ClickPic2The IASC/CliC workshop on “The influence of the lower stratospheric polar vortex on cold air outbreaks under climate warming” was held at the University of Lincoln, Lincoln, UK, on 11-13 September 2023 .Even now with warmer winter average midlatitude temperatures, there are still major winter cold events affecting the lives and economics of millions of people in eastern North American and Asia and Europe. 

The connection between Arctic change and midlatitude weather events is a scientific challenge as events appear local, intermittent, and do not occur every year. This has led to ongoing controversy in the atmospheric community. We hypothesize that movement of the lower stratospheric polar vortex to over the North American or Eurasia continents provides a mechanism for enhancing regional cold air outbreaks. This small (19-person) workshop, including a diverse range of participants from research institutes in the UK, Finland, Germany, USA, China, Korea and Japan, involved focused presentation from established subject experts and promising Early Career Scientists as well as intensive discussion to advance the understanding of this meteorological connection.

Picture3Presentations were on the following topics: Overview of polar vortex studies; The twisted and tortured path of Arctic influence on mid latitude extreme weather; The polar vortex response to sea-ice loss and its state dependence; Greenland Blocking as a conduit of stratosphere-troposphere coupling and Stratospheric Polar Vortex (SPV) impacts; Factors influencing predictability of Northern European cold spells; Drivers of extreme cold events in Europe; Arctic-east Asia teleconnection via troposphere and stratosphere;  North American extreme winter weather and the polar vortex; Extreme cold events in North America and Eurasia in November-December 2022: a potential vorticity gradient perspective; Tropical role in the Arctic-midlatitude linkage; The potential vorticity theory of atmospheric blocking in the nonlinear multi-scale interaction model: an application to the Arctic-midlatitude linkage; A new approach to identifying stratospheric polar vortex configurations and connections; Stratosphere-troposphere oscillation and its contribution to cold air outbreaks; The varied surface impacts associated with sudden stratospheric warming in observations and CMIP6; Internal variability increased Arctic amplification during 1980-2022; Investigating pathways connecting tropospheric precursors to stratospheric extreme events; The impact of sea-ice concentration and sea-surface temperature boundary forcing in different experimental settings with ECHAM6 on the polar stratosphere.

            During break-out discussions the following themes were identified as key priorities for further research in this area:

  1. Improving weather/climate predictions: improving our ability to predict and understand Arctic-Midlatitude linkages in global climate and Numerical Weather Prediction models for more accurate extreme weather, seasonal to sub-seasonal (S2S) and climate projections.
  2. Stratosphere-troposphere coupling: developing a comprehensive framework for stratosphere-troposphere coupling events beyond just Sudden Stratospheric Warming (SSW), including asymmetric structures of the SPV, the role of large-scale circulation, and more detailed spatio-temporal analysis of SPV.
  3. Impact on extreme weather: investigating the influence of stratospheric forcing and blocking on extreme weather events, such as temperature and precipitation extremes and identifying precursors in the troposphere.
  4. Climate change and Linkages: Examining the impact of climate change on Arctic Amplification and Arctic-Midlatitude linkages, particularly in relation to the Quasi-Biennial Oscillation (QBO) and other tropical drivers, and the changing jet stream. Detection and attribution studies of Arctic influence, using AI methods.
  5. Model improvements: addressing challenges in numerical models, including their ability to capture Arctic-Midlatitude linkages, blocking, SPV interactions with the jet stream, and the need for better representation of Arctic Amplification (AA) in simulations while considering the trade-offs between significance and ensemble size.
  6. Clarify terminology (e.g. weak SPV & prolonged structure of SPV, locations of SPV centre).
  7. Cross-timescale interaction.
  8. Nonlinearity: assumption of linearity in many current analyses - more non-linear tests are needed.

The workshop organisers are currently working on a review/synthesis paper(s) for a high-profile peer-reviewed journal. The accompanying photos show University of Lincoln Minerva Building (inside and outside the meeting room), in the Georgian Town Hall ball room and in front of the Norman castle at Newark-on-Trent, Nottinghamshire, UK - a day excursion to Edward Hanna’s home town near Lincoln. The workshop was deemed by participants to have been highly successful and enjoyable. We thank the co-sponsors: IASC, WCRP CliC and the University of Lincoln.

Workshop Agenda [PDF]

Photos credit: courtesy of the organisers 

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