2016–2019 North Atlantic Oscillation

2016–2019 North Atlantic Oscillation
Name	2016–2019 North Atlantic Oscillation
Period	2016–2019
Region	North Atlantic
Index	NAO index
Notable	prolonged negative phase, extreme winter patterns

Contents

2016–2019 North Atlantic Oscillation The 2016–2019 North Atlantic Oscillation was a multi-year period of anomalous North Atlantic Oscillation behavior characterized by extended negative phases and pronounced variability that influenced weather across Europe, North America, and North Africa. Researchers from National Oceanic and Atmospheric Administration and European Centre for Medium-Range Weather Forecasts assessed teleconnections linking the event to stratospheric processes, Arctic variability, and Atlantic sea surface temperature anomalies, while teams at University of Oxford, Massachusetts Institute of Technology, and University of Exeter produced influential analyses.

Background and definition

The North Atlantic Oscillation (NAO) is defined as the leading mode of wintertime atmospheric variability over the North Atlantic, typically represented by the difference in sea-level pressure between Azores High positions near Azores and the Icelandic Low near Iceland, with indices maintained by NOAA Climate Prediction Center and European Centre for Medium-Range Weather Forecasts. Foundational work by Sir Gilbert Walker and later formalization by David B. Robinson and researchers at University of Southampton connected the NAO to storm track shifts, jet stream variations, and temperature patterns examined in reports by Intergovernmental Panel on Climate Change and studies published in journals like Nature Climate Change and Journal of Climate. The NAO phase modulates influences described in classic teleconnection frameworks alongside El Niño–Southern Oscillation, Arctic Oscillation, and Polar Vortex dynamics.

Between late 2016 and early 2019 the NAO index exhibited recurrent negative anomalies documented by NOAA Climate Prediction Center, Met Office analyses, and reanalyses such as ERA-Interim and ERA5. Winter 2016–2017 showed strong negative NAO values compared in studies from Alfred Wegener Institute and Woods Hole Oceanographic Institution to the post-1990 variability, while winters 2017–2018 and 2018–2019 retained below-average indices per datasets from Hadley Centre and National Center for Atmospheric Research. The anomalies were notable in gridded products from National Centers for Environmental Information and satellite-era syntheses by NASA Goddard Institute for Space Studies and Jet Propulsion Laboratory, prompting retrospective comparisons with historical episodes like the winters of 1962–1963 and 1995–1996 reviewed by Royal Netherlands Meteorological Institute and Danish Meteorological Institute.

Analyses attributed the prolonged negative NAO to combined atmospheric and oceanic drivers including stratosphere–troposphere coupling during Sudden Stratospheric Warming events studied by teams at University of Reading and University of Colorado Boulder, Atlantic multi-decadal variability linked to Atlantic Meridional Overturning Circulation investigations at Woods Hole Oceanographic Institution and Max Planck Institute for Meteorology, and sea surface temperature patterns reminiscent of Atlantic Multidecadal Oscillation phases examined by Princeton University and Scripps Institution of Oceanography. Forcing from tropical Pacific conditions associated with El Niño–Southern Oscillation episodes and remote influences traced in model experiments at Lawrence Livermore National Laboratory and NOAA Geophysical Fluid Dynamics Laboratory were implicated alongside sea ice variability documented by Norwegian Polar Institute and Scott Polar Research Institute.

The negative NAO phase produced regionally coherent impacts: Western and central Europe experienced colder, snowier spells that affected transport systems noted by Deutsche Bahn and flight operations at Heathrow Airport, while southern Europe and Maghreb saw drier conditions discussed in reports by European Environment Agency and United Nations Environment Programme. Over eastern Canada and the northeastern United States storms and cold-air outbreaks linked to the NAO were documented by Environment and Climate Change Canada and National Weather Service, and the Mediterranean basin exhibited altered cyclone tracks analyzed by Instituto Español de Oceanografía and Istituto Nazionale di Geofisica e Vulcanologia. Storm surge and coastal flooding events along the North Sea were assessed by Deltares and Danish Coastal Authority in the context of NAO phase anomalies.

Societal consequences included transportation disruptions impacting Eurostar and regional rail networks, energy demand spikes reported by National Grid (UK) and utilities in France and Spain, and agricultural stressors described by Food and Agriculture Organization case studies in Portugal and Italy. Ecological consequences encompassed shifts in marine ecosystems recorded by International Council for the Exploration of the Sea and fisheries agencies such as Marine Scotland and Plymouth Marine Laboratory, northward and depth-distribution changes in species noted by Woods Hole Oceanographic Institution and Institute of Marine Research (Norway), and altered phenology across terrestrial systems monitored by Royal Botanic Gardens, Kew and Smithsonian Institution biodiversity programs. Public health impacts tied to cold snaps were analyzed by European Centre for Disease Prevention and Control and national health services including NHS England.

Research efforts incorporated observational diagnostics from Copernicus services and paleoclimate context provided by National Oceanography Centre and Lamont–Doherty Earth Observatory, while modeling studies used ensembles from Coupled Model Intercomparison Project phases coordinated by World Climate Research Programme and regional simulations from Met Office Hadley Centre. Attribution analyses combining experiments from Lawrence Berkeley National Laboratory, Potsdam Institute for Climate Impact Research, and Centre National de la Recherche Scientifique evaluated the roles of anthropogenic forcing described in Intergovernmental Panel on Climate Change assessments versus internal variability highlighted in work by Columbia University and University of Hamburg. Continued monitoring by European Space Agency missions and integration into seasonal forecast systems at NOAA and European Centre for Medium-Range Weather Forecasts aim to refine predictive skill for future NAO behavior and impacts.