Pulses of warm and moist air from lower latitudes provide energy to the Arctic and form its main energy source outside of the summer months. These pulses can cause substantial surface warming and trigger ice melt. Air-mass transport in the opposite direction, away from the Arctic, leads to cold-air outbreaks. The outbreaks are often associated with cold extremes over continents, and extreme surface heat fluxes and occasional polar lows over oceans. Air masses advected across the strong Arctic-to-mid-latitude temperature gradient are rapidly transformed into colder and dryer or warmer and moister air masses by clouds, radiative and turbulent processes, particularly in the boundary layer. Phase changes from liquid to ice within boundary-layer clouds are critical in these air-mass transformations. The presence of liquid water determines the radiative effects of these clouds, whereas the presence of ice is crucial for subsequent cloud decay or dissipation, processes that are poorly represented in weather and climate models. We argue that a better understanding of how air masses are transformed on their way into and out of the Arctic is essential for improved prediction of weather and climate in the Arctic and mid-latitudes. Observational and modelling exercises should take an air-mass-following Lagrangian approach to attain these goals.

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ERA-Interim data for Fig. 1 have been obtained from the European Centre for Medium-range Weather Forecasts’ (ECMWF) data server. The satellite image in Fig. 2 is from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite, provided by the National Aeronautics and Space Administration (NASA) via https://earthdata.nasa.gov

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We would like to thank all participants of the 2017 workshop on Arctic air-mass transformations in Stockholm for their contributions, and the International Meteorological Institute at Stockholm University and the Helmholtz Association for sponsoring the workshop. Parts of Fig. 2 have been adapted from https://www.mpimet.mpg.de/en/science/the-land-in-the-earth-system/modelling-of-boundary-layer-processes/les-of-cold-air-outbreaks/. We acknowledge support from the Helmholtz Society through the grant ‘Understanding the role of atmosphere-surface coupling for large-scale dynamics’ (F.P.), the German Research Foundation (DFG, Deutsche Forschungsgemeinschaft) within the Transregional Collaborative Research Center (TR 172) ‘ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3’ (D.C.,R.N. and M.W.) and from the U.S. Department of Energy (DE-SC0011918) and National Science Foundation (PLR-1303879, OPP-1724551) (M.D.S.).

Author information


  1. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany

    • Felix Pithan
    •  & Dmitry Chechin
  2. Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden

    • Gunilla Svensson
    • , Rodrigo Caballero
    • , Annica M. L. Ekman
    •  & Michael Tjernström
  3. A.M. Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciences, Moscow, Russia

    • Dmitry Chechin
  4. Department of Earth, Atmospheric, and Planetary Science, MIT, Cambridge, MA, USA

    • Timothy W. Cronin
  5. Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany

    • Roel Neggers
  6. Cooperative Institute for Research in Environmental Science, University of Colorado and NOAA Earth System Research Laboratory Physical Science Division, Boulder, CO, USA

    • Matthew D. Shupe
    •  & Amy Solomon
  7. Institute for Meteorology, University of Leipzig, Leipzig, Germany

    • Manfred Wendisch


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All authors wrote the paper, which was coordinated by F.P. and G.S. T.W.C. and D.C. produced the figures.

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