially and temporally and whether the Atlantic ocean plays a important role. 
 
Description ACSIS - OSNAP - RAPID meeting in Oxford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Presentation on causes and consequences of a pronounced cold anomaly that occurred in the North Atlantic ocean. The meeting was attended by 100+ international scientists.
Year(s) Of Engagement Activity 2017
 
Description ACSIS - OSNAP - RAPID meeting in Oxford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Talk about state of the art coupled ocean-atmosphere simulations to study the Atmospheric Response to the 2015 cold anomaly in the North Atlantic Ocean. The meeting was attended by 100+ international scientists
Year(s) Of Engagement Activity 2017
 
Description ACSIS - OSNAP - RAPID meeting in Oxford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Presentation on chaotic vs externally forced variability of the Atlantic Meridional overturning circulation on intra and inter-annual timescales. The meeting was attended by 100+ international scientists.
Year(s) Of Engagement Activity 2017
 
Description Article in the Environmental Science Journal for Kids 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact Article explaining in very simple, accessible terms how ocean temperatures and European summers are linked.
Year(s) Of Engagement Activity 2016
URL http://www.sciencejournalforkids.org/articles/cold-ocean-hot-summer
 
Description Invited Seminar - University of Berne (Switzerland) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact About 100-150 people attended my seminar at the University of Berne on 21st October 2015
Year(s) Of Engagement Activity 2015
 
Description Presentation - Southwestern Arms 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Around 30-40 people attended my presentation in the Southwestern Arms Pub (Southampton)
Year(s) Of Engagement Activity 2015
 
Description Short article on NOC news 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Short article on NOC news website describing the finding of Duchez et al. (2016).
Year(s) Of Engagement Activity 2016
URL http://www.noc.ac.uk/news/atlantic-precursors-european-heat-waves